A monolithic photocatalytic hydrogen peroxide production foam ceramic based on selective two-electron oxygen reduction of tin dioxide, its preparation method and application

Abstract

This application discloses a monolithic photocatalytic H2O2 production foam ceramic based on the selective two-electron oxygen reduction of SnO2, its preparation method, and its applications. This application involves preparing a composite slurry from SnO2 powder, selective control components, sintering aids, defect control agents, and reinforcing fibers, followed by organic foam impregnation, drying and degumming, and controlled sintering. The sintering process utilizes in-situ reaction to construct a highly selective two-electron oxygen reduction active interface, precisely controlling the reaction pathway to directionally generate H2O2. This material exhibits high porosity and excellent mechanical properties; its three-dimensional channels can rapidly transport products and inhibit their decomposition, achieving highly selective in-situ photocatalytic synthesis in a continuous flow system. It is suitable for various fields such as drinking water disinfection, food sterilization, emergency water supply, and wastewater pretreatment.

Description

Technical Field

[0001] This application relates to an integral photocatalytic hydrogen peroxide (H2O2) foam ceramic based on selective two-electron oxygen reduction of tin dioxide (SnO2), its preparation method and application, belonging to the interdisciplinary fields of inorganic non-metallic functional materials, semiconductor photocatalysis and green chemical synthesis. Background Technology

[0002] Hydrogen peroxide (H2O2) is an important green oxidant and disinfectant. Its oxidation products are only water and oxygen, producing no secondary pollution. It is widely used in drinking water disinfection, pulp bleaching, food processing disinfection, medical device sterilization, semiconductor cleaning, and advanced oxidation water treatment. Currently, the global annual production of H2O2 exceeds 5 million tons, and market demand continues to grow.

[0003] Currently, industrial H2O2 production mainly relies on the anthraquinone process (AQ process). This process uses 2-ethylanthraquinone as the working carrier and completes the process through multiple steps such as hydrogenation, oxidation, extraction, and concentration. The anthraquinone process has the following significant drawbacks: (1) The process flow is complex and lengthy, involving at least four independent steps such as hydrogenation, oxidation, extraction, and purification; (2) The energy consumption is extremely high (the comprehensive energy consumption is about 25–50 kJ / g H2O2), requiring high-pressure hydrogen (0.3–0.5 MPa) and a large amount of organic solvents; (3) The anthraquinone carrier inevitably degrades during the cycle, generating a large amount of anthraquinone derivative waste; (4) The product is a 60–70 wt.% concentrated liquid, which poses an explosion risk during transportation and storage; (5) The equipment investment is huge, and it is only suitable for large-scale centralized chemical production, which cannot meet the needs of remote areas and decentralized application scenarios. Therefore, developing photocatalytic technology that enables green in-situ synthesis of H2O2 using only light energy, water, and air under mild conditions (normal temperature and pressure, no need for hydrogen, no need for organic solvents) has significant energy and environmental implications.

[0004] Photocatalysis utilizes photogenerated electrons generated by semiconductor materials under illumination to selectively reduce dissolved oxygen (O2) to H2O2. Its core reaction is the two-electron oxygen reduction reaction (2e2O2). - ORR):

[0005] O2+ 2H + + 2e - → H2O2 (E° = +0.68 V vs NHE) However, photocatalytic production of H2O2 faces the following key technological challenges: First, the issue of selectivity. The reduction of O2 on a semiconductor surface involves three competing pathways: (1) the single-electron pathway (O2 + e) - → O2 - E° = 0.33 V vs NHE), the product is superoxide radical rather than H2O2; (2) two-electron path (O2 + 2H + +2e - → H2O2, E° = +0.68 V vs NHE), is the target path; (3) Four-electron path (O2 + 4H + + 4e - → 2H2O, E° = +1.23 V vs NHE), the over-reduction product is H2O, and the H2O2 yield is zero. Most traditional photocatalytic semiconductors (such as TiO2, ZnO, g-C3N4, etc.) have insufficient selectivity for the two electron pathways, resulting in low H2O2 yield and selectivity.

[0006] Secondly, there is the issue of product decomposition. The generated H₂O₂ is readily reduced and decomposed on the catalyst surface by photogenerated electrons (H₂O₂ + 2H₂O → H₂O). + + 2e - → 2H2O) or oxidative decomposition by valence band holes (H2O2 + 2h) + → O2 + 2H + This results in the net cumulative concentration of H2O2 being far lower than the theoretical yield.

[0007] Third, there is the issue of catalyst morphology. Most photocatalytic H2O2 production systems reported in the literature currently employ powder suspension systems, which present engineering bottlenecks such as difficulties in catalyst recovery, challenges in continuous production, and high costs associated with separating the product from the catalyst. Furthermore, in powder suspension systems, the H2O2 product remains near the catalyst surface for extended periods, exacerbating the aforementioned product decomposition problems.

[0008] SnO2 (tin dioxide) is a rutile (space group P42 / mnm) n-type wide bandgap semiconductor with a bandgap of approximately 3.5–3.8 eV. It possesses the following unique two-electron ORR selectivity advantage: Firstly, the conduction band position naturally aligns with the two-electron ORR thermodynamic window: the conduction band position of SnO2 is approximately... 0.1 to 0.5 Vvs NHE is precisely within the thermodynamically favorable window of the two-electron ORR—its conduction band electrons have sufficient reduction driving force to perform the O2→ H2O2 conversion (ΔG<0), but not enough to efficiently drive the complete breaking of the O–O bond in the four-electron path, which is naturally thermodynamically favorable for two-electron selectivity.

[0009] Secondly, the surface geometry is conducive to end-on O2 adsorption: SnO2 surface Sn 4+ The adsorption of O2 molecules at the site tends to be "end-on" rather than "side-on". The end-on configuration is conducive to the retention of O–O bonds (producing H2O2), while the side-on configuration is conducive to the breaking of O–O bonds (producing H2O). The surface geometry of SnO2 naturally favors the two-electron path.

[0010] Third, it has extremely high electron mobility: SnO2 has an electron mobility of 100–250 cm² / V·s, which is far superior to TiO2 (~1 cm² / V·s) and most photocatalytic semiconductors. This is beneficial for the rapid transport of photogenerated electrons to the surface to perform ORR reaction and reduce bulk recombination loss.

[0011] Fourth, it has excellent chemical stability: SnO2 does not dissolve or corrode in the entire pH range of 1–14, and its rutile structure does not undergo phase change from room temperature to melting point (1630℃), making it suitable for long-term operation in various water chemical environments.

[0012] However, single SnO2 photocatalysts have the following drawbacks: SnO2's wide bandgap (3.5–3.8 eV) means it can only utilize ultraviolet light (accounting for less than 5% of the solar spectrum); SnO2 has a fast photogenerated carrier recombination rate, resulting in a low actual quantum efficiency; pure SnO2 is one of the most difficult metal oxides to sinter—its densification sintering temperature is as high as 1500–1600℃, and at high temperatures, mass transfer occurs through an evaporation-condensation mechanism rather than bulk diffusion, leading to neck growth rather than densification, requiring the introduction of an effective sintering aid system.

[0013] Developing SnO2 into monolithic photocatalytic H2O2 production foam ceramics and applying it to continuous flow H2O2 synthesis still faces the following technical bottlenecks: Firstly, precise control of the two-electron ORR selectivity: Although the conduction band position and surface structure of SnO2 naturally favor the two-electron pathway, the H2O2 selectivity of a single SnO2 is still not ideal (typically 60–75%), with four-electron and single-electron pathways still accounting for a certain proportion. It is necessary to introduce selectivity-regulating components to further improve the two-electron ORR selectivity at the atomic / interface level.

[0014] Secondly, the in-situ decomposition inhibition of H2O2 products: Even with high two-electron ORR selectivity, if the generated H2O2 is further reduced or oxidized on the catalyst surface, the net cumulative concentration will still be very low. Synergistic optimization of material design and reactor configuration is needed to suppress H2O2 decomposition.

[0015] Third, the densification of SnO2 by sintering is difficult: the evaporation-condensation mass transfer mechanism of pure SnO2 makes it difficult to achieve densification sintering at conventional temperatures, and an effective low-temperature liquid-phase assisted sintering system needs to be developed.

[0016] Fourth, insufficient mechanical properties: Foam ceramics need to withstand fluid erosion and their own weight in dynamic water flow environments, and need to be reinforced with fibers / whiskers to ensure structural integrity.

[0017] There is no existing technology that combines SnO2 with selectively controlled components to prepare an integral foam ceramic morphology, and then uses in-situ sintering to build a two-electron ORR selective active interface to achieve continuous flow high-selectivity photocatalytic production of H2O2.

[0018] In summary, existing technologies have failed to address the challenges of precisely controlling the two-electron ORR selectivity, inhibiting H2O2 product decomposition, achieving synergistic optimization of sintering densification, and improving mechanical stability in SnO2-based monolithic foam ceramics for photocatalytic H2O2 production. This application overcomes four major bottlenecks—insufficient two-electron ORR selectivity, severe H2O2 product decomposition, high sintering temperature, and insufficient mechanical strength—through a synergistic system of fiber / whisker reinforcement, low-temperature sintering aids, selectively controlling components, and defect control agents. This provides a feasible technical pathway for the engineering of SnO2-based photocatalytic H2O2 production. Summary of the Invention

[0019] The purpose of this invention is to address the technical bottlenecks in existing SnO2-based photocatalytic materials, such as insufficient two-electron ORR selectivity, severe H2O2 product decomposition, low mechanical strength of monolithic foam ceramics, and difficulty in SnO2 sintering densification. This invention provides a monolithic photocatalytic H2O2 production foam ceramic based on SnO2 selective two-electron oxygen reduction, its preparation method, and its applications. This application utilizes in-situ solid-state reactions or atomic interdiffusion during controlled sintering to form a tight chemically bonded interface between the selectively controlled component and the SnO2 matrix at the phase boundary, thus constructing a two-electron ORR selectively active interface structure in situ. It leverages the unique advantage of SnO2's conduction band electron reduction potential being naturally within the thermodynamically optimal window of two-electron ORR, combined with the selectively controlled component's... By stabilizing the OOH intermediate, regulating the O2 adsorption configuration, and suppressing excessive H2O2 reduction, highly selective (>85%) photocatalytic H2O2 synthesis is achieved. Simultaneously, through a systematically designed multi-component sintering aid system adapted to the sintering characteristics of SnO2 and a precise defect control scheme, the conduction band electron reduction potential is precisely tuned while ensuring mechanical strength. The continuous flow operation mode of the three-dimensional interconnected foam ceramic allows H2O2 products to rapidly detach from the catalyst surface, effectively inhibiting product decomposition and significantly increasing the net cumulative concentration of H2O2.

[0020] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a method for preparing monolithic photocatalytic H2O2 production foam ceramics based on selective two-electron oxygen reduction of SnO2, comprising the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; SnO2 powder, selective control components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a SnO2-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a SnO2-based selective ORR composite slurry. Step S2: Preparation of SnO2-based foam ceramic wet blank The organic foam is completely immersed in the SnO2-based selective ORR 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 SnO2-based selective ORR composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain SnO2-based foam ceramic wet blank. Step S3: Preparation of SnO2-based foam ceramic green body The SnO2-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 SnO2 particles, selective control components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form SnO2-based foam ceramic green body with three-dimensional interconnected pore structure; Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, SnO2 and selective control components form a continuous ceramic skeleton network through particle densification and phase boundary bonding, effectively achieving densification of the SnO2 system and ensuring the structural integrity of the three-dimensional interconnected channels. At the same time, the defect control agent suppresses grain coarsening caused by the evaporation-condensation mass transfer of SnO2 during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms, controlling the grain size within a small range, maintaining a high specific surface area of ​​the material, and precisely controlling the Fermi level position and conduction band electron reduction potential of SnO2 to place it in the thermodynamically optimal window of two-electron ORR. The selective control components form a tight chemical bond interface with the SnO2 matrix at the phase boundary through in-situ solid-phase reaction or atomic interdiffusion, constructing a two-electron ORR selective active interface structure in situ, and realizing highly selective photocatalytic H2O2 synthesis.

[0021] In some embodiments, in step S1, the average particle size of the SnO2 powder is 10 nm–80 μm, preferably 50 nm–5 μm, and can be selected from any one or a combination of rutile SnO2 powder (space group P42 / mnm), orthorhombic SnO2 powder, amorphous SnO2 powder or modified powder thereof.

[0022] Rutile SnO2 is a thermodynamically stable phase at room temperature and pressure, with no risk of phase transformation during sintering. Furthermore, its (110) plane is the most thermodynamically stable exposed surface, and the surface Sn... 4+ The geometry of the adsorption site favors the end-on adsorption configuration of O2; The modified powder is SnO2 powder obtained by any of the following modification methods: 1) Cation doping, wherein the cation is selected from Li + Na + K + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Bi³ + Sb³ + Sb 5+ ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Mn² + Mn³ + Mn 4+ Fe²+ Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Zn² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ W 6+ Re 4+ Ir 4+ Pt² + Pt 4+ and Au³ + Any one or more of the following, with a doping concentration of 0.1–15 at%; doping can adjust the Fermi level position and conduction band electron concentration of SnO2, and optimize the two-electron ORR selectivity window; 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%; F - Replace O² - Donor-type doping, forming FTO (F-doped SnO2), can improve conductivity and electron transport efficiency; N doping can introduce intermediate energy levels in the band gap to extend the visible light response. 3) Oxygen vacancy regulation, with an oxygen vacancy concentration of 10¹ 8 -10²¹ cm - ³; An appropriate amount of oxygen vacancies, as preferred end-on adsorption sites for O2, is beneficial for the two-electron pathway. 4) Defect engineering modification, dislocation / grain boundary density 10¹4 –10¹ 6 cm - ²; The modified powder must still possess semiconductor properties and have a bandgap range of 2.5–4.5 eV. The selective control component is a functional component that can form a two-electron ORR selective active interface with SnO2 during sintering through in-situ solid-state reaction or atomic interdiffusion, and enhances the two-electron ORR selectivity through one or more of the following mechanisms: (1) Stabilization (1) Key intermediate OOH (inhibit O–O bond breaking); (2) Regulate the adsorption configuration of O2 on the catalyst surface (promote end-on adsorption); (3) Regulate the reduction potential of conduction band electrons (avoid excessive reduction of H2O2); (4) Inhibit the decomposition reaction of H2O2 on the catalyst surface.

[0023] After sintering, the selective control component forms a chemical bonding interface or heterogeneous phase interface with a two-electron ORR selective enhancement function between itself and the SnO2 matrix. The selective regulatory component is selected from at least one component of the following I)–VI): I) p-block metal oxides – stable due to lone pair electron effect OOH intermediate type Oxides containing p-block metal cations with lone pairs of electrons. The ns² lone pair electron orbitals of the p-block metal undergo moderate orbital hybridization with the antibonding π orbitals of the adsorbed OOH intermediate, stabilizing the adsorption state of the OOH intermediate. OOH is a key intermediate in the two-electron ORR pathway—O₂ first accepts the first electron and a proton to form OOH, then OOH accepts the second electron and a proton to form H₂O₂ for desorption. The lone pair electron effect of the p-block metal provides the... The moderate adsorption of OOH, which is "neither too strong nor too weak" (in accordance with the Sabatier principle), makes the two-electron pathway dominant.

[0024] Including Bi2O3 (Bi³) + 6s² lone pairs), In2O3 (In³) + 5s² lone pairs can be obtained by doping with In. + (obtained), Sb2O3 (Sb³) + One or more of the following: 5s² lone pairs, Sb2O5, Tl2O3, PbO, PbO2, GeO2, and their modified derivatives.

[0025] During sintering, Bi2O3 can react with SnO2 to form Bi2Sn2O7 (pyrochlore type) or a Bi-doped SnO2 solid solution layer. In this interface layer, Bi³⁺… + The 6s² lone pairs of electrons form a high density OOH stable sites.

[0026] II)d 0 Configuration of transition metal oxides – O2 selective adsorption type Contains d 0 Configurational transition metal cations (W 6+ Mo 6+ 、Nb 5+ Ta 5+ V 5+ Ti 4+ Zr 4+ Hf 4+ The oxide of ) has a completely empty d orbital. 0 The characteristics of the configuration cation are: (1) the empty d orbital can accept the lone pair electrons of the O2 molecule to form σ coordination (end-on configuration), but since there is no d electron back-donation to the π orbital of O2, the O–O bond will not be weakened / broken - which is exactly favorable for the two-electron path; (2) d 0 The surface of metal oxides is usually rich in terminal oxygen (M=O), which can form hydrogen bonds with OOH (O=M···HOO-), further stabilizing the OOH intermediate.

[0027] It includes one or more of WO3, MoO3, Nb2O5, Ta2O5, V2O5, TiO2, ZrO2, HfO2 and their modified derivatives.

[0028] Nb 5+ (Ionic radius 0.64 Å) and Ta 5+ The radius of (ionic radius 0.64 Å) and Sn 4+ (0.69 Å) is close, and its solid solubility in SnO2 is relatively high. It can diffuse in large quantities into the SnO2 lattice to form a uniform donor-type doped solid solution Sn. 1- x Nb x O2 or Sn 1-x Ta x O2. WO3 (melting point 1473℃) has limited solid solubility in SnO2, and mainly exists as an independent WO3 phase at the SnO2 grain boundaries, forming a SnO2 / WO3 heterogeneous interface.

[0029] III) Oxygen-storing oxides – oxygen vacancy dynamic regeneration type This oxide possesses abundant surface oxygen vacancies and oxygen storage capacity. Its surface oxygen vacancies provide preferred end-on adsorption sites for O2—the O2 molecule adsorbs by inserting one O atom into the oxygen vacancy, while the other O atom faces the solution, naturally favoring a two-electron pathway. Furthermore, the oxygen vacancy concentration can be dynamically regenerated through redox cycles under light irradiation, maintaining the stability of ORR active sites.

[0030] Including CeO2 (Ce 4+ / Ce³ + Reversible cycle), Pr6O 11 One or more of Tb4O7, MnO2, Mn2O3, Mn3O4, Co3O4, Fe2O3, Fe3O4 and their modified derivatives.

[0031] CeO2 (fluorite type) has extremely low solid solubility in SnO2 and is mainly distributed as independent nanoparticles at the SnO2 grain boundaries, forming a chemical bonding interface through Ce-O-Sn bond bridges.

[0032] IV) Wide bandgap semiconductor oxides – conduction band potential modulated type Semiconductor oxides with appropriate conduction band positions, after forming a Type II heterointerface with SnO2, allow photogenerated electrons to transfer from the SnO2 conduction band to the conduction band of this component to perform ORR (Organic Reduction). The key advantage lies in the fact that the conduction band electron reduction potentials of these components are mild (e.g., WO3 conduction band approximately +0.0~+0.4 V vs NHE), sufficient to drive a two-electron ORR (ΔG<0), but thermodynamically insufficient to efficiently drive further reduction of H2O2 (H2O2 + 2H+ ⇌ H+). + + 2e - → 2H2O requires overcoming a large activation energy, therefore it does not naturally decompose the already generated H2O2.

[0033] Including one or more of WO3, MoO3, Fe2O3, BiVO4, Bi2WO6, Bi2MoO6, AgNbO3 and their modified derivatives; V) Precursor compound: is the water-insoluble oxalate and / or carbonate corresponding to the metal oxide in I)–IV), wherein the precursor compound decomposes in situ during sintering heat treatment to generate the corresponding selectively regulated oxide; VI) The selectively controlled components described in any of I) to IV) above are modified by one or more of the following methods, and the resulting powder satisfies a band gap of 1.5–5.5 eV; The amount of selectively controlled component added is 5–80 wt.% of the SnO2 powder mass; the amount of precursor compound added is based on the theoretical mass of the corresponding selectively controlled oxide generated by its complete thermal decomposition, i.e., oxide equivalent.

[0034] In some embodiments, in step S1, the sintering aid is a composite aid system suitable for the sintering of SnO2-based materials and the synergistic regulation of the construction of two-electron ORR selective active interfaces.

[0035] SnO2 is one of the most difficult metal oxides to sinter—the densification sintering temperature of pure SnO2 is as high as 1500–1600℃, and at high temperatures, SnO2 undergoes mass transfer through an evaporation-condensation mechanism rather than bulk diffusion, leading to neck growth rather than densification. To achieve densification that meets the mechanical strength requirements of foam ceramics below 1400℃, sintering aids must be introduced to form liquid phase sintering (LPS). Sintering aids can be classified according to their mechanism of action into low-melting-point liquid phase forming agents, reactive bifunctional aids, grain boundary regulating rare earth aids and their corresponding precursor forms; The total amount of the sintering aid is 0.2–30 wt.% of the SnO2 powder mass.

[0036] 1) Low-melting-point liquid phase forming agents: Bi2O3 (melting point 817℃) is a classic sintering aid for SnO2. Its liquid Bi2O3 wets the surface of SnO2 particles, driving the rearrangement and densification of SnO2 particles through a dissolution-reprecipitation mechanism, which can reduce the densification temperature to 1000–1200℃. Other low-melting-point liquid phase forming agents include V2O5 (melting point 690℃), MoO3 (melting point 795℃), B2O3 (melting point 450℃), P2O5, CuO (reacts with SnO2 at >1000℃), ZnO (reacts with SnO2 to form Zn2SnO4), PbO (melting point 886℃), low-temperature glass powder, etc.

[0037] 2) Reactive bifunctional additives: These additives can undergo solid-state reactions with SnO2 at sintering temperatures to generate new phases with two-electron ORR selective regulation functions, achieving a synergistic effect of sintering aid and selective active interface construction. For example, Bi2O3 reacts with SnO2 at >1000℃ to generate the Bi2Sn2O7 pyrochlore phase, and ZnO reacts with SnO2 to generate the Zn2SnO4 anti-spinel phase.

[0038] 3) Grain boundary regulation rare earth additives: rare earth oxides such as Y2O3 and La2O3 inhibit grain coarsening caused by the evaporation-condensation mass transfer of SnO2 through grain boundary segregation.

[0039] The core function of the defect control agent is: (1) to regulate the Fermi level position and conduction band electron reduction potential of SnO2, so that it is precisely in the thermodynamically optimal window of the two-electron ORR (0 ~ (2) Regulate the concentration of conduction band electrons—sufficient electrons to supply the ORR reaction, but not too much to cause excessive reduction of H2O2; (3) Regulate the concentration of oxygen vacancies on the surface to the optimal range for two-electron ORR selectivity; (4) Suppress the formation of deep-level recombination centers at the interface.

[0040] Through donor type (Sb) 5+ 、Nb 5+ Ta 5+ F - ) and acceptor type (Co²) + / Co³ + Mn 4+ Fe³ + Ni² + Cu² + The ratio of defect control agents can be adjusted so that the Fermi level of SnO2 can be continuously adjusted within the range of ±0.3 eV, thereby achieving precise setting of the conduction band electron reduction potential. The total amount of the defect control agent added is 0.1–30 wt. of the SnO2 powder mass.

[0041] In some embodiments, in step S1, the organic additive includes at least one of binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; The SnO2-based selective ORR composite slurry has a solid content of 20–70 vol.% and a pH of 2–14. 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. The impregnation is carried out using normal pressure, negative pressure assistance, or alternating negative pressure and normal pressure. After each impregnation-desizing-drying cycle, and 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 and a pore blockage rate of <40%.

[0042] In continuous flow reactor applications, the choice of pore density depends on the application scenario: for drinking water disinfection, a higher pore density (30–60 PPI) is preferred to increase the specific surface area and the number of ORR active sites; for large-flow wastewater pretreatment applications, a lower pore density (10–25 PPI) is preferred to reduce fluid flow resistance.

[0043] In some embodiments, step S3 includes a three-stage gradient heating process, with air or an oxygen atmosphere introduced to ensure complete oxidation and removal of organic matter.

[0044] In some embodiments, in step S4, the controlled sintering heat treatment is performed at a temperature of 800–1400°C, a heating rate of 0.5–20°C / min, and a holding time of 0.01–24 hours. This application employs a controlled sintering process, and the sintering temperature is dynamically adjusted based on the system composition. Low-temperature system (with a large amount of low-melting-point additives such as Bi2O3 and V2O5): sintering temperature 800–1100℃, achieving densification and selective active interface construction with the assistance of a large amount of liquid phase.

[0045] Medium-temperature system (appropriate amount of Bi2O3 combined with CuO and ZnO): sintering temperature 1000–1250℃, liquid-phase assisted sintering and solid-phase reaction proceed simultaneously.

[0046] High-temperature systems (mainly composed of high-melting-point selectively controlled components such as WO3 and Nb2O5): sintering temperature 1200–1400℃, requiring high-temperature driven solid-state reaction or Nb 5+ / Ta 5+ Bulk diffusion solid solution.

[0047] Through the above process control, this application can achieve the precise construction of the following microstructures and two-electron ORR selective active systems: (1) In-situ chemical bonding at the two-electron ORR selective active interface: During sintering, SnO2 and the selective control component form a chemically bonded transition layer or solid solution layer with a thickness of 1–200 nm at the interface through in-situ solid-state reaction or inter-atomic interdiffusion. This transition layer enhances the two-electron ORR selectivity through the following mechanisms: a) Stabilization of the lone pair electron effect of the p-block metal. OOH intermediate; b)d 0 c) End-on O2 selective adsorption at configuration sites; d) O2 activation pathway regulated by oxygen vacancy concentration gradient; d) H2O2 decomposition inhibited by conduction band potential regulation.

[0048] (2) Precise tuning of Fermi level and conduction band electron reduction potential: donor defect control agent moves up the Fermi level, acceptor defect control agent moves down the Fermi level. By matching the ratio, the reduction potential of SnO2 conduction band electrons is precisely set in the optimal thermodynamic window of the two-electron ORR - which has enough driving force to reduce O2 to H2O2, but is not too strong to cause H2O2 to be further reduced.

[0049] (3) Sintering neck and pore structure: Liquid-phase assisted sintering forms a stable sintering neck connection between SnO2 particles. The width of the sintering neck between particles can be controlled within the range of 0.1 μm to 20 μm, achieving mechanical load-bearing capacity while ensuring high connectivity (connectivity > 60%) and low fluid resistance of the three-dimensional channels. The three-dimensional interconnected channels ensure that water can flow continuously through the entire thickness direction of the foam ceramic, allowing the generated H2O2 to be quickly carried away from the catalyst surface with the water flow, effectively inhibiting the surface decomposition of H2O2.

[0050] (4) Interface bonding morphology: For chemically inert reinforcing phases (such as glass fiber and basalt fiber), reinforcement is mainly achieved through surface microstructure anchoring and physical interlocking; for active reinforcing phases (such as aluminum borate and magnesium borate whiskers), chemical bonding layers are generated in situ at the interface.

[0051] This application also provides an integral photocatalytic H2O2 production foam ceramic based on selective two-electron oxygen reduction of SnO2 prepared by the above preparation method. The foam ceramic has the following performance indicators: compressive strength greater than or equal to 0.2 MPa, porosity of 60% to 90%, pore structure connectivity greater than 60%, and H2O2 selectivity greater than 80% (based on electron transfer number n < 2.4 determined by RRDE method).

[0052] The core points of the technical solution in this application This application provides a monolithic photocatalytic H2O2 production foam ceramic based on the selective two-electron oxygen reduction of SnO2, its preparation method, and its application. The key technical points are: First, the in-situ construction of the two-electron ORR selective active interface is the core technical feature of this application. Using SnO2 powder as the main raw material, and in combination with selectively controlled components (such as Bi2O3, Nb2O5, WO3, CeO2, etc.), a tight chemically bonded interface is formed between SnO2 and the selectively controlled components through in-situ solid-state reactions or atomic interdiffusion during controlled sintering. This interface is stabilized by the p-block metal lone pair electron effect. OOH intermediate, d 0 The synergistic effect of multiple mechanisms, such as selective adsorption of O2 at configuration sites, regulation of oxygen vacancy concentration gradient, and regulation of conduction band potential, precisely regulates the reduction path of O2 on the catalyst surface so that it selectively takes a two-electron path to produce H2O2, achieving H2O2 selectivity >80%.

[0053] Second, precise tuning of the conduction band electron reduction potential of SnO2. With the precise ratio of donor and acceptor defect control agents, the Fermi level and conduction band electron reduction potential of SnO2 are precisely tuned to the thermodynamically optimal window for two-electron ORR (0~). (0.5 V vs NHE) provides sufficient driving force to reduce O2 to H2O2, but is not so strong that it would cause H2O2 to be further reduced and decomposed, thus achieving the optimal balance between "production efficiency" and "decomposition inhibition".

[0054] Third, liquid-phase assisted low-temperature sintering overcomes the densification difficulties of SnO2. By introducing appropriate amounts of low-temperature sintering aids (Bi2O3, V2O5, CuO, etc.), the densification temperature of SnO2 is effectively reduced (from 1500–1600℃ to 800–1350℃) through a dissolution-reprecipitation mechanism, thus ensuring the mechanical strength of the skeleton while avoiding the increase in energy consumption caused by excessively high sintering temperatures.

[0055] Fourth, the continuous flow mode of foam ceramics inhibits the decomposition of H2O2 products. The continuous flow operation mode of three-dimensional interconnected foam ceramics allows the generated H2O2 to quickly detach from the catalyst surface with the water flow (the residence time is determined by the flow rate and the thickness of the foam ceramics), which significantly reduces the contact time between H2O2 and the catalyst surface and effectively inhibits the side reactions of H2O2 being further reduced by photogenerated electrons or oxidized and decomposed by holes.

[0056] Fifth, the construction of a three-dimensional reinforcement network. High aspect ratio whiskers or fibers are introduced in situ to construct a three-dimensional interlocking reinforcement network, ensuring the structural integrity of the foam ceramic in a dynamic water flow environment.

[0057] This application also provides the application of the above-mentioned monolithic photocatalytic H2O2 production foam ceramic based on SnO2 selective two-electron oxygen reduction. The foam ceramic is placed in an aqueous solution containing dissolved oxygen, and under light conditions, dissolved oxygen is converted into H2O2 through a selective two-electron oxygen reduction reaction of SnO2 conduction band photogenerated electrons, thereby realizing the in-situ synthesis of H2O2.

[0058] Specific application scenarios include: (1) Drinking water disinfection: H2O2 concentration of 1–10 mg / L can effectively kill pathogenic bacteria such as Escherichia coli (contact time 30–60 min), and 10–50 mg / L can inactivate viruses. Compared with traditional chlorination disinfection, H2O2 disinfection does not produce toxic disinfection byproducts such as trihalomethanes (THMs).

[0059] (2) Pulp bleaching: H2O2 is a green bleaching agent (the core of the ECF / TCF bleaching process). Its oxidation products are only H2O and O2, which can replace chlorine-containing bleaching agents to avoid the generation of organic chloride (AOX) pollution.

[0060] (3) Food processing disinfection: The US FDA has approved H2O2 for the disinfection of food contact surfaces and the cleaning of fruits and vegetables.

[0061] (4) Emergency water supply disinfection: The foam ceramic of this application can be installed in a portable solar water supply device, which can generate H2O2 in situ to disinfect natural water sources by relying solely on natural sunlight and O2 in the air, without the need for electricity or chemical agents.

[0062] (5) Wastewater pretreatment supply of H2O2: As the front-end unit of the "H2O2 generator" in the wastewater treatment system, it generates H2O2 in situ under light and directly supplies it to the downstream Fenton reaction (Fe²⁺). + + H2O2→ ·OH), photo-Fenton reaction or UV / H2O2 advanced oxidation process to achieve "on-demand production and use" of H2O2.

[0063] Compared with the prior art, the beneficial effects of this application are as follows: (1) A technical solution for constructing an integral foam ceramic morphology photocatalytic H2O2 production reactor using SnO2 as the main material was proposed for the first time, and a two-electron ORR selective active interface was built through in-situ sintering. The conduction band electron reduction potential of SnO2 falls exactly within the thermodynamically optimal window of the two-electron ORR, and has a natural two-electron selectivity advantage; its surface Sn 4+ The geometry of the site is conducive to end-on adsorption of O2, further enhancing the selectivity of O–O bond retention.

[0064] (2) By introducing selective control components and constructing chemically bonded two-electron ORR selective active interfaces in situ during high-temperature sintering, the precise control of the O2 reduction pathway was achieved—both the four-electron pathway (over-reduction to H2O) and the further reduction and decomposition of the generated H2O2 were suppressed, and the H2O2 selectivity was increased to >80%.

[0065] (3) The three-dimensional interconnected foam ceramic morphology gives the product the engineering advantages of an integral reactor: the catalyst is immobilized and does not need to be recycled and separated; the continuous flow operation allows the generated H2O2 to be quickly carried away from the catalyst surface by the water flow, which significantly reduces the residence time of H2O2 on the catalyst surface, effectively suppresses the product decomposition problem, and greatly increases the net cumulative concentration of H2O2.

[0066] (4) By precisely matching the donor / acceptor type defect control agent, the Fermi level and conduction band electron reduction potential of SnO2 are precisely tuned to the optimal thermodynamic range of the two-electron ORR, thus avoiding the two extreme cases of "insufficient driving force" and "excessive driving force".

[0067] (5) Liquid phase assisted sintering aids form a liquid phase at a relatively low temperature to promote the densification of SnO2, which overcomes the inherent defect that pure SnO2 is extremely difficult to sinter and achieves a balance between mechanical strength (compressive strength ≥ 0.2 MPa) and porosity (60–90%).

[0068] (6) The reinforcing phase (fibers and / or whiskers) forms a three-dimensional interlocking network in the foam ceramic skeleton, which significantly improves the structural reliability and thermal shock resistance.

[0069] (7) SnO2’s excellent chemical stability (insoluble in the pH range of 1–14) and structural stability (rutile type has no phase change from room temperature to melting point) give the product an extremely long service life.

[0070] (8) The product of this application can synthesize H2O2 in situ with only light energy, water and air, without the need for any chemical reagent input. Attached Figure Description

[0071] Figure 1 This is a process flow diagram for the preparation of monolithic photocatalytic H2O2 foam ceramics based on the selective two-electron oxygen reduction of SnO2. Detailed Implementation

[0072] 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.

[0073] Unless otherwise specified, the experimental or testing methods described in the following examples are conventional methods; the reagents and materials described are obtained from conventional commercial sources unless otherwise specified.

[0074] This application provides a method for preparing monolithic photocatalytic H2O2 production foam ceramics based on selective two-electron oxygen reduction of SnO2, comprising the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; SnO2 powder, selective control components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a SnO2-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a SnO2-based selective ORR composite slurry. Step S2: Preparation of SnO2-based foam ceramic wet blank The organic foam is completely immersed in the SnO2-based selective ORR 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 SnO2-based selective ORR composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain SnO2-based foam ceramic wet blank. Step S3: Preparation of SnO2-based foam ceramic green body The SnO2-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 SnO2 particles, selective control components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form SnO2-based foam ceramic green body with three-dimensional interconnected pore structure; Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green body obtained in step S3 is subjected to controlled sintering heat treatment to achieve densification of the SnO2 system under the action of sintering aids; the Fermi level and conduction band electron reduction potential are precisely controlled by the defect control agent; and the two-electron ORR selective active interface structure is constructed in situ by selectively controlling the components to achieve highly selective photocatalytic H2O2 synthesis.

[0075] Example 1 SnO2 / Bi2O3 system – stable due to p-block metal lone pair electron effect OOH intermediates are used for drinking water disinfection. This embodiment provides a SnO2-based monolithic photocatalytic H2O2 production foam ceramic with Bi2O3 as a selectively controlled component, utilizing Bi3... + The 6s² lone pair electron effect is stable The OOH intermediate enhances the selectivity of the two-electron ORR.

[0076] The preparation method of the SnO2-based monolithic photocatalytic H2O2 production foam ceramic includes the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry (1) Take 120 mL of deionized water and place it in a polytetrafluoroethylene beaker. Add 3.0 g of polyvinyl alcohol (PVA), 1.0 g of ammonium polyacrylate (NH4PAA), 1.5 g of glycerol, 0.3 g of polysorbate 80 (Tween-80), 0.4 g of xanthan gum (XG), and 0.15 g of polydimethylsiloxane (PDMS) in sequence. Stir at 500 rpm for 60 min to completely dissolve the organic additives and form a homogeneous solution. Add ammonia (3 mol / L) to adjust the pH to 9.5. (2) Add the following powder raw materials to the above homogenized solution in three batches (stir for 40 min after each batch is added, stirring at a speed of 800 rpm): Rutile SnO2 powder (average particle size 200 nm, purity 99.5%): 100.0 g; Selective control component – ​​Bi2O3 powder (average particle size 300 nm, purity 99.9%): 25.0 g (25 wt.% of SnO2 powder mass); Bi2O3 also functions as a sintering aid (melting point 817℃ forms a liquid phase to assist sintering). Sintering aid – CuO powder (average particle size 500 nm): 5.0 g (5 wt.% of SnO2 powder mass); CuO serves as an auxiliary sintering aid to further promote densification; Defect control agent – ​​Sb₂O₅ powder (average particle size 100 nm): 3.0 g (3 wt.% of SnO₂ powder mass); Sb 5+ Donor-type doping, replacing Sn 4+ Releasing electrons to the conduction band increases the electron concentration in the conduction band, thereby enhancing the ORR reaction rate. At the same time, the Fermi level is shifted upward so that the conduction band electron reduction potential is in the optimal window for two-electron ORR. After all the powder was added, the mixture was stirred at a speed of 1000 rpm for 120 min to form a SnO2-based suspension slurry. (3) Add 10.0 g of alumina fiber (average diameter 8 μm, average length 200 μm, aspect ratio 25) and 3.3 g of silicon carbide whiskers (average diameter 0.5 μm, average length 15 μm, aspect ratio 30) to the above suspension slurry. The total mass of the reinforcing phase is 10 wt.% of the total mass of SnO2 powder, selective control component, sintering aid and defect control agent (100.0+25.0+5.0+3.0=133.0 g). Stir at a stirring rate of 500 rpm for 60 min to form SnO2-based selective ORR composite slurry. The solid content of the slurry is about 35 vol.%, and the pH is 9.5.

[0077] Step S2: Preparation of SnO2-based foam ceramic wet blank A polyurethane foam template (pore density 25 PPI, size 100 mm × 100 mm × 30 mm, cuboid) was completely immersed in the SnO2-based selective ORR composite slurry obtained in step S1. A negative-pressure-normal-pressure alternating impregnation method was used: first, the system was evacuated to boiling point (absolute pressure approximately 5 kPa) within 3 minutes, maintained at boiling point for 3 minutes, and then normal pressure was restored. This negative-pressure-normal-pressure alternation was repeated 3 times. After removal, the slurry was manually descrambled (pressure approximately 0.3 MPa, compressed to 55% of the original thickness), and this was repeated twice. Subsequently, it was placed in a temperature-controlled drying oven, with the temperature increased from 25℃ to 55℃ at a rate of 0.5℃ / min, and the relative humidity gradually decreased from 80% to 20%, drying until the mass change rate was <20% / h. This impregnation-descrambling-drying cycle was repeated 4 times, resulting in a cumulative slurry loading of 550% of the original organic foam mass, a coating thickness of approximately 1.0 mm, and a pore blockage rate of approximately 20%, thus obtaining a SnO2-based foam ceramic wet blank.

[0078] Step S3: Preparation of SnO2-based foam ceramic green body The wet blank obtained in step S2 was first air-dried at 25°C in a ventilated environment for 16 hours (relative humidity 50%, ventilation rate 1.0 m / s); then it was transferred into a forced-air drying oven, heated to 80°C at 2°C / min, and kept at that temperature for 16 hours (airflow rate 0.5 m / s) until the mass change rate was <0.1% / h. Then transfer it to a box-type atmosphere furnace, introduce air (flow rate 500 mL / min), and perform degumming heat treatment: First stage: Increase to 220℃ at a rate of 2℃ / min and hold for 120 min; Second stage: Increase to 400℃ at 1℃ / min and hold for 240 min; Third stage: Increase to 600℃ at 1℃ / min and hold for 120 min; The pressure inside the furnace was maintained at gauge pressure +200 Pa to obtain SnO2-based foam ceramic green body.

[0079] Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green blank obtained in step S3 was subjected to controlled sintering heat treatment in a box-type atmosphere furnace: air was introduced (flow rate 800 mL / min), and sintering was carried out in two stages: First stage sintering: The temperature is increased to 900℃ at a rate of 3℃ / min and held for 2 hours. During this stage, Bi₂O₃ (melting point 817℃) forms a liquid phase, wetting the surfaces of SnO₂ and CuO particles, driving particle rearrangement and initial densification. Bi³⁺ in the Bi₂O₃ liquid phase... + It begins to diffuse towards the surface of the SnO2 lattice.

[0080] Second stage sintering: Temperature increased to 1150℃ at a rate of 2℃ / min, held for 4 hours. During this stage, Bi³… + With Sn 4+ Sufficient interdiffusion occurs at the interface, forming a Bi-doped SnO2 (Bi:SnO2) solid solution layer (approximately 20–80 nm thick) on the surface of the SnO2 particles. Simultaneously, a Bi2Sn2O7 pyrochlore phase is formed at some interfaces. Bi³ + The 6s² lone pair electron sites constitute The stable site of the OOH intermediate imparts high selectivity for the two-electron ORR. Sb 5+ Donor-type doping is achieved by bulk diffusion into the SnO2 lattice, which increases the concentration of conduction band electrons and shifts the Fermi level upward.

[0081] Maintain the pressure inside the furnace at gauge pressure +300 Pa; allow it to cool naturally to room temperature.

[0082] The mechanism of two-electron ORR selective active interface construction during sintering: The Bi₂O₃ liquid phase and the SnO₂ surface have an extremely low contact angle (good wettability), forming a continuous liquid phase film between SnO₂ particles. Under liquid-phase assisted diffusion conditions, Bi₂O₃… + Bi³⁺ diffuses into the surface of the SnO₂ lattice to form a Bi-doped SnO₂ (Bi:SnO₂) solid solution layer. The Bi³⁺ in the Bi-doped SnO₂ surface layer... + Bi₂Sn₂O₇ provides a 6s² lone pair electron site, which, through the hybridization interaction between Bi₂Sn₂ and the O–O σ orbitals of the adsorbed OOH, moderately stabilizes the OOH intermediate (conforming to the Sabatier principle), inhibits the breaking of its O–O bond (avoiding a four-electron path), and simultaneously ensures the desorption of the H₂O₂ product (avoiding excessive OOH adsorption). In the Bi₂Sn₂O₇ pyrochlore phase, Bi₃⁻… + Existing in an ordered arrangement, it provides periodicity. OOH stable site array. Furthermore, Bi³ + Replace Sn 4+ By adopting acceptor-type doping, the surface electron concentration is reduced, which weakens the surface's ability to excessively reduce the generated H2O2 and reduces the decomposition loss of H2O2 on the catalyst surface.

[0083] The performance indicators of the obtained product are as follows: porosity of 78%, compressive strength of 0.45 MPa, and pore structure connectivity of 75%; X-ray diffraction (XRD) analysis shows that its phase composition is rutile SnO2 (main phase), Bi2Sn2O7 pyrochlore phase (secondary phase) and trace CuO residual phase; the average grain size of SnO2 is 1.5 μm.

[0084] Photocatalytic H2O2 production performance test: The obtained foam ceramic was placed in a continuous flow reactor, using deionized water containing saturated dissolved oxygen (approximately 8.2 mg / L, saturated with air at 25°C and atmospheric pressure) as the reaction medium. The water flow rate was 50 mL / min, and air was continuously introduced to maintain dissolved oxygen saturation. The surface of the foam ceramic was irradiated with a 300 W xenon lamp.

[0085] After 6 hours of reaction, the cumulative concentration of H2O2 in the effluent reached 28.5 μmol / L (approximately 0.97 mg / L). The electron transfer number n of the catalyst was determined to be 2.3 by rotating ring-disk electrode (RRDE) method, corresponding to an H2O2 selectivity of approximately 85%, indicating that the two-electron ORR pathway is dominant.

[0086] After 72 hours of continuous operation, the H2O2 yield decreased by less than 8%, indicating that the foamed ceramic exhibits good operational stability. The H2O2 concentration in the reactor effluent (on the order of ~1 mg / L) meets the minimum effective concentration requirement for drinking water disinfection (≥1 mg / L, with a contact time ≥30 min capable of killing >99.9% of E. coli).

[0087] Validation of drinking water disinfection applications: using an initial concentration of approximately 10 5 Simulated contaminated drinking water containing CFU / mL *E. coli* (ATCC25922) was used as the treatment target. After passing through the aforementioned continuous flow reactor, the effluent was collected and allowed to stand at 25°C for 30 min before plate counting. The results showed an *E. coli* kill rate >99.9%, meeting the microbiological requirements of the *Standards for Drinking Water Quality* (GB 5749-2022). After five cycles (72 h continuous operation each time), the H2O2 yield decreased from 28.5 μmol / L to 26.2 μmol / L, a decrease of <8%, indicating that the chemically bonded Bi2Sn2O7 / SnO2 selectively active interface has good stability under long-term water flow scouring.

[0088] Example 2 SnO2 / Nb2O5 system — d 0 Donor-type solid solution doping for supplying H2O2 in wastewater pretreatment This embodiment provides a SnO2-based monolithic photocatalytic H2O2 production foam ceramic with Nb2O5 as a selectively controlled component, utilizing Nb... 5+ d 0 The configuration creates active sites on the SnO2 surface that exhibit end-on selective adsorption of O2 without weakening the O–O bond.

[0089] The preparation method of the SnO2-based monolithic photocatalytic H2O2 production foam ceramic includes the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry (1) Take 100 mL of deionized water and 20 mL of anhydrous ethanol and place them in a polypropylene mixing tank. Then add 2.5 g of hydroxypropyl methylcellulose (HPMC), 0.8 g of sodium hexametaphosphate (SHMP), 2.0 g of polyethylene glycol (PEG-400), 0.5 g of octyl phenyl polyoxyethylene ether (Triton X-100), 0.3 g of guar gum (GG), and 0.1 g of n-octanol in sequence. Stir at 600 rpm for 45 min to completely dissolve the organic additives. Add nitric acid (2 mol / L) to adjust the pH to 3.5. (2) Add the following powder raw materials to the above homogenized solution in four batches (stir for 30 min after each batch is added, stirring at a speed of 900 rpm): Rutile SnO2 powder (purity 99.9%, average particle size 100 nm): 100.0 g; Selective control component – ​​Nb2O5 powder (average particle size 150 nm, purity 99.9%): 15.0 g (15 wt.% of SnO2 powder mass); Sintering aids—Bi2O3 powder (average particle size 500 nm): 8.0 g, V2O5 powder (average particle size 200 nm): 2.0 g (Bi2O3 and V2O5 together account for 10 wt.% of the mass of SnO2 powder); Defect control agent – ​​Fe2O3 powder (average particle size 50 nm): 2.0 g (2 wt.% of SnO2 powder mass); Fe³ + Acceptor-type doping, replacing Sn 4+ Introducing an acceptor level and appropriately reducing the conduction band electron concentration to suppress excessive reduction and decomposition of H2O2, while Fe³ + The oxygen vacancy compensation accompanying doping provides end-on adsorption sites for O2; After all the powder was added, it was transferred to a polytetrafluoroethylene ball mill jar for ball milling and mixing for 240 min (half of the zirconia grinding balls were 3 mm and half were 8 mm in diameter, with a ball-to-material weight ratio of 3:1) to form a SnO2-based suspension slurry. (3) Transfer the suspension slurry back to the mixing tank, add 6.3 g of mullite fiber (average diameter 5 μm, average length 150 μm, aspect ratio 30) and 2.5 g of aluminum borate whiskers (average diameter 1.0 μm, average length 20 μm, aspect ratio 20), the total mass of the reinforcing phase is 7 wt.% of the total mass of the powder (100.0+15.0+10.0+2.0=127.0 g), stir at a stirring rate of 400 rpm for 90 min to form SnO2-based selective ORR composite slurry; the solid content of the slurry is about 38 vol.%, pH 3.5.

[0090] Step S2: Preparation of SnO2-based foam ceramic wet blank A polyurethane foam template (pore density 40 PPI, size 150 mm × 150 mm × 20 mm, cuboid) was completely immersed in the SnO2-based selective ORR composite slurry obtained in step S1. A negative-pressure-normal-pressure alternating impregnation method was used: first, the system was evacuated to boiling point (absolute pressure approximately 3 kPa) within 2 minutes, maintained at boiling for 2 minutes, and then normal pressure was restored. This negative-pressure-normal-pressure alternation was repeated 4 times. After removal, the slurry was deslurried by centrifugation (1500 rpm, centrifugation time 60 seconds). Subsequently, it was placed in a temperature-controlled drying oven, with the temperature increased from 25℃ to 60℃ at a rate of 1.0℃ / min, and the relative humidity gradually decreased from 85% to 15%, drying until the mass change rate was <20% / h. The above impregnation-deslurry-drying cycle was repeated 3 times, resulting in a cumulative slurry loading of 420% of the original organic foam mass, a coating thickness of approximately 0.7 mm, and a pore blockage rate of approximately 25%, thus obtaining a SnO2-based foam ceramic wet blank.

[0091] Step S3: Preparation of SnO2-based foam ceramic green body The wet blank obtained in step S2 was first air-dried at 25°C in a ventilated environment for 12 hours (relative humidity 45%, ventilation rate 1.5 m / s); then it was transferred into a forced-air drying oven, heated to 90°C at 2°C / min, and kept at that temperature for 12 hours (airflow rate 1.0 m / s) until the mass change rate was <0.1% / h. Then transfer it to a tubular atmosphere furnace, introduce air (flow rate 600 mL / min), and perform degumming heat treatment: First stage: Increase to 200℃ at a rate of 2℃ / min and hold for 90 min; Second stage: Increase to 380℃ at 1℃ / min and hold for 180 min; Third stage: Increase to 650℃ at a rate of 1.5℃ / min and hold for 90 min; The furnace pressure was maintained at gauge pressure +150 Pa to obtain SnO2-based foam ceramic green body.

[0092] Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green blank obtained in step S3 was subjected to controlled sintering heat treatment in a tube atmosphere furnace: air was introduced (flow rate 600 mL / min), and sintering was carried out in two stages. First stage sintering: The temperature is increased to 850℃ at 2℃ / min and held for 3 hours. During this stage, V2O5 (melting point 690℃) and Bi2O3 (melting point 817℃) form liquid phases one after another, which together wet the surface of SnO2 and Nb2O5 particles, driving particle rearrangement and initial densification.

[0093] Second stage sintering: Temperature is increased to 1200℃ at a rate of 1.5℃ / min and held for 5 hours. During this stage, Nb... 5+ (Ionic radius 0.64 Å) enters the SnO2 lattice in large quantities through bulk diffusion. 4+ With an ionic radius of 0.69 Å and a radius difference of only 7%, it exhibits high solid solubility, forming a uniform donor-type solid solution, Sn. 1-x Nb x O2. Meanwhile, Fe³ + Acceptor-doped partial compensation Nb 5+ The excess electrons from donor doping precisely tune the Fermi level to the optimal position for the two-electron ORR.

[0094] Maintain the furnace pressure at gauge pressure +400 Pa; allow it to cool naturally to room temperature.

[0095] Mechanism of two-electron ORR selective active interface construction during sintering: Nb 5+ Donor doping shifts the Fermi level of SnO2 upwards, increasing the conduction band electron concentration—thus improving the ORR reaction rate. More importantly: Nb... 5+ d 0 Its configuration prevents its surface sites from having d-π feedback capability for O2 molecules, when O2 adsorbs onto Nb 5+ At the site, the O–O bond is not weakened. The adsorption free energy (ΔGOOH) of OOH on the Nb-doped SnO2(110) surface falls within the optimal window for two-electron ORR selectivity (approximately 3.5–4.0 eV), which is far superior to that on the pure SnO2 surface. Nb2O5 has completely dissolved into the SnO2 lattice, forming a homogeneous solid solution rather than an independent phase interface, but its global modification of the electronic structure of the SnO2 surface is equivalent to constructing a "distributed two-electron ORR selective active surface".

[0096] The performance indicators of the obtained product are as follows: porosity of 82%, compressive strength of 0.35 MPa, and pore connectivity of 80%; X-ray diffraction (XRD) analysis shows that its phase composition is rutile SnO2 (main phase), and the diffraction peaks are slightly shifted relative to pure SnO2, indicating that Nb 5+The presence of solid solution and trace amounts of Bi₂Sn₂O₇ pyrochlore phase (derived from the reaction product of the sintering aid Bi₂O₃ and SnO₂) was observed. No independent Nb₂O₅ phase was detected, indicating that Nb₂O₅ has been completely dissolved into the SnO₂ lattice.

[0097] Photocatalytic H2O2 production performance test: The obtained foam ceramic was placed in a continuous flow reactor, using deionized water containing saturated dissolved oxygen (approximately 8.2 mg / L) as the reaction medium. The water flow rate was 80 mL / min, and air was continuously introduced to maintain dissolved oxygen saturation. The surface of the foam ceramic was irradiated with a 36 W UV-A LED lamp.

[0098] After 6 hours of reaction, the cumulative concentration of H2O2 in the effluent reached 42.3 μmol / L (approximately 1.44 mg / L). The electron transfer number n = 2.15, determined by the RRDE method, corresponds to an H2O2 selectivity of approximately 93%, indicating that Nb... 5+ donor-doped d 0 The surface configuration exhibits extremely high selectivity for the two electron pathways.

[0099] After 120 hours of continuous operation, the H2O2 yield decreased by less than 5%, indicating that Nb 5+ Solid solution catalysts exhibit excellent structural stability (no phase change, no dissolution).

[0100] Application verification of H2O2 supply for wastewater pretreatment: The effluent (H2O2 concentration ~1.44 mg / L) from the foam ceramic reactor was directly fed into a Fenton reactor (pH 3.0, Fe²⁺) containing FeSO₄ catalyst. + With a concentration of 5 mg / L, H2O2 in the effluent drives the Fenton reaction to produce ·OH, achieving a 92% decolorization rate for 100 mg / L methylene blue wastewater (reaction time 60 min). This verifies the feasibility of using this foam ceramic as an "H2O2 generator" to supply H2O2 to the downstream Fenton process.

[0101] Example 3 SnO2 / WO3 system – conduction band potential-modulated heterogeneous interface for inhibiting H2O2 decomposition, used for pulp bleaching. This embodiment provides a SnO2-based monolithic photocatalytic H2O2 production foam ceramic with WO3 as a selectively regulated component. It utilizes the unique band structure of the SnO2 / WO3 heterostructure interface—after photogenerated electrons are transferred to the conduction band of WO3, the mild reduction potential of the electrons in the conduction band of WO3 naturally prevents the decomposition of the generated H2O2.

[0102] The preparation method of the SnO2-based monolithic photocatalytic H2O2 production foam ceramic includes the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry (1) Take 130 mL of deionized water and place it in a polytetrafluoroethylene beaker. Add 2.0 g of sodium carboxymethyl cellulose (CMC), 1.2 g of sodium polyacrylate (NaPAA), 1.0 g of triethyl citrate (TEC), 0.4 g of sodium dodecyl sulfate (SDS), 0.5 g of hydroxyethyl cellulose (HEC), and 0.2 g of polyether defoamer in sequence. Stir at 400 rpm for 50 min to completely dissolve the organic additives. Add triethanolamine to adjust the pH to 10.0. (2) Add the following powder raw materials to the above homogenized solution in three batches (stir for 35 min after each batch is added, at a stirring speed of 1000 rpm): Rutile SnO2 powder (purity 99.5%, average particle size 300 nm): 100.0 g; Selective control of the component—monoclinic WO3 powder (average particle size 200 nm, purity 99.9%): 40.0 g (40 wt.% of the SnO2 powder mass); the high amount of WO3 is because WO3 has extremely low solid solubility in SnO2 and mainly exists as an independent phase at the SnO2 grain boundaries to form a SnO2 / WO3 heterostructure interface. Sufficient WO3 phase is required to form a sufficient heterostructure interface area; Sintering aids – B2O3 powder (average particle size 100 nm): 4.0 g, low-temperature glass powder (Bi2O3-B2O3-ZnO system, softening point 520℃, average particle size 10 μm): 6.0 g (the total of B2O3 and low-temperature glass powder is 10 wt.% of the mass of SnO2 powder). Defect control agent – ​​Ta₂O₅ powder (average particle size 200 nm): 5.0 g (5 wt.% of SnO₂ powder mass); Ta 5+ As a donor-type dopant, the Ta-O bond energy (799 kJ / mol) is higher than the Nb-O bond energy (771 kJ / mol). 5+ After doping, it is more stable in the SnO2 lattice and less likely to dissolve; After all the powder was added, continue stirring at a stirring rate of 1200 rpm for 150 min to form a SnO2-based suspension slurry. (3) Add 7.0 g of silicon carbide fiber (average diameter 10 μm, average length 300 μm, aspect ratio 30) and 5.0 g of potassium titanate whiskers (average diameter 0.8 μm, average length 25 μm, aspect ratio 31) to the above suspension slurry. The total mass of the reinforcing phase is about 8 wt.% of the total mass of the powder (100.0+40.0+10.0+5.0=155.0 g). Stir at a stirring rate of 500 rpm for 80 min to form SnO2-based selective ORR composite slurry. The solid content of the slurry is about 40 vol.% and the pH is 10.0.

[0103] Step S2: Preparation of SnO2-based foam ceramic wet blank A polyurethane foam template (pore density 20 PPI, size 200 mm × 200 mm × 40 mm, cuboid) was completely immersed in the SnO2-based selective ORR composite slurry obtained in step S1 and impregnated at 25°C under normal pressure for 300 seconds. After removal, the slurry was manually descrambled (pressure approximately 0.5 MPa, compressed to 50% of the original thickness), and the extrusion was repeated 3 times. Subsequently, it was placed in a programmable temperature-controlled drying oven, and the temperature was increased from 22°C to 50°C at a rate of 0.3°C / min, while the relative humidity was gradually reduced from 75% to 25%, until the mass change rate was <20% / h. The above impregnation-descrambling-drying cycle was repeated 5 times, and the cumulative slurry loading reached 680% of the original mass of the organic foam, the coating thickness was approximately 1.5 mm, and the pore blockage rate was approximately 18%, thus obtaining a SnO2-based foam ceramic wet blank.

[0104] Step S3: Preparation of SnO2-based foam ceramic green body The wet blank obtained in step S2 was first air-dried at 22°C in a ventilated environment for 24 hours (relative humidity 55%, ventilation rate 0.8 m / s); then it was transferred to a forced-air drying oven, heated to 70°C at 1.5°C / min, and kept at that temperature for 20 hours (airflow rate 0.3 m / s) until the mass change rate was <0.1% / h. Then transfer it to a box-type atmosphere furnace, introduce air (flow rate 800 mL / min), and perform degumming heat treatment: First stage: Increase the temperature to 230℃ at a rate of 1.5℃ / min and hold for 150 min; Second stage: Increase to 420℃ at 0.8℃ / min and hold for 260 min; Third stage: Increase to 580℃ at 1℃ / min and hold for 150 min; The furnace pressure was maintained at gauge pressure +300 Pa to obtain SnO2-based foam ceramic green body.

[0105] Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green blank obtained in step S3 was subjected to controlled sintering heat treatment in a box-type atmosphere furnace: air was introduced (flow rate 1000 mL / min), and sintering was carried out in two stages: First stage sintering: The temperature is increased to 950℃ at a rate of 2℃ / min and held for 2 hours. During this stage, the liquid phase provided by B2O3 (melted at 450℃) and low-temperature glass powder (softened at 520℃) fully wets the SnO2 and WO3 particles, driving particle rearrangement and densification. WO3 (melting point 1473℃) remains solid and does not melt at this temperature.

[0106] The second stage of sintering: The temperature is increased to 1100℃ at a rate of 1.5℃ / min and held for 4 hours. During this stage, the SnO2 particles continue to densify through a liquid-phase assisted dissolution-reprecipitation mechanism. WO3 still exists as an independent phase at the SnO2 grain boundaries, forming a SnO2 / WO3 chemically bonded heterogeneous interface—connected at the interface by Sn-OW bond bridges. 5+ At this temperature, WO3 diffuses into the SnO2 lattice to form a donor-type solid solution. The sintering temperature is controlled at 1100℃ to avoid sublimation of WO3 at higher temperatures.

[0107] Maintain the pressure inside the furnace at gauge pressure +500 Pa; allow it to cool naturally to room temperature.

[0108] The mechanism of two-electron ORR selective active interface construction during sintering: SnO2 / WO3 heterointerface forms Type II band alignment—SnO2 conduction band (approximately The SnO2 conduction band potential (0.3 V vs NHE) is higher than that of WO3 (approximately +0.1 V vs NHE). Photogenerated electrons transfer from the SnO2 conduction band to the WO3 conduction band and perform ORR on the WO3 surface. The key advantage is that while the reduction potential of the WO3 conduction band electrons (approximately +0.1 V) is sufficient to drive a two-electron ORR (O2 + 2H+), the reduction potential of the WO3 conduction band electrons is still relatively low. + + 2e - → H2O2, E° = +0.68 V, ΔG<0), but not enough to efficiently drive further reduction of H2O2 (requiring a large activation energy), therefore the WO3 surface naturally does not decompose the already generated H2O2. In addition, the abundant terminal W=O double bonds on the WO3 surface stabilize the OOH intermediate through hydrogen bonds (W=O···HOO-).

[0109] The performance indicators of the obtained product are as follows: porosity of 72%, compressive strength of 0.55 MPa, and pore structure connectivity of 68%; X-ray diffraction (XRD) analysis shows that its phase composition is rutile SnO2 (main phase), monoclinic WO3 (secondary phase, with independent grains distributed at SnO2 grain boundaries) and trace amounts of borosilicate glass phase.

[0110] Photocatalytic H2O2 production performance test: The obtained foam ceramic (200 mm × 200 mm × 40 mm) was placed in a continuous flow reactor. Deionized water containing saturated dissolved oxygen (approximately 8.2 mg / L) was used as the reaction medium, with a water flow rate of 200 mL / min. Air was continuously introduced to maintain dissolved oxygen saturation. The surface of the foam ceramic was irradiated with a 300 W xenon lamp (equipped with an AM1.5 filter to simulate sunlight, with a light intensity of 100 mW / cm²).

[0111] After 6 hours of reaction, the cumulative concentration of H2O2 in the effluent reached 36.8 μmol / L (approximately 1.25 mg / L). The electron transfer number n of the catalyst, determined by the RRDE method, was 2.08, corresponding to an H2O2 selectivity of approximately 96%.

[0112] The reason for the extremely high H2O2 selectivity (96%, the highest among all embodiments) of this system is that the mild reduction potential of the conduction band electrons of WO3 thermodynamically inhibits the over-reduction of H2O2—even if a small number of H2O2 molecules come into contact with the WO3 surface, they will not be effectively decomposed. Simultaneously, the W=O terminal oxygen pairs... The hydrogen bond stability of OOH further ensures the dominance of the two-electron pathway.

[0113] After 96 hours of continuous operation, the H2O2 yield decreased by <6%. The effluent from this foam ceramic reactor was directly fed into a Fenton reactor (pH 3.0, Fe²⁺) containing a FeSO₄ catalyst. + With a concentration of 5 mg / L, H2O2 in the effluent drives the Fenton reaction to produce ·OH, achieving a decolorization rate of over 90% for 100 mg / L methylene blue wastewater (reaction time 60 min), verifying the feasibility of using this foam ceramic as an "H2O2 generator".

[0114] Validation of Pulp Bleaching Application: The same batch of foam ceramics was placed in a circulating reactor containing 5 g / L bleached eucalyptus pulp suspension (Kappa number 15) and continuously circulated for 24 hours under 300 W xenon lamp irradiation. The cumulative concentration of H2O2 in the effluent reached ~5 mg / L. After treatment, the pulp brightness (ISO brightness) increased from 45% to 58%, and the Kappa number decreased from 15 to 11, demonstrating that the H2O2 generated in situ by photocatalysis has an effective bleaching and oxidizing effect on pulp lignin.

[0115] Example 4 SnO2 / CeO2 system – oxygen vacancy dynamic regeneration type, used for solar-driven emergency water disinfection. This embodiment provides a SnO2-based monolithic photocatalytic H2O2 production foam ceramic with CeO2 as a selectively controlled component, utilizing the abundant CeO2 surface on CeO2. 4+ / Ce³+ The redox cycle continuously regenerates oxygen vacancies, providing a high density of end-on adsorption activation sites for O2. A high specific surface area is achieved using a high-pore-density (50 PPI) melamine foam template, making it suitable for solar-driven emergency water supply disinfection applications.

[0116] The preparation method of the SnO2-based monolithic photocatalytic H2O2 production foam ceramic includes the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry (1) Take 110 mL of deionized water and place it in a polypropylene mixing tank. Add 1.8 g of methylcellulose (MC), 1.5 g of ammonium citrate, 1.2 g of diethylene glycol (DEG), 0.2 g of sorbitan monooleate (Span-80), 0.2 g of gellan gum (GeG), and 0.08 g of isooctanol (IOA) in sequence. Stir at a mechanical stirring rate of 450 rpm for 70 min to completely dissolve the organic additives. Add acetic acid to adjust the pH to 4.5. (2) Add the following powder raw materials to the above homogenized solution in three batches (stir for 45 min after each batch is added, stirring at a speed of 850 rpm): Rutile SnO2 powder (purity 99.0%, average particle size 500 nm): 100.0 g; Selective control of the component—CeO2 powder (fluorite type, average particle size 80 nm, purity 99.95%): 20.0 g (20 wt.% of SnO2 powder mass); nano-sized CeO2 (80 nm) was selected to increase the interfacial contact area with SnO2 and the Ce-O-Sn bond bridge density; Sintering aids—Bi2O3 powder (average particle size 400 nm): 5.0 g, ZnO powder (average particle size 200 nm): 3.0 g (Bi2O3 and ZnO together account for 8 wt.% of the mass of SnO2 powder); Bi2O3 provides the main liquid phase, and ZnO can react with SnO2 to form Zn2SnO4 spinel phase to enhance grain boundary strength; Defect control agent – ​​F-doped SnO2 (FTO) powder (F content 3 at.%, average particle size 150 nm): 4.0 g, NiO powder (average particle size 100 nm): 1.0 g (FTO and NiO combined account for 5 wt.% of the SnO2 powder mass); F in FTO - Replace O² - As a donor-type doped NiO, Ni²⁺ + Replace Sn 4+This is an acceptor-type doping strategy. The donor / acceptor co-doping strategy involves the amount of donor electrons provided by FTO being partially compensated by acceptors in NiO, ultimately resulting in the Fermi level being precisely tuned to the optimal window for the two-electron ORR. After all the powder was added, it was transferred to a polytetrafluoroethylene ball mill jar for ball milling and mixing for 180 min (zirconia milling ball diameter 5 mm, ball-to-material weight ratio 4:1) to form SnO2-based suspension slurry; (3) Transfer the suspension slurry back to the mixing tank, add 5.3 g of glass fiber (average diameter 12 μm, average length 250 μm, aspect ratio 21) and 1.3 g of zinc oxide whiskers (quadrupedal shape, average diameter 1.5 μm, average length 30 μm, aspect ratio 20), the total mass of the reinforcing phase is 5 wt.% of the total mass of the powder (100.0+20.0+8.0+5.0=133.0 g), stir at a stirring rate of 350 rpm for 100 min to form SnO2-based selective ORR composite slurry; the solid content of the slurry is about 32 vol.%, pH 4.5.

[0117] Step S2: Preparation of SnO2-based foam ceramic wet blank A melamine foam template (50 PPI pore density, 80 mm × 80 mm × 25 mm, cuboid) was completely immersed in the SnO2-based selective ORR composite slurry obtained in step S1. An alternating negative and normal pressure impregnation method was used: first, the system was evacuated to boiling point (absolute pressure approximately 4 kPa) within 4 minutes, maintained at boiling for 4 minutes, then normal pressure was restored, and this alternating negative and normal pressure method was repeated 5 times. High-pore-density foams have greater capillary resistance, requiring more alternating negative and normal pressure methods to ensure complete penetration of the slurry into the foam interior.

[0118] After removal, the material is deslurried by centrifugation (2000 rpm, 90 seconds); then placed in a temperature-controlled drying oven, the temperature is increased from 23℃ to 45℃ at a rate of 0.3℃ / min, and the relative humidity is gradually reduced from 90% to 25%, until the mass change rate is <20% / h. Drying high-porosity foam requires a particularly slow process—the heating rate is only 0.3℃ / min and the initial humidity is as high as 90%—to prevent the thin-walled coating from cracking due to rapid shrinkage.

[0119] Repeat the above impregnation-desizing-drying cycle 6 times, and the cumulative slurry loading reaches 780% of the original mass of melamine foam. The coating thickness is about 0.5 mm (the coating should be thinner under high pore density to avoid pore blockage), and the pore blockage rate is about 30%, thus obtaining a wet SnO2-based foam ceramic blank.

[0120] Step S3: Preparation of SnO2-based foam ceramic green body The wet blank obtained in step S2 was first air-dried at 23°C in a ventilated environment for 20 hours (relative humidity 55%, ventilation rate 0.7 m / s); then it was transferred to a forced-air drying oven, heated to 65°C at 1°C / min, and kept at that temperature for 24 hours (airflow rate 0.2 m / s) until the mass change rate was <0.1% / h. Then transfer it to a tubular atmosphere furnace, introduce air (flow rate 400 mL / min), and perform degumming heat treatment: First stage: Increase to 190℃ at a rate of 1℃ / min and hold for 180 min; The second stage involves heating to 380℃ at a rate of 0.5℃ / min and holding for 300 min. The thermal decomposition of melamine foam mainly occurs between 350 and 400℃. This stage employs an extremely slow heating rate of 0.5℃ / min to prevent the thin-walled coating under high porosity from collapsing due to the impact of rapidly decomposing gases from the template. Third stage: Increase to 600℃ at 1℃ / min and hold for 150 min; The furnace pressure was maintained at gauge pressure +100 Pa to obtain SnO2-based foam ceramic green body.

[0121] Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green blank obtained in step S3 was subjected to controlled sintering heat treatment in a tube atmosphere furnace: air was introduced (flow rate 500 mL / min), and sintering was carried out in two stages. First stage sintering: The temperature is increased to 880℃ at a rate of 1.5℃ / min and held for 3 hours. During this stage, Bi2O3 (melting at 817℃) forms a liquid phase, and ZnO begins to react with SnO2 in the liquid phase. CeO2 (melting point 2613℃) remains completely solid at this temperature.

[0122] The second sintering stage involves heating to 1050℃ at a rate of 1℃ / min and holding for 6 hours. During this stage, SnO2 particles densify. CeO2 nanoparticles are encapsulated by the SnO2 matrix and distributed at the grain boundaries. The CeO2 / SnO2 interface forms chemical bonds through Ce-O-Sn bonds. Due to the significant difference in crystal structure between CeO2 (fluorite type, a = 5.41 Å) and SnO2 (rutile type), they do not form a solid solution; CeO2 is embedded as independent nanocrystals within the SnO2 grain boundaries. The sintering temperature (1050℃) in this embodiment is relatively low because: (a) CeO2 nanoparticles (80 nm) undergo Ostwald ripening and growth at excessively high temperatures, reducing specific surface area and oxygen vacancy density; (b) the thin-walled coating (0.5 mm) corresponding to the high porosity (50 PPI) is prone to collapse due to excessive shrinkage at excessively high temperatures. The F in FTO... - Ni² in NiO +At this temperature, the dopant diffuses into the SnO2 lattice to complete the donor / acceptor co-doping.

[0123] Maintain the pressure inside the furnace at gauge pressure +200 Pa; allow it to cool naturally to room temperature.

[0124] The construction mechanism of the two-electron ORR selective active interface during sintering: CeO2 surface rich in Ce 4+ / Ce³ + Reversible cycling is accompanied by the dynamic formation of oxygen vacancies. At the CeO2 / SnO2 chemical bonding interface, Ce³⁺… + The oxygen vacancies generated at the site provide active sites for end-on adsorption of O2. Under light irradiation, conduction band electrons of SnO2 are transferred to the CeO2 surface through the Ce-O-Sn bond bridge interface, reducing Ce. 4+ For Ce³ + Oxygen vacancies are formed → O2 is end-on adsorbed at the oxygen vacancy → it accepts two photogenerated electrons from SnO2 and is reduced to H2O2 → H2O2 desorbs and re-oxidizes Ce³. + For Ce 4+ The excellent oxygen storage capacity (OSC) of CeO2 ensures the continuous regeneration of oxygen vacancies and maintains the stability of ORR active sites, thus completing the catalytic cycle.

[0125] The performance indicators of the obtained product are as follows: porosity of 85%, compressive strength of 0.25 MPa, and pore structure connectivity of 72%; X-ray diffraction (XRD) analysis shows that its phase composition is rutile SnO2 (main phase), fluorite CeO2 (secondary phase, independent nanocrystals), trace Zn2SnO4 spinel phase (from the reaction product of sintering aid ZnO and SnO2), and trace Bi2Sn2O7 phase.

[0126] Photocatalytic H2O2 production performance test: The obtained foam ceramic was placed in a continuous flow reactor, using deionized water containing saturated dissolved oxygen (approximately 8.2 mg / L) as the reaction medium. The water flow rate was 30 mL / min, and air was continuously introduced to maintain dissolved oxygen saturation. The surface of the foam ceramic was irradiated with a UV-C low-pressure mercury lamp.

[0127] After 6 hours of reaction, the cumulative concentration of H2O2 in the effluent reached 52.1 μmol / L (approximately 1.77 mg / L). The electron transfer number n of the catalyst was determined to be 2.22 by rotating ring-disk electrode (RRDE) method, corresponding to an H2O2 selectivity of approximately 89%.

[0128] The H2O2 yield of this system was the highest in the four examples (52.1 μmol / L), which is because: (1) the CeO2 surface is rich in Ce 4+ / Ce³ +Reversible cycling continuously regenerates oxygen vacancies, providing a high density of end-on adsorption activation sites for O2, resulting in a large number of ORR active sites that can be continuously regenerated; (2) The high pore density of 50 PPI provides a large specific surface area (significantly increased compared to 20–40 PPI in Examples 1-3) and a CeO2 / SnO2 selective active interface area; (3) The UV-C 254 nm photon energy (4.88 eV) far exceeds the band gap of SnO2 (3.6 eV), resulting in high photon absorption efficiency, a large photogenerated carrier generation rate, and a high quantum yield; (4) Donor / acceptor co-doping (FTO + NiO) precisely modulates the Fermi level of SnO2 to the optimal position for two-electron ORR, taking into account both the ORR reaction rate (sufficient supply of conduction band electrons) and the suppression of H2O2 decomposition (avoiding excessive conduction band electrons leading to excessive reduction of H2O2).

[0129] After 168 hours of continuous operation, the H2O2 yield decreased by less than 10%. XPS analysis showed that the Ce³⁺ content on the CeO2 surface was significantly reduced. + / Ce 4+ The ratio did not change significantly before and after the reaction (Ce³ before the reaction). + / Ce 4+ = 0.32, Ce³ after 168 h of reaction + / Ce 4+ = 0.30), indicating that Ce 4+ / Ce³ + The redox cycle exhibits good reversibility and long-term stability, and the dynamic regeneration mechanism of oxygen vacancies can operate sustainably. After five cycles (6 hours of light exposure each time), the cumulative concentration of H2O2 decreased from 52.1 μmol / L to 47.6 μmol / L, a decrease of approximately 9%, indicating that the CeO2 / SnO2 chemical bonding interface (Ce-O-Sn bond bridge) has good structural stability under long-term water flow erosion.

[0130] Validation of drinking water disinfection applications: using an initial concentration of approximately 10 6 Simulated contaminated drinking water containing CFU / mL *E. coli* (ATCC25922) was used as the treatment target. After passing through the aforementioned continuous flow reactor, the effluent was collected and allowed to stand at 25°C for 30 min before plate counting. The results showed that the *E. coli* survival rate was <0.1% (kill rate >99.9%), meeting the microbiological requirements of the *Standards for Drinking Water Quality* (GB 5749-2022). Extending the contact time to 60 min resulted in an *E. coli* kill rate >99.99%, reaching the 4-log inactivation level.

[0131] Further validation of solar-driven emergency water supply disinfection was conducted: the same batch of foam ceramics was placed in a transparent acrylic container (internal dimensions 100 mm × 100 mm × 30 mm, with the top open to receive sunlight), containing approximately 10 5 A simulated natural water source containing CFU / mL of E. coli was poured into a container, and without connecting to any external power supply, it was left to stand in natural sunlight (sunny day, midday, light intensity 60–90 mW / cm²) for 6 hours. The H₂O₂ concentration in the water inside the container was measured to reach 0.85 mg / L, and the E. coli kill rate was >99% (2-log inactivation). This result indicates that even without external power supply or chemical reagents, sufficient concentration of H₂O₂ can be generated in situ by the ultraviolet component of natural sunlight (approximately 5% of the solar spectrum) to achieve drinking water-grade disinfection. This verifies the feasibility of applying this product in a solar-driven distributed emergency water supply disinfection scenario.

[0132] Further simulation of extreme emergency scenarios: Under cloudy conditions (light intensity 20–35 mW / cm²), after 8 hours of exposure to sunlight using the same device, the H₂O₂ concentration in the water was 0.41 mg / L, and the E. coli kill rate was 95%. Although lower than under sunny conditions, the kill rate can be increased to >99% by extending the contact time to 120 min, which still meets the minimum disinfection effect requirements recommended by the World Health Organization (WHO) for Household Water Treatment and Safe Storage (HWTS) technology.

[0133] This application solution requires no electricity, chemicals, or complex equipment. A complete solar-powered water supply and disinfection unit can be formed with just a transparent container and a piece of foam ceramic. It meets the WHO's recommended Point-of-Use (POU) water treatment technology requirements for developing countries and post-disaster emergency scenarios, and corresponds to the United Nations Sustainable Development Goal 6 (Clean Water and Sanitation).

[0134] The above description is merely a preferred embodiment of this application and does not constitute any limitation on 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. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the disclosed technical content without departing from the spirit and scope of this application are equivalent embodiments of this application; furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of this application still fall within the scope of the technical solution of this application.

Claims

1. A method for preparing monolithic photocatalytic H2O2 production foam ceramic based on selective two-electron oxygen reduction of SnO2, characterized in that, Includes the following steps: Step S1: Preparation of SnO2-based selective ORR composite slurry Organic additives and pH adjusters are added to deionized water and dispersed evenly to form a homogeneous solution; SnO2 powder, selective control components, sintering aids, and defect control agents are added to the homogeneous solution in batches and dispersed evenly to form a SnO2-based suspension slurry; fiber and / or whisker reinforcing phases are added to the suspension slurry and dispersed evenly to form a SnO2-based selective oxygen reduction reaction (ORR) composite slurry; Step S2: Preparation of SnO2-based foam ceramic wet blank The organic foam is completely immersed in the SnO2-based selective ORR 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 SnO2-based selective ORR composite slurry to accumulate layer by layer on the surface of the organic foam skeleton to obtain SnO2-based foam ceramic wet blank. Step S3: Preparation of SnO2-based foam ceramic green body The SnO2-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 SnO2 particles, selective control components, sintering aids, defect control agents and reinforcing phases are initially sintered together to form SnO2-based foam ceramic green body with three-dimensional interconnected pore structure; Step S4: Controlled sintering and in-situ two-electron ORR selective active interface construction The green body obtained in step S3 is subjected to controlled sintering heat treatment. Under the action of sintering aids, SnO2 and selective control components form a continuous ceramic skeleton network through particle densification and phase boundary bonding, achieving densification of the SnO2 system and ensuring the structural integrity of the three-dimensional interconnected channels. Simultaneously, the defect control agent regulates the grain growth, evaporation-condensation mass transfer behavior, and oxygen vacancy concentration of SnO2 during high-temperature sintering through solid solution substitution and grain boundary segregation mechanisms, controlling grain size, specific surface area, and porosity, and precisely controlling the Fermi level position and conduction band electron reduction potential of SnO2. The selective control components form a tight chemical bond interface with the SnO2 matrix at the phase boundary through in-situ solid-state reaction or atomic interdiffusion, constructing a two-electron ORR selective active interface structure in situ, thereby regulating the adsorption configuration of O2 molecules and stabilizing… The key intermediate OOH inhibits O–O bond breaking and suppresses excessive reducing decomposition of H2O2 products, enabling SnO2 conduction band photogenerated electrons to selectively execute the two-electron oxygen reduction pathway (O2 + 2H+). + + 2e - → H2O2) instead of the four-electron pathway (O2 + 4H) + + 4e - → 2H2O), to achieve highly selective and high-yield photocatalytic in-situ synthesis of H2O2.

2. The preparation method according to claim 1, characterized in that, In step S1, the average particle size of the SnO2 powder is 10 nm–80 μm, and it is selected from any one or a combination of rutile SnO2 powder, orthorhombic SnO2 powder, amorphous SnO2 powder or modified powder thereof. The modified powder is SnO2 powder obtained by any of the following modification methods: 1) Cation doping, wherein the cation is selected from Li + Na + K + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Bi³ + Sb³ + Sb 5+ ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Zn² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ W 6+ Re 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 10¹ 8 -10²¹ cm - ³; 4) Defect engineering modification, dislocation / grain boundary density 10¹ 4 –10¹ 6 cm - ²; The modified powder must still possess semiconductor properties and have a bandgap range of 2.5–4.5 eV. The selective control component is a functional component capable of forming a two-electron ORR selective active interface with SnO2 during sintering through in-situ solid-state reaction or atomic interdiffusion, enabling O2 to selectively take a two-electron path to produce H2O2 on the catalyst surface, with a band gap ranging from 1.5 to 5.5 eV; after sintering, the selective control component forms a chemically bonded interface or heterogeneous phase interface with the SnO2 matrix that enhances two-electron ORR selectivity; selected from at least one component of the following I)–VI): I) p-block metal oxides – stable due to lone pair electron effect OOH intermediate type Oxides containing p-block metal cations with lone pairs of electrons stabilize the key intermediate OOH in the two-electron ORR pathway and inhibit O–O bond breaking through moderate hybridization interaction between the lone pair electron orbitals and the OOH intermediate. Including one or more of Bi2O3, In2O3, Sb2O3, Sb2O5, Tl2O3, PbO, PbO2, GeO2 and their modified derivatives; II)d 0 Configuration of transition metal oxides—O2 selective adsorption type Contains d 0 Oxides of transition metal cations with an empty d orbital accepting O2σ coordination (end-on configuration) but without d electrons moving to O2π Back-donation does not weaken the O–O bond and is beneficial for the production of H2O2 via a two-electron pathway; including one or more of WO3, MoO3, Nb2O5, Ta2O5, V2O5, TiO2, ZrO2, HfO2 and their modified derivatives; III) Oxygen-storing oxides – oxygen vacancy dynamic regeneration type Oxides with abundant surface oxygen vacancies and oxygen storage capacity provide preferred end-on adsorption sites for O2, and the oxygen vacancy concentration can be dynamically regenerated through redox cycles; including CeO2, Ce2O3, and Pr6O. 11 One or more of the following: Tb4O7, MnO2, Mn2O3, Mn3O4, Co3O4, Fe2O3, Fe3O4, and their modified derivatives; IV) Wide bandgap semiconductor oxides – conduction band potential modulated type Wide-bandgap semiconductor oxides with appropriate conduction band positions, after forming a heterointerface with SnO2, allow photogenerated electrons to transfer from the SnO2 conduction band to the conduction band of this component to perform ORR (Organic Reduction). The mild reduction potential of its conduction band electrons (sufficient to drive two-electron ORR to produce H2O2 but insufficient to efficiently drive excessive reduction of H2O2) naturally inhibits H2O2 decomposition. This includes one or more of WO3, MoO3, Fe2O3, BiVO4, Bi2WO6, Bi2MoO6, AgNbO3, and their modified derivatives. V) Precursor compound: is the water-insoluble oxalate and / or carbonate corresponding to the metal oxide in I)–IV), wherein the precursor compound decomposes in situ during sintering heat treatment to generate the corresponding selectively regulated oxide; Wherein, "insoluble in water" means: solubility in deionized water at 25℃ ≤ 0.1 g / 100 mL; the precursor compound must meet the following requirements: decomposition temperature between 200–1200℃, residual carbon content after decomposition < 0.1 wt.%, and no introduction of impurity anions that are harmful to the two-electron ORR selectivity; VI) The selectively modulating 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 + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Sn 4 + Sb³ + Sb 5+ Bi³ + ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Zn² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce 4+ Pr³ + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ 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 10¹ 8 -10²¹ cm - ³; d) Defect engineering modification, dislocation / grain boundary density 10¹ 4 –10¹ 6 cm - ²; The amount of selectively controlled component added is 5–80 wt.% of the SnO2 powder mass; the amount of precursor compound added is based on the theoretical mass of the corresponding selectively controlled oxide generated by its complete thermal decomposition, i.e., oxide equivalent.

3. The preparation method according to claim 1, characterized in that, In step S1, the sintering aid is a composite aid system suitable for sintering SnO2-based materials and for the synergistic regulation of selective active interfaces for two-electron ORR. Based on the mechanism of action, it is divided into low-melting-point liquid phase forming agents, reactive bifunctional aids, grain boundary regulating rare earth aids, and their corresponding precursor forms. Among them, some components can simultaneously play multiple roles such as liquid phase assisting sintering, reaction activation, selective active interface construction, and grain boundary regulation. The total amount of the sintering aid is 0.2–30 wt.% of the SnO2 powder mass; when using a precursor, the amount added is based on the theoretical mass of the oxides generated after the complete thermal decomposition of the precursor. The sintering aid is selected from at least one of the following components: 1) Low melting point liquid phase forming agent: with a melting point below 1200℃, it forms an instantaneous liquid phase during sintering to promote mass transfer and densification, and at the same time acts as an interfacial binder to promote the interfacial bonding between selectively controlled components and the SnO2 matrix. The main components include: low-melting-point oxides such as Bi2O3, V2O5, MoO3, B2O3, P2O5, Sb2O3, GeO2, PbO, TeO2, CuO, and ZnO; alkali metal carbonates such as Li2CO3, Na2CO3, and K2CO3; alkaline earth metal carbonates such as MgCO3, CaCO3, SrCO3, and BaCO3; glass network forming agents such as SiO2, P2O5, TeO2, and GeO2; and low-temperature glass powders (Bi2O3-B2O3-ZnO system, PbO-B2O3-SiO2 system, or V2O5-P2O5 system, with softening points of 400–700℃). 2) Reactive bifunctional additives: can undergo solid-phase reaction with SnO2 at sintering temperature to generate a new composite oxide phase with two-electron ORR selective regulation function. This new phase participates in the selective regulation of H2O2 as a key component of the selective active interface and forms an active interface during the sintering process, thereby achieving the synergistic effect of sintering and selective active interface construction. The main components include one or more of the following: Bi2O3, CuO, Cu2O, Fe2O3, Fe3O4, TiO2, ZnO, Nb2O5, Ta2O5, ZrO2, HfO2, In2O3, CeO2, MnO2, Mn2O3, Co3O4, NiO, Cr2O3, Ga2O3, WO3, MoO3, and V2O5; or, a pre-synthesized tin-based functional phase is directly introduced as a composite additive, wherein the tin-based functional phase includes one or more of Bi2Sn2O7, Zn2SnO4, BaSnO3, SrSnO3, CaSnO3, and In2O3-SnO2 (ITO) solid solutions; the above components also include their corresponding nitrates, carbonates, oxalates, acetates, hydroxides, and other convertible precursors that can be thermally decomposed into the oxides or tin-based functional phases. 3) Grain boundary regulation type rare earth additives: By utilizing the rare earth ion radius matching, lattice distortion regulation and grain boundary segregation characteristics, through the synergistic effect of grain boundary pinning, defect regulation and interface energy regulation, grain boundary migration behavior is regulated, grain coarsening caused by SnO2 evaporation-condensation mass transfer is inhibited, and the densification degree, microstructure uniformity and two-electron ORR selective active interface quality of the material are improved. Mainly includes: Y₂O₃, La₂O₃, CeO₂, Pr₆O 11 Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3 and Lu2O3; Each of the above components can be a corresponding oxide, or a precursor that can decompose in situ during sintering to generate the corresponding active component; the precursor is preferably an insoluble or slightly soluble precursor with a solubility of no more than 0.1 g / 100 mL in deionized water at 25°C, including but not limited to carbonates, oxalates, hydroxides, oxycarbonates, basic carbonates, basic salts, acetates and other compounds that can be thermally decomposed into the corresponding oxides or functional phases; Some of the auxiliary components have multiple functions, including but not limited to Bi2O3, V2O5, MoO3, CuO, ZnO, CeO2, Nb2O5, Ta2O5, and rare earth oxides such as Y2O3, La2O3, Sm2O3, and Gd2O3. In practical applications, these components can simultaneously play roles such as liquid phase formation, reactive phase construction, selective active interface formation, defect control, grain boundary migration inhibition, and microstructure homogenization, thereby producing a synergistic effect. The defect control agent is a functional component system suitable for the sintering process, microstructure evolution, selective active interface defect optimization, and synergistic regulation of H2O2 yield performance in SnO2-based two-electron ORR selective systems. Based on its mechanism of action, it can be classified into donor-type defect control agents, acceptor-type defect control agents, oxygen vacancy-regulated defect control agents, interface defect and trap state-regulated defect control agents, local structure distortion-regulated defect control agents, and their corresponding precursor forms. Some components can simultaneously exert multiple functions, including Fermi level regulation, conduction band electron concentration adjustment, oxygen vacancy induction, selective active interface optimization, grain boundary segregation regulation, and sintering activation aid. The defect control agent is selected from at least one of the following components: 1) Donor-type defect control agent: Sn is controlled by substituting high-valence ions. 4+ O² is substituted with an anion or positional ion. - Introducing a donor level increases the conduction band electron concentration, shifts the Fermi level upward, and enhances the electron supply rate of the ORR reaction. The donor-type defect control agent is selected from one or more of Sb2O5, Nb2O5, Ta2O5, F-doped SnO2 (FTO) powder, P2O5, WO3, MoO3, and Cl-doped SnO2 powder; 2) Acceptor-type defect control agent: Sn is replaced by a low-valence ion. 4+ The introduction of acceptor levels reduces the concentration of electrons in the conduction band, shifts the Fermi level downward, and suppresses the excessive reduction and decomposition of H2O2. The acceptor-type defect control agent is selected from one or more of Co3O4, CoO, MnO2, Mn2O3, Mn3O4, Fe2O3, Fe3O4, NiO, CuO, Cu2O, Cr2O3, Al2O3, Ga2O3, In2O3, and ZnO; 3) Oxygen vacancy-regulated defect control agent: used to adjust the oxygen vacancy concentration, spatial distribution and formation energy in the SnO2-based system. An appropriate amount of oxygen vacancy serves as the preferred end-on adsorption site for O2, which is beneficial for the two-electron pathway. An excessive amount of oxygen vacancy leads to the dual-coordination adsorption of O2, which is beneficial for the four-electron pathway. The oxygen vacancy-regulated defect control agent is selected from one or more of CeO2, Ce2O3, TiO2, Ti2O3, Fe2O3, Fe3O4, FeO, MnO2, Mn2O3, Mn3O4, Co3O4, CoO, NiO, CuO, Cu2O, Cr2O3, V2O5, VO2, V2O3, MoO3, MoO2, WO3, WO2, SnO, Sb2O3, Sb2O5, Bi2O3, Ga2O3, GeO2, Nb2O5, Ta2O5, ZrO2, HfO2, and ZnO. 4) Interface defect and trap state modulation type defect control agent: used to adjust the defect state density and energy level position at the SnO2 / selective modulation component interface, suppress the formation of deep energy level recombination centers at the interface, and improve the transmission efficiency of photogenerated electrons at the interface and the utilization rate of ORR reaction; The interface defect and trap-state controlled defect agents are selected from CeO2, Y2O3, La2O3, and Pr6O. 11 One or more of the following: Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, ZnO, TiO₂, Nb₂O₅, Ta₂O₅, ZrO₂, HfO₂, Al₂O₃, SiO₂, GeO₂, and Bi₂O₃; 5) Localized structural distortion-regulated defect control agents: These agents regulate defect formation energy, electronic state distribution, and lattice matching degree at selectively active interfaces by adjusting ionic radius differences, coordination number changes, and the introduction of local stress. The localized structural distortion-modulating defect control agent is selected from La2O3, CeO2, and Pr6O. 11 One or more of the following: Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, Y₂O₃, Sc₂O₃, ZrO₂, HfO₂, TiO₂, Nb₂O₅, Ta₂O₅, GeO₂, Ga₂O₃, Bi₂O₃, and Al₂O₃; 6) Precursor form: Each of the above components can be its corresponding oxide, or a precursor that can decompose in situ during sintering to generate the corresponding active component; the precursor can be selected from one or more of the following: carbonates, oxalates, hydroxides, oxycarbonates, basic carbonates, acetates, and citrates of the corresponding metal element; the precursor is preferably an insoluble or slightly soluble precursor with a solubility of no more than 0.1 g / 100 mL in deionized water at 25°C. The aforementioned defect control agent components possess multiple functions, and their synergistic effects are explained below: Components such as CeO2, WO3, MoO3, V2O5, TiO2, Nb2O5, Ta2O5, ZnO, CuO, Fe2O3, MnO2, Co3O4, NiO, as well as Y2O3, La2O3, Sm2O3, and Gd2O3 can simultaneously play roles in practical applications, including Fermi level modulation, conduction band electron concentration regulation, oxygen vacancy regulation, selective active interface defect optimization, introduction of local structural distortion, grain boundary segregation regulation, and sintering activation. This allows for the control of Fermi level position, conduction band electron reduction potential, and O2 adsorption configuration in SnO2-based two-electron ORR selective systems. Synergistic optimization of OOH intermediate stability and H2O2 product decomposition inhibition; The total amount of the defect control agent added is 0.1–30 wt.% of the SnO2 powder mass; for precursor compound forms, the amount added is based on the theoretical mass of the corresponding oxide generated by complete thermal decomposition.

4. The preparation method according to claim 1, characterized in that, The organic additives include 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 SnO2 powder, selective control components, sintering aids, and defect control agents. The adhesive is selected from at least one of the following components: polyethylene oxide, sodium alginate, chitosan, polyurethane emulsion, polyacrylamide, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, polyethylene glycol with a molecular weight of 200–20,000, polyacrylic acid, polyvinyl acetate, starch and its derivatives. The plasticizer is selected from at least one of the following components: triethyl acetylglucosamine citrate, epoxidized soybean oil, polycaprolactone, glycerin, dibutyl phthalate, triethyl citrate, polyethylene glycol, sorbitol, and dioctyl sebacate; The dispersant is selected from at least one of the following components: polycarboxylate superdispersant, polymaleic anhydride, polyaspartic acid, ammonium polyacrylate, sodium polyacrylate, tetramethylammonium hydroxide, ammonium citrate, gum arabic, and polyvinylpyrrolidone. The surfactant is selected from at least one of the following components: sorbitan monooleate, cocamidopropyl betaine, sodium lauryl sulfate, hexadecyltrimethylammonium bromide, polysorbate 80, octylphenyl polyoxyethylene ether, lecithin, and fluorocarbon surfactants. The rheology modifier is selected from at least one of the following components: guar gum, gellan gum, polyacrylic acid thickener, xanthan gum, sodium carboxymethyl cellulose, bentonite, fumed silica and polyacrylamide; The defoamer is selected from at least one of the following components: 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, tantalum whiskers, palladium whiskers, chromium whiskers, magnesium 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, cobalt fiber, chromium fiber, nickel-titanium alloy fiber, iron-chromium-aluminum alloy fiber, nickel-chromium alloy fiber; The reinforcing phase has an aspect ratio ≥10, a length of 2 μm–10 mm, and a diameter of 0.1–1000 μm. The SnO2-based selective ORR 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 SnO2 powder, selective control components, sintering aids, and defect control agents, 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.

5. The preparation method according to claim 1, characterized in that, In step S1, the homogeneous solution is uniformly dispersed by mechanical stirring; the SnO2-based suspension slurry and the SnO2-based selective ORR composite slurry are 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 100–3000 rpm for 0.5–180 min, using an inert stirring paddle, and maintaining a distance of 0.1–2 cm between the paddle blades and the bottom of the slurry container. When mechanical stirring is used to uniformly disperse the SnO2-based suspension slurry and the SnO2-based selective ORR 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 the SnO2-based suspension slurry and SnO2-based selective ORR composite slurry are uniformly dispersed by ball milling, the ball milling jar used for ball milling is made of an inert material; the ball-to-material weight 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 SnO2-based selective ORR 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 a time of 10–900 seconds. The drying process employs a programmed temperature increase method, with a temperature range of 20–95°C and a 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, with a slurry coating thickness variation coefficient <30% and a pore blockage rate <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°C at a rate of 0.1–20°C / min, and the temperature is maintained for 4–24 hours. The airflow rate inside 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. The second stage involves increasing the temperature at a rate of 0.5–10℃ / min to 350–500℃ and holding the temperature for 1–360 min. The third stage involves increasing the temperature at a rate of 0.5–10℃ / min to 550–700℃ and holding the temperature 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, 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 to +9000 Pa.

8. The preparation method according to claim 1, characterized in that, In step S4, the controlled sintering heat treatment is performed at a temperature of 800–1400℃, a heating rate of 0.5–20℃ / min, and a holding time of 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 helium, argon, nitrogen, 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 to +2000 Pa.

9. The monolithic photocatalytic H2O2 production foam ceramic based on selective two-electron oxygen reduction of SnO2 prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the monolithic photocatalytic H2O2 production foam ceramic based on selective two-electron oxygen reduction of SnO2 prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The foam ceramic is placed in an aqueous solution containing dissolved oxygen, and under light irradiation, dissolved oxygen is converted into H2O2 through a selective two-electron oxygen reduction reaction using photogenerated electrons in the SnO2 conduction band, thus achieving in-situ synthesis of H2O2. Specifically, this includes: i) applications of photocatalytic in-situ synthesis of H2O2 under ultraviolet and / or visible light irradiation for drinking water disinfection, pulp bleaching, food processing disinfection, or medical device sterilization; ii) applications in the preparation of solar-driven distributed H2O2 synthesis reactors or emergency water supply disinfection devices; and iii) applications in photocatalytic in-situ production of H2O2 to supply H2O2 raw materials for downstream Fenton reactions, photo-Fenton reactions, or UV / H2O2 advanced oxidation processes.

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