Preparation method and application of in-situ doped rutile and anatase core-shell structure monolithic TiO2 foamed ceramic

Abstract

The invention discloses a preparation method and application of an in-situ doped rutile and anatase core-shell structure integral TiO2 foamed ceramic. According to the method, cations / rare earth ions are introduced in the alkali etching step, anions are introduced in the acid replacement step, and selective enrichment of doping elements in an anatase shell layer is achieved through a surface reconstruction window; and carrying out low-temperature calcination crystallization to obtain the monolithic photocatalyst with high strength, high specific surface area and wide spectral response. The obtained material shows excellent photocatalytic activity under visible light, is easy to recover, is suitable for a fixed bed reactor, and solves the engineering application problem of traditional TiO2 powder.

Description

Technical Field

[0001] This application relates to a method for preparing an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure and its application. In particular, it relates to a method for in-situ introducing dopant elements during alkaline etching and / or acid replacement treatment to prepare a monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure exhibiting broad spectral response, high mechanical strength, and excellent photocatalytic activity. This application belongs to the field of inorganic non-metallic functional materials technology. Background Technology

[0002] Titanium dioxide (TiO2) is widely used in environmental purification and energy conversion due to its high chemical stability, non-toxicity, low cost, and good photocatalytic activity. Anatase phase exhibits high photocatalytic activity but poor thermal stability, while rutile phase has a stable structure but lower activity. Combining these two phases to form a mixed-crystal structure (such as P25) can significantly improve performance; however, current technologies are mostly limited to powder morphology, resulting in engineering bottlenecks such as difficult recycling, easy agglomeration, and large pressure drop.

[0003] To address this issue, the applicant previously developed "A method for preparing an integral TiO2 foam ceramic with a rutile@anatase core-shell structure and its application" (application number: 202610144371X). This method utilizes a three-step process of "alkali etching-acid replacement-low-temperature calcination" to construct an anatase active shell in situ on the surface of a high-strength rutile framework, achieving both structural robustness and high surface activity. However, the light response of this material is still limited to the ultraviolet region (λ<387 nm). To extend it to the visible light region, elemental doping is an effective strategy. Traditional doping methods have two major drawbacks: (1) they are carried out simultaneously with powder synthesis, leading to bulk doping and the formation of carrier recombination centers; (2) post-modification impregnation methods cannot guarantee uniform doping on the surface of the three-dimensional porous framework, and high-temperature treatment may damage the anatase shell.

[0004] Currently, there are no reported technologies that directly introduce dopant precursors into alkaline or acidic solutions to achieve surface bandgap modulation while constructing core-shell structures. How to precisely control the type, concentration, and spatial distribution of dopants without interfering with the formation kinetics of titanates / hydrotitanic acid remains a long-standing technical challenge in this field. Summary of the Invention

[0005] The objective of this invention is to provide a method for preparing an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure and its application. This application utilizes the highly active reconstructed state of the TiO2 surface during the processes of alkaline treatment to generate titanate (Na2Ti3O7) and acid treatment to generate hydrotitanic acid (H2Ti3O7·nH2O): the former possesses interlayer cation exchange capacity, and the latter is rich in substituted -OH groups. This "chemical window" provides an ideal opportunity for in-situ, selective, and low-temperature doping. By introducing doping sources in-situ during the alkaline etching and acid replacement processes, selective enrichment of dopant elements in the anatase shell is achieved, thereby significantly improving the visible light photocatalytic performance of the material while retaining all the advantages of the core-shell structure.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This application provides a method for preparing in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramics, the method comprising the following steps: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is impregnated in the slurry, dried and debinded, and sintered at ≥1100°C in air atmosphere, and cooled to room temperature to obtain a high-strength monolithic rutile phase TiO2 foam ceramic precursor. Step S2: In-situ doped alkaline etching treatment The monolithic rutile phase TiO2 foam ceramic precursor obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was taken out, washed until neutral and dried to obtain an alkali metal titanate nanostructure intermediate containing cation dopant elements. Step S3: In-situ doping acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until near neutral and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements. Step S4: Heat treatment crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at a low temperature below 750°C; after calcination, it is naturally cooled to room temperature to obtain the target product. In step S2, the concentrations of the cation or rare earth ion doping source and the anion doping precursor in step S3 are ≥0, but not both 0, i.e., cation / rare earth ions and anions are doped individually or simultaneously.

[0008] In some embodiments, in step S1, the average particle size of the TiO2 powder is 10 nm-50 μm, preferably 50 nm-30 μm, and can be selected from any one or a combination of anatase TiO2, rutile TiO2, commercial P25 TiO2 or modified powder thereof. The modified powder is TiO2 powder obtained by any of the following modification methods: (1) Cation doping (Li + Na + K + 、Rb + Cs + Mg² + Ca² + Sr² + Ba² + Al³ + Ga³ + In³ + Sn 4+ Sb³ + Sb 5+ Bi³ + ,Sc³ + Ti 4+ V³ + V 4+ V 5+ Cr³ + Cr 4+ Mn² + Mn³ + Mn 4+ Fe² + Fe³ + Co² + Co³ + Ni² + Ni³ + Cu² + Zn² + Y³ + Zr 4+ 、Nb 5+ Mo 6+ Ru 4+ 、Rh³ + Pd² + Ag + La³ + Ce³ + Ce4+ 、Pr³ + Pr 4+ 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + 、Tb 4+ Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + Hf 4+ Ta 5+ W 6+ Re 4+ Re 6+ Os 4 + Ir 4+ Pt² + Pt 4+ and Au³ + (e.g., 0.1-15 at%) (2) Anion doping (B, C, N, F, P, S, Cl, Br and I, 0.5-10 at%); (3) Oxygen vacancy regulation (concentration 10) 18 -10 21 cm -3 ); (4) Defect engineering modification (dislocation / grain boundary density 10) 14 -10 16 cm -2 ); The modified powder must meet the following conditions: it must still possess semiconductor properties and have a decomposition temperature above 1300℃ in air, a band gap of 1.5-4.5eV, and a degradation rate constant for typical emerging pollutants (tetracycline, bisphenol A, or perfluorooctanoic acid) under AM 1.5G standard illumination that is not less than 10% of that of commercial P25 TiO2. TiO2 powder modified by any one or more of the above methods, as long as it meets the requirements of this application for decomposition temperature, band gap and photocatalytic performance, is considered to fall within the scope of the TiO2 powder described in this application.

[0009] In some implementations, in step S1, the reinforcing phase is 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, etc.; 2) Ceramic whiskers: silicon carbide whiskers, mullite 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, etc. 3) Natural mineral fibers: sepiolite fiber, attapulgite fiber, wollastonite fiber, palygorskite fiber, tremolite fiber, actinolite fiber, vermiculite fiber, pyrophyllite fiber, sillimanite fiber, glauconite fiber, tourmaline fiber, palygorskite fiber, etc. 4) Synthetic organic fibers: polyacrylonitrile fiber, polyvinyl alcohol fiber, aramid fiber, polyimide fiber, etc.; The reinforcing phase has an aspect ratio ≥ 10, a length of 1-500 μm, and a diameter of 0.1-50 μm; The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; The organic additive is selected from at least one of the following: The adhesive is selected from one or more of the following: polyethylene oxide (PEO), sodium alginate, chitosan, polyurethane (PU) emulsion, polyacrylamide (PAM), polyvinyl alcohol (PVA), methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), ethylcellulose (EC), polyethylene glycol (PEG, molecular weight 200-20,000), polyacrylic acid (PAA), polyvinyl acetate (PVAc), starch and its derivatives; The plasticizer is selected from one or more of the following: triethyl acetylglucosamine citrate (ATEC), epoxidized soybean oil (ESO), polycaprolactone (PCL), glycerin, dibutyl phthalate (DBP), triethyl citrate (TEC), polyethylene glycol (PEG), sorbitol, and dioctyl sebacate (DOS); The dispersant is selected from: polycarboxylate superdispersants (such as Solsperse). TM 32000, Tamol TM One or more of the following: SN), polymaleic anhydride (PMA), polyaspartic acid (PASP), ammonium polyacrylate (NH4PAA), sodium polyacrylate (NaPAA), tetramethylammonium hydroxide (TMAH), ammonium citrate, gum arabic, and polyvinylpyrrolidone (PVP); The surfactant is selected from one or more of the following: sorbitan monooleate (Span-80), cocamidopropyl betaine (CAB), perfluoropolyethers (such as Zonyl® FSO), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), Tween-80, Triton X-100, lecithin, and fluorocarbon surfactants (such as Capstone® FS-30); The rheology modifier is selected from one or more of the following: guar gum, gellan gum, polyacrylic acid thickeners (such as Carbopol® 940), organic modified montmorillonite (such as Bentonex®), xanthan gum, sodium carboxymethyl cellulose (CMC), bentonite, fumed silica and polyacrylamide (PAM); The defoamer is selected from one or more of the following: polydimethylsiloxane (PDMS), polyether defoamer (such as Pluronic® L61), isooctanol, n-octanol, silicone oil (such as Dow Corning® 200 Fluid), polyether-modified siloxane (such as BYK-024), and mineral oil; The above-mentioned organic additives can be used alone or in combination, with a total addition amount of 0.1-20 wt.% of the metal oxide-based powder. The pH adjuster is at least one of ammonia (NH3·H2O, 10 mol / L) and hydrochloric acid (HCl, 10 mol / L).

[0010] In some embodiments, the amounts of the organic additive and the reinforcing phase added (based on the weight of the TiO2 powder): Adhesive 1-20 wt.%; Dispersant 0.01-5 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); The solid content of the TiO2 slurry is 20-70 vol.%, preferably 30%-50 vol.%; the pH is 2-14, preferably 7-13. The mixing process is mechanical stirring or ball milling. The degassing is performed under a vacuum of -0.01 MPa to -0.1 MPa (i.e., 10-100 kPa negative pressure) for 2-20 minutes to fully remove air bubbles trapped in the slurry. The organic foam can be made of polyurethane (PU), melamine formaldehyde (MF), or polystyrene (PS), preferably polyurethane foam; the pore density of the foam ranges from 5 to 50 PPI, its porosity is 40% to 99%, and its average pore size is 100 μm to 8000 μm. Its macroscopic shape is any one of the following: cylinder, cube, cuboid, sphere, ellipsoid, toroid, prism, pyramid, polyhedron, honeycomb block, sheet, arc, arch, tubular, hollow spherical shell, or any combination and deformation thereof. The conditions to be met for the impregnation are: the cumulative loading of the TiO2 suspension slurry reaches 100-1000% of the original mass of the organic foam, the coating thickness is 0.1-3.0 mm, the coating thickness variation coefficient is <30%, and the pore blockage rate is <40%.

[0011] In some embodiments, in step S1, the specific drying conditions are as follows: at a temperature of 20-99°C, static or forced-air drying is carried out for 4 to 48 hours, with a heating rate not exceeding 5°C / min, in order to avoid cracking. The debinding process involves placing the dried green body in a sintering furnace and heating it to 200°C to 800°C at a heating rate of 0.1-6°C / min in an air atmosphere, and holding it at this temperature for 2 to 10 hours to completely remove organic components (including templates and various organic additives). The high-temperature sintering is performed after the binder is removed, by continuing to heat the furnace in an air atmosphere at a rate of 1-20°C / min to 1100-1600°C and holding it at that temperature for 0.1-30 hours, followed by furnace cooling or controlled cooling to room temperature at a rate of 5-50°C / min. The final product is a high-strength monolithic rutile phase TiO2 foam ceramic with a porosity of 40% to 95% and a compressive strength of 0.1-50 MPa. The phase composition is mainly rutile phase (XRD detection shows that the rutile phase content is ≥80%).

[0012] In some embodiments, in step S2, the alkaline aqueous solution is an aqueous solution of NaOH, KOH, LiOH, CsOH, or a mixture thereof, with a concentration of 1-20 mol / L; preferably, it is an aqueous solution of NaOH, and more preferably, the concentration is 3-15 mol / L. The cation doping source is a non-rare earth metal ion doping source and / or a rare earth ion doping source. The non-rare earth metal ion doping source is selected from soluble inorganic salts of any one or more of the following elements: iron (Fe), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), tantalum (Ta), tungsten (W), molybdenum (Mo), magnesium (Mg), calcium (Ca), titanium (Ti), zirconium (Zr), hafnium (Hf), tin (Sn), antimony (Sb), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), aluminum (Al), gallium (Ga), indium (In), and bismuth (Bi). The soluble inorganic salts include, but are not limited to, any one or more combinations of nitrates, chlorides, sulfates, acetates, oxalates, ammonium salts, or their hydrates. The rare earth ion doping source is selected from at least one of scandium (Sc), yttrium (Y), and soluble salts of lanthanides (excluding promethium (Pm). The lanthanides include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The soluble salts include, but are not limited to, any one or more combinations of nitrates, chlorides, sulfates, or their hydrates. The total concentration of the dopant source in the alkaline aqueous solution is 0.001-0.5 mol / L, preferably 0.005-0.2 mol / L; When the doping element is of the easily hydrolyzable type (including but not limited to Fe³⁺) + Cr³ + Al³ + When using all rare earth ions, the concentration of a single element should preferably not exceed 0.1 mol / L, and a pre-complexation process must be adopted. The dopant source and the complexing agent are pre-mixed to form a uniform and transparent complexation precursor solution, and then the precursor solution is added to an alkaline aqueous solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The complexing agent is selected from any one or more of the following: (1) Hydroxycarboxylic acids: citric acid, trisodium citrate, ammonium citrate, tartaric acid, potassium sodium tartrate, gluconic acid, sodium gluconate; (2) Aminocarboxylic acids: ethylenediaminetetraacetic acid (EDTA), disodium ethylenediaminetetraacetic acid (EDTA-2Na), diethylenetriaminepentaacetic acid (DTPA), trisodium diethylenetriaminepentaacetic acid (DTPA-3Na), aminotriacetic acid (NTA); (3) High molecular weight polymers: low molecular weight polyacrylic acid (PAA, molecular weight 1,000–10,000), ammonium polyacrylate; The molar ratio of the complexing agent to the metal ion is 1-10:1; When the doping element is of the oxyanion-stabilized type (including but not limited to W, Mo, Nb, Ta, V), it exists in strong bases as a soluble oxyanion (such as WO4²). - MoO4² - VO4³ - It exists stably, with single-element concentrations up to 0.3 mol / L, requiring no pre-complexation process; The hydrothermal reaction uses a commercially available reactor and liner, which can be a stainless steel reactor, a nickel-based alloy reactor, or a carbon manganese steel reactor. The reactor liner can be a polytetrafluoroethylene (PTFE) liner or a modified polytetrafluoroethylene (PPL / TFM) liner, preferably a stainless steel reactor and a polytetrafluoroethylene (PTFE) liner. The hydrothermal reaction temperature is 25-250°C, preferably 80-150°C; The liquid-to-solid ratio of the hydrothermal reaction is 5-50 mL / g, preferably 10-30 mL / g; The reaction time of the hydrothermal reaction is 0.1-100 hours, preferably 5-20 hours; The washing process involves first rinsing with tap water for 1-60 minutes, then washing with deionized water for 0.1-10 minutes, until the system is neutral. The drying process involves a drying temperature of 15-150°C and a drying time of 0.1-100 hours. The average thickness of the alkali metal titanate nanostructure intermediate is 20 nm-20 μm.

[0013] In some embodiments, in step S3, the acidic aqueous solution is an aqueous solution of an inorganic acid, wherein the inorganic acid is selected from any one or more combinations of hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), perchloric acid (HClO4), and hydrofluoric acid (HF), preferably an HCl solution or an HNO3 solution; the concentration is 0.01-10 mol / L; The anion-doped precursor is selected from at least one of the following nitrogen-containing compounds, carbon-containing compounds, sulfur-containing compounds, fluorine-containing compounds, phosphorus-containing compounds, or boron-containing compounds: Nitrogen-containing compounds: urea, ammonia, melamine, ethylenediamine, ammonium nitrate, guanidine, dicyandiamide, urea nitrate; Carbon-containing compounds: glucose, sucrose, fructose, glycerol, ethylene glycol, glycerol, citric acid, oxalic acid, tartaric acid, malic acid, ascorbic acid, and water-soluble derivatives of chitosan; Sulfur-containing compounds: thiourea, L-cysteine, L-methionine, sodium thiosulfate, mercaptoacetic acid, sodium sulfide (Na2S), potassium thiocyanate (KSCN), L-glutathione; Fluorine-containing compounds: ammonium fluoride (NH4F), sodium fluoride (NaF), potassium fluoride (KF), ammonium hydrogen fluoride (NH4HF2), hydrofluoric acid (HF). Phosphorus-containing compounds: phosphoric acid (H3PO4), diammonium hydrogen phosphate (NH4H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), hypophosphorous acid (H3PO2), phosphorous acid (H3PO3), phytic acid, sodium pyrophosphate; Boron-containing compounds: boric acid (H3BO3), sodium tetraborate (Na2B4O7), sodium metaborate (NaBO2), borax; The total concentration of the anion-doped precursor in the solution is 0.01-5 mol / L, preferably 0.05-0.5 mol / L; wherein, the concentration of organic precursors (such as glucose, urea, citric acid) is preferably not more than 0.5 mol / L to avoid excessive carbonization under acidic conditions leading to pore blockage; the concentration of sulfur-containing / phosphorus-containing precursors is preferably not more than 0.3 mol / L to inhibit the formation of byproducts such as H2S and PH3; The immersion treatment temperature range is 5-95°C, and the immersion time is 0.1-48 h; in order to promote the effective doping of heat-sensitive precursors (such as ammonia, L-cysteine), the temperature is preferably controlled at 20-50°C. The liquid-to-solid ratio (i.e., the ratio of the volume of the treatment solution to the mass of the intermediate) of the acid replacement treatment is 5-50 mL / g, preferably 10-30 mL / g; The final pH of the washing process is controlled at 6.0-7.0; the drying temperature is 60-100°C, and the drying time is 0.2-24 h. The amorphous hydrogen titanate intermediate has chemically bonded anionic dopant elements (such as one or more of Ti–N, Ti–C, Ti–S, Ti–F, Ti–P, and Ti–B bonds) originating from the precursor. The surface nanostructure of the amorphous hydrogen titanate intermediate has an average thickness of 20 nm to 20 μm, and the presence and chemical state of the dopant elements can be confirmed by XPS depth profiling, TOF-SIMS or ICP-OES quantitative analysis.

[0014] In some embodiments, in step S4, the heat treatment is carried out in a programmable temperature controlled sintering furnace; the calcination atmosphere is selected from air, nitrogen (N2), argon (Ar) or a mixture thereof, the gas purity is not less than 99.99%, the flow rate is 10 mL / min to 2000 mL / min, and the pressure inside the furnace is maintained at atmospheric pressure or slightly positive pressure (0-5 kPa gauge pressure) to isolate external oxygen / moisture; The calcination temperature is 300-750°C, preferably 350-600°C: 1) For samples containing volatile anions such as nitrogen (N), sulfur (S), and carbon (C), the calcination temperature is preferably no more than 500°C to suppress the thermal decomposition loss of N / S / C elements; 2) For samples containing fluorine (F), phosphorus (P), boron (B), or high-valence cations (W... 6+ Mo 6+ 、Nb 5+ For samples containing precious metals (Ag, Au, Pt, Pd), the calcination temperature can be up to 600°C; 3) For samples containing precious metals (Ag, Au, Pt, Pd), the preferred calcination temperature is 350°C to 500°C to avoid metal agglomeration or reduction. The calcination time is 0.1 h to 5 h, preferably 1 h to 2 h; the heating rate is 0.5°C / min to 20°C / min, preferably 1°C / min to 10°C / min, in order to relieve thermal stress and prevent cracking of the foam ceramic skeleton. After calcination, the cooling method is selected from: 1) natural cooling in the furnace (suitable for most doped systems); 2) programmed cooling (cooling rate from 0.5°C / min to 10°C / min, suitable for co-doped systems with large differences in thermal expansion coefficients, such as Bi-N co-doping). The resulting product is an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure. The thickness of the anatase shell is 20 nm-20 μm, preferably 50 nm-5 μm. The doping elements are mainly distributed in the anatase shell 0-5 μm from the material surface, and XPS depth profiling or TOF-SIMS confirms that they exist stably in a chemically bonded form (such as Ti–N, Ti–F, Ti–S, Ti–P, Ti–B, or M–O–Ti, where M is the doping metal). The anatase phase content ranges from 60 wt% to 95 wt% (XRD Rietveld refined), the rutile phase content ranges from 5 wt% to 40 wt%, and there are no impurities. The porosity is maintained at 60% to 95%, and the macroscopic channels are unobstructed. The macroscopic shape of the in-situ doped monolithic TiO2 foam ceramic with rutile@anatase core-shell structure is any one of the following: cylinder, cube, cuboid, sphere, ellipsoid, toroid, prism, pyramid, polyhedron, honeycomb block, sheet, arc, arch, tubular, hollow spherical shell, or any combination and deformation thereof; Under visible light (λ ≥ 420 nm) irradiation, the degradation rate constant of subunit blue (10 mg / L) is 1.5 to 10 times that of the undoped sample, and the activity retention rate is ≥90% after 5 cycles.

[0015] This application also provides the application of the monolithic TiO2 foam ceramic prepared by the above preparation method in water treatment or photocatalytic degradation of organic pollutants.

[0016] This application also provides the application of the monolithic TiO2 foam ceramic prepared by the above preparation method in the preparation of water treatment devices or devices for degrading organic pollutants.

[0017] The monolithic TiO2 foam ceramic exhibits a photocatalytic degradation rate of ≥70% for organic pollutants in water under ultraviolet light irradiation.

[0018] The organic pollutants mentioned include, but are not limited to, emerging organic pollutants, which include those listed in the Shanghai Key Controlled New Pollutants List (2023 Edition). Perfluorooctyl sulfonic acid and its salts and perfluorooctyl sulfonyl fluoride (PFOS class); Perfluorooctanoic acid and its salts and related compounds (PFOA class); Decabromodiphenyl ether; Short-chain chlorinated paraffins; Hexachlorobutadiene; Pentachlorophenol and its salts and esters; Trichlorfon; Perfluorohexyl sulfonic acid and its salts and related compounds (PFHxS class); Declone and its cis and trans isomers; Dichloromethane; chloroform; Nonylphenol; Antibiotics (antibacterial drugs); New pollutants that have been phased out (such as anticides and cypermethrin); Microplastics; Bisphenol A.

[0019] The preparation method provided in this application simultaneously achieves in-situ elemental doping within the dynamic reconstruction window of alkaline etching and acid replacement, precisely transforming the surface layer of the monolithic rutile TiO2 foam ceramic into a doped anatase shell layer, thus constructing an integrated core-shell structure of "rutile core-doped anatase shell". The preparation method and the resulting material have the following characteristics: Firstly, the structure and process work together to preserve the integrity of the framework: the internal rutile phase is sintered at 1100-1600°C to form a high-strength framework, giving the material excellent mechanical strength (compressive strength 1-50MPa), thermal stability and electron transport channels; while this application adopts a low-temperature doping (steps S2-S3) + low-temperature crystallization process ≤750°C (step S4), avoiding the phase transformation damage and pore collapse of the rutile framework caused by traditional high-temperature doping, ensuring that the macroscopic structure of the monolithic foam ceramic is stable and the porosity (60%-95%) and interconnected channels are maintained for a long time during preparation and application; Secondly, the composition-performance synergistic activation of surface function: The surface anatase phase not only provides a high specific surface area and abundant active sites, but also precisely controls the band structure through in-situ doping (N, C, S, F, P, B or metal ions)—the doping elements are embedded in the lattice in the form of Ti–X chemical bonds (X=N, F, S, etc.), which redshifts the light absorption edge to 450-800nm, significantly improving the visible light photocatalytic activity (degradation rate increased by 2-10 times), and enhancing the targeted adsorption and degradation ability of specific pollutants (such as sulfur / nitrogen-containing organic matter); Third, the interface-carrier synergistic enhancement of energy utilization: an atomically compact heterojunction interface is formed between the rutile core and the doped anatase shell. Combined with the intermediate energy levels or defect states (such as oxygen vacancies) introduced by the doping elements, a triple charge regulation mechanism of "band gradient-interface electric field-doping trap" is constructed, which significantly promotes the cross-interface separation and migration of photogenerated electron-hole pairs, suppresses recombination (extends carrier lifetime by 2-10 times), and achieves global optimization of "structural stability-photoresponse width-charge utilization efficiency". Its comprehensive performance far exceeds that of single crystal materials, physical hybrid systems or non-in-situ doped modified products.

[0020] Compared with the prior art, this application has the following significant advantages and beneficial effects: 1) Highly integrated processes, green and efficient By innovatively embedding elemental doping into the "surface reconstruction window" of alkaline etching (step S2) and acid replacement (step S3), the four-step process of "skeleton construction → surface activation → doping integration → low-temperature crystallization" is achieved in one step. Compared with the traditional two-stage process of "powder doping + molding" (which requires high-temperature sintering and leads to doping loss) or "molding followed by impregnation doping" (which results in pore blockage and weak bonding), this application eliminates redundant steps such as independent impregnation and multiple calcinations, shortens the preparation cycle, reduces energy consumption, and avoids structural damage and doping unevenness caused by multiple heat treatments, significantly improving process economy and batch consistency.

[0021] 2) Precise doping space selectivity and clear functional positioning By leveraging the dynamic interface of alkaline treatment to generate titanate nanosheets (interlayer exchangeable sites) and acid treatment to form hydrotitanic acid (–OH active groups), dopant elements are selectively enriched within the 0-20 nm depth of the anatase shell (verified by XPS depth profiling and TOF-SIMS 3D imaging), rather than being uniformly distributed in the bulk phase. The advantages of this "surface-confined doping" strategy are: ① Maximizing the efficiency of dopant elements in controlling surface bandgap (e.g., N introduces intermediate energy levels, F controls surface acidity); ② Avoiding carrier recombination centers induced by bulk doping; ③ Retaining the intrinsic electron transport advantages of the rutile core, achieving a precise synergy between "activity enhancement" and "structure preservation".

[0022] 3) The doping is firmly bonded and exhibits excellent environmental stability. Doping elements are produced through ion exchange (e.g., La³⁺). + Intercalation between titanate layers), lattice substitution (such as W) 6+ Replace Ti 4+ The material structure is deeply integrated with a triple mechanism of covalent bonding (such as Ti–N, Ti–F, and Ti–S bonds); after subsequent low-temperature calcination, the doping retention rate is high, which is significantly better than that of physically adsorbed doped materials, meeting the requirements of long-term industrial operation.

[0023] 4) The spectral response range is significantly broadened, and the catalytic efficiency is doubled. Precise control of the anatase shell electronic structure through in-situ doping: the absorption edge of the N / F co-doped sample redshifted to 520 nm, and that of the Fe-N co-doped sample reached 580 nm; the absorption intensity in the visible light (λ≥420 nm) region increased by 3-5 times (verified by UV-Vis DRS); and the degradation rate constant for methylene blue (10 mg / L) reached 0.025-0.085 min. - ¹, which is 2-10 times that of undoped core-shell materials; it exhibits broad-spectrum and efficient degradation capabilities for various pollutants such as rhodamine B, tetracycline, and phenol, and extends carrier lifetime by 2-3 times (TRPL test), confirming that doping effectively suppresses electron-hole recombination.

[0024] 5) The doped system is highly flexible and has great potential for application expansion. It is compatible with single / co-doped combinations of 27 non-rare earth cations, 16 rare earth ions, and 6 types of anion precursors, and can be customized with functions according to application scenarios: water treatment, photocatalytic water splitting, CO2 reduction, antibacterial disinfection, etc. Its integrated form facilitates modular integration and is suitable for large-scale scenarios such as continuous flow wastewater treatment, air purification, and self-cleaning coatings, with broad industrialization prospects. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow for the preparation method of this application. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] This application provides a method for preparing in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramics, the preparation process as follows: Figure 1 As shown, the specific steps include the following: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is impregnated in the slurry, dried and debinded, and sintered at high temperature in air atmosphere and cooled to room temperature to obtain a high-strength monolithic rutile phase TiO2 foam ceramic.

[0029] Step S2: Alkali etching treatment The monolithic rutile TiO2 foam ceramic obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was removed, washed until neutral, and dried to obtain an intermediate alkali metal titanate nanostructure containing cation dopant elements.

[0030] Step S3: Acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until neutral, and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements.

[0031] Step S4: Low-temperature heat treatment for crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at low temperature in air or an inert atmosphere. After calcination, it is cooled to room temperature to obtain the target product—an in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramic. In step S2, the concentrations of the cation or rare earth ion doping source and the anion doping precursor in step S3 are ≥0, but not both 0, i.e., cation / rare earth ions and anions are doped individually or simultaneously.

[0032] The following description, in conjunction with specific embodiments, illustrates this point.

[0033] Example 1 A method for preparing an in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramic, specifically including the following steps: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is impregnated in the slurry, dried and debinded, and sintered at high temperature in air atmosphere and cooled to room temperature to obtain a high-strength monolithic rutile phase TiO2 foam ceramic.

[0034] Step S2: Alkali etching treatment The monolithic rutile TiO2 foam ceramic obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was removed, washed until neutral, and dried to obtain an intermediate alkali metal titanate nanostructure containing cation dopant elements.

[0035] Step S3: Acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until neutral, and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements.

[0036] Step S4: Low-temperature heat treatment for crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at low temperature in air or an inert atmosphere; after calcination, it is cooled to room temperature to obtain the target product.

[0037] In step S1, the average particle size of the TiO2 powder is 25 μm, and it is selected from anatase phase TiO2. The reinforcing phase is silicon carbide whiskers; The organic additives include the binder polyvinyl alcohol (PVA), the plasticizer glycerin, the dispersant ammonium polyacrylate (NH4PAA), the surfactant sodium dodecyl sulfate (SDS), the rheology modifier xanthan gum, and the defoamer polyether modified siloxane (BYK-024). The pH adjuster is ammonia water (NH3·H2O, 10 mol / L). Amounts of organic additives and reinforcing phases added (based on the weight of TiO2 powder): Adhesive 2.2 wt.%; Dispersant 0.6 wt.%; Plasticizer 0.5 wt.%; Surfactant 0.8 wt.%; Rheology modifier 0.5 wt.%; Defoamer 1.5 wt.%; Reinforcing phase: 5 wt.%; The average length of the reinforcing phase silicon carbide whiskers is 16 μm, and the average diameter is 0.6 μm. The TiO2 slurry has a solid content of 53 vol.% and a pH of 10. The mixing process is mechanical stirring; The degassing process involves degassing for 1 minute under a negative pressure of 80 kPa to fully remove air bubbles trapped in the slurry. The organic foam is made of polyurethane (PU); the pore density of the foam ranges from 10 PPI, and its macroscopic shape is a cuboid. The impregnation process involves multiple cycles of impregnation-deslurrying-drying to achieve a cumulative loading of 430% of the original mass of the organic foam in the TiO2 suspension slurry, with a pore blockage rate of <30%. The specific drying conditions are as follows: static drying at 90°C for 1 hour with a heating rate of 2°C / min to avoid cracking; The debinding process involves placing the dried green body in a sintering furnace and heating it to 600°C at a rate of 1.5°C / min in an air atmosphere, and holding it at this temperature for 1 hour to completely remove organic components (including templates and various organic additives). The high-temperature sintering process involves continuing to heat the material in air at a rate of 10°C / min to 1400°C after the binder has been removed, holding the temperature for 0.1 hours, and then cooling the material in the furnace to room temperature. The final product is a high-strength monolithic rutile phase TiO2 foam ceramic with a porosity of 87% and a compressive strength of 0.2 MPa. The phase composition is mainly rutile phase (XRD detection shows that the rutile phase content is ≥95%). In step S2, the alkaline aqueous solution is a NaOH aqueous solution with a concentration of 10 mol / L; The cation doping source is ferric nitrate (Fe(NO3)3), which has a concentration of 0.05 mol / L in an alkaline aqueous solution. A pre-complexation process must be used to pre-mix the doping source Fe(NO3)3 with the complexing agent to form a uniform and transparent complexation precursor solution. The precursor solution is then added to the alkaline aqueous solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The complexing agent is trisodium citrate, and the complexing agent trisodium citrate reacts with Fe... 3+ The molar ratio of the ions is 5:1; The hydrothermal reaction was carried out in a stainless steel reactor with a polytetrafluoroethylene (PTFE) lining. The hydrothermal reaction temperature is 120°C; The liquid-to-solid ratio of the hydrothermal reaction is 10 mL / g; The hydrothermal reaction time is 15 hours; The washing process involves first rinsing with tap water for 5 minutes, then washing with deionized water for 1 minute, until the system is neutral. The drying temperature is 95°C and the time is 0.5 hours; The average thickness of the alkali metal titanate nanostructure intermediate is 10 μm; In step S3, the acidic aqueous solution is an aqueous solution of an inorganic acid, wherein the inorganic acid is selected from hydrochloric acid (HCl) and has a concentration of 3 mol / L; The anion-doped precursor is urea at a concentration of 0.25 mol / L; The soaking treatment was performed at a temperature of 50°C for 2 hours. The liquid-to-solid ratio (i.e., the ratio of the volume of the treatment solution to the mass of the intermediate) of the soaking treatment is 15 mL / g; The final pH of the washing process is controlled at 7; the drying temperature is 90°C and the drying time is 2 hours. The amorphous hydrogen titanate intermediate has an anionic dopant element (Ti–N bond) derived from the precursor chemically bonded in its structure. The surface nanostructure of the amorphous hydrogen titanate intermediate has an average thickness of 10 μm. In step S4, the low-temperature heat treatment is carried out in a programmable temperature controlled sintering furnace; the calcination atmosphere is selected from air with a flow rate of 400 mL / min, and the pressure inside the furnace is maintained at atmospheric pressure or slightly positive pressure (1 kPa gauge pressure) to isolate external moisture; The calcination temperature was 490°C, the calcination time was 2 h, and the heating rate was 10°C / min. After calcination, the cooling method is natural cooling with the furnace. The resulting product is an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure and an anatase shell thickness of 8 μm. The anatase phase content was 85 wt.%, and the rutile phase content was 10 wt%. The porosity is 87%, and the macroscopic channels are unobstructed. The macroscopic shape of the obtained in-situ doped monolithic TiO2 foam ceramic with rutile@anatase core-shell structure is cuboid; Under visible light (λ ≥ 380 nm) irradiation, the degradation rate constant of subunit blue (10 mg / L) is 4 times that of the undoped sample, and the activity retention rate is ≥96% after 5 cycles.

[0038] The resulting monolithic TiO2 foam ceramic exhibits a photocatalytic degradation rate of ≥80% for organic pollutants (BPA) in water under xenon lamp irradiation.

[0039] Example 2 A method for preparing an in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramic, specifically including the following steps: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is impregnated in the slurry, dried and debinded, and sintered at high temperature in air atmosphere and cooled to room temperature to obtain a high-strength monolithic rutile phase TiO2 foam ceramic.

[0040] Step S2: Alkali etching treatment The monolithic rutile TiO2 foam ceramic obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was removed, washed until neutral, and dried to obtain an intermediate alkali metal titanate nanostructure containing cation dopant elements.

[0041] Step S3: Acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until neutral, and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements.

[0042] Step S4: Low-temperature heat treatment for crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at low temperature in air or an inert atmosphere; after calcination, it is cooled to room temperature to obtain the target product.

[0043] In step S1, the average particle size of the TiO2 powder is 45 μm, and it is selected from anatase phase TiO2. The reinforcing phase is mullite whiskers; The organic additives include binder methyl cellulose (MC), plasticizer dibutyl phthalate (DBP), dispersant sodium polyacrylate (NaPAA), surfactant cetyltrimethylammonium bromide (CTAB), rheology modifier sodium carboxymethyl cellulose (CMC), and defoamer silicone oil (Dow Corning® 200 Fluid). The pH adjuster is ammonia water (NH3·H2O, 10 mol / L). Amounts of organic additives and reinforcing phases added (based on the weight of TiO2 powder): Adhesive 1.5 wt.%; Dispersant 1.0 wt.%; Plasticizer 1.0 wt.%; Surfactant 0.9 wt.%; Rheology modifier 1.5 wt.%; Defoamer 2.0 wt.%; Reinforcing phase: 5 wt.%; The reinforcing phase (mullite whiskers) has an average length of 12 μm and an average diameter of 0.5 μm. The TiO2 slurry has a solid content of 55 vol.% and a pH of 11. The mixing process is mechanical stirring; The degassing process involves degassing for 3 minutes under a negative pressure of 60 kPa to fully remove air bubbles trapped in the slurry. The organic foam is made of polyurethane (PU); the pore density of the foam ranges from 10 PPI, and its macroscopic shape is cubic. The impregnation process involves multiple cycles of impregnation-deslurry-drying to achieve a cumulative loading of 450% of the original mass of the organic foam in the TiO2 suspension slurry, with a pore blockage rate of <30%. The specific drying conditions are as follows: static drying at 99°C for 0.5 hours with a heating rate of 1°C / min to avoid cracking; The debinding process involves placing the dried green body in a sintering furnace and heating it to 600°C at a rate of 3°C / min in an air atmosphere, and holding it at this temperature for 0.3 hours to completely remove organic components (including templates and various organic additives). The high-temperature sintering process involves continuing to heat the material in air at a rate of 10°C / min to 1400°C after the binder has been removed, holding the temperature for 0.1 hours, and then cooling the material in the furnace to room temperature. The final product is a high-strength monolithic rutile phase TiO2 foam ceramic with a porosity of 83% and a compressive strength of 0.4 MPa. The phase composition is mainly rutile phase (XRD detection shows that the rutile phase content is ≥95%). In step S2, the alkaline aqueous solution is a NaOH aqueous solution with a concentration of 5 mol / L; The cation doping source, rare earth ion doping source scandium nitrate (Sc(NO3)3), has a concentration of 0.04 mol / L in alkaline aqueous solution and must be pre-complexed. The doping source Sc(NO3)3 and the complexing agent are pre-mixed to form a uniform and transparent complexing precursor solution, and then the precursor solution is added to the alkaline aqueous solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The complexing agent is diethylenetriaminepentaacetic acid (DTA), and the complexing agent DTA reacts with Sc. 3+ The molar ratio of the ions is 6:1; The hydrothermal reaction was carried out in a stainless steel reactor with a polytetrafluoroethylene (PTFE) lining. The hydrothermal reaction temperature is 130°C; The liquid-to-solid ratio of the hydrothermal reaction is 8 mL / g; The hydrothermal reaction time is 12 hours; The washing process involves first rinsing with tap water for 8 minutes, then washing with deionized water for 2 minutes, until the system is neutral. The drying temperature was 99°C, and the time was 0.1 hours; The average thickness of the alkali metal titanate nanostructure intermediate is 12 μm; In step S3, the acidic aqueous solution is an aqueous solution of an inorganic acid, wherein the inorganic acid is selected from hydrochloric acid (HCl) and has a concentration of 2 mol / L; The anion-doped precursor is glucose at a concentration of 0.3 mol / L; The soaking treatment was performed at a temperature of 80°C for 3 hours. The liquid-to-solid ratio (i.e., the ratio of the volume of the treatment solution to the mass of the intermediate) of the soaking treatment is 10 mL / g; The final pH of the washing process was controlled at 6.5; the drying temperature was 90°C and the drying time was 1 hour. The amorphous hydrogen titanate intermediate has chemically bonded anionic dopant elements (such as Ti–C bonds) originating from the precursor in its structure. The surface nanostructure of the amorphous hydrotitanic acid intermediate has an average thickness of 8 μm. In step S4, the low-temperature heat treatment is carried out in a programmable temperature controlled sintering furnace; the calcination atmosphere is selected from air with a flow rate of 600 mL / min, and the pressure inside the furnace is maintained at atmospheric pressure or slightly positive pressure (2 kPa gauge pressure) to isolate external moisture; The calcination temperature was 500°C, the calcination time was 1 h, and the heating rate was 10°C / min. After calcination, the cooling method is natural cooling with the furnace. The resulting product is an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure and an anatase shell thickness of 8 μm. The anatase phase content was 88 wt.%, and the rutile phase content was 7 wt%. The porosity is 83%, and the macroscopic channels are unobstructed. The macroscopic shape of the obtained in-situ doped monolithic TiO2 foam ceramic with rutile@anatase core-shell structure is cubic. Under visible light (λ ≥ 380 nm) irradiation, the degradation rate constant of subunit blue (10 mg / L) is 8 times that of the undoped sample, and the activity retention rate is ≥92% after 5 cycles.

[0044] The obtained monolithic TiO2 foam ceramic exhibits a photocatalytic degradation rate of ≥95% for organic pollutants (tetracycline) in water under xenon lamp irradiation.

[0045] Example 3 A method for preparing an in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramic, specifically including the following steps: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is impregnated in the slurry, dried and debinded, and sintered at high temperature in air atmosphere and cooled to room temperature to obtain a high-strength monolithic rutile phase TiO2 foam ceramic.

[0046] Step S2: Alkali etching treatment The monolithic rutile TiO2 foam ceramic obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was removed, washed until neutral, and dried to obtain an intermediate alkali metal titanate nanostructure containing cation dopant elements.

[0047] Step S3: Acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until neutral, and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements.

[0048] Step S4: Low-temperature heat treatment for crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at low temperature in air or an inert atmosphere; after calcination, it is cooled to room temperature to obtain the target product.

[0049] In step S1, the average particle size of the TiO2 powder is 45 μm, and it is selected as rutile phase TiO2. The reinforcing phase is aluminum borate whiskers; The organic additives include the binder hydroxypropyl methylcellulose (HPMC), the plasticizer triethyl citrate (TEC), the dispersant tetramethylammonium hydroxide (TMAH), the fluorocarbon surfactant (Capstone® FS-30), the rheology modifier polyethylene glycol (PEG, molecular weight 20000), and the defoamer silicone oil (Dow Corning® 200 Fluid). The pH adjuster is ammonia water (NH3·H2O, 10 mol / L). Amounts of organic additives and reinforcing phases added (based on the weight of TiO2 powder): Adhesive 1.6 wt.%; Dispersant 1.2 wt.%; Plasticizer 1.5 wt.%; Surfactant 1.4 wt.%; Rheology modifier 0.8 wt.%; Defoamer 1.9 wt.%; Reinforcing phase: 5 wt.%; The reinforcing phase (aluminum borate whiskers) has an average length of 20 μm and an average diameter of 0.5 μm. The TiO2 slurry has a solid content of 53 vol.% and a pH of 10. The mixing process is mechanical stirring; The degassing process involves degassing for 4 minutes under a negative pressure of 50 kPa to fully remove air bubbles trapped in the slurry. The organic foam is made of polyurethane (PU); the pore density of the foam ranges from 10 PPI, and its macroscopic shape is cylindrical. The impregnation process involves multiple cycles of impregnation-deslurry-drying, resulting in a cumulative loading of the TiO2 suspension slurry to 420% of the original mass of the organic foam, with a pore blockage rate of <20%. The specific drying conditions are as follows: static drying at 95°C for 1 hour, with a heating rate of 1.7°C / min, to avoid cracking; The debinding process involves placing the dried green body in a sintering furnace and heating it to 600°C at a rate of 4°C / min in an air atmosphere, and holding it at this temperature for 1 hour to completely remove organic components (including templates and various organic additives). The high-temperature sintering process involves continuing to heat the material in an air atmosphere at a rate of 10°C / min to 1350°C after the binder has been removed, holding the temperature for 2 hours, and then cooling the material in the furnace to room temperature. The final product is a high-strength monolithic rutile phase TiO2 foam ceramic with a porosity of 82% and a compressive strength of 0.3 MPa. The phase composition is mainly rutile phase (XRD detection shows that the rutile phase content is ≥95%). In step S2, the alkaline aqueous solution is a NaOH aqueous solution with a concentration of 10 mol / L; The cation doping source is sodium tungstate dihydrate Na2WO4·2H2O, and its concentration in alkaline aqueous solution is 0.1 mol / L; The hydrothermal reaction was carried out in a stainless steel reactor with a polytetrafluoroethylene (PTFE) lining. The hydrothermal reaction temperature is 150°C; The liquid-to-solid ratio of the hydrothermal reaction is 10 mL / g; The hydrothermal reaction time is 10 hours; The washing process involves first rinsing with tap water for 2 minutes, then washing with deionized water for 1 minute, until the system is neutral. The drying temperature is 90°C and the time is 1 hour; The average thickness of the alkali metal titanate nanostructure intermediate is 13 μm; In step S3, the acidic aqueous solution is an aqueous solution of an inorganic acid, wherein the inorganic acid is selected from hydrochloric acid (HCl) and has a concentration of 4 mol / L; The anion-doped precursor is thiourea at a concentration of 0.5 mol / L; The soaking treatment was performed at a temperature of 60°C for 10 hours. The liquid-to-solid ratio (i.e., the ratio of the volume of the treatment solution to the mass of the intermediate) of the soaking treatment is 8 mL / g; The final pH of the washing process is controlled at 7; the drying temperature is 90°C and the drying time is 1 hour. The amorphous hydrogen titanate intermediate has chemically bonded anionic dopant elements (such as Ti–S bonds) originating from the precursor in its structure. The surface nanostructure of the amorphous hydrogen titanate intermediate has an average thickness of 16 μm. In step S4, the low-temperature heat treatment is carried out in a programmable temperature controlled sintering furnace; the calcination atmosphere is selected from air with a flow rate of 300 mL / min, and the pressure inside the furnace is maintained at atmospheric pressure or slightly positive pressure (1 kPa gauge pressure) to isolate external moisture; The calcination temperature was 550°C, the calcination time was 0.5 h, and the heating rate was 8 °C / min. After calcination, the cooling method is natural cooling with the furnace. The resulting product is an in-situ doped monolithic TiO2 foam ceramic with a rutile@anatase core-shell structure and an anatase shell thickness of 12 μm. The anatase phase content was 70 wt.%, and the rutile phase content was 25 wt.%. The porosity is 82%, and the macroscopic channels are unobstructed. The macroscopic shape of the obtained in-situ doped monolithic TiO2 foam ceramic with rutile@anatase core-shell structure is cylindrical. Under visible light (λ ≥ 380 nm) irradiation, the degradation rate constant of subunit blue (10 mg / L) is 5 times that of the undoped sample, and the activity retention rate is ≥96% after 5 cycles.

[0050] The obtained monolithic TiO2 foam ceramic exhibits a photocatalytic degradation rate of ≥90% for organic pollutants (ciprofloxacin) in water under xenon lamp irradiation.

[0051] The above description is merely a preferred embodiment of this application and is not intended to limit this application in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from this application, and these improvements and additions should also be considered within the scope of protection of this application.

Claims

1. A method for preparing an in-situ doped rutile@anatase core-shell structured monolithic TiO2 foam ceramic, characterized in that, The preparation method includes the following steps: Step S1: Preparation of monolithic rutile TiO2 foam ceramic precursor TiO2 powder, reinforcing phase, organic additives and pH adjuster are added to deionized water, mixed and degassed to obtain a uniform and stable TiO2 suspension slurry; then, an organic foam template is immersed in the slurry, dried and debinded, and sintered at high temperature at ≥1100°C in air atmosphere, and cooled to room temperature to obtain an integral rutile phase TiO2 foam ceramic precursor. Step S2: In-situ doped alkaline etching treatment The monolithic rutile phase TiO2 foam ceramic precursor obtained in step S1 was completely immersed in an alkaline aqueous solution containing a cation dopant source for hydrothermal reaction. After the reaction was completed, the sample was taken out, washed until neutral and dried to obtain an alkali metal titanate nanostructure intermediate containing cation dopant elements. Step S3: In-situ doping acid replacement treatment The intermediate obtained in step S2 was completely immersed in an acidic aqueous solution containing anion-doped precursor for soaking treatment; after soaking, the sample was taken out, washed until near neutral and dried to obtain an amorphous hydrogen titanate intermediate containing anion-doped elements. Step S4: Heat treatment crystallization The intermediate obtained in step S3 is placed in a sintering furnace and calcined at a low temperature below 750°C; after calcination, it is cooled to room temperature to obtain the target product. In step S2, the concentrations of the cation or rare earth ion doping source and the anion doping precursor in step S3 are ≥0, but not both 0, i.e., cation / rare earth ions and anions are doped individually or simultaneously.

2. The preparation method according to claim 1, characterized in that, In step S1, the TiO2 powder is selected from any one or a combination of anatase TiO2, rutile TiO2, commercial P25 TiO2 or modified powder thereof, and its average particle size is 10nm-50μm. The modified powder is TiO2 powder obtained by any of the following modification methods: 1) Cation doping; 2) Anion doping; 3) Oxygen vacancy regulation; 4) Defect engineering modification; The modified powder must meet the following conditions: it still has semiconductor properties and its decomposition temperature in air is higher than 1600℃, its band gap is 1.5-4.5eV, and its degradation rate constant for typical emerging pollutants tetracycline, bisphenol A or perfluorooctanoic acid under AM 1.5G standard illumination is not less than 10% of that of commercial P25 TiO2.

3. The preparation method according to claim 1, characterized in that, In step S1, the reinforcing phase is 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; 2) Ceramic whiskers: silicon carbide whiskers, mullite 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. 3) Natural mineral fibers: sepiolite fiber, attapulgite fiber, wollastonite fiber, palygorskite fiber, tremolite fiber, actinolite fiber, vermiculite fiber, pyrophyllite fiber, sillimanite fiber, glauconite fiber, tourmaline fiber, palygorskite fiber; 4) Synthetic organic fibers: polyacrylonitrile fiber, polyvinyl alcohol fiber, aramid fiber, polyimide fiber; The organic additives include binders, plasticizers, dispersants, surfactants, rheology modifiers, and defoamers; The organic additives may be used alone or in combination, with a total addition amount of 0.1-15 wt.% of the metal oxide-based powder. The adhesive is selected from any one or more of polyethylene oxide, sodium alginate, chitosan, polyurethane emulsion, polyacrylamide, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, polyethylene glycol, polyacrylic acid, polyvinyl acetate, starch and its derivatives; The plasticizer is selected from one or more of the following: triethyl acetylglucosamine citrate, epoxidized soybean oil, polycaprolactone, glycerin, dibutyl phthalate, triethyl citrate, polyethylene glycol, sorbitol, and dioctyl sebacate. The dispersant is selected from one or more of the following: polycarboxylate superdispersant, polymaleic anhydride, polyaspartic acid, ammonium polyacrylate, sodium polyacrylate, tetramethylammonium hydroxide, ammonium citrate, gum arabic, and polyvinylpyrrolidone. The surfactant is selected from one or more of the following: sorbitan monooleate, cocamidopropyl betaine, perfluoropolyethers, sodium lauryl sulfate, hexadecyltrimethylammonium bromide, Tween-80, Triton X-100, lecithin, and fluorocarbon surfactants. The rheology modifier is selected from one or more of guar gum, gellan gum, polyacrylic acid thickeners, organic modified montmorillonite, xanthan gum, sodium carboxymethyl cellulose, bentonite, fumed silica and polyacrylamide; The defoamer is selected from one or more of polydimethylsiloxane, polyether defoamer, isooctanol, n-octanol, silicone oil, polyether-modified siloxane, and mineral oil; The pH adjuster is at least one of ammonia and hydrochloric acid.

4. The preparation method according to claim 1, characterized in that, In step S1, the amounts of the organic additive and the reinforcing phase added, based on the weight of the TiO2 powder, are as follows: Adhesive 1-20 wt.%; Dispersant 0.01-5 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; The reinforcing phase has an aspect ratio ≥ 10, a length of 1-5000 μm, and a diameter of 0.01-200 μm; The solid content of the TiO2 slurry is 20-70 vol.%, and the pH is 2-14; The mixing process is mechanical stirring or ball milling. The degassing conditions are: vacuum degree controlled at -0.01 MPa to -0.1 MPa, degassing time 2-20 minutes, so as to fully remove the air bubbles trapped in the slurry; The organic foam is made of polyurethane, melamine formaldehyde, or polystyrene. The pore density of the organic foam ranges from 5 to 50 PPI, its porosity is 40% to 99%, and its average pore size is 100 μm to 8000 μm. 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 conditions to be met for the impregnation are: the cumulative loading of the TiO2 suspension slurry reaches 100-1000% of the original mass of the organic foam, the coating thickness is 0.1-3.0 mm, the coating thickness variation coefficient is <30%, and the pore blockage rate is <40%.

5. The preparation method according to claim 1, characterized in that, The specific drying conditions are as follows: static or forced-air drying at a temperature of 20-99°C for 4-48 hours, with a heating rate not exceeding 5°C / min, to avoid cracking; The debinding process involves placing the dried blank in a sintering furnace and heating it to 200-800°C at a rate of 0.1-6°C / min in an air atmosphere, holding it at that temperature for 2-10 hours to completely remove organic components, including organic foam templates and organic additives. The sintering process involves heating the material to 1100-1600°C in air at a rate of 1-20°C / min after debinding, holding it at that temperature for 0.1-30 hours, and then cooling it in the furnace or at a rate of 5-50°C / min to room temperature. The obtained monolithic TiO2 foam ceramic has a porosity of 40%-95%, a compressive strength of 0.1-50 MPa, and a phase composition dominated by rutile phase: rutile phase content ≥80wt%.

6. The preparation method according to claim 1, characterized in that, In step S2, the alkaline aqueous solution is an aqueous solution of NaOH, KOH, LiOH, CsOH, or a mixture thereof, with a concentration of 1-20 mol / L; The cation doping source is a non-rare earth metal ion doping source and / or a rare earth ion doping source. The non-rare earth metal ion doping source is selected from soluble inorganic salts of any one or more of the following elements: iron, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, niobium, tantalum, tungsten, molybdenum, magnesium, calcium, titanium, zirconium, hafnium, tin, antimony (Sb), silver, gold, platinum, palladium, aluminum, gallium, indium, and bismuth. The soluble inorganic salt includes any one or more of nitrates, chlorides, sulfates, acetates, oxalates, ammonium salts, or their hydrates. The rare earth ion doping source is selected from any one or more soluble salts of the following elements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); the soluble salt includes any one or more of nitrates, chlorides, sulfates, or their hydrates. The total concentration of the cation dopant source in the alkaline treatment solution is 0.001-0.5 mol / L; When the dopant element is of the type that is easily hydrolyzed, its single element concentration shall not exceed 0.1 mol / L, and a pre-complexation process shall be adopted to pre-mix the dopant source and the complexing agent to form a uniform and transparent complexation precursor solution, and then add the complexation precursor solution to an alkaline aqueous solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The complexing agent is selected from any one or more of the following: 1) Hydroxycarboxylic acids: citric acid, trisodium citrate, ammonium citrate, tartaric acid, potassium sodium tartrate, gluconic acid, sodium gluconate; 2) Aminocarboxylic acids: ethylenediaminetetraacetic acid (EDTA), disodium ethylenediaminetetraacetic acid (EDTA-2Na), diethylenetriaminepentaacetic acid (DTPA), trisodium diethylenetriaminepentaacetic acid (DTPA-3Na), aminotriacetic acid (NTA); 3) Polymers: Polyacrylic acid (PAA) and ammonium polyacrylate with molecular weights of 1,000–10,000; The molar ratio of the complexing agent to the metal ions is 1-15:1; When the dopant element is of the oxyanion-stabilized type, it exists stably in strong bases as a soluble oxyanion anion with a single element concentration ≤0.3 mol / L, and no pre-complexation process is required. The hydrothermal reaction is carried out at a temperature of 25-250°C, a liquid-to-solid ratio of 5-50 mL / g, and a reaction time of 0.1-100 hours. The washing process includes: first rinsing with tap water for 1-60 minutes, then washing with deionized water for 0.1-10 minutes, until the washing solution is neutral; The drying temperature is 15-150°C, and the time is 0.1-100 hours; The average thickness of the obtained alkali metal titanate nanostructure intermediates is 20 nm-50 μm.

7. The preparation method according to claim 1, characterized in that, In step S3, the acidic aqueous solution is an aqueous solution of an inorganic acid, wherein the inorganic acid is selected from any one or more combinations of hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and hydrofluoric acid, and the concentration is 0.01-10 mol / L; The anion-doped precursor is selected from at least one of the following nitrogen-containing compounds, carbon-containing compounds, sulfur-containing compounds, fluorine-containing compounds, phosphorus-containing compounds, and boron-containing compounds: Nitrogen-containing compounds: urea, ammonia, melamine, ethylenediamine, ammonium nitrate, guanidine, dicyandiamide, urea nitrate; Carbon-containing compounds: glucose, sucrose, fructose, glycerol, ethylene glycol, glycerol, citric acid, oxalic acid, tartaric acid, malic acid, ascorbic acid, and water-soluble derivatives of chitosan; Sulfur-containing compounds: thiourea, L-cysteine, L-methionine, sodium thiosulfate, mercaptoacetic acid, sodium sulfide, potassium thiocyanate, L-glutathione; Fluorine-containing compounds: ammonium fluoride, sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, hydrofluoric acid; Phosphorus-containing compounds: phosphoric acid, diammonium dihydrogen phosphate, diammonium hydrogen phosphate, hypophosphoric acid, phosphorous acid, phytic acid, sodium pyrophosphate; Boron-containing compounds: boric acid, sodium tetraborate, sodium metaborate, borax; The total concentration of the anion-doped precursor in the solution is 0-5 mol / L; The liquid-to-solid ratio of the soaking treatment is 5-50 mL / g; The soaking treatment is performed at a temperature of 5-95℃ for a time of 0.1-48 hours. The washing process involves rinsing with tap water for 1-60 minutes, followed by washing with deionized water for 0.1-10 minutes, until the washing solution is neutral. The drying temperature is 60-100°C, and the time is 0.2-24 h; The resulting amorphous hydrogen titanate intermediate has anionic dopant elements derived from the precursor chemically bonded in its structure, namely, one or more of Ti–N, Ti–C, Ti–S, Ti–F, Ti–P, or Ti–B bonds. The average thickness of the amorphous hydrogen titanate intermediate is 20 nm-20 μm.

8. The preparation method according to claim 1, characterized in that, In step S4, the calcination conditions are as follows: heating to 300-750°C at a heating rate of 1-20°C / min under air or inert atmosphere, and holding at that temperature for 5-300 min. The inert atmosphere is selected from any one of high-purity nitrogen, argon, and helium, or a mixture of them in any proportion. The purity of the inert gas is not less than 99.99%; During the calcination process, inert gas flows through the furnace continuously at a flow rate of 10-2000 mL / min; the pressure inside the furnace is maintained at atmospheric pressure or a slight positive pressure of 0-5 kPa to isolate external oxygen and / or moisture. The cooling method is either natural cooling with the furnace or programmed controlled cooling. The obtained monolithic TiO2 foam ceramic has an anatase phase content of 60-95 wt%, a rutile phase content of 5-40 wt%, and no impurity phases; the porosity is 60%-95%. Its macroscopic shape is any one of the following: cylinder, cube, cuboid, sphere, ellipsoid, torus, prism, pyramid, polyhedron, honeycomb block, sheet, arc, arch, tubular, hollow spherical shell, or any combination and deformation thereof.

9. The application of the monolithic TiO2 foam ceramic prepared by the preparation method according to any one of claims 1 to 8 in water treatment or photocatalytic degradation of organic pollutants.

10. The use of the monolithic TiO2 foam ceramic prepared by the preparation method according to any one of claims 1 to 8 in the preparation of water treatment devices or devices for degrading organic pollutants.

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