A fiber / whisker reinforced monolithic zinc oxide-based photocatalytic foam ceramic and a preparation method and application thereof

Abstract

This application discloses a fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, its preparation method, and its application. The method includes: uniformly dispersing organic additives and pH adjusters in deionized water to form a homogeneous solution; adding zinc oxide powder, sintering aid, defect control agent, and photocatalytically active components to the solution in batches, uniformly dispersing them to form a suspension slurry; adding fiber and / or whisker reinforcing phases to form a composite slurry; impregnating organic foam in the composite slurry, followed by desizing and drying to form a composite; subjecting the composite to gradient heating heat treatment to remove organic matter, forming a green body; and finally sintering to obtain the finished product. Based on the electronic characteristics and molecular structure of the target pollutants, a specific heterojunction system is matched and constructed to achieve highly efficient targeted degradation of emerging pollutants such as antibiotics, perfluorinated compounds, and phenols. The obtained product possesses high structural strength, high photocatalytic activity, and excellent environmental stability.

Description

Technical Field

[0001] This application relates to a fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, its preparation method and application, belonging to the field of inorganic non-metallic functional materials technology. Background Technology

[0002] Monolithic photocatalytic foam ceramics are a type of functional material composed of photocatalytic ceramic materials, possessing a three-dimensional interconnected porous structure. Their core lies in the "structure-function integration" design, effectively addressing the pain points of traditional photocatalytic water technologies, such as the difficulty in separating nanoparticle catalysts and insufficient specific surface area of ​​immobilized catalysts, providing a feasible path for the large-scale application of water treatment technologies. However, existing technologies still face three major bottlenecks that urgently need to be addressed: 1) Insufficient mechanical properties and poor engineering applicability; 2) Easy loss of active components, posing environmental risks. To solve the problem of nanocatalyst recovery, existing technologies often employ the strategy of loading nano-photocatalytic particles onto the surface of foam ceramic supports (such as Al2O3, SiC, etc.). However, in such composite structures, there is only weak physical adsorption between nanoparticles and the support, lacking strong chemical bonding, leading to continuous leaching of active components during long-term water treatment. 3) Insufficient catalytic specificity, making it difficult to adapt to complex pollutants. Different types of emerging pollutants, due to significant differences in their molecular structure, electronic properties, and environmental behavior, often require specific photocatalytic material systems to achieve the most efficient degradation effect. Existing monolithic photocatalytic foam ceramics suffer from a severe lack of catalytic diversity and specificity, and lack systematic matching principles based on pollutant molecular characteristics and catalyst band structure and surface active sites, resulting in a lack of targeted material design.

[0003] Zinc oxide (ZnO) is an important wide-bandgap photocatalyst material with a bandgap of approximately 3.37 eV and a conduction band position of approximately [missing information]. With a valence of 0.31 eV (vs NHE) and a valence band position of approximately +3.06 eV (vs NHE), it possesses extremely strong oxidizing photogenerated holes, which facilitate the generation of high concentrations of ·OH hydroxyl radicals, exhibiting excellent oxidative degradation capabilities for various organic pollutants; its electron mobility (approximately 200 cm²·V) -1 ·s -1 The value is much higher than that of TiO2 (approximately 10 cm²·V). -1 ·s -1 ZnO-based foam ceramics exhibit faster carrier transport rates. However, the preparation of ZnO-based foam ceramics faces unique challenges: ZnO has a significant risk of zinc vapor volatilization at high temperatures (>1300℃), limiting the available sintering temperature window; Zn²⁺… + Excessive reduction to Zn occurs during high-temperature sintering. 0 (Formation of zinc vapor and zinc interstitial defects ZnO) 1-xThe risks associated with ZnO include lattice distortion and color center defects, which severely impair photocatalytic activity; the solubility of ZnO in strong acid (pH < 4) and strong alkaline (pH > 11) environments limits its stability under extreme water quality conditions; furthermore, there is a lack of systematic defect control strategies and precise pollutant-heterojunction matching mechanisms for ZnO-based foam ceramics.

[0004] In summary, existing photocatalytic foam ceramic technologies suffer from common problems such as low mechanical strength, easy loss of active components, and insufficient catalytic specificity. Furthermore, ZnO-based systems face unique challenges related to high-temperature volatilization, defect control, and chemical stability. To address these technical bottlenecks, there is an urgent need to develop a monolithic zinc oxide-based photocatalytic foam ceramic that combines high mechanical strength, structural stability, and targeted pollutant degradation capabilities. Additionally, it is crucial to establish material design principles based on molecular properties to lay the material foundation for the engineering application of photocatalytic water treatment technology. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, its preparation method, and its applications. This invention significantly improves the material's mechanical properties by in-situ introducing a high aspect ratio reinforcing phase to construct a three-dimensional interlocking network. Zinc oxide and the photocatalytically active component form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. Simultaneously, a defect control agent suppresses Zn²⁺ segregation during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion and abnormal ZnO grain growth are addressed by controlling the grain size within a small range to maintain a high specific surface area and porosity of the material. Through precise design of photocatalytic heterojunctions, the separation efficiency of photogenerated carriers is optimized. Simultaneously, based on the matching mechanism between pollutant molecular characteristics and photocatalytic heterojunctions, targeted and efficient degradation of various emerging pollutants is achieved, providing a material solution with both structural robustness and functional specificity for the engineering application of photocatalytic water treatment technology.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, comprising the following steps: Step S1: Preparation of zinc oxide-based composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a zinc oxide-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a zinc oxide-based composite slurry. Step S2: Preparation of zinc oxide-based foam ceramic wet blank The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying treatment is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. Step S3: Preparation of zinc oxide-based foam ceramic green body The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is subjected to debinding heat treatment by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. Step S4: Sintering and Heterogeneous Structure Construction The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, defect control agents suppress Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0007] In some embodiments, in step S1, the average particle size of the ZnO powder is 10 nm-80 μm, preferably 200 nm-20 μm, and can be selected from wurtzite phase ZnO (hexagonal phase, room temperature stable phase), zincblende phase ZnO (cubic phase), and non-stoichiometric ZnO. 1-x (Zinc gap control type), commercial ZnO powder or its modified powder, or any combination thereof; 1) Cation doping, wherein the cation is selected from Li + Na + K + 、Rb + Cs + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Sn 4+ Sb³ + Sb 5+ Bi³ + ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Cr 4+ Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + Pr 4+ 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + 、Tb 4+ Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta5+ W 6+ Re 4 + Re 6+ Os 4+ Ir 4+ Pt² + Pt 4+ and Au³ + Any one or more of the following, with a doping concentration of 0.1-15 at% 2) Anion doping, wherein the anion is selected from any one or more of B, C, N, F, P, S, Cl, Br and I, and the doping concentration is 0.5-10 at% 3) Oxygen vacancy regulation, with an oxygen vacancy concentration of 10. 18 -10 21 cm -3 ; 4) Defect engineering modification, dislocation / grain boundary density 10 14 -10 16 cm -2 ; The modified powder must still possess semiconductor properties and have a bandgap range of 1.5-5.5 eV. The photocatalytic active component is an inorganic oxide powder with semiconductor properties, and its band gap ranges from 1.5 to 5.5 eV; it is selected from at least one component from the following I) - V); I) Single metal oxides The general chemical formula is M m O n M is a single metallic element, m = 1-3, n = 1-5; including one or more of TiO2, WO3, Bi2O3, Fe2O3, Cu2O, V2O5, MoO3, SnO2, MnO2, ZrO2, Ga2O3, Nb2O5, Ta2O5, In2O3, GeO2, RuO2, IrO2, Co3O4, NiO, Mn3O4, CuO, Ag2O, CoO, MnO, SnO, Sb2O3, Fe3O4, and Au2O and their modified derivatives; II) Composite metal oxides Composed of two or more metal cations, and further subdivided according to crystal structure as: a) Perovskites and their derived phases: general formula ABO3 or A (n+1) B n O (3n+1), where n is an integer from 1 to 3, A is selected from at least one of La, Bi, Ba, Sr, Ca, Pb, Na and K, and B is selected from at least one of Ti, Zr, Hf, Nb, Ta, W, Mo, V, Cr, Mn, Fe, Co, Ni, Al, Ga and Sn; b) Spinel-type oxides: with the general formula AB2O4, wherein A is selected from at least one of Mg, Zn, Ni, Co, Cu, Fe, Mn and Li, and B is selected from at least one of Al, Ga, Cr, Fe, Mn, Co and Ti; c) Layered oxyacid salts having a layered crystal structure with an interlayer spacing of 0.5 nm to 1.5 nm, selected from at least one of the following: c1) Layered titanates, with the general formula A2Ti3O7 or ATi2O5, wherein A is selected from H, Li, Na, K, Rb or Cs; c2) Protonated layered niobates or tantalates, with the general formula HNb3O8 or HTa2O6; c3) Aurivillius phase bismuth-based oxides, selected from Bi2WO6, Bi2MoO6, Bi4Ti3O 12 At least one of them; c4) Layered nickelates, with the general formula ANiO2, wherein A is selected from Li or Na; d) Other functional oxoacid salts, selected from at least one of the following groups: d1) Scheelite-type oxides, with the general formula AWO4, AMoO4 or AVO4, wherein A is selected from Bi, Ca, Sr, Zn or Pb; d2) Perovskite-type rare earth ferrates, with the general formula LnFeO3, wherein Ln is selected from La, Pr, Nd or Sm; d3) Pyrochlore-type oxides, with the general formula Ln2B2O7, wherein Ln is selected from La, Gd, Sm or Nd, and B is selected from Ti, Zr or Sn; d4) Tungsten bronze type oxide, with the general formula M x TO3, where T is selected from W, Nb, or Ta, M is selected from Na or K, and 0.1 ≤ x ≤ 1.0; d5) Olivine-type oxides, with the general formula M2SiO4 or M2GeO4, wherein M is selected from Mg, Zn, Fe or Mn; d6) Inverse spinel-type stannate Zn2SnO4; d7) Copper-iron ore type oxides, with the general formula CuMO2, wherein M is selected from Fe, Al, Ga or Cr; III) Rare earth-based oxides a) Single rare earth oxide Ln a O x , where Ln is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, a = 1–2, x = 1.5–3; b) Rare earth composite oxides: including perovskite-type LaMO3, NdMO3, ScMO3, YMO3, PrMO3, SmMO3, EuMO3, GdMO3, TbMO3, DyMO3, HoMO3, ErMO3, TmMO3, YbMO3, and LuMO3, where M is selected from transition metals Fe, Co, Sc, Ti, V, Cr, Mn, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, and W. Re, Os, Ir, Pt, Au, or Hg; pyrochlore-type Gd₂Ti₂O₇, Y₂Zr₂O₇, Sc₂Ti₂O₇, La₂Ti₂O₇, Ce₂Ti₂O₇, Pr₂Ti₂O₇, Nd₂Ti₂O₇, Sm₂Ti₂O₇, Eu₂Ti₂O₇, Tb₂Ti₂O₇, Dy₂Ti₂O₇, Ho₂Ti₂O₇, Er₂Ti₂O₇, Tm₂Ti₂O₇, Yb₂Ti₂O₇, Lu₂Ti₂O₇; bismuth rare earth co-doped oxides Bi. 1-x Ln x VO4, wherein Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, x = 0.1-0.5, and at least one of the layered rare earth oxides La2O2CO3, Pr4O7, Ce2O2CO3, Nd2O2CO3, Sm2O2CO3, Eu2O2CO3, Gd2O2CO3, Tb2O2CO3, Dy2O2CO3, Ho2O2CO3, Er2O2CO3, Tm2O2CO3, Yb2O2CO3, Lu2O2CO3, Sc2O2CO3, Y2O2CO3; the interlayer spacing of the layered rare earth oxide structure is 0.8-1.2 nm; IV) Frontier structural metal oxides a) High-entropy oxides: general formula is (M1, M2, ... M n ) a O M1, M2, ..., Mn are at least five different metallic elements, each independently selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Al, Li, Zr, Nb, Mo, Sn, Hf, Ta, W, or Ce, with each metallic element accounting for 5% to 35% of the total metallic elements, and the configuration entropy ΔS of the high-entropy oxide is... mix ≥ 1.5R, where R is the ideal gas constant 8.314 J·mol - ¹·K - ¹; (b) A two-dimensional nano-metal oxide, wherein the matrix material of the two-dimensional nano-metal oxide is selected from at least one of TiO2, MnO2, MoO3, V2O5, Co3O4, Fe2O3, SnO2, WO3 and Nb2O5, has a plate-like or layered morphology, has a thickness of 0.5 nm to 10 nm, has a lateral dimension to thickness ratio ≥ 50, and the two-dimensional nano-metal oxide has preferentially exposed crystal planes, wherein the crystal planes are selected from at least one of the {001}, {010}, {100} and {110} plane families; c) MOF-derived porous oxides, wherein the MOF-derived porous oxides are obtained by heat treatment conversion of metal-organic framework precursors, wherein the metal center of the precursor is selected from at least one of Zn, Co, Fe, Cu, Zr, Ti, Ni and Al, and the resulting oxides retain the morphological characteristics and pore structure of the precursors, with a specific surface area ≥ 50 m² / g, pore volume ≥ 0.1 cm³ / g, and pore size distribution spanning from micropores to mesopores, ranging from 0.5 nm to 50 nm; V) Precursor compound: is the water-insoluble oxalate and / or carbonate corresponding to the metal oxides in I)-II), wherein the precursor compound decomposes in situ during sintering heat treatment to generate the corresponding photocatalytically active oxide; Wherein, "insoluble in water" means: solubility in deionized water at 25°C ≤ 0.1 g / 100 mL; the precursor compound must meet the following requirements: decomposition temperature between 200-1200°C, residual carbon content after decomposition < 0.1 wt.%, and no introduction of impurity anions harmful to photocatalytic activity; VI) The photocatalytic active component described in any of I) to IV) above is modified using one or more of the following methods, and the resulting powder satisfies a band gap of 1.5-5.5 eV: a) Cation doping, wherein the cation is selected from Li + Na + K + 、Rb + Cs +、Mg² + 、Ca² + 、Sr² + 、Ba² + 、Al³ + 、Ga³ + 、In³ + 、Sn 4+ 、Sb³ + 、Sb 5+ 、Bi³ + 、Sc³ + 、Tea 4+ 、V³ + 、V 4+ 、V 5+ 、Cr³ + 、Cr 4+ 、Mn² + 、Mn³ + 、 Mr 4+ 、Fe² + 、Fe³ + 、Co² + 、Co³ + 、Ni² + 、Ni³ + 、Cu² + 、Y³ + 、Zr 4+ 、Nb 5+ 、Mo 6+ 、Ru 4+ 、Rh³ + 、Pd² + 、Ag + 、Day³ + 、Ce³ + 、Ce 4+ 、Pr³ + 、Pr 4+ 、Nd³ + 、Sm³ + 、Eu³ + 、Gd³ + 、Tb³ + 、Tb 4+ 、Dy³ + 、Ho³ + 、Er³ + 、Tm³ + 、Yb³ + 、Lu³ + 、Hf 4+ 、Ta 5+ 、Re 4+ 、Re 6+ 、Os 4+ 、Ir 4+ 、Pt² + 、Pt4+ W 6+ and Au³ + At least one of them, with a doping ratio of 0.1-15 at%; b) Anion doping, wherein the anion is selected from one or more of B, C, N, F, P, S, Cl, Br and I, and the doping ratio is 0.5-10 at% c) Oxygen vacancy regulation, with an oxygen vacancy concentration of 10. 18 -10 21 cm -3 ; d) Defect engineering modification, dislocation / grain boundary density 10 14 -10 16 cm -2 ; The amount of photocatalytic active component added is 5-80 wt.% of the zinc oxide powder mass; the amount of precursor compound added is based on the theoretical mass of the corresponding photocatalytic active oxide generated by its complete thermal decomposition, i.e., oxide equivalent.

[0008] The sintering aid is selected from at least one of the following components: (a) Low melting point oxides With a melting point <900℃, it partially melts within the sintering temperature window, providing a transient liquid phase to promote mass transfer and densification between ZnO particles. It mainly comprises the following components: Bismuth trioxide (Bi2O3), vanadium pentoxide (V2O5), boron trioxide (B2O3), molybdenum trioxide (MoO3); (b) Eutectic type / active oxide Its individual melting point can exceed 900℃, but it forms a low-melting-point eutectic with ZnO, or undergoes a solid-state reaction with ZnO to generate a low-melting-point active phase, promoting low-temperature densification. It mainly includes the following components: Copper oxide (CuO), ferric oxide (Fe2O3), nickel oxide (NiO), cobalt oxide (CoO), cobalt oxide (Co3O4), tin oxide (SnO2), manganese oxide (MnO2), manganese oxide (Mn2O3), chromium oxide (Cr2O3), gallium oxide (Ga2O3), indium oxide (In2O3); (c) Network forming agent A low-viscosity glassy liquid phase is formed at the sintering temperature, filling the gaps between ZnO particles. The ZnO particles rearrange themselves through surface tension, achieving low-temperature liquid phase sintering. It mainly comprises the following components: Silicon dioxide (SiO2), phosphorus pentoxide (P2O5), germanium dioxide (GeO2), tellurium dioxide (TeO2), and boron trioxide (B2O3); (d) Alkali metal and alkaline earth metal oxides As a network modifier, it reduces liquid phase viscosity by breaking bridging oxygen bonds in the glass network; simultaneously, it can form alkali metal / alkaline earth metal zincates with ZnO, controlling the sintering path. Its main components include the following: Magnesium oxide (MgO), lithium carbonate (Li2CO3), calcium carbonate (CaCO3), strontium carbonate (SrCO3), barium carbonate (BaCO3); (e) Rare earth oxide sintering aids Rare earth ion radii are much larger than Zn² + It has extremely low solid solubility in the ZnO lattice and mainly segregates to the grain boundaries to form rare earth zinc composite oxide grain boundary phases. It plays a role in both sintering aid and grain growth inhibition through liquid-phase assisted sintering and grain boundary pinning mechanisms. It mainly consists of the following components: Lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), neodymium oxide (Nd₂O₃), samarium oxide (Sm₂O₃), gadolinium oxide (Gd₂O₃), dysprosium oxide (Dy₂O₃), erbium oxide (Er₂O₃), ytterbium oxide (Yb₂O₃), cerium oxide (CeO₂), praseodymium oxide (Pr₆O₃) 11 Terbium oxide (Tb4O7), europium oxide (Eu2O3), holmium oxide (Ho2O3), thulium oxide (Tm2O3), and lutetium oxide (Lu2O3); (f) Pre-synthesized zinc-based functional compounds Pre-synthesized zinc salts or zinc-based composite oxides are directly introduced into the system as sintering aids, preferentially providing activated mass transfer channels between ZnO particles to promote densification, while simultaneously constructing ZnO heterojunction interfaces in situ. The main components include: Zinc tungstate (ZnWO4), zinc-iron spinel (ZnFe2O4), zinc-aluminum spinel (ZnAl2O4), zinc titanate (Zn2TiO4), zinc titanate (ZnTiO3), zinc stannate (Zn2SnO4), zinc stannate (ZnSnO3), zinc indium oxide (ZnIn2O4), zinc indium oxide (Zn2In2O5), zinc silicate (Zn2SiO4), zinc bismuthate (Bi2ZnB2O7), zinc bismuthate (Bi2Zn2O5); (g) Precursor compounds The water-insoluble oxalates, carbonates, and hydroxides corresponding to each component in (a) to (f) above decompose in situ during degumming or sintering heat treatment to generate corresponding oxides or oxygen-containing compounds. Herein, "insoluble in water" means that the solubility in deionized water at 25°C is ≤0.1 g / 100 mL. In particular, the oxides corresponding to the network forming agent in item c and the pre-synthesized zinc-based functional compound in item f can be obtained by thermal decomposition and conversion of their corresponding carbonate precursors.

[0009] The precursor compound is uniformly dispersed in solid particle form during the slurry stage, and decomposes in situ during heat treatment to produce nano-sized active powder. The dispersion uniformity is better than that of directly adding oxides. A typical precursor compound includes the following components: Bismuth carbonate (Bi2(CO3)3), copper oxalate (CuC2O4), ferrous oxalate (FeC2O4), tin oxalate (SnC2O4), nickel oxalate (NiC2O4), cobalt oxalate (CoC2O4), manganese oxalate (MnC2O4), calcium carbonate (CaCO3), barium carbonate (BaCO3), lanthanum carbonate (La2(CO3)3), lanthanum oxalate (La2(C2O4)3), cerium oxalate (Ce2(C2O4)3), lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3); The amount of the sintering aid added is 0.1-30 wt.% of the zinc oxide powder: for components (a) to (g), it is based on the actual added mass; for component (h), it is based on the theoretical mass (oxide equivalent) of the corresponding oxide generated by its complete thermal decomposition. It is particularly noted that the bifunctional sintering aids (such as Bi2O3, CuO, Fe2O3, ZnFe2O4, In2O3, etc.) in the sintering aids can promote the low-temperature densification of ZnO, and at the same time, they can undergo in-situ solid-phase reactions with ZnO to generate new phases with photocatalytic activity (such as Bi2ZnO4, ZnFe2O4, ZnIn2O4, etc.), thus realizing the dual contribution of sintering aids in densification promotion and photocatalytic function enhancement. The defect control agent (also known as grain growth inhibitor, valence state compensator, or grain boundary modifier, etc.) is selected from at least one of the following components: (a) Equivalent substitution stabilizers With Zn 2+ With the same valence, the ZnO lattice is stabilized through a solid solution substitution mechanism, suppressing Zn 2+ →Zn 0 Excessive reduction and zinc interstitial defects ZnI (Excessive generation), including the following components: Magnesium oxide (MgO), beryllium oxide (BeO), manganese oxide (MnO), ferrous oxide (FeO); (b) Donor-type substitution stabilizers M 3+ Replace Zn 2+ This generates a net positive charge (MZn•), which compensates for Zn vacancies by providing additional electrons (VZn′′ acceptors) and suppresses the formation of additional donor defects (ZnI•• or VO••); simultaneously, due to the ionic radius and Zn 2+The difference lies in the fact that, after solid solubility saturation, the ZnO grains segregate to the grain boundaries, forming a spinel-type grain boundary pinning phase, which effectively inhibits abnormal ZnO grain growth. This phase includes the following components: Aluminum oxide (Al2O3), gallium oxide (Ga2O3), indium oxide (In2O3), scandium oxide (Sc2O3), boron oxide (B2O3); (c) Grain boundary segregation inhibitor. The ionic radius is much larger than that of Zn. 2+ Primarily based on grain boundary segregation, it inhibits abnormal ZnO grain growth through the solute drag effect, maintaining a fine-grained structure and high specific surface area. It includes the following components: Lanthanum trioxide (La₂O₃), yttrium oxide (Y₂O₃), neodymium oxide (Nd₂O₃), praseodymium oxide (Pr₆O₃) 11 Samarium oxide (Sm2O3), europium oxide (Eu2O3), gadolinium oxide (Gd2O3), terbium oxide (Tb4O7), dysprosium oxide (Dy2O3), holmium oxide (Ho2O3), erbium oxide (Er2O3), thulium oxide (Tm2O3), ytterbium oxide (Yb2O3), cerium dioxide (CeO2); (d) Grain boundary / lattice dual stabilizer Ionic radius and Zn 2+ The phase difference is moderate, with limited solid solubility. After solid solubility saturation, it segregates to the grain boundaries, inhibiting grain growth and defect formation through a synergistic effect of solid solution strengthening and grain boundary pinning. Some components form a photocatalytically active second phase within ZnO, achieving a synergistic effect of defect control and enhanced photocatalytic function. These components include the following: Zirconium dioxide (ZrO2), hafnium dioxide (HfO2), titanium dioxide (TiO2), silicon dioxide (SiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), phosphorus pentoxide (P2O5), molybdenum trioxide (MoO3), tungsten trioxide (WO3); (e) Oxygen activity self-regulating stabilizer Compounds with reversible redox pairs maintain a localized oxidizing atmosphere around ZnO particles during ZnO sintering through a dynamic oxygen release / storage mechanism, thereby thermodynamically inhibiting Zn oxidation. 2+ →Zn 0 Reduction reaction, including the following components: Cerium dioxide (CeO2), manganese dioxide (MnO2), manganese trioxide (Mn2O3), manganese trioxide (Mn3O4), praseodymium oxide (P6O) 11 ), Terbium oxide (Tb4O7), Cobalt oxide (Co3O4), Cobalt oxide (CoO); (f) Precursor compounds The water-insoluble oxalates and / or carbonates corresponding to each component in (a)-(e) above decompose in situ during the sintering heat treatment to generate the corresponding oxides, wherein "water-insoluble" means having a solubility of ≤0.1 g / 100 mL in deionized water at 25 °C, and includes the following components: Typical precursor compounds include: magnesium oxalate (MgC2O4), aluminum oxalate (Al2(C2O4)3), yttrium oxalate (Y2(C2O4)3), lanthanum oxalate (La2(C2O4)3), neodymium oxalate (Nd2(C2O4)3), samarium oxalate (Sm2(C2O4)3), gadolinium oxalate (Gd2(C2O4)3), zirconium carbonate (ZrOCO3), titanium oxalate (TiO2(C2O4)), tin oxalate (SnC2O4), and cerium oxalate (Ce2(C2O4)3). The total amount of the defect control agent added is 0.1-30 wt.% of the zinc oxide powder mass; for components (a)-(e), it is based on the actual added mass; for component (f), it is based on the theoretical mass (oxide equivalent) of the corresponding oxide generated by its complete thermal decomposition. The defect control agent is used to suppress Zn²⁺ during high-temperature sintering. + Excessive reduction (forming Zn) 0 Vapor and zinc gap defects ZnI Excessive generation of oxygen vacancies, lattice distortion, and abnormal growth of ZnO grains are controlled to keep the grain size within a small range, maintain a high specific surface area and porosity of the material, and ensure a high retention ratio of the ZnO photocatalytic active phase (wurtzite phase). It should be noted that the defect control mechanism in the ZnO system differs fundamentally from that in the TiO2 system. In the TiO2 system, Nb... 5+ Ta 5+ By replacing Ti with a high price 4+ This forms a single donor (net positive charge +1), releases O2, and suppresses oxygen vacancies; while in the ZnO system, the Zn site is Zn². + M³ + Replace Zn² + (e.g. Al³) + →Zn² + MZn•donor (net positive charge +1) is formed, M 4+ / M 5+ / M 6+ Replace Zn² + The formation of higher-priced donors is achieved by providing additional electrons to compensate for Zn vacancies (V Zn′′); simultaneously, donor-type dopants (such as Al2O3 and Ga2O3) have ionic radii that are similar to Zn²⁺. +The difference in crystal structure, preferential segregation to grain boundaries to form spinel-type pinned phases (ZnA₂O₄, ZnGa₂O₄), is the most effective grain growth inhibition mechanism in the ZnO system; equivalent substitution stabilizers (such as MgO) directly stabilize the ZnO lattice by increasing lattice energy, thus inhibiting Zn²⁺ crystal growth. + The defect control agent described in this application is specifically optimized and screened for the ZnO system, taking into account four major mechanisms: equivalent solid solution stability, donor-type grain boundary segregation, rare earth grain inhibition, and oxygen activity self-regulation. The organic additives include at least one of binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; The organic additives may be used alone or in combination, with a total addition amount of 0.1-30 wt.% of the metal oxide-based powder. The adhesive is selected from at least one of the following components: polyethylene oxide (PEO), sodium alginate (SA), chitosan (CTS), polyurethane emulsion (PU), polyacrylamide (PAM), polyvinyl alcohol (PVA), methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), ethylcellulose (EC), polyethylene glycol (PEG, molecular weight 200-20,000), polyacrylic acid (PAA), polyvinyl acetate (PVAc), starch (ST) and its derivatives; The plasticizer is selected from at least one of the following components: triethyl acetylglucosamine citrate (ATEC), epoxidized soybean oil (ESO), polycaprolactone (PCL), glycerin (GLY), dibutyl phthalate (DBP), triethyl citrate (TEC), polyethylene glycol (PEG), sorbitol (SORB), and dioctyl sebacate (DOS). The dispersant is selected from at least one of the following components: polycarboxylate superdispersants (such as Solsperse). TM 32000, Tamol TM SN), polymaleic anhydride (PMA), polyaspartic acid (PASP), ammonium polyacrylate (NH4PAA), sodium polyacrylate (NaPAA), tetramethylammonium hydroxide (TMAH), ammonium citrate (AC), gum arabic (GA) and polyvinylpyrrolidone (PVP). The surfactant is selected from at least one of the following components: sorbitan monooleate (Span-80), cocamidopropyl betaine (CAB), perfluoropolyethers (such as Zonyl® FSO), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), polysorbate 80 (Tween-80), octylphenyl polyoxyethylene ether (Triton X-100), lecithin (LC), and fluorocarbon surfactants (such as Capstone® FS-30); The rheology modifier is selected from at least one of the following components: guar gum (GG), gellan gum (GeG), polyacrylic acid thickeners (such as Carbopol® 940), organic modified montmorillonite (such as Bentonex®), xanthan gum (XG), sodium carboxymethyl cellulose (CMC), bentonite (BT), fumed silica (FS), and polyacrylamide (PAM). The defoamer is selected from at least one of the following components: polydimethylsiloxane (PDMS), polyether defoamer (such as Pluronic® L61), isooctanol (IOA), n-octanol (NOA), silicone oil (such as Dow Corning® 200 Fluid), polyether modified siloxane (such as BYK-024), and mineral oil (MO). The pH adjuster is at least one of ammonia (NH3·H2O, 1-10 mol / L) and hydrochloric acid (HCl, 1-10 mol / L); The reinforcing phase is fibers and / or whiskers, selected from any one or more of the following: (1) Inorganic fibers: glass fiber, basalt fiber, silicon carbide fiber, alumina fiber, mullite fiber, quartz fiber, potassium titanate fiber, aluminum nitride fiber, etc. (2) Ceramic whiskers: silicon carbide whiskers, zinc oxide whiskers, calcium sulfate whiskers, silicon nitride whiskers, barium titanate whiskers, aluminum borate whiskers, magnesium borate whiskers, sodium titanate whiskers, potassium titanate whiskers, zirconium oxide whiskers, aluminum oxide whiskers, calcium carbonate whiskers, aluminum nitride whiskers, etc. (3) Natural mineral fibers: sepiolite fiber, attapulgite fiber, wollastonite fiber, palygorskite fiber, tremolite fiber, actinolite fiber, vermiculite fiber, sillimanite fiber, tourmaline fiber, etc. (4) Synthetic organic fibers: polyacrylonitrile fiber, polyvinyl alcohol fiber, aramid fiber, polyimide fiber, etc. (completely pyrolyzed during degumming heat treatment, playing a role in pore formation and pre-toughening). (5) Metal whiskers: tin whiskers, copper whiskers, silver whiskers, nickel whiskers, iron whiskers, zinc whiskers, aluminum whiskers, gold whiskers, platinum whiskers, cobalt whiskers, titanium whiskers, niobium whiskers, zirconium whiskers, tungsten whiskers, molybdenum whiskers, rhenium whiskers, tantalum whiskers, palladium whiskers, chromium whiskers, magnesium whiskers, cadmium whiskers, etc. (6) Metal fibers: stainless steel fiber, copper fiber, aluminum fiber, nickel fiber, titanium fiber, silver fiber, gold fiber, platinum fiber, palladium fiber, iron fiber, steel fiber, tungsten fiber, molybdenum fiber, niobium fiber, tantalum fiber, zirconium fiber, hafnium fiber, magnesium fiber, zinc fiber, tin fiber, lead fiber, cadmium fiber, cobalt fiber, chromium fiber, beryllium fiber, nickel-titanium alloy fiber, iron-chromium-aluminum alloy fiber, nickel-chromium alloy fiber, Invar alloy fiber, etc. Wherein, the aspect ratio of the reinforcing phase is ≥ 10; The zinc oxide-based composite slurry has a solid content of 20-70 vol.% and a pH of 2-14. The amounts of organic additives and reinforcing phases added (based on the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents) are as follows: Adhesive 1-20 wt.%; Dispersant 0.1-5 wt.%; Plasticizer 0.1-10 wt.%; Surfactant 0.01-5 wt.%; Rheology modifier 0.1-10 wt.%; Defoamer 0.05-10 wt.%; pH adjuster 0.01-10 wt.%; Reinforcing phase: 0.01-30 wt.% (fibers) or 0.01-50 wt.% (whiskers); In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based suspension slurry and the composite slurry are uniformly dispersed by mechanical stirring and / or ball milling. For uniform dispersion of the homogeneous solution, the mechanical stirring rate is 100-3000 rpm; the stirring time is 0.5-180 min; the stirring paddle is made of inert material, preferably polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container is 0.1-2 cm. When mechanically dispersing zinc oxide-based suspension slurry and zinc oxide-based composite slurry, the stirring speed range is 20-3000 rpm; the stirring time range is 15-1500 min; the stirring paddle material is inert; and the distance between the stirring paddle blade and the bottom of the slurry container ranges from 0.1-50 cm. When using ball milling to uniformly disperse zinc oxide-based suspension slurry and zinc oxide-based composite slurry, the ball milling container used for ball milling is made of an inert material, preferably polytetrafluoroethylene; the ball-to-material mass ratio is 0.2-12; the ball milling time is 30-1500 min; the diameter of a single grinding ball is 0.2-12 mm, and the average diameter is 3-8 mm.

[0010] In some embodiments, in step S2, the organic foam is made of polyurethane (PU), melamine formaldehyde (MF), or polystyrene (PS), preferably polyurethane foam (PU); the pore density of the organic foam is in the range of 6-70 PPI, and its macroscopic shape is any one of the following: cylinder, cube, cuboid, sphere, ellipsoid, torus, prism, pyramid, polyhedron, honeycomb block, sheet, arc, arch, tubular, hollow spherical shell, or any combination and deformation thereof; The impregnation is carried out using normal pressure, negative pressure assisted, or alternating negative and normal pressure methods; the impregnation process is carried out at 25±20℃, the normal pressure impregnation time is 30-1800 seconds, and the number of negative and normal pressure alternating impregnations is 1-5 times per impregnation cycle; The negative pressure assistance involves completely immersing the organic foam in the zinc oxide-based composite slurry described in step S1, then evacuating the composite slurry to boiling point within 3 minutes, maintaining boiling for 0.5-10 minutes to ensure that all air in the system is expelled, and then restoring it to ambient pressure. The pressure of the extrusion desizing is controlled at 0.1-10 MPa, and the thickness of the organic foam after extrusion is compressed to 30-95% of the original thickness; The centrifugal desizing process is performed at a speed of 500-5000 rpm for 10-900 seconds. The drying process employs a programmed temperature increase method, with a temperature range of 20~95℃ and relative humidity gradually decreasing from ≥70% to <10%, drying until the mass change rate is <20% / h. After each impregnation-desizing-drying-impregnation cycle, the mass gain rate of the composite slurry loaded in the organic foam is 20-600%. After 2-5 cycles, the cumulative loading of the composite slurry reaches 150-1000% of the original mass of the organic foam, forming a coating thickness of 0.1-3.0 mm, a slurry coating thickness variation coefficient of <30%, and a pore blockage rate of <40%.

[0011] In step S3, the natural air drying is carried out in a ventilated environment with a temperature of 5-45℃, a relative humidity of 30-90%, a ventilation rate of 0.1-10.0 m / s, and a natural air drying time of 2-24 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 50-95℃ at a rate of 0.1-20℃ / min, and the temperature is maintained for 4-24 hours. The airflow rate in the oven is 0.01-10 m / s, and the drying endpoint is a mass change rate of <0.1% / h. The degumming heat treatment includes: The first stage involves raising the temperature at a rate of 1-10℃ / min to 150-250℃ and holding it for 1-360 min. In the second stage, the temperature is increased to 350-450℃ at a rate of 0.5-10℃ / min, and then held for 1-360 min. The third stage involves raising the temperature at a rate of 0.5-10℃ / min to 550-600℃ and holding it for 1-360 min. The degumming heat treatment process is carried out under vacuum or atmospheric conditions. The vacuum conditions are: no gas is introduced and the absolute pressure inside the furnace is maintained below 100 Pa. The atmospheric conditions are: at least one of helium, argon, nitrogen, ammonia, air or oxygen is introduced, the gas flow rate is 0-9000 mL / min, and the pressure inside the furnace is maintained at gauge pressure +50 ~ +9000 Pa.

[0012] In some embodiments, in step S4, the controlled sintering heat treatment temperature is 900-1500℃, the heating rate is 2-20℃ / min, and the holding time is 0.01-24 hours; The controlled sintering heat treatment is carried out under vacuum or atmospheric conditions. The vacuum conditions are: no gas is introduced and the absolute pressure inside the furnace is maintained below 10 Pa. The atmospheric conditions are: at least one of hydrogen, helium, argon, nitrogen, ammonia, air and oxygen is introduced, the gas flow rate is 0-9000 mL / min, and the pressure inside the furnace is maintained at gauge pressure +50~+9000 Pa. It is specifically noted that the upper limit of the controlled sintering heat treatment temperature is set at 1500°C, not exceeding 1500°C, to effectively avoid significant zinc vapor volatilization loss and rapid ZnO grain growth at high temperatures (>1500°C). The actual sintering temperature should be determined comprehensively based on the melting point and eutectic temperature of the sintering aids in the system, with a preferred temperature range of 750~1400°C, to achieve the optimal balance between densification and volatilization suppression. The selection of this temperature window comprehensively considers the melting point characteristics of the sintering aids in the system and the eutectic reaction temperature, aiming to find the optimal balance between the matrix densification process and the suppression of volatile components. Furthermore, the various process parameters of the controlled sintering heat treatment (including heating rate, holding time, and atmosphere control) are synergistically regulated based on the sintering kinetics, thermal stability threshold, microstructural evolution of microstructures, and grain growth behavior of zinc oxide-based photocatalytic foam ceramics, while also fully considering the thermal sensitivity of the active components. Through the above precise regulation, this process can synergistically achieve the following technical objectives: (1) Zinc oxide and photocatalytic active components synergistically construct a foam ceramic mesh skeleton rib structure. At the same time, the width range of the interparticle connection area is controlled within 0.1-50 μm. Under the premise of ensuring high connectivity of the three-dimensional pore structure, the mechanical strength and reactant mass transfer efficiency of the material are synergistically optimized. (2) Through the solid solution substitution and grain boundary segregation mechanism of defect control agents, the Mg² of MgO and other equivalent substitutes is reduced. + Occupy Zn² + Lattice sites stabilize the ZnO lattice structure; enabling Al³⁺ + Ga³ +Donor-type dopants segregate to the ZnO grain boundaries to form spinel-type pinned phases such as ZnAl2O4 and ZnGa2O4; thus enabling La³ + Y³ + Zr 4+ Larger ionic radii accumulate in the grain boundary region, inhibiting abnormal ZnO grain growth through a solute dragging mechanism, effectively preventing Zn²⁺ crystal growth. + Excessive reduction and excessive generation of zinc interstitial defects prevent the increase of composite centers caused by excessive accumulation of oxygen vacancies; the average grain size is controlled within the range of 0.1-10 to maintain a high specific surface area and porosity of the foam ceramic. (3) Significantly enhances the interfacial chemical bonding strength between the reinforcing phase and the ZnO foam ceramic matrix, ensuring that the sintering aid and photocatalytic active components are uniformly distributed at the atomic level inside the skeleton ribs and form a stable chemical bond with the main structure, thus avoiding component peeling during service. (4) Maintain the structural integrity of the three-dimensional interconnected porous framework during the sintering densification process, with a pore structure connectivity rate of >60%, providing channels for the rapid diffusion of pollutant molecules; (5) Maintain and fully utilize the photocatalytic activity of ZnO (band gap of about 3.37 eV), ensure a high retention ratio of the wurtzite phase ZnO photocatalytic active phase, and at the same time broaden the photoresponse range to the visible light region through the construction of heterostructure; while retaining the intrinsic advantage of high carrier mobility of ZnO, ensure a high proportion of the wurtzite phase, which is the high photocatalytic active phase of ZnO, so that ZnO foam ceramics can achieve specific and efficient degradation of target pollutants while possessing excellent mechanical strength and high photocatalytic activity.

[0013] During sintering, based on the chemical properties of the reinforcing phase, the interfacial bonding exhibits two forms: (1) For chemically inert reinforcing phases (such as glass fiber and basalt fiber), they do not undergo significant chemical reactions with the foam ceramic matrix, and the reinforcement is mainly achieved through surface microstructure anchoring and physical integration; (2) For active reinforcing phases (such as silicon carbide whiskers, mullite whiskers, aluminum borate whiskers, and potassium titanate whiskers), they react in situ with the ZnO matrix or photocatalytic functional phase at high temperature to form a chemical bonding layer at the interface. The thickness is controlled within the range of 0.01-5 μm to ensure the interfacial bonding strength while avoiding thermal stress cracking. The crystal phase composition of the monolithic zinc oxide-based photocatalytic foam ceramic is determined by the sintering reaction of the raw material powder used in step S1, including the unreacted original phase and / or the new crystal phase generated in situ during the sintering process; when there are two or more photocatalytic functional phases with different crystal structures or chemical compositions in the ceramic, their phase interfaces can form a heterojunction structure, providing a channel for the efficient separation and migration of photogenerated electron-hole pairs; This application also provides a monolithic zinc oxide-based photocatalytic foam ceramic prepared by the above preparation method. The monolithic zinc oxide-based photocatalytic foam ceramic has a compressive strength ≥0.1 MPa, a porosity of 60-95%, a pore structure connectivity >60%, a ZnO dissolution amount <0.3 mg / L in neutral to weakly alkaline water (pH 6-11), a degradation rate of organic pollutants greater than 85% under visible light, and a degradation rate of organic pollutants greater than 90% under ultraviolet-visible light.

[0014] This application also provides the application of the monolithic zinc oxide-based photocatalytic foam ceramic prepared by the above preparation method in i) the degradation of organic pollutants or water treatment; ii) the application in the preparation of devices for degrading organic pollutants or water treatment devices.

[0015] The organic pollutants mentioned include those listed in the Shanghai Key Controlled New Pollutants List (2023 Edition): Perfluorooctyl sulfonic acid and its salts and perfluorooctyl sulfonyl fluoride (PFOS class); Perfluorooctanoic acid and its salts and related compounds (PFOA class); Decabromodiphenyl ether; Short-chain chlorinated paraffins; Hexachlorobutadiene; Pentachlorophenol and its salts and esters; Trichlorfon; Perfluorohexyl sulfonic acid and its salts and related compounds (PFHxS class); Declone and its cis and trans isomers; Dichloromethane; chloroform; Nonylphenol; Antibiotics (antibacterial drugs); New pollutants that have been phased out (such as anticides and cypermethrin); Microplastics; Bisphenol A.

[0016] This application provides a method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramics and its application in water treatment. The key technical points are: using zinc oxide powder as the main raw material, fully utilizing the inherent photocatalytic activity of ZnO (band gap approximately 3.37 eV, valence band position +3.06 eV vs NHE); supplemented with appropriate defect control agents (MgO, Al2O3, La2O3, ZrO2, etc.) to synergistically regulate grain growth and defect structure during sintering, and suppress Zn²⁺ degradation during high-temperature sintering. +Excessive reduction, excessive generation of zinc interstitial defects, and abnormal growth of ZnO grains are addressed by introducing high aspect ratio whiskers or fibers in situ as reinforcing phases into the preparation system. After controlled sintering, the reinforcing phase and the zinc oxide framework form a three-dimensional interlocking network structure, strengthening the porous framework and significantly improving the material's compressive strength, ensuring structural reliability under complex water flow conditions. Simultaneously, the photocatalytic active component and zinc oxide form a continuous and dense photocatalytic functional phase network through particle fusion and phase boundary bonding. This network itself constitutes the mechanical framework of the foam ceramic, completely avoiding the leaching risk of active components in traditional supported catalysts. Based on the electronic characteristics and molecular structure of the target pollutants, specific heterojunction systems are precisely matched and constructed, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity, achieving efficient targeted degradation of emerging pollutants.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Solving the problems of catalyst shedding and insufficient strength of foam ceramics Using zinc oxide as the main component, its excellent photocatalytic activity and high electron mobility (approximately 200 cm²·V) are fully utilized. -1 ·s -1 By precisely controlling the grain size with defect control agents, high aspect ratio whiskers / fibers are introduced in situ to construct a three-dimensional interlocking network, which greatly improves the compressive strength of foam ceramics. The photocatalytic active components and zinc oxide skeleton form a photocatalytic functional phase network in situ through solid-phase diffusion and interfacial reaction. This network continuously forms three-dimensional skeleton ribs, effectively avoiding the risk of loss of active components caused by physical adsorption. (2) Defect control strategy for ZnO to suppress Zn² + Excessive reduction and abnormal grain growth For Zn² in ZnO system + →Zn 0 To address the unique defect challenges posed by reduction (zinc interstitial defects and oxygen vacancy formation), this application screened and optimized a synergistic defect control strategy involving equivalent substituents (MgO), donor-type grain boundary segregating agents (A2O3, Ga2O3, etc.), and rare earth grain inhibitors (La2O3, Y2O3, etc.), effectively suppressing Zn²⁺. + While excessive reduction and abnormal growth of ZnO grains occur, the high retention ratio of the ZnO wurtzite active phase is maintained, ensuring the long-term photocatalytic stability of the material. At the same time, the introduction of grain boundary modifying phases such as Zn2SiO4 and ZrO2 can improve the chemical stability of ZnO foam ceramics in neutral to weakly alkaline water. (3) The precise matching mechanism between pollutants and heterojunctions breaks through the bottlenecks of degradation efficiency and specificity. Based on the molecular structure, electronic properties, and bond energy characteristics of the target pollutants, a ZnO-based heterojunction system is systematically matched. The high valence band position of ZnO (+3.06 eV vs NHE) endows it with extremely strong oxidizing holes, which is conducive to the efficient generation of ·OH. The photoresponse range can be further broadened to the visible light region through the construction of heterostructures (such as ZnO / ZnFe2O4 (1.9~2.1 eV), ZnO / ZnWO4 (2.7~3.0 eV), etc.), to achieve full-spectrum photocatalytic degradation in the ultraviolet-visible light range. (4) Significant advantages in engineering applicability and green application Foam ceramics possess high structural strength, environmental stability, and easy cutting characteristics, and can be directly filled into reactors such as fixed beds and fluidized beds without the need for downstream separation processes; the three-dimensional interconnected channels enhance mass transfer efficiency and help improve light scattering effects; ZnO raw materials are widely available and inexpensive, giving them a significant engineering cost advantage. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for the preparation of monolithic zinc oxide-based photocatalytic foam ceramics. Detailed Implementation

[0019] To make the technical solution of this application clearer and easier to understand, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0020] Unless otherwise specified, the experimental or testing methods described in the following examples are conventional methods; the reagents and materials described are of analytical grade and obtained from conventional commercial sources unless otherwise specified.

[0021] This application provides a method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, comprising the following steps: Step S1: Preparation of zinc oxide-based composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a zinc oxide-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a zinc oxide-based composite slurry. Step S2: Preparation of zinc oxide-based foam ceramic wet blank The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying treatment is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. Step S3: Preparation of zinc oxide-based foam ceramic green body The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is subjected to debinding heat treatment by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. Step S4: Sintering and Heterogeneous Structure Construction The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, defect control agents suppress Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0022] The following description, in conjunction with specific embodiments, illustrates this point.

[0023] Example 1 A method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic includes the following steps: S1: Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a zinc oxide-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a zinc oxide-based composite slurry; S2: The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. S3: The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is debonded by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. S4: The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, the defect control agent inhibits Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0024] In step S1, the zinc oxide powder has a purity > 98 wt.% and an average particle size D50 of 0.5 μm; The photocatalytic active component is indium trioxide (In₂O₃) with a purity >98 wt.%, an average particle size D50 of 0.6 μm, and an addition amount of 60 wt.% of the zinc oxide powder mass. The sintering aid is bismuth trioxide (Bi2O3) with a purity >98 wt.% and an average particle size D50 of 3 μm, and is added at a rate of 6 wt.% of the zinc oxide powder mass. The defect control agent is magnesium oxide (MgO) with a purity >98 wt.% and an average particle size D50 of 0.5 μm, and is added at an amount of 8 wt.% of the zinc oxide powder mass. The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; wherein the binder is polyvinyl alcohol (PVA); the plasticizer is dibutyl phthalate (DBP); the dispersant is tetramethylammonium hydroxide (TMAH); the surfactant is sorbitan monooleate (Span-80); the rheology modifier is a polyacrylic acid thickener (Carbopol® 940); and the defoamer is a polyether-modified siloxane (BYK-024). The pH adjuster is ammonia water (NH3·H2O, 2 mol / L); The reinforcing phase is mullite whiskers with an average length of 12 μm and an average diameter of 0.8 μm; The zinc oxide-based composite slurry has a solid content of 53 vol.% and a pH of 10. The addition amounts of each component of the organic additive and the reinforcing phase are based on the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents, specifically as follows: binder, 2.7 wt.%; dispersant, 1.1 wt.%; plasticizer, 3.4 wt.%; surfactant, 0.8 wt.%; rheology modifier, 2.0 wt.%; defoamer, 3.9 wt.%; reinforcing phase, 18 wt.%. In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based suspension slurry and the composite slurry are also uniformly dispersed by mechanical stirring. For uniform dispersion of the homogeneous solution, the mechanical stirring rate was 1500 rpm; the stirring time was 5 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. The stirring rate for both the zinc oxide-based suspension slurry and the composite slurry was 1900 rpm; the stirring time was 60 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. In step S2, the organic foam is made of polyurethane (PU), has a pore density of 10 PPI, and has a macroscopic shape of cuboid. The impregnation is carried out under normal pressure; the impregnation process is conducted at 20°C for 180 seconds. The pressure of the extrusion desizing is controlled within 1 MPa, and the thickness of the organic foam after extrusion is compressed to 90% of the original thickness; The drying process employs a programmed temperature increase method, with a drying temperature of 70℃, and continues until the mass change rate is <1% / h. After five cycles of impregnation-desizing-drying-impregnation, the cumulative loading of the composite slurry reaches 540% of the original mass of the organic foam. In step S3, the natural air drying is carried out in a ventilated environment at a temperature of 35°C, a relative humidity of 20%, a ventilation rate of 1 m / s, and a natural air drying time of 15 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 75°C at a rate of 10°C / min, and the temperature is maintained for 6 hours. The airflow rate inside the oven is 1 m / s, and the drying endpoint is a mass change rate of <0.05% / h. The degumming heat treatment includes: In the first stage, the temperature is increased to 250℃ at a rate of 10℃ / min and held for 20 min. The second stage involves raising the temperature to 450℃ at a rate of 5℃ / min and holding it for 10 minutes. The third stage involves raising the temperature to 600℃ at a rate of 3℃ / min and holding it for 5 minutes. The degumming heat treatment process is carried out under a selected atmosphere, namely air, with a gas flow rate of 1000 mL / min and the furnace pressure maintained at gauge pressure +800 Pa. In step S4, the process conditions for the controlled sintering heat treatment include: sintering temperature 1350℃, constant temperature time 1min, and heating rate 10℃ / min. During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: (1) Liquid-phase activation and particle densification reaction of sintering aids The sintering aid, bismuth trioxide (Bi2O3), has a melting point of approximately 817°C. In this embodiment, it completely melts much earlier than the sintering temperature during the heating process, forming a low-viscosity liquid bismuth oxide phase. During the holding stage at 1350°C, the Bi2O3 liquid phase exhibits extremely low viscosity and high fluidity, providing excellent wettability to the surfaces of ZnO and In2O3 particles. This allows for particle rearrangement driven by capillary forces, filling neck voids and significantly accelerating the densification process. The width of the neck connection region between particles is precisely controlled within 10 μm, effectively promoting the formation of a continuous skeletal network structure in the foam ceramic. During the high-temperature holding stage at 1350°C, in-situ liquid formation occurs at the interface between the molten Bi2O3 liquid phase and the ZnO particles. Solid-state interface reaction, forming bismuth-zinc composite oxide phase: Bi₂O₃(l) + 2ZnO → Bi₂Zn₂O₅ [Interfacial traces, liquid-assisted, 1350°C] The generated Bi2Zn2O5 phase is enriched at the neck interface between ZnO particles, playing a role in chemically bonding particles and strengthening the neck connection; at the same time, the Bi2O3 liquid phase is continuously replenished to the interparticle gaps through the concentration gradient, maintaining the continuous driving force of liquid phase sintering, and ensuring the high densification efficiency and structural integrity of the three-dimensional skeleton ribs of the system at the sintering temperature of 1350°C.

[0025] (2) Equivalent solid solution substitution of defect control agents and grain boundary stabilization reaction The defect control agent, magnesium oxide (MgO), is an equivalent substitution stabilizer. Mg²⁺ + The ionic radius is 0.072 nm, similar to Zn²⁺. + (r=0.074 nm) are extremely close (difference only about 2.7%), have the same charge (both +2 valence), and highly satisfy the size and valence matching conditions of the Hume-Rothery solid solution rule. They can be massively dissolved into the ZnO wurtzite lattice through an equivalent substitution mechanism to form (Mg 1-x Zn x O continuous solid solution: Mg² + Replace Zn² + Lattice sites → (Mg,Zn)O solid solution, x≤0.3 [equivalent substitution, neutral defects MgZn×] Mg² + Equivalent solid solution substitution does not generate additional charge carrier defects, directly stabilizing the ZnO wurtzite structure through a lattice energy enhancement mechanism, and thermodynamically suppressing Zn²⁺ during high-temperature sintering. + →Zn 0 Excessive reduction reaction and zinc interstitial defects (Zn I •• Excessive formation of MgO is prevented to avoid damage to photocatalytic activity caused by lattice distortion and color center defects. When the amount of MgO added exceeds the upper limit of ZnO lattice solid solution, supersaturated Mg²⁺... + The MgO is enriched at the grain boundaries of ZnO through a grain boundary segregation mechanism, forming a nanoscale MgO segregation layer. This layer, through a solute dragging effect, synergistically suppresses the abnormal growth of ZnO and In₂O₃ grains, reducing the average grain size D of the two phases. 50 The synergistic control is within 3 μm, maintaining a high specific surface area and photocatalytic active site density of the foam ceramic skeleton.

[0026] (3) Enhanced in-situ interfacial reaction between the phase and the matrix The mullite (3Al2O3·2SiO2) whiskers described as the reinforcing phase are partially active reinforcing phases. Mullite whiskers have a melting point of approximately 1840°C, and the main framework is chemically stable at 1350°C without bulk decomposition. However, under the synergistic effect of the high temperature of 1350°C and the Bi2O3 liquid phase, the SiO2 and Al2O3 components on the whisker surface undergo in-situ solid-liquid phase reaction with the ZnO matrix. (Solid) Interfacial reaction, generating two types of chemically bonded phases at the whisker-matrix interface: SiO2 (mullite surface) + 2ZnO → Zn2SiO4 [zinc silicate, white calcium silicate type, 1350°C] Al₂O₃ (mullite surface) + ZnO → ZnAl₂O₄ [spinel, zinc aluminum spinel, 1350°C] The generated Zn₂SiO₄ (zinc silicate, Eg approx. 5.5 eV) and ZnAl₂O₄ (zinc aluminum spinel, Eg approx. 3.8 eV) together form a layer approximately 5 mm thick at the interface between the mullite whiskers and the ZnO matrix. A 20 nm continuous chemically bonded interface layer upgrades the bonding mode between whiskers and the matrix from purely physical anchoring to chemical bonding, significantly improving the interfacial shear strength and ensuring effective stress transfer. The excellent mechanical properties of mullite whiskers (elastic modulus of about 225 GPa and flexural strength of about 300 MPa) provide a high-modulus load transfer path for the foam ceramic skeleton, significantly improving compressive strength and crack propagation resistance, and completely avoiding the risk of reinforcing phase detachment under water treatment conditions.

[0027] (4) In-situ formation reaction of photocatalytically active new phase The photocatalytic active component, indium trioxide (In₂O₃), undergoes an interfacial reaction with ZnO via solid-phase diffusion during sintering at 1350°C. + Diffusion towards the ZnO particle interface, Zn² + Reverse diffusion towards the In2O3 particle interface leads to the in-situ generation of a new photocatalytically active zinc-indium composite oxide phase at the two-phase contact interface. ZnO + In₂O₃ → ZnIn₂O₄ [Spinel zinc indium salt, 1350°C] The generated ZnIn2O4 has a spinel (AB2O4) crystal structure, Zn² + Occupying a tetrahedral position, In³ + Occupying an octahedral position, the band gap width is approximately 2.5. 3.0 eV (near-edge response in visible light, λ < 420) 500 nm), the conduction band position is approximately The valence band is approximately +2.5 eV (vs NHE) at 0.5 eV (vs NHE). Due to the extremely short holding time (only 1 min) at the sintering temperature of 1350°C in this embodiment, solid-phase diffusion is kinetically limited. The new ZnIn2O4 phase is mainly enriched in the form of nano-scale thin films at the interface between ZnO and In2O3 particles. A large amount of unreacted ZnO phase and In2O3 phase maintain the original wurtzite and ferruginous crystalline phase structures, jointly participating in the construction of the photocatalytic functional phase network.

[0028] (5) Heterogeneous structure construction and tetracycline-targeted degradation mechanism The ZnIn2O4 generated in situ during the controlled sintering heat treatment process, together with the residual In2O3 phase and ZnO phase, jointly construct a ZnO / In2O3 / ZnIn2O4 ternary S-scheme heterojunction system. (1) In2O3 (RP, reduced photocatalyst): The conduction band position is approximately The valence band is approximately +2.3 eV (vs NHE), with a band gap of approximately 2.9 eV (λ < 427 nm, near-edge response in visible light), providing extremely strong reducing conduction band electrons (overpotential up to 0.27 eV relative to O2). - (Generation potential), efficiently generating O2 - Superoxide radicals synergistically participate in the oxidative degradation of tetracycline multifunctional groups; (2) ZnO (OP, oxidative photocatalyst): The conduction band position is approximately With a valence band of approximately +3.06 eV (vs NHE) and a band gap of approximately 3.37 eV (UV activity), it provides extremely strong oxidizing photogenerated holes (overpotential up to 0.34 eV relative to ·OH generation potential +2.72 eV), efficiently oxidizing water molecules / OH. - High concentrations of ·OH hydroxyl radicals are generated; (3) ZnIn2O4 (band gradient bridging intermediate phase): the conduction band position is approximately At 0.5 eV (vs NHE), the valence band position is approximately +2.5 eV (vs NHE), and the energy band position is between In₂O₃ and ZnO, forming an energy band gradient bridging structure; the built-in electric field between the ZnIn₂O₄ conduction band and the ZnO valence band drives the weakly reducing conduction band electrons of ZnO ( The valence band vacancy (+2.3 eV) of In2O3 (0.31 eV) and the weakly oxidizing hole (+2.3 eV) recombine directionally at the ZnIn2O4 bridging interface, while retaining the strong reducing conduction band electrons of In2O3 (0.31 eV). The valence band vacancy of ZnO (+3.06 eV) and the strong oxidizing properties of ZnO (+3.06 eV) enable the synergistic and efficient supply of dual active species.

[0029] The above system targets the pollutant tetracycline (TC, C). 22 H 24 Targeted degradation of N2O8 (MW=444.45 g / mol) was achieved based on the multifunctional group bond energy distribution characteristics of the TC molecule and the aforementioned ·OH-dominated / ·O2-dominated degradation. - Precise matching of the synergistic system. The TC molecule consists of four fused rings (A... Composed of a D-ring, the bond energies and breaking difficulties of each key chemical bond are as follows: C4 N,N-dimethylamino ( C of N(CH3)2) The N-bond energy is approximately 305. 315 kJ / mol, the lowest bond energy site in the entire molecule, is most easily attacked by the electrophilic ·OH group, making it the core attack target for targeted initiation; the phenolic hydroxyl group at C12a... OH (approximately 360 kJ / mol) and enol C OH (approximately 360 kJ / mol) is the second most potent; the highest bond energies are found in the aromatic C=C conjugated bond of the D ring of the benzene ring (approximately 510 kJ / mol) and the carbonyl C=O bond at the C1 and C11 positions (approximately 745 kJ / mol), requiring multi-step synergy of active species to achieve ring-opening mineralization. Therefore, the targeted degradation of tetracycline by the ZnO / In2O3 / ZnIn2O4S-type heterojunction system proceeds in three steps: (1) Target-induced (C4) N,N (Dimethylamino demethylation and side chain degradation): ·OH, due to its high electrophilicity, preferentially attacks the N,N-dimethylamino group at the C4 position of the TC molecule. N-key (305) (315 kJ / mol) triggers the gradual oxidative degradation of N-demethylation and amino side chains, generating demethyltetracycline and a series of deamination derivatives, accompanied by the release of formaldehyde (HCHO); during this stage, ·OH also simultaneously attacks the D ring of the benzene ring containing the phenolic hydroxyl group at C12a (360 kJ / mol), triggering benzene ring hydroxylation, introducing an additional -OH functional group, which greatly weakens the conjugation stability of the D ring, providing a low-barrier channel for subsequent ring opening of the D ring; (2) Oxidative destruction of chromophores (cooperative attack by C1, C11 carbonyl groups and C=C conjugated systems): In2O3 conduction band has high reducing electrons ( (0.6 eV) drives the single-electron reduction of O2 to produce a large amount of ·O2. - Superoxide radicals; O2 - With enol type C=C in TC molecule The C=O conjugated chromophore system undergoes nucleophilic addition, which, in conjunction with the ·OH, oxidatively attacks the C=O carbonyl groups at the C1 and C11 positions, gradually destroying the π-conjugated absorption system of the TC molecule. This causes the characteristic absorption peak of the solution absorbance near 420 nm to decrease rapidly, the chromophore structure to disintegrate, and the TC molecule to be transformed into a low-toxicity non-chromophore intermediate. (3) Ring opening and complete mineralization of polycyclic structures: After pretreatment in steps (1) and (2), the conjugation stability of the TC tetracyclic structure is significantly weakened; high concentrations of ·OH and ·O2 - Coordinated and continuous attack on the remaining A The C=C fused ring aromatic conjugated system (approximately 510 kJ / mol) overcomes the cyclization stabilization energy, sequentially driving the ring opening of each fused ring. Through the gradual oxidation and mineralization of short-chain organic acid intermediates such as oxalic acid, acetic acid, and formic acid, TC is ultimately completely mineralized into CO2, H2O, and NH4. + NO3 - and SO4² - Inorganic small molecules, etc., to achieve complete harmlessness of tetracycline.

[0030] The specificity of this targeted matching stems from the precise fit between the distribution of active species in the system and the bond energy gradient of the TC molecule: the high electrophilicity of ·OH and the N,N-dimethylamino group at the C4 position of the TC molecule. Minimum bond energy of N-bond (305) The high matching of ZnO's strong oxidizing valence band hole (+3.06 eV) to the C12a phenolic hydroxyl benzene ring (oxidation potential approximately +0.8 eV vs NHE) provides a direct oxidation driving force far exceeding that of ZnO itself; In2O3's high reducing conduction band (315 kJ / mol) O2 produced at 0.6 eV - The nucleophilic addition of the conjugated system with the TC enol chromophore achieves precise matching, resulting in efficient destruction of the chromophore; the S-type heterojunction mechanism simultaneously preserves the strong reducing conduction band electrons of In2O3. 0.6 eV) and ZnO strong oxidation valence band holes (+3.06 eV), in ultraviolet light Synergistic targeting and complete mineralization of tetracycline multifunctional groups under visible light synergistic driving.

[0031] The monolithic zinc oxide-based photocatalytic foam ceramic has a rectangular parallelepiped shape; compressive strength ≥ 0.7 MPa, porosity ≥ 85%, pore structure connectivity ≥ 85%, and UV resistance. The degradation rate of tetracycline (TC) under visible light is ≥91%; Those skilled in the art can determine the process window that satisfies the above effects through limited experiments under conventional equipment conditions, based on the specific type of zinc oxide powder, the type of photocatalytic active component, and the characteristics of the reinforcing phase.

[0032] Example 2 A method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic includes the following steps: S1: Add organic additives and pH adjusters to deionized water and disperse them evenly to form a homogeneous solution; add zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents to the solution in batches and disperse them evenly to form a zinc oxide-based suspension slurry; add fiber and / or whisker reinforcing phase to the suspension slurry and disperse it evenly to form a zinc oxide-based composite slurry; S2: The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. S3: The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is debonded by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. S4: The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, the defect control agent inhibits Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0033] In step S1, the zinc oxide powder has a purity > 98 wt.% and an average particle size D50 of 0.5 μm; The photocatalytic active component is tungsten trioxide (WO3) with a purity >98 wt.% and an average particle size D50 of 1 μm, and is added at an amount of 60 wt.% of the zinc oxide powder mass. The sintering aid is copper oxide (CuO) with a purity >98 wt.% and an average particle size D50 of 2 μm, and is added at an amount of 8 wt.% of the zinc oxide powder mass. The defect control agent is lanthanum trioxide (La₂O₃) with a purity >98 wt.% and an average particle size D50 of 3 μm, and is added at 4 wt.% of the zinc oxide powder mass. The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; wherein the binder is methylcellulose (MC); the plasticizer is triethyl citrate (TEC); the dispersant is ammonium citrate (AC); the surfactant is cocamidopropyl betaine (CAB); the rheology modifier is organically modified montmorillonite (Bentonex®); and the defoamer is mineral oil (MO). The pH adjuster is ammonia water (NH3·H2O, 2 mol / L); The reinforcing phase is silicon carbide (SiC) whiskers with an average length of 20 μm and an average diameter of 0.8 μm; The zinc oxide-based composite slurry has a solid content of 57 vol.% and a pH of 10. The addition amounts of each component of the organic additive and the reinforcing phase are based on the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents, specifically as follows: binder, 0.5 wt.%; dispersant, 3.5 wt.%; plasticizer, 1.8 wt.%; surfactant, 2.6 wt.%; rheology modifier, 0.9 wt.%; defoamer, 1.4 wt.%; reinforcing phase, 21.8 wt.%. In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based suspension slurry and the composite slurry are also uniformly dispersed by mechanical stirring. For the uniform dispersion of the homogeneous solution, the mechanical stirring rate was 1300 rpm; the stirring time was 20 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. The stirring rate for both the zinc oxide-based suspension slurry and the composite slurry was 2000 rpm; the stirring time was 150 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. In step S2, the organic foam is made of polyurethane (PU), the pore density of the organic foam is 10 PPI, and its macroscopic shape is a cube. The impregnation is carried out under normal pressure; the impregnation process is conducted at 25°C for 120 seconds. The pressure of the extrusion desizing is controlled within 1 MPa, and the thickness of the organic foam after extrusion is compressed to 90% of the original thickness; The drying process employs a programmed temperature increase method, with a drying temperature of 65℃, and continues until the mass change rate is <1% / h. After five cycles of impregnation-desizing-drying-impregnation, the cumulative loading of the composite slurry reaches 550% of the original mass of the organic foam. In step S3, the natural air drying is carried out in a ventilated environment at a temperature of 30°C, a relative humidity of 10%, a ventilation rate of 1 m / s, and a natural air drying time of 8 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 72°C at a rate of 5°C / min, and the temperature is maintained for 12 hours. The airflow rate inside the oven is 1 m / s, and the drying endpoint is a mass change rate of <0.05% / h. The degumming heat treatment includes: In the first stage, the temperature is increased to 250℃ at a rate of 10℃ / min and held for 30 min. The second stage involves raising the temperature to 450℃ at a rate of 5℃ / min and holding it for 5 minutes. The third stage involves raising the temperature to 600℃ at a rate of 2℃ / min and holding it for 1 min. The degumming heat treatment process is carried out under a selected atmosphere, namely air, with a gas flow rate of 1000 mL / min and the furnace pressure maintained at gauge pressure +600 Pa. In step S4, the process conditions for the controlled sintering heat treatment include: sintering temperature 1000℃, constant temperature time 1min, and heating rate 10℃ / min. During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: (1) Activation of the eutectic liquid phase and interfacial densification reaction of sintering aids The sintering aid, copper oxide (CuO), has a melting point of approximately 1326°C. In this embodiment, it exists in a solid state at the sintering temperature (1000°C) and cannot generate an intrinsic liquid phase. However, CuO... ZnO The WO3 ternary system is approximately 860 A eutectic reaction occurs within the 920°C range, significantly lower than the melting points of each component. During the heating to 1000°C, a Cu-rich activated liquid phase forms at the interface between ZnO and WO3 particles. During the 1000°C holding period, the wettability of the activated liquid phase increases, driving the rearrangement and densification of ZnO and WO3 particles. The width of the neck connection region between particles is precisely controlled within 10 μm, effectively promoting the formation of a continuous skeletal network structure in the foam ceramic. Simultaneously, CuO undergoes an in-situ solid-state reaction with ZnO and WO3 at the interface, generating a new phase with photocatalytic activity. CuO + WO3 → CuWO4 [cuplotungstate, scheelite type, 1000°C] CuO + ZnO → (Cu,Zn)O solid solution [low temperature region] or CuO remains stable [high temperature region] The generated CuWO4 (copper tungstate, monoclinic crystal system, Eg about 2.3 eV, visible light response λ < 540 nm) is preferentially enriched at the neck interface of WO3 particles in the form of a nanoscale interfacial film. It not only plays a mechanical role in strengthening the chemical bonding between grains, but more importantly, it provides an additional visible light responsive active phase, realizing the dual contribution of sintering aid in both densification promotion and photocatalytic function synergistic enhancement.

[0034] (2) Grain boundary segregation stabilization reaction of defect control agents The defect control agent, lanthanum trioxide (La₂O₃), belongs to the grain boundary segregation inhibitor category. La³ + The ionic radius is 0.116 nm, which is much larger than that of Zn²⁺. + (0.074 nm) and W 6+ (0.060 nm), does not satisfy the solid solution rule, and has extremely low solid solubility in ZnO and WO3 lattices. La³ + It mainly accumulates in the grain boundary region of ZnO and WO3 grains through grain boundary segregation mechanism, in the form of nano-sized La2Zn3O6 (or La x Zn O u The grain boundary phase is dispersed at the grain boundaries and simultaneously suppresses the abnormal growth of ZnO and WO3 grains through the solute drag effect, thus reducing the average grain size D of the two phases. 50 The synergistic control is within 4 μm, maintaining a high specific surface area and photocatalytic active site density of the foam ceramic skeleton.

[0035] Furthermore, La2O3 enriched at grain boundaries can undergo a trace solid-phase interfacial reaction with ZnO under sintering conditions at 1000°C, forming a lanthanum-zinc composite oxide grain boundary pinning phase in situ. La₂O₃ + 2ZnO → La₂Zn₂O₅ [trace grain boundaries, solute-stretched pinned phase, 1000°C] The generated La2Zn2O5 phase forms a continuous pinning coating layer at the ZnO grain boundaries, further locking the grain boundary migration rate and synergistically suppressing Zn²⁺ migration. + →Zn 0 Excessive reduction and zinc interstitial defects (Zn I •• Excessive aggregation of ZnO (wurtzite) is prevented to maintain a high retention ratio of the active phase and ensure the long-term photocatalytic stability of the material.

[0036] (3) Enhanced in-situ interfacial reaction between the phase and the matrix The silicon carbide (SiC) whiskers described are chemically extremely stable and belong to the inert reinforcing phase. Under sintering conditions of 1000°C in air atmosphere, slight controllable oxidation occurs on the whisker surface (the oxidation rate is controlled by the dense SiO2 passivation film), forming a layer approximately 1 mm thick on the whisker surface. 5 nm continuous SiO2 passivation film: SiC (surface) + O2 → SiO2 (passivation layer) + CO2 [1000°C, air, slightly controllable] The generated SiO2 passivation film undergoes a trace solid-phase interfacial reaction with ZnO at 1000°C, forming a Zn2SiO4 zinc silicate interfacial bonding layer in situ on the surface of SiC whiskers: SiO2 (SiC surface passivation layer) + 2ZnO → Zn2SiO4 [trace amount at the interface, 1000°C] The generated Zn2SiO4 achieves a strong bond between SiC whiskers and the foam ceramic skeleton through surface microstructure anchoring and chemical intercalation mechanism; the excellent mechanical properties of SiC whiskers (elastic modulus of about 480 GPa, flexural strength of about 800 MPa) provide a high modulus load transfer path for the foam ceramic skeleton ribs, significantly improving compressive strength and crack propagation resistance, and ensuring structural reliability under water flow impact conditions.

[0037] (4) In-situ formation reaction of photocatalytically active new phase The photocatalytic active component, tungsten trioxide (WO3), undergoes an interfacial reaction with ZnO via solid-phase diffusion during high-temperature sintering at 1000°C. + Diffusion towards the WO3 particle interface leads to in-situ generation of a new photocatalytically active phase, ferrotungstate-type zinc tungstate (ZnWO4). ZnO + WO3 → ZnWO4 [ferrotungsten structure, 1000°C] ZnWO4 (ferrotungsten-iron type, monoclinic system, space group P2 / c) has a band gap of approximately 3.7. 4.0 eV (UV response), exhibiting excellent photochemical stability. The formation of the ZnWO4 phase will enhance the W content of WO3. 6+ Fixed in the form of tungstate, the volatilization loss of WO3 component is effectively suppressed at a sintering temperature of 1000°C, maintaining the stability of the stoichiometry of the photocatalytic active components; the conduction band position of the ZnWO4 phase is approximately... At a voltage of 0.4–0 eV (vs NHE), it forms a band gradient ladder with ZnO and WO3, participating in the subsequent carrier transport of the Z-type heterojunction. Due to the extremely short sintering time (1 min) in this embodiment, the new ZnWO4 phase is mainly enriched in the form of nanofilms at the interface between ZnO and WO3 particles. A large amount of unreacted ZnO phase and WO3 phase maintain their original crystal structure and jointly participate in the construction of the photocatalytic functional phase network.

[0038] (5) The heterostructure construction and nonylphenol targeted degradation mechanism The ZnWO4 generated in situ during the controlled sintering heat treatment process, together with the residual ZnO phase, WO3 phase, and a small amount of CuWO4 phase at the interface, jointly construct a ZnO / WO3 / ZnWO4 direct Z-scheme heterojunction system. CuWO4 participates in carrier transport as an interface gain phase. (1) ZnO (RP, reduced photocatalyst): The conduction band position is approximately With a voltage of 0.31 eV (vs NHE) and a valence band position of approximately +3.06 eV (vs NHE), it provides strongly reducing conduction band electrons, efficiently driving the single-electron reduction of O2 to produce O2. - Superoxide radicals; (2) WO3 (OP, oxidizing photocatalyst): The conduction band position is approximately +0.3 eV (vs NHE), and the valence band position is approximately +3.1 eV (vs NHE), providing extremely strong oxidizing photogenerated holes (overpotential reaches 0.38 eV relative to ·OH generation potential), efficiently oxidizing water molecules / OH - It produces a high concentration of ·OH; the band gap of WO3 is approximately 2.6. 2.8 eV (λ<460 nm), achieving efficient photon utilization in the visible light region; (3) ZnWO4 (band bridging intermediate phase): the conduction band position is approximately With a valence band of 0.3–0 eV and a valence band position of approximately +3.5–4.0 eV (vs NHE), it serves as a band gradient bridging phase between ZnO and WO3, where the built-in electric field of ZnWO4 assists electron exchange at the Z-type interface. Directed recombination and annihilation of holes; under ultraviolet light irradiation, ZnWO4 itself also generates photogenerated carriers, which contribute to the photocatalytic activity inside the framework ribs; (4) CuWO4 (visible light gain phase): conduction band position approximately It has a valence band of approximately +1.8 eV (vs NHE) and a band gap of approximately 2.3 eV (λ<540 nm). It is distributed in the form of a thin film at the interface of WO3 particles. Under visible light (λ<540 nm) irradiation, it generates additional photogenerated holes, thus broadening the overall visible light response coverage.

[0039] Under visible light irradiation, the built-in electric field at the ZnO / WO3 interface drives the weakly reducing electrons (+0.3 eV) in the WO3 conduction band and the weakly oxidizing holes (+3.06 eV) in the ZnO valence band to recombine and annihilate in a directional manner at the ZnWO4 bridging interface; simultaneously, the reducing electrons in the ZnO conduction band are retained. 0.31 eV) Highly efficient reduction of O2 to produce O2 - And the highly oxidizing holes in the WO3 valence band (+3.1 eV, far exceeding the standard redox potential of ·OH +2.72 eV vs NHE) efficiently oxidize water molecules / OH. - It generates ·OH, enabling a synergistic and efficient supply of dual active species.

[0040] The above system is effective against the target pollutant nonylphenol (NP, C). 15 H 24 The targeted degradation of 4-nonylphenol (O, MW = 220.35 g / mol) is based on the precise matching of the bond energy characteristics of the NP molecule with the aforementioned strong ·OH system. The NP molecule is a phenol with a nonyl group substituted at the 4-position (C9H). 19 ) via C The structure is composed of C bonds, and the bond energies and breaking priorities of the key chemical bonds are as follows: Benzene ring - nonyl chain connection C The C bond energy is approximately 346 kJ / mol, the lowest among all bond energy sites in the molecule, making it a preferred target for the ·OH group; phenol C The OH bond (approximately 360 kJ / mol) is the second most important; the nonyl chain contains various C atoms. The C bond (approximately 346 kJ / mol) constitutes the secondary target of attack; the aromatic C=C conjugated bond of the benzene ring (approximately 510 kJ / mol) has the highest bond energy, requiring multi-step synergy of active species to achieve ring-opening mineralization. Accordingly, the targeted degradation of nonylphenol by the system proceeds in three steps: (1) Targeted initiation (benzene ring) nonyl chain C C-bond breaking and side-chain oxidative degradation: WO3 valence band strong oxidizing holes (+3.1 eV) directly oxidize the phenolic hydroxyl groups of NP molecules ( OH), inducing single-electron oxidation to form phenoxy radicals (PhO·); high concentrations of ·OH simultaneously and preferentially attack the C-terminal junction between the benzene ring and the nonyl chain. C bond (346 kJ / mol), inducing C C homolytic cleavage, gradually stripping the nonyl chain ( C9H 19 →CO2+H2O), converting long-chain nonylphenol into short-chain alkylphenol intermediates (such as p-cresol), reducing molecular hydrophobicity and biotoxicity; (2) Phenolic ring hydroxylation activation (phenol C) OH oxygenation, activation before ring opening: · OH continuously attacks the high electron cloud density carbons (C2 and C4) of the phenol ring. (OH, ortho / para position), introducing additional [OH group] via electrophilic addition and oxidation reaction. OH groups sequentially convert phenol into catechol (catechol) and hydroquinone (hydroquinone); ZnO carries reducing electrons ( 0.31 eV) drives O2 production. - , O2 - Further nucleophilic addition with the benzoquinone intermediate accelerates the destruction of the benzene ring π-conjugated system, providing a low-barrier channel for subsequent ring opening; (3) Ring opening and complete mineralization of benzene ring: ·OH and ·O2 - Synergistic and sustained attack on the C=C aromatic conjugated system of catechol / hydroquinone (approximately 510 kJ / mol) via hydroxyl radical addition. The elimination mechanism overcomes the conjugation stabilization energy of the aromatic ring, sequentially driving the ring-opening of the benzene ring. Through the gradual oxidation and mineralization of short-chain fatty acid intermediates such as maleic acid, oxalic acid, acetic acid, and formic acid, NP is finally completely mineralized into inorganic small molecules such as CO2 and H2O, achieving efficient degradation of nonylphenol from a hydrophobic long-chain phenol to complete mineralization.

[0041] The specificity of this targeted matching stems from the precise fit between the strong ·OH system and the bond energy gradient of the NP molecule: the high electrophilicity of ·OH and the C-phase of the NP benzene ring-nonyl chain. The lowest bond energy of the C bond (346 kJ / mol) is highly matched, enabling preferential stripping of the alkyl side chain; the strong oxidizing hole of WO3 (+3.1 eV) has a significantly stronger driving force for the direct oxidation of the phenolic hydroxyl group than the traditional TiO2 system (+2.7 eV), resulting in more sufficient accumulation of phenoxy radicals; the Z-type heterojunction mechanism simultaneously retains the reducing conduction band electrons of ZnO ( O2 produced at 0.31 eV - The ·OH generated by the strong oxidative valence band hole (+3.1 eV) of WO3 enables efficient targeted degradation of nonylphenol under visible light.

[0042] The monolithic zinc oxide-based photocatalytic foam ceramic has a cubic shape; compressive strength ≥ 0.5 MPa, porosity ≥ 81%, pore structure connectivity ≥ 85%, and nonylphenol (NP) degradation rate ≥ 93% under ultraviolet light. Those skilled in the art can determine the process window that satisfies the above effects through limited experiments under conventional equipment conditions, based on the specific type of zinc oxide powder, the type of photocatalytic active component, and the characteristics of the reinforcing phase.

[0043] Example 3 A method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic includes the following steps: S1: Add organic additives and pH adjusters to deionized water and disperse them evenly to form a homogeneous solution; add zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents to the solution in batches and disperse them evenly to form a zinc oxide-based suspension slurry; add fiber and / or whisker reinforcing phase to the suspension slurry and disperse it evenly to form a zinc oxide-based composite slurry; S2: The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. S3: The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is debonded by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. S4: The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, the defect control agent inhibits Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. +Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0044] In step S1, the zinc oxide powder has a purity > 98 wt.% and an average particle size D50 of 0.5 μm; The photocatalytic active component is tin dioxide (SnO2) with a purity >98 wt.%, an average particle size D50 of 3 μm, and an addition amount of 60 wt.% of the zinc oxide powder. The sintering aid is calcium carbonate (CaCO3) with a purity >98 wt.% and an average particle size D50 of 5 μm, and is added at a rate of 5.5 wt.% of the zinc oxide powder mass. The defect control agent is ferrous oxide (FeO) with a purity >98 wt.% and an average particle size D50 of 3 μm, and is added at 7.8 wt.% of the zinc oxide powder mass. The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; wherein the binder is ethyl cellulose (EC); the plasticizer is sorbitol (SORB); the dispersant is polyvinylpyrrolidone (PVP); the surfactant is a perfluoropolyether (Zonyl® FSO); the rheology modifier is fumed silica (FS); and the defoamer is polydimethylsiloxane (PDMS). The pH adjuster is ammonia water (NH3·H2O, 2 mol / L); The reinforcing phase consists of aluminum borate whiskers and silicon carbide fibers; wherein the aluminum borate whiskers have an average length of 9 μm and an average diameter of 0.5 μm; and the silicon carbide fibers have an average length of 25 μm and an average diameter of 0.6 μm. The zinc oxide-based composite slurry has a solid content of 56 vol.% and a pH of 10. The addition amounts of each component of the organic additive and the reinforcing phase are based on the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents, specifically as follows: binder, 3.3 wt.%; dispersant, 0.9 wt.%; plasticizer, 2.5 wt.%; surfactant, 1.6 wt.%; rheology modifier, 3.8 wt.%; defoamer, 0.7 wt.%; reinforcing phase, 25 wt.%. In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based suspension slurry and the composite slurry are also uniformly dispersed by mechanical stirring. For the uniform dispersion of the homogeneous solution, the mechanical stirring speed was 1100 rpm; the stirring time was 15 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. The stirring rate for both the zinc oxide-based suspension slurry and the composite slurry was 1700 rpm; the stirring time was 200 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. In step S2, the organic foam is made of polyurethane (PU), has a pore density of 10 PPI, and has a cylindrical shape. The impregnation is carried out under normal pressure; the impregnation process is conducted at 25°C for 150 seconds. The pressure of the extrusion desizing is controlled within 1 MPa, and the thickness of the organic foam after extrusion is compressed to 90% of the original thickness; The drying process employs a programmed temperature increase method, with a drying temperature of 75℃, and continues until the mass change rate is <1% / h. After four cycles of impregnation-desizing-drying-impregnation, the cumulative loading of the composite slurry reaches 480% of the original mass of the organic foam. In step S3, the natural air drying is carried out in a ventilated environment at a temperature of 28°C, a relative humidity of 30%, a ventilation rate of 1 m / s, and a natural air drying time of 12 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 75°C at a rate of 5°C / min, and the temperature is maintained for 6 hours. The airflow rate inside the oven is 1 m / s, and the drying endpoint is a mass change rate of <0.05% / h. The degumming heat treatment includes: In the first stage, the temperature is increased to 250℃ at a rate of 10℃ / min and held for 30 min. The second stage involves raising the temperature to 450℃ at a rate of 5℃ / min and holding it for 2 minutes. The third stage involves raising the temperature to 600℃ at a rate of 2℃ / min and holding it for 1 min. The degumming heat treatment process is carried out under a selected atmosphere, namely air, with a gas flow rate of 1000 mL / min and the furnace pressure maintained at gauge pressure +700 Pa. In step S4, the process conditions for the controlled sintering heat treatment include: sintering temperature 1400℃, constant temperature time 5min, and heating rate 5℃ / min. During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: (1) Thermal decomposition and activation reaction of sintering aids The sintering aid, calcium carbonate (CaCO3), undergoes a thermal decomposition reaction during heat treatment. The initial decomposition temperature of CaCO3 is approximately 840°C, and in this embodiment, complete decomposition is achieved when the temperature is raised to approximately 900°C, generating highly active nano-sized CaO particles and CO2 gas. CaCO3 → CaO + CO2↑ [≥840°C, thermal decomposition] The in-situ generated nanoscale CaO exhibits extremely high activity (large surface area and high lattice defect density). Under high-temperature sintering conditions of 1400°C, it rapidly undergoes a solid-phase reaction at the interface with ZnO particles, generating a scheelite-type calcium zincate interface activated phase. Since 1400°C exceeds the eutectic temperature range of ZnO and CaO, the system enters a high-temperature liquid-phase densification stage under the guidance of CaO. CaO drives the rearrangement of ZnO and SnO2 particles through a local liquid-phase mass transfer mechanism, with the width of the neck connection region between particles precisely controlled within 15 μm, effectively promoting the formation of a continuous skeletal network structure in the foam ceramic. Simultaneously, trace amounts of CaO undergo a solid-phase interface reaction with SnO2, generating a calcium stannate interface phase. CaO + ZnO → CaZnO2 [Calcium zincate, trace amount at interface, 1400°C] CaO + SnO2 → CaSnO3 [Calcium stannate, perovskite type, 1400°C] The generated CaSnO3 (perovskite type, Eg about 4.4 eV, UV active) is preferentially enriched at the neck interface of ZnO and SnO2 particles. It strengthens the interparticle connection through chemical bonding, thereby improving densification and achieving the superposition of the sintering aid's functions in mechanical strengthening and photocatalysis.

[0045] (2) Equivalent solid solution substitution of defect control agents and oxygen activity adjustment reaction The defect control agent, ferrous oxide (FeO), is used in a high-temperature oxidizing atmosphere (air) at 1400°C. +It is oxidized at high temperature and partially converted into Fe³ + This forms a mixed state of Fe2O3 and Fe3O4, which then undergoes a solid-state reaction with ZnO, resulting in the in-situ formation of zinc-iron spinel (ZnFe2O4) grain boundary pinning phase at the grain boundaries. 4FeO + O2 → 2Fe2O3 [High-temperature oxidation, air, ≥1000°C] Fe₂O₃ + ZnO → ZnFe₂O₄ [Spinel-type zinc ferrite, 1400°C] The resulting ZnFe2O4 (spinel type, Eg approx. 1.9) 2.1 eV, visible light response λ<590 A nanoscale pinning phase (650 nm) is formed at the grain boundaries of ZnO grains, suppressing abnormal growth of ZnO grains at 1400°C through the Zener pinning mechanism; simultaneously, Fe³⁺… + Through donor doping (Fe³) + Replace Zn² + MFe_Zn• (net positive charge +1) forms a shallow donor level, compensating for Zn vacancy acceptor (V_Zn) defects and suppressing zinc interstitial defects (Zn). I •• Excessive formation of ZnFe2O4 phase. The ZnFe2O4 phase exhibits reversible Fe³⁺ formation. + / Fe² + The redox pair, during high-temperature sintering at 1400°C, locally maintains an oxidizing atmosphere around ZnO particles through a dynamic oxygen release / storage mechanism, thus thermodynamically synergistically inhibiting Zn²⁺ oxidation. + →Zn 0 Excessive reduction enables the self-regulating and stabilizing function of oxygen activity.

[0046] (3) Enhanced in-situ interfacial reaction between the phase and the matrix In this embodiment, the reinforcing phase consists of aluminum borate whiskers (Al). 18 B4O 33 It is composed of silicon carbide fiber (SiC) and silicon carbide fiber, and the two exhibit different interfacial bonding mechanisms during sintering at 1400°C: ① Aluminum borate whiskers (Al 18 B4O 33 — Active reinforcing phase, forming a zinc aluminate bonding layer at the interface: aluminum borate (Al) 18 B4O 33 Whiskers belong to the active-enhancing phase (Al). B During the high-temperature sintering process at 1400°C, the B2O3 (boron oxide, melting point approximately 450°C, which is already liquefied) on the surface of the whiskers diffuses into the ZnO matrix interface in liquid phase, while the Al³⁺ on the surface of the whiskers... +Migrate outwards and interact with the ZnO matrix in the whiskers An in-situ solid-liquid reaction occurs at the matrix interface, forming a zinc aluminate bonded layer: Al2O3 (Al 18 B4O 33 Surface diffusion) + ZnO → ZnAl2O4 [spinel bonded layer, 1400°C] B₂O₃ (liquid) + ZnO → Zn₂B₂O₅ [Zinc borate, interface-assisted, 1400°C] The generated ZnAl2O4 (zinc aluminum spinel, Eg approx. 3.8 eV) forms a layer approximately 10 mm thick at the interface between the aluminum borate whiskers and the ZnO matrix. A 20 nm continuous chemically bonded interface layer upgrades the bonding mode between whiskers and the matrix to chemical bonding, significantly improving the interfacial shear strength; Zn2B2O5 (zinc borate) helps fill the pores of the bonding layer, further strengthening the interfacial bonding; the excellent mechanical properties of aluminum borate whiskers (elastic modulus of about 400 GPa) provide a high-rigidity load transfer path for the foam ceramic skeleton ribs.

[0047] ②SiC fiber – Inert reinforcing phase, high-temperature oxidation to form SiO2 anchoring layer: SiC fibers have extremely high chemical stability. Under a high-temperature air atmosphere of 1400°C, the fiber surface undergoes controllable oxidation to form a SiO2 anchoring layer with a thickness of approximately 2 mm. An 8 nm continuous SiO2 passivation film; the SiO2 passivation film undergoes a solid-phase interfacial reaction with ZnO at 1400°C, forming an in-situ Zn2SiO4 (zinc silicate) anchoring layer: SiC (surface) + O2 → SiO2 + CO2 [1400°C, air, controllable] SiO2 (passivation layer) + 2ZnO → Zn2SiO4 [interface anchoring layer, 1400°C] The generated Zn2SiO4 achieves a strong bond between SiC fibers and the foam ceramic skeleton through a surface microstructure anchoring mechanism; the SiC fibers (elastic modulus of about 430 GPa and tensile strength of about 3.5 GPa) provide high-strength tensile toughening for the foam ceramic, and work synergistically with the bending toughening of aluminum borate whiskers to comprehensively improve the overall mechanical properties of the foam ceramic skeleton.

[0048] (4) In-situ formation reaction of photocatalytically active new phase The photocatalytically active component, tin dioxide (SnO2), undergoes an interfacial reaction with ZnO through solid-phase diffusion during sintering at 1400°C. + Diffusion towards the SnO2 particle interface, Sn 4+ Reverse diffusion towards the ZnO particle interface leads to the in-situ formation of a new photocatalytically active phase of zinc-tin composite oxide at the contact interface. 2ZnO + SnO2 → Zn2SnO4 [Spinel-type zinc stannate, 1400°C, ZnO-rich region] ZnO + SnO2 → ZnSnO3 [orthorhombic crystal form, 1400°C, localized reaction] The amount of the aforementioned zinc-tin composite oxide new phase formed is determined by both the sintering temperature (1400°C) and the holding time (5 min), and it is mainly enriched at the interface between ZnO and SnO2 particles. Specifically, Zn2SnO4 (spinel type, Eg approximately 3.6 eV, UV near-edge response) and ZnSnO3 (perovskite type, Eg approximately 3.5 eV) form a bandgap distribution at the interface, while a large amount of unreacted ZnO phase (Eg ≈ 3.37 eV) and SnO2 phase (Eg ≈ 3.6 eV) maintain their original crystal structure. Simultaneously, ZnFe2O4 (Eg approximately 1.9 eV) derived from the defect control agent... 2.1 The (eV) phase, as a visible light active phase, participates in the construction of a multi-element photocatalytic functional phase network.

[0049] (5) Heterogeneous structure construction and bisphenol A targeted degradation mechanism The Zn2SnO4, ZnSnO3, and ZnFe2O4 generated in situ during the controlled sintering heat treatment process, together with the residual ZnO and SnO2 phases, jointly construct a ZnO / SnO2 / Zn2SnO4 / ZnFe2O4 multi-element heterojunction system. ZnO / SnO2 constitutes the core type II heterojunction, while ZnFe2O4 provides the extended visible light response. (1) ZnO (OP, oxidized photocatalyst): The conduction band position is approximately 0.31 eV (vs NHE), with a valence band position of approximately +3.06 eV (vs NHE), providing extremely strong oxidizing photogenerated holes and efficiently generating ·OH; (2) SnO2 (RP, reduced photocatalyst): The conduction band position is approximately 0.07 eV (vs NHE), valence band position approximately +3.53 eV (vs NHE), Eg approximately 3.6 eV; SnO2 / ZnO forms a type II heterojunction, with SnO2 conduction band electron transfer to ZnO conduction band driving O2. - The generation of ZnO valence band holes and their transfer to SnO2 valence band synergistically enhances the strong oxidizing hole pool; (3) Zn2SnO4 (interface bridging phase): the conduction band position is approximately The valence band is 0.5 eV, the valence band position is approximately +3.1 eV (vsNHE), and the Eg is approximately 3.6 eV. It is distributed in the form of a nanofilm at the ZnO and SnO2 interface to assist in the directional transport of charge carriers and optimize the charge separation efficiency at the heterojunction interface. (4) ZnFe2O4 (visible light gain phase): the conduction band position is approximately 0.6 eV, valence band position is approximately +1.5 eV (vs NHE), Eg approximately 1.9 eV. 2.1 eV (λ<590) (650 nm, full visible light spectrum response), under visible light irradiation, additional photogenerated electrons are generated, participating in O2. - The generation of superoxide radicals significantly expands the overall photoresponse range into the visible light region.

[0050] In ultraviolet Under visible light irradiation, at the ZnO / SnO2 type II heterojunction interface, photogenerated electrons in the SnO2 conduction band ( 0.07eV) transferred to the ZnO conduction band ( 0.31 eV (thermodynamically favorable), which in turn drives the reduction of O2 to produce ·O2. - ZnO valence band holes (+3.06 eV) are retained in the ZnO valence band, synergistically with SnO2 valence band strong oxidizing holes (+3.53 eV) to oxidize water molecules / OH groups. - High concentrations of ·OH are generated; ZnFe2O4 supplements photogenerated carriers under visible light, achieving full-spectrum photocatalytic synergy.

[0051] The above system is effective against the target pollutant bisphenol A (BPA, C). 15 H 16 O2, MW = 228.29 g / mol, i.e., 4,4' Targeted degradation of isopropylidene bisphenol (BPA) based on the bond energy characteristics of the BPA molecule and the aforementioned ·OH-dominant / ·O2-dominant properties. - Precise matching of the synergistic system. The BPA molecule consists of two p-hydroxyphenol groups connected by an isopropylidene group (…). C(CH3)2 The carbon bridges connect the bonds, and the bond energies and breaking priorities of the key chemical bonds are as follows: Isopropylidene carbon bridge C The C bond energy is approximately 346 kJ / mol, the lowest bond energy site in the entire molecule, and the core attack target initiated by ·OH; phenol C The OH bond (approximately 360 kJ / mol) has the second highest bond energy; the aromatic C=C conjugated bond in the benzene ring (approximately 510 kJ / mol) has the highest bond energy, requiring multi-step synergistic ring-opening mineralization by active species. Therefore, the targeted degradation of bisphenol A in this system proceeds in three steps: (1) Targeted initiation (isopropylene carbon bridge C) C-bond breakage, dissociation of the two phenolic rings): ZnO's strong oxidizing properties, including a valence band vacancy (+3.06 eV), directly oxidize the phenolic hydroxyl groups of the BPA molecule. OH), inducing single-electron oxidation to form phenoxy radicals (PhO·); high concentrations of ·OH preferentially attack the isopropylidene carbon bridge C. C bond (346 kJ / mol), inducing C C homolytic cleavage breaks the BPA bibenzene ring structure into two independent p-hydroxybenzyl alcohol / benzoquinone intermediates and acetone small molecules (CH3COCH3), thus completing the dissociation of the BPA core structure; (2) Phenolic ring hydroxylation activation (phenol introduces additional OH (forming a catechol / hydroquinone intermediate): ·OH attacks the high electron cloud density carbons at C2 and C4 positions of the phenol ring, introducing additional electrons through an electrophilic addition-hydroxylation reaction. OH, converting phenol sequentially into catechol (catechol) and hydroquinone (hydroquinone); ZnFe2O4 generates ·O2 driven by visible light. - Nucleophilic addition with benzoquinone intermediates accelerates the destruction of the π-conjugated system of the benzene ring, providing a low-barrier channel for subsequent ring opening; (3) Ring opening and complete mineralization of benzene ring: ·OH and ·O2 - The synergistic attack on the catechol / hydroquinone benzene ring C=C aromatic conjugated system (approximately 510 kJ / mol) drives the benzene ring to open sequentially. Through the gradual oxidation and mineralization of short-chain organic acid intermediates such as maleic acid, oxalic acid, acetic acid, and formic acid, BPA is finally completely mineralized into inorganic small molecules such as CO2 and H2O.

[0052] The specificity of this targeted matching stems from the precise adaptation between the distribution of active species in the system and the bond energy gradient of BPA: ·OH and the strong oxidizing holes of ZnO (+3.06 eV) synergistically target the isopropylidene carbon bridge C of BPA. Targeted initiation of C bonds (346 kJ / mol) enables preferential breakage of the core structure; ZnO / SnO2 type II heterojunction pairs ·OH and ·O2 - The simultaneous retention of dual active species ensures continuous and efficient attack on the high bond energy benzene ring system (510 kJ / mol); the visible light gain of ZnFe2O4 enables the system to maintain high degradation activity under visible light irradiation, thereby achieving efficient and targeted degradation of bisphenol A from core structure dissociation to complete mineralization.

[0053] The monolithic zinc oxide-based photocatalytic foam ceramic has a cylindrical macroscopic shape; compressive strength ≥ 0.4 MPa, porosity ≥ 83%, pore structure connectivity ≥ 82%, and bisphenol A (BPA) degradation rate ≥ 95% under ultraviolet light; Those skilled in the art can determine the process window that satisfies the above effects through limited experiments under conventional equipment conditions, based on the specific type of zinc oxide powder, the type of photocatalytic active component, and the characteristics of the reinforcing phase.

[0054] Example 4 A method for preparing fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic includes the following steps: S1: Add organic additives and pH adjusters to deionized water and disperse them evenly to form a homogeneous solution; add zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents to the solution in batches and disperse them evenly to form a zinc oxide-based suspension slurry; add fiber and / or whisker reinforcing phase to the suspension slurry and disperse it evenly to form a zinc oxide-based composite slurry; S2: The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. S3: The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is debonded by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. S4: The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding, effectively reducing the sintering temperature and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, the defect control agent inhibits Zn²⁺ during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms. + Excessive reduction, zinc interstitial defects and excessive oxygen vacancies, lattice distortion, and abnormal ZnO grain growth are controlled to keep the grain size within a small range, maintaining a high specific surface area and porosity of the material. During sintering, the reinforcing phase and the foam ceramic skeleton are firmly bonded together. The components construct band-matched heterojunction interfaces or generate new photocatalytically active phases in situ through solid-phase diffusion and interfacial reactions. The electronic structure of the heterojunction interface or the new photocatalytically active phase is precisely matched with the molecular characteristics of the target pollutant, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The three-dimensional skeleton of this ceramic is composed of a continuous network of photocatalytic functional phases, which has excellent mechanical strength, high photocatalytic activity, and specific and efficient degradation ability for the target pollutant.

[0055] In step S1, the zinc oxide powder has a purity > 98 wt.% and an average particle size D50 of 0.5 μm; The photocatalytic active component is copper oxide (CuO) with a purity >98 wt.% and an average particle size D50 of 0.5 μm, and is added at an amount of 60 wt.% of the zinc oxide powder mass. The sintering aid is lanthanum oxide (La₂O₃) with a purity >98 wt.% and an average particle size D50 of 1 μm, and is added at 7 wt.% of the zinc oxide powder mass. The defect control agent is gallium trioxide (Ga2O3) with a purity >98 wt.%, an average particle size D50 of 5 μm, and an addition amount of 9 wt.% of the zinc oxide powder mass. The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; wherein the binder is hydroxypropyl methylcellulose (HPMC); the plasticizer is polyethylene glycol (PEG); the dispersant is gum arabic (GA); the surfactant is lecithin (LC); the rheology modifier is bentonite (BT); and the defoamer is a polyether defoamer (Pluronic® L61). The pH adjuster is ammonia water (NH3·H2O, 2 mol / L); The reinforcing phase is magnesium borate whiskers with an average length of 18 μm and an average diameter of 0.8 μm. The zinc oxide-based composite slurry has a solid content of 59 vol.% and a pH of 10. The amounts of each component of the organic additive and the reinforcing phase added are based on the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents, and are as follows: binder, 1.9 wt.%; dispersant, 2.4 wt.%; plasticizer, 1.7 wt.%; surfactant, 3.1 wt.%; rheology modifier, 1.5 wt.%; defoamer, 2.8 wt.%; reinforcing phase, 30 wt.%. In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based suspension slurry and the composite slurry are also uniformly dispersed by mechanical stirring. For the uniform dispersion of the homogeneous solution, the mechanical stirring speed was 800 rpm; the stirring time was 23 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. The stirring rate for both the zinc oxide-based suspension slurry and the composite slurry was 2200 rpm; the stirring time was 300 min; the stirring paddle material was polytetrafluoroethylene; and the distance between the stirring paddle blade and the bottom of the slurry container was 0.5 cm. In step S2, the organic foam is made of polyurethane (PU), has a pore density of 10 PPI, and has a macroscopic shape of cuboid. The impregnation is carried out under normal pressure; the impregnation process is conducted at 25°C for 150 seconds. The pressure of the extrusion desizing is controlled within 1 MPa, and the thickness of the organic foam after extrusion is compressed to 90% of the original thickness; The drying process employs a programmed temperature increase method, with a drying temperature of 75℃, and continues until the mass change rate is <1% / h. After five cycles of impregnation-desizing-drying-impregnation, the cumulative loading of the composite slurry reaches 460% of the original mass of the organic foam. In step S3, the natural air drying is carried out in a ventilated environment at a temperature of 25°C, a relative humidity of 20%, a ventilation rate of 1 m / s, and a natural air drying time of 12 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 75°C at a rate of 5°C / min, and the temperature is maintained for 6 hours. The airflow rate inside the oven is 1 m / s, and the drying endpoint is a mass change rate of <0.05% / h. The degumming heat treatment includes: In the first stage, the temperature is increased to 250℃ at a rate of 10℃ / min and held for 20 min. The second stage involves raising the temperature to 450℃ at a rate of 5℃ / min and holding it for 5 minutes. The third stage involves raising the temperature to 600℃ at a rate of 3℃ / min and holding it for 1 min. The degumming heat treatment process is carried out under a selected atmosphere, namely air, with a gas flow rate of 1000 mL / min and the furnace pressure maintained at gauge pressure +800 Pa. In step S4, the process conditions for the controlled sintering heat treatment include: sintering temperature 110℃, constant temperature time 3min, and heating rate 10℃ / min. During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: During the controlled sintering heat treatment, the components undergo the following chemical reactions in sequence, ultimately constructing a cascaded heterojunction system with targeted degradation function: (1) Liquid-phase assisted sintering and interfacial activation reaction of sintering aids The sintering aid, lanthanum trioxide (La₂O₃), is a rare earth oxide sintering aid. + The ionic radius (0.116 nm) is much larger than that of Zn². +(0.074 nm), with extremely low solid solubility in the ZnO lattice, mainly segregates to the ZnO grain boundaries, forming a rare-earth zinc composite oxide grain boundary phase. Through liquid-phase assisted sintering and grain boundary pinning mechanisms, it simultaneously plays a role in sintering aid and grain growth inhibition. During the 1100°C high-temperature holding stage, La₂O₃ and ZnO undergo a solid-state reaction at the grain boundaries, generating a lanthanum-zinc composite oxide grain boundary activation phase. La₂O₃ + 2ZnO → La₂Zn₂O₅ [Lanium-zinc composite oxide, grain boundary phase, 1100°C] The generated La2Zn2O5 phase (orthorhombic crystal system) is enriched at the grain boundaries of ZnO and CuO particles. Through the grain boundary liquid-assisted mass transfer mechanism, it drives the rearrangement of ZnO and CuO particles, promotes the neck connection between particles (the neck width is controlled within 10 μm), and ensures the structural integrity of the foam ceramic skeleton rib network. At the same time, the La2Zn2O5 grain boundary phase effectively inhibits the abnormal growth of ZnO and CuO grains at 1100°C through the solute drag effect, maintains a high specific surface area of ​​the skeleton, and provides microstructure guarantee for the high-density distribution of subsequent photocatalytic active sites.

[0056] (2) Donor-type solid solution and grain boundary pinning stabilization reaction of defect control agents The defect control agent, gallium trioxide (Ga2O3), is a donor-type substitution stabilizer. Ga³ + The ionic radius is 0.062 nm, similar to Zn²⁺. + The difference in ionic radius (0.074 nm) is approximately 16%, yet it still possesses a certain degree of solid solubility; Ga³ + Replace Zn² + Lattice site (Ga Zn • Net positive charge +1), by providing additional electron compensation for Zn vacancy acceptor defects (V Zn Suppressing additional donor defects (Zn) I •• or V O •• The formation of ); solid solution substitution reaction is represented as: Ga³ + Replace Zn² + Lattice site → GaZn • Donor (net positive charge +1) + Electron compensation → Suppressed Zn I •• Over-generation When the amount of Ga2O3 added (9 wt%) exceeds the upper limit of the solid solubility of the ZnO lattice, the supersaturated Ga³⁺... + It accumulates at the grain boundaries of ZnO through grain boundary segregation, and undergoes a solid-state reaction with ZnO to form the in-situ zinc gallium spinel (ZnGa2O4) grain boundary pinning phase. ZnO + Ga2O3 → ZnGa2O4 [zinc gallium spinel, grain boundary, 1100°C] The generated ZnGa2O4 (spinel type, Eg approximately 4.4 eV) forms a continuous nanoscale pinning layer at the ZnO grain boundaries, suppressing abnormal ZnO grain growth through the Zener pinning mechanism and reducing the average ZnO grain size D. 50 Controlled to within 3 μm, while completely blocking Zn² + →Zn 0 The grain boundary diffusion channels of zinc vapor during the reduction process maintain the high structural stability of the active phase of ZnO wurtzite.

[0057] (3) Enhanced in-situ interfacial reaction between the phase and the matrix The magnesium borate (Mg2B2O5) whiskers, which are the reinforcing phase, are active reinforcing phases. Their interfacial bonding mechanism during sintering at 1100°C is as follows: At high temperature, the surface B2O3 (melting point approximately 450°C, already melted) of the Mg2B2O5 whiskers (rod-shaped, magnesium pentaborate) diffuses into the ZnO matrix interface in liquid form. Simultaneously, Mg²⁺ on the whisker surface... + Migrating outward through solid-state diffusion, it interacts with the ZnO matrix in the whiskers. An in-situ solid-liquid interface reaction occurs at the matrix interface, forming a magnesium-zinc composite oxide bonding layer: B₂O₃ (liquid, on the surface of Mg₂B₂O₅) + ZnO → Zn₄B₆O 13 (Or ZnB2O4) [Interfacial bonded phase, 1100°C] MgO (Mg₂B₂O₅ surface diffusion) + ZnO → (Mg,Zn)O solid solution [interfacial bonding layer, 1100°C] The resulting zinc borate (ZnB₂O₄, etc.) and (Mg,Zn)O solid solution form a layer approximately 5 mm thick at the interface between the Mg₂B₂O₅ whiskers and the ZnO matrix. A 15 nm continuous chemically bonded interface layer upgrades the bonding mode between whiskers and the matrix from physical intercalation to chemical bonding, significantly improving the interfacial shear strength. Mg2B2O5 whiskers (elastic modulus of approximately 270 GPa) provide a uniformly distributed load transfer path for the foam ceramic skeleton, and together with the interlocking network formed by them in the three-dimensional skeleton, significantly improve the overall compressive strength and toughness of the foam ceramic.

[0058] (4) In-situ formation reaction of photocatalytically active new phase During the high-temperature sintering process at 1100°C, the photocatalytically active components copper oxide (CuO) and ZnO undergo an interfacial reaction via solid-phase diffusion to form a ZnO / CuO pn heterojunction interface. Simultaneously, a new photocatalytically active phase of copper-zinc composite oxide is generated in situ at the contact interface. CuO + ZnO → CuZn2O3 (or Cu2ZnO3) [Copper-zinc composite oxide, trace amounts at the interface, 1100°C] The residual CuO phase possesses the following key optoelectronic properties: a bandgap of approximately 1.7 eV (λ < 730 nm, full visible light spectrum response), classifying it as a narrow-bandgap p-type semiconductor; and a conduction band position of approximately... The valence band gap is 0.3 eV (vs NHE), and the valence band position is approximately +1.4 eV (vs NHE). The narrow band gap of CuO endows the system with efficient photon utilization in the visible light (and even near-infrared) range, making it the core visible light-responsive component for the entire multi-element heterojunction system to achieve visible light-driven degradation. ZnO (n-type) and CuO (p-type) form a pn heterojunction at the interface: due to the difference in their Fermi levels, charge transfer occurs at the interface until thermodynamic equilibrium is reached, forming a built-in electric field in the interface region, pointing from n-type ZnO to p-type CuO, which significantly enhances the interface separation efficiency of photogenerated electron-hole pairs.

[0059] (5) Heterogeneous structure construction and ciprofloxacin targeted degradation mechanism The ZnO / CuO pn heterojunction constructed in situ during the controlled sintering heat treatment process described above, together with the residual ZnO phase, CuO phase, and ZnGa2O4 phase at the grain boundaries, jointly construct a ZnO / CuO pn type heterojunction photocatalytic system: (1) ZnO (n-type semiconductor, RP): The conduction band position is approximately 0.31 eV (vs NHE), valence band position approximately +3.06 eV (vs NHE), Eg approximately 3.37 eV (UV activity); provides strongly reducing conduction band electrons, efficiently driving O2 generation. - The built-in electric field of the pn junction effectively suppresses photogenerated electron-hole recombination on the ZnO side. (2) CuO (p-type semiconductor, OP): The conduction band position is approximately 0.3 eV (vs NHE), valence band position approximately +1.4 eV (vs NHE), Eg approximately 1.7 eV (λ<730 nm, full visible light spectrum response); provides visible light-driven photogenerated holes, which migrate directionally towards the ZnO valence band under the drive of the built-in electric field of the pn junction, and jointly generate ·OH with the strongly oxidizing holes of ZnO (+3.06 eV); (3) ZnGa2O4 (grain boundary stable phase): Eg about 4.4 eV (deep ultraviolet response), distributed in the form of grain boundary phase, mainly plays the role of structural stability and interface isolation, preventing excessive interface diffusion of ZnO and CuO particles during high-temperature sintering, which would lead to mixing of active phase components, and maintaining the structural clarity and built-in electric field strength of pn junction interface.

[0060] Under visible light irradiation, CuO (Eg≈1.7 eV) first absorbs visible light to generate photogenerated electron-hole pairs; CuO conduction band photogenerated electrons ( 0.3 eV) is transferred to the ZnO conduction band under the drive of the built-in electric field of the pn junction ( 0.31 eV), which in turn drives the single-electron reduction of O2 to produce ·O2. - Superoxide radicals (E°(O2 / ·O2)) - )= (0.33 eV, ZnO conduction band potential is sufficient to drive); the strong oxidizing holes (+3.06 eV) in the ZnO valence band are retained in the ZnO valence band under the influence of the built-in electric field of the pn junction, efficiently oxidizing water molecules / OH-. - It generates ·OH (overpotential reaches 0.34 eV), achieving a balance between the strong oxidizing ·OH and the reducing ·O2. - Coordinated and efficient supply.

[0061] The above system targets the pollutant ciprofloxacin (CIP, C 17 H 18 The targeted degradation of FN3O3 (MW=331.34 g / mol) is based on the precise match between the bond energy characteristics of the CIP molecule and the aforementioned strong ·OH system. The CIP molecule consists of a quinolone-benzopyridine bicyclic core (quinoline ring) and a carboxyl group at the C3 position (…). COOH, 350 kJ / mol), C4 ketone carbonyl group (C=O, 745 kJ / mol), C6 fluorine substituent ( F, 484 kJ / mol) and piperazinyl group at C7 (C7 position). N-key 305 It consists of five major structural units (315 kJ / mol). The bond energies and breaking priorities of the key chemical bonds are as follows: C7 piperazine ring C N-bond (approximately 305) The site with the lowest total molecular bond energy (315 kJ / mol) is the preferential target site for ·OH-targeted attack; the C3 carboxyl group... The COOH bond (approximately 350 kJ / mol) is the next strongest; the C6 position C... The F bond (approximately 484 kJ / mol) is the target of defluorination attack; the C=C aromatic conjugated bond (approximately 510 kJ / mol) and C4=O carbonyl group (approximately 745 kJ / mol) of the quinolone ring have the highest bond energies, requiring multi-step synergistic ring-opening mineralization by active species. Accordingly, the targeted degradation of ciprofloxacin by the system proceeds in three steps: (1) Target-induced (C7) Piperazine C N-bond preferential breakage and side chain removal: ·OH, due to its high electrophilicity, preferentially attacks the piperazine ring at C7 position of the CIP molecule. N-key (305) (315 kJ / mol), triggering ring-opening of the piperazine ring and stepwise removal of the ethylenediamine side chain, generating a depiperazinylquinolone intermediate accompanied by the release of NH3; simultaneously, the ·OH group also attacks the C3 carboxyl group. COOH bond (350 kJ / mol), triggering decarboxylation reaction ( COOH → H + CO2), further reducing molecular stability and weakening the conjugation stabilization of the quinoline ring; (2) C6-position defluorination activation (·OH driven C F-bond breakage): Strong oxidizing holes (+3.06 eV) in the ZnO valence band attack the C6 position of the CIP molecule through a high concentration of ·OH. The F bond (484 kJ / mol) enables a defluorination reaction via an electrophilic addition substitution mechanism, with the F atom reacting as F... - Released into the water in form, C6 position transforms into C The OH or C=O groups disrupt the π-conjugated system of the quinolone ring, significantly weakening its aromaticity; CuO generates additional ·O2 driven by visible light. - Synergistically participate in the reductive activation of the quinolone ring, accelerating C F-bond breaking rate; (3) Ring opening and complete mineralization of quinolone nucleus: ·OH and ·O2 - The synergistic and continuous attack on the bicyclic C=C aromatic conjugated system of quinolone (approximately 510 kJ / mol) and C4=O carbonyl group (approximately 745 kJ / mol) overcomes the aromatic ring conjugation stabilization energy, driving the sequential ring opening of the quinolone core. Through the gradual mineralization of various small molecule intermediates (oxalic acid, acetic acid, formic acid, etc.), CIP is ultimately completely mineralized into CO2, H2O, and F. - and NH4 + NO3 - Inorganic small molecules, etc.

[0062] The specificity of this targeted matching stems from the precise fit between the distribution of active species in the system and the bond energy gradient of the CIP molecule: the high electrophilicity of ·OH and the CIP piperazine C Minimum bond energy of N-bond (305) The ZnO strong oxidizing property (315 kJ / mol) highly matches the ring-opening initiation, enabling preferential ring-opening initiation; the ZnO strong oxidizing property's valence band hole (+3.06 eV) is highly compatible with C. The breaking of the F bond (484 kJ / mol) provides sufficient thermodynamic driving force to achieve complete defluorination; the narrow band gap of CuO (1.7 eV) endows the system with efficient photon utilization across the entire visible light spectrum, making the CIP degradation activity under actual visible light irradiation significantly better than that of the purely UV-active ZnO system; the synergistic effect of the built-in electric field of the pn heterojunction and the interfacial ZnGa2O4 grain boundary pinning phase enables the reaction of ·OH and ·O2 under visible light driving force. - The long-term, stable, and efficient supply of dual active species enables highly efficient targeted degradation of ciprofloxacin throughout the entire process, from targeted initiation and defluorination activation to complete mineralization.

[0063] The monolithic zinc oxide-based photocatalytic foam ceramic has a cuboid macroscopic shape; compressive strength ≥ 0.5 MPa, porosity ≥ 82%, pore structure connectivity ≥ 80%, and a ciprofloxacin (CIP) degradation rate ≥ 91% under ultraviolet light; Those skilled in the art can determine the process window that satisfies the above effects through limited experiments under conventional equipment conditions, based on the specific type of zinc oxide powder, the type of photocatalytic active component, and the characteristics of the reinforcing phase.

[0064] The above description is merely a preferred embodiment of this application and is not intended to limit this application in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from this application, and these improvements and additions should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a fiber / whisker-reinforced monolithic zinc oxide-based photocatalytic foam ceramic, characterized in that, Includes the following steps: Step S1: Preparation of zinc oxide-based composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; Zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents are added to the homogeneous solution in batches and uniformly dispersed to form a zinc oxide-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and uniformly dispersed to form a zinc oxide-based composite slurry; Step S2: Preparation of zinc oxide-based foam ceramic wet blank The organic foam is completely immersed in the zinc oxide-based composite slurry obtained in step S1 for impregnation treatment; after impregnation, the organic foam is removed and excess slurry on the surface is removed by squeezing or centrifugation; then drying treatment is performed; the above impregnation-deslurry-drying cycle is repeated several times to allow the zinc oxide-based composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain a zinc oxide-based foam ceramic wet blank. Step S3: Preparation of zinc oxide-based foam ceramic green body The zinc oxide-based foam ceramic green body obtained in step S2 is first air-dried to remove surface free moisture; then it is dried by programmed temperature rise to further remove internal moisture; then the dried green body is subjected to debinding heat treatment by gradient temperature rise to fully remove organic foam and organic additives by thermal debonding, while zinc oxide particles, photocatalytic active components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form a zinc oxide-based foam ceramic green body with a three-dimensional interconnected pore structure. Step S4: Sintering and Heterogeneous Structure Construction The green body obtained in step S3 is subjected to controlled sintering heat treatment, so that zinc oxide and photocatalytic active components form a continuous and dense ceramic skeleton network through particle fusion and phase boundary bonding under the action of sintering aids. The defect control agent inhibits the generation of defects and abnormal grain growth during sintering through solid solution substitution and grain boundary segregation mechanisms. The reinforcing phase and the foam ceramic skeleton are firmly bonded through solid phase diffusion and interfacial reaction, and a band-matched heterojunction interface is constructed in situ or a new photocatalytic active phase is generated. Finally, a monolithic zinc oxide-based photocatalytic foam ceramic reinforced with fibers and / or whiskers is obtained. The photocatalytic foam ceramic has a three-dimensional interconnected pore structure, and its three-dimensional skeleton is composed of a continuous photocatalytic functional phase network.

2. The preparation method according to claim 1, characterized in that, In step S1, the ZnO powder has an average particle size of 10 nm-80 μm and is selected from wurtzite phase ZnO, zincblende phase ZnO, and non-stoichiometric ZnO. 1-x Any one or a combination of commercial ZnO powder or its modified powder; The modified powder is zinc oxide powder obtained by any of the following modification methods: 1) Cation doping, wherein the cation is selected from Li + Na + K + 、Rb + Cs + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Sn 4+ Sb³ + Sb 5+ Bi³ + ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Cr 4+ Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + Pr 4 + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + 、Tb 4+ Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ W 6+ Re 4+ Re 6 + Os 4+ Ir 4+ Pt² + Pt 4+ and Au³ + Any one or more of the following, with a doping concentration of 0.1-15 at% 2) Anion doping, wherein the anion is selected from any one or more of B, C, N, F, P, S, Cl, Br and I, and the doping concentration is 0.5-10 at% 3) Oxygen vacancy regulation, with an oxygen vacancy concentration of 10. 18 -10 21 cm -3 ; 4) Defect engineering modification, dislocation / grain boundary density 10 14 -10 16 cm -2 ; The modified powder must still possess semiconductor properties and have a bandgap range of 1.5-5.5 eV. The photocatalytic active component is an inorganic oxide powder with semiconductor properties, and its band gap ranges from 1.5 to 5.5 eV; it is selected from at least one component from the following I) - V); I) Single metal oxides The general chemical formula is M m O n M is a single metallic element, m = 1-3, n = 1-5; including one or more of TiO2, WO3, Bi2O3, Fe2O3, Cu2O, V2O5, MoO3, SnO2, MnO2, ZrO2, Ga2O3, Nb2O5, Ta2O5, In2O3, GeO2, RuO2, IrO2, Co3O4, NiO, Mn3O4, CuO, Ag2O, CoO, MnO, SnO, Sb2O3, Fe3O4, and Au2O and their modified derivatives; II) Composite metal oxides Composed of two or more metal cations, and further subdivided according to crystal structure as: a) Perovskites and their derived phases: general formula ABO3 or A (n+1) B n O (3n+1) , where n is an integer from 1 to 3, A is selected from at least one of La, Bi, Ba, Sr, Ca, Pb, Na and K, and B is selected from at least one of Ti, Zr, Hf, Nb, Ta, W, Mo, V, Cr, Mn, Fe, Co, Ni, Al, Ga and Sn; b) Spinel-type oxides: with the general formula AB₂O₄, wherein A is selected from at least one of Mg, Zn, Ni, Co, Cu, Fe, Mn and Li, and B is selected from at least one of Al, Ga, Cr, Fe, Mn, Co and Ti; c) Layered oxyacid salts having a layered crystal structure with an interlayer spacing of 0.5 nm to 1.5 nm, selected from at least one of the following: c1) Layered titanates, with the general formula A2Ti3O7 or ATi2O5, wherein A is selected from H, Li, Na, K, Rb or Cs; c2) Protonated layered niobates or tantalates, with the general formula HNb3O8 or HTa2O6; c3) Aurivillius phase bismuth-based oxides, selected from Bi₂WO₆, Bi₂MoO₆, and Bi₄Ti₃O₆. 12 At least one of them; c4) Layered nickelates, with the general formula ANiO2, wherein A is selected from Li or Na; d) Other functional oxoacid salts, selected from at least one of the following groups: d1) Scheelite-type oxides, with the general formula AWO4, AMoO4 or AVO4, wherein A is selected from Bi, Ca, Sr, Zn or Pb; d2) Perovskite-type rare earth ferrates, with the general formula LnFeO3, wherein Ln is selected from La, Pr, Nd or Sm; d3) Pyrochlore-type oxides, with the general formula Ln2B2O7, wherein Ln is selected from La, Gd, Sm or Nd, and B is selected from Ti, Zr or Sn; d4) Tungsten bronze type oxide, with the general formula M x TO3, where T is selected from W, Nb, or Ta, M is selected from Na or K, and 0.1 ≤ x ≤ 1.0; d5) Olivine-type oxides, with the general formula M2SiO4 or M2GeO4, wherein M is selected from Mg, Zn, Fe or Mn; d6) Inverse spinel-type stannate Zn2SnO4; d7) Copper-iron ore type oxides, with the general formula CuMO2, wherein M is selected from Fe, Al, Ga or Cr; III) Rare earth-based oxides a) Single rare earth oxide Ln a O x , where Ln is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, a = 1–2, x = 1.5–3; b) Rare earth composite oxides: including perovskite-type LaMO3, NdMO3, ScMO3, YMO3, PrMO3, SmMO3, EuMO3, GdMO3, TbMO3, DyMO3, HoMO3, ErMO3, TmMO3, YbMO3, and LuMO3, where M is selected from transition metals Fe, Co, Sc, Ti, V, Cr, Mn, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, and W. Re, Os, Ir, Pt, Au, or Hg; pyrochlore-type Gd₂Ti₂O₇, Y₂Zr₂O₇, Sc₂Ti₂O₇, La₂Ti₂O₇, Ce₂Ti₂O₇, Pr₂Ti₂O₇, Nd₂Ti₂O₇, Sm₂Ti₂O₇, Eu₂Ti₂O₇, Tb₂Ti₂O₇, Dy₂Ti₂O₇, Ho₂Ti₂O₇, Er₂Ti₂O₇, Tm₂Ti₂O₇, Yb₂Ti₂O₇, Lu₂Ti₂O₇; bismuth rare earth co-doped oxides Bi. 1-x Ln x VO4, wherein Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, x = 0.1-0.5, and at least one of the layered rare earth oxides La2O2CO3, Pr4O7, Ce2O2CO3, Nd2O2CO3, Sm2O2CO3, Eu2O2CO3, Gd2O2CO3, Tb2O2CO3, Dy2O2CO3, Ho2O2CO3, Er2O2CO3, Tm2O2CO3, Yb2O2CO3, Lu2O2CO3, Sc2O2CO3, Y2O2CO3; the interlayer spacing of the layered rare earth oxide structure is 0.8-1.2 nm; IV) Frontier structural metal oxides a) High-entropy oxides: general formula is (M1, M2, ... M n ) a O M1, M2, ..., Mn are at least five different metallic elements, each independently selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Al, Li, Zr, Nb, Mo, Sn, Hf, Ta, W, or Ce. Each metallic element accounts for 5% to 35% of the total molar fraction of all metallic elements, and the configurational entropy ΔS of the high-entropy oxide is... mix ≥ 1.5R, where R is the ideal gas constant 8.314 J·mol - ¹·K - ¹; b) A two-dimensional nano-metal oxide, wherein the matrix material of the two-dimensional nano-metal oxide is selected from at least one of TiO2, MnO2, MoO3, V2O5, Co3O4, Fe2O3, SnO2, WO3 and Nb2O5, has a plate-like or layered morphology, has a thickness of 0.5 nm to 10 nm, has a lateral dimension to thickness ratio ≥ 50, and the two-dimensional nano-metal oxide has preferentially exposed crystal planes, wherein the crystal planes are selected from at least one of the {001}, {010}, {100} and {110} plane families; c) MOF-derived porous oxides, wherein the MOF-derived porous oxides are obtained by heat treatment conversion of metal-organic framework precursors, wherein the metal center of the precursor is selected from at least one of Zn, Co, Fe, Cu, Zr, Ti, Ni and Al, and the resulting oxides retain the morphological characteristics and pore structure of the precursors, with a specific surface area ≥ 50 m² / g, pore volume ≥ 0.1 cm³ / g, and pore size distribution spanning from micropores to mesopores, ranging from 0.5 nm to 50 nm; V) Precursor compound: is the water-insoluble oxalate and / or carbonate corresponding to the metal oxides in I)-II), wherein the precursor compound decomposes in situ during sintering heat treatment to generate the corresponding photocatalytically active oxide; Wherein, "insoluble in water" means: solubility in deionized water at 25°C ≤ 0.1 g / 100 mL; the precursor compound must meet the following requirements: decomposition temperature between 200-1200°C, residual carbon content after decomposition < 0.1 wt.%, and no introduction of impurity anions harmful to photocatalytic activity; VI) The photocatalytic active component described in any of I) to IV) above is modified using one or more of the following methods, and the resulting powder satisfies a band gap of 1.5-5.5 eV: a) Cation doping, wherein the cation is selected from Li + Na + K + 、Rb + Cs + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Sn 4+ Sb³ + Sb 5+ Bi³ + ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Cr 4+ Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + Pr 4 + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + 、Tb 4+ Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ Re 4+ Re 6+ Os 4 + Ir 4+ Pt² + Pt 4+ W 6+ and Au³ + At least one of them, with a doping ratio of 0.1-15 at%; b) Anion doping, wherein the anion is selected from one or more of B, C, N, F, P, S, Cl, Br and I, and the doping ratio is 0.5-10 at% c) Oxygen vacancy regulation, with an oxygen vacancy concentration of 10. 18 -10 21 cm -3 ; d) Defect engineering modification, dislocation / grain boundary density 10 14 -10 16 cm -2 ; The amount of photocatalytic active component added is 5-80 wt.% of the zinc oxide powder mass; the amount of precursor compound added is based on the theoretical mass of the corresponding photocatalytic active oxide generated by its complete thermal decomposition, i.e., oxide equivalent.

3. The preparation method according to claim 1, characterized in that, The sintering aid is selected from at least one of the following components: a) Low-melting-point oxides: bismuth trioxide, vanadium pentoxide, boron trioxide, molybdenum trioxide; b) Eutectic / Active Oxides: Copper oxide, ferric oxide, nickel oxide, cobalt oxide, tin oxide, manganese oxide, manganese oxide, chromium oxide, gallium oxide, indium oxide; c) Network forming agents: silicon dioxide, phosphorus pentoxide, germanium dioxide, tellurium dioxide, boron trioxide; d) Alkali metal or alkaline earth metal oxides: magnesium oxide, lithium carbonate, calcium carbonate, strontium carbonate, barium carbonate; e) Rare earth oxide sintering aids: lanthanum oxide, yttrium oxide, neodymium oxide, samarium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, ytterbium oxide, cerium oxide, praseodymium oxide, terbium oxide, europium oxide, holmium oxide, thulium oxide, lutetium oxide; f) Pre-synthesized zinc-based functional compounds: zinc tungstate ZnWO4, zinc-iron spinel ZnFe2O4, zinc-aluminum spinel ZnAl2O4, zinc titanate Zn2TiO4, zinc titanate ZnTiO3, zinc stannate Zn2SnO4, zinc stannate ZnSnO3, zinc indium oxide ZnIn2O4, zinc indium oxide Zn2In2O5, zinc silicate Zn2SiO4, zinc bismuthate Bi2ZnB2O7, zinc bismuthate Bi2Zn2O5; g) Precursor compounds At least one of the water-insoluble oxalates, carbonates, and hydroxides corresponding to each component in a)-f) above decomposes in situ during degumming or sintering heat treatment to generate the corresponding oxides or oxygen-containing compounds; the water-insoluble meaning: solubility in deionized water at 25°C ≤0.1 g / 100 mL; in particular, the oxides corresponding to the network forming agent in item 3 and the pre-synthesized zinc-based functional compound in item 6 can be obtained by thermal decomposition and conversion of their corresponding carbonate precursors. The precursor compound is uniformly dispersed in the form of solid particles during the slurry stage, and decomposes in situ during the heat treatment process to produce nano-sized active powders. The dispersion uniformity is better than that of directly adding oxides. The amount of sintering aid added is 0.2-30 wt.% of the zinc oxide powder mass: for the sintering aids mentioned in a) to f), it is based on the actual added mass; for the precursor compound mentioned in g), it is based on the theoretical mass of the corresponding oxide generated by its complete thermal decomposition, i.e., the oxide equivalent. The defect control agent is selected from at least one of the following components: i) Equivalent substitute stabilizers: magnesium oxide, beryllium oxide, manganese oxide, ferrous oxide; ii) Donor-type substitution stabilizers: aluminum oxide, gallium oxide, indium oxide, scandium oxide, boron oxide; iii) Grain boundary segregation inhibitors: Lanthanum trioxide, yttrium oxide, neodymium oxide, praseodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, cerium dioxide; iv) Grain boundary / lattice dual-effect stabilizers: zirconium dioxide, hafnium dioxide, titanium dioxide, silicon dioxide, niobium pentoxide, tantalum pentoxide, phosphorus pentoxide, molybdenum trioxide, tungsten trioxide; v) Oxygen activity self-regulating stabilizers: cerium dioxide, manganese dioxide, manganese trioxide, manganese tetroxide, praseodymium oxide, terbium oxide, cobalt oxide, cobalt oxide; vi) Precursor compounds The water-insoluble oxalates and / or carbonates corresponding to each component in i)-v) above decompose in situ to generate corresponding oxides during the sintering heat treatment; wherein, the water-insoluble means: solubility in deionized water at 25℃ ≤0.1 g / 100 mL; The total amount of the defect control agent added is 0.1-30 wt.% of the zinc oxide powder mass: for the defect control agents described in i)-v), it is based on their actual added mass; for the precursor compounds described in vi), it is based on the theoretical mass of the corresponding oxides generated by their complete thermal decomposition, i.e., the oxide equivalent.

4. The preparation method according to claim 1, characterized in that, In step S1, the organic additive includes at least one of binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; The organic additives are used alone or in combination, with a total addition amount of 0.1-30 wt.% of the total mass of zinc oxide powder, photocatalytic active components, sintering aids, and defect control agents. The adhesive is selected from any one or more of polyethylene oxide, sodium alginate, chitosan, polyurethane emulsion, polyacrylamide, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, polyethylene glycol, polyacrylic acid, polyvinyl acetate, starch and its derivatives; The plasticizer is selected from any one or more of the following: triethyl acetylglucosamine citrate, epoxidized soybean oil, polycaprolactone, glycerin, dibutyl phthalate, triethyl citrate, polyethylene glycol, sorbitol, and dioctyl sebacate. The dispersant is selected from any one or more of the following: polycarboxylate superdispersant, polymaleic anhydride, polyaspartic acid, ammonium polyacrylate, sodium polyacrylate, tetramethylammonium hydroxide, ammonium citrate, gum arabic, and polyvinylpyrrolidone. The surfactant is selected from any one or more of the following: sorbitan monooleate, cocamidopropyl betaine, perfluoropolyethers, sodium lauryl sulfate, hexadecyltrimethylammonium bromide, polysorbate 80, octylphenyl polyoxyethylene ether, lecithin, and fluorocarbon surfactants. The rheology modifier is selected from any one or more of guar gum, gellan gum, polyacrylic acid thickeners, organic modified montmorillonite, xanthan gum, sodium carboxymethyl cellulose, bentonite, fumed silica and polyacrylamide; The defoamer is selected from one or more of polydimethylsiloxane, polyether defoamer, isooctanol, n-octanol, silicone oil, polyether-modified siloxane, and mineral oil; The pH adjuster is at least one of ammonia and hydrochloric acid; The reinforcing phase is fibers and / or whiskers, selected from any one or more of the following: 1) Inorganic fibers: glass fiber, basalt fiber, silicon carbide fiber, alumina fiber, mullite fiber, quartz fiber, potassium titanate fiber, aluminum nitride fiber; 2) Ceramic whiskers: silicon carbide whiskers, zinc oxide whiskers, calcium sulfate whiskers, silicon nitride whiskers, barium titanate whiskers, aluminum borate whiskers, magnesium borate whiskers, sodium titanate whiskers, potassium titanate whiskers, zirconium oxide whiskers, aluminum oxide whiskers, calcium carbonate whiskers, aluminum nitride whiskers. 3) Natural mineral fibers: sepiolite fiber, attapulgite fiber, wollastonite fiber, palygorskite fiber, tremolite fiber, actinolite fiber, vermiculite fiber, sillimanite fiber, tourmaline fiber; 4) Synthetic organic fibers: polyacrylonitrile fiber, polyvinyl alcohol fiber, aramid fiber, and polyimide fiber are completely pyrolyzed during the degumming heat treatment process, which plays a role in pore formation and pre-toughening. 5) Metal whiskers: tin whiskers, copper whiskers, silver whiskers, nickel whiskers, iron whiskers, zinc whiskers, aluminum whiskers, gold whiskers, platinum whiskers, cobalt whiskers, titanium whiskers, niobium whiskers, zirconium whiskers, tungsten whiskers, molybdenum whiskers, rhenium whiskers, tantalum whiskers, palladium whiskers, chromium whiskers, magnesium whiskers, cadmium whiskers; 6) Metal fibers: stainless steel fiber, copper fiber, aluminum fiber, nickel fiber, titanium fiber, silver fiber, gold fiber, platinum fiber, palladium fiber, iron fiber, steel fiber, tungsten fiber, molybdenum fiber, niobium fiber, tantalum fiber, zirconium fiber, hafnium fiber, magnesium fiber, zinc fiber, tin fiber, lead fiber, cadmium fiber, cobalt fiber, chromium fiber, beryllium fiber, nickel-titanium alloy fiber, iron-chromium-aluminum alloy fiber, nickel-chromium alloy fiber, Invar alloy fiber; Wherein, the aspect ratio of the reinforcing phase is ≥ 10; The zinc oxide-based composite slurry has a solid content of 20-70 vol.% and a pH of 2-14. The amounts of organic additives and reinforcing phases added are based on the total mass of zinc oxide powder, photocatalytically active components, sintering aids, and defect control agents, and are as follows: Adhesive 1-20 wt.%; Dispersant 0.1-5 wt.%; Plasticizer 0.1-10 wt.%; Surfactant 0.01-5 wt.%; Rheology modifier 0.1-10 wt.%; Defoamer 0.05-10 wt.%; pH adjuster 0.01-10 wt.%; Reinforcing phase: 0.01-30 wt.% of fibers or 0.01-50 wt.% of whiskers.

5. The preparation method according to claim 1, characterized in that, In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the zinc oxide-based composite slurry is uniformly dispersed by mechanical stirring and / or ball milling. The uniform dispersion of the homogeneous solution is achieved by mechanical stirring at a rate of 10-1800 rpm for 0.1-60 min, using an inert stirring paddle, and maintaining a distance of 0.01-2 cm between the paddle blades and the bottom of the slurry container. When mechanical stirring is used to uniformly disperse the zinc oxide-based suspension slurry and the zinc oxide-based composite slurry, the stirring speed is 20-3000 rpm; the stirring time is 15-1500 min; the stirring paddle is made of inert material; and the distance between the stirring paddle blade and the bottom of the slurry container is 0.1-20 cm. When the zinc oxide-based suspension slurry and zinc oxide-based composite slurry are uniformly dispersed by ball milling, the ball milling tank used for ball milling is made of an inert material; the ball-to-material mass ratio is 0.2-12; the ball milling time is 30-1500 min; the diameter of a single grinding ball is 0.2-12 mm, and the average diameter is 3-8 mm.

6. The preparation method according to claim 1, characterized in that, In step S2, the organic foam is made of polyurethane, melamine formaldehyde, or polystyrene; the pore density of the organic foam ranges from 6 to 70 PPI, and its macroscopic shape is any one of the following: cylinder, cube, cuboid, sphere, ellipsoid, torus, prism, pyramid, polyhedron, honeycomb block, sheet, arc, arch, tubular, hollow spherical shell, or any combination or deformation thereof. The impregnation is carried out using normal pressure, negative pressure assisted, or alternating negative and normal pressure methods; the impregnation process is carried out at 25±20℃, the normal pressure impregnation time is 30-1800 seconds, and the number of negative and normal pressure alternating impregnations is 1-5 times per impregnation cycle; The negative pressure assistance involves completely immersing the organic foam in the zinc oxide-based composite slurry described in step S1, then evacuating the composite slurry to boiling point within 3 minutes, maintaining boiling for 0.5-10 minutes to ensure that all air in the system is expelled, and then restoring it to ambient pressure. The pressure of the extrusion desizing is controlled at 0.05-5.0 MPa, and the thickness of the organic foam after extrusion is compressed to 30-95% of the original thickness; the centrifugal desizing speed is 500-2000 rpm, and the centrifugation time is 10-600 seconds; The drying process employs a programmed temperature increase method, with a temperature range of 20~95℃ and a relative humidity decreasing from ≥70% to <10%, drying until the mass change rate is <20% / h. After each impregnation-desizing-drying cycle, the mass gain rate of the composite slurry loaded in the organic foam is 50-500%. After 2-5 cycles, the cumulative loading of the composite slurry reaches 150-1000% of the original mass of the organic foam, forming a coating thickness of 0.1-3.0 mm, a coating thickness variation coefficient of <30%, and a pore blockage rate of <40%.

7. The preparation method according to claim 1, characterized in that, In step S3, the natural air drying is carried out in a ventilated environment with a temperature of 5-45℃, a relative humidity of 30-90%, a ventilation rate of 0.1-10.0 m / s, and a natural air drying time of 2-24 hours. The heating program for the drying process is as follows: the temperature is increased from room temperature to 50-95℃ at a rate of 0.01-10.00℃ / min, and the temperature is maintained for 4-8 hours. The airflow rate inside the oven is 0.01-10.00 m / s, and the drying endpoint is a mass change rate of <0.1% / h. The degumming heat treatment includes: The first stage involves raising the temperature at a rate of 1-10℃ / min to 150-250℃ and holding it for 1-360 min. In the second stage, the temperature is increased to 350-450℃ at a rate of 0.5-10℃ / min, and then held for 1-360 min. The third stage involves raising the temperature at a rate of 0.5-10℃ / min to 550-600℃ and holding it for 1-360 min. The degumming heat treatment process is carried out under vacuum or atmospheric conditions. The vacuum conditions are: no gas is introduced and the absolute pressure inside the furnace is maintained below 100 Pa. The atmospheric conditions are: at least one of helium, argon, nitrogen, ammonia, air and oxygen is introduced, the gas flow rate is 0-9000 mL / min, and the pressure inside the furnace is maintained at gauge pressure +50 to +9000 Pa.

8. The preparation method according to claim 1, characterized in that, In step S4, the controlled sintering heat treatment temperature is 900-1500℃, the heating rate is 2-20℃ / min, and the holding time is 0.01-24 hours; The controlled sintering heat treatment is carried out under vacuum or atmospheric conditions. The vacuum conditions are: no gas is introduced and the absolute pressure inside the furnace is maintained below 10 Pa. The atmospheric conditions are: at least one of hydrogen, helium, argon, nitrogen, ammonia, air and oxygen is introduced, the gas flow rate is 0-9000 mL / min, and the pressure inside the furnace is maintained at gauge pressure +50 to +9000 Pa.

9. The monolithic zinc oxide-based photocatalytic foam ceramic obtained by the preparation method according to any one of claims 1 to 8.

10. The monolithic zinc oxide-based photocatalytic foam ceramic prepared by the preparation method according to any one of claims 1 to 8 is used in i) the degradation of organic pollutants or water treatment; ii) in the preparation of an apparatus for degrading organic pollutants or a water treatment apparatus.

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