In-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method and application

Abstract

This application discloses an in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its applications. The powder has a rutile core@anatase shell structure, with dopant elements enriched in the shell through chemical bonding. The preparation method utilizes an integrated "alkali treatment-acid treatment-low-temperature crystallization" process: rutile phase TiO2 is embedded with cation dopant via an alkaline hydrothermal reaction to form an alkali metal titanate shell; then, acid treatment replaces the anion dopant to construct a hydrotitanate shell; finally, low-temperature calcination yields the core-shell structure. This technology utilizes a dynamic surface reconstruction window to simultaneously integrate doping, overcoming particle size limitations (nanometer to centimeter scale). The resulting material exhibits highly efficient photocatalytic degradation performance of organic pollutants in water under visible light, making it suitable for engineering applications. Its innovation lies in simultaneously completing structure construction, doping integration, and crystallization, avoiding the complexity and defects of step-by-step processes, combining technological advancement with practicality.

Description

Technical Field

[0001] This application relates to an in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method and application, and particularly to a method of in-situ introducing doping elements during alkaline treatment and / or acid treatment to prepare rutile@anatase core-shell structure TiO2 powder with a wide spectral response and excellent photocatalytic activity, belonging to the field of photocatalytic material preparation technology. Background Technology

[0002] Titanium dioxide (TiO2), as a high-performance, multifunctional inorganic semiconductor material, is widely used in various fields such as photocatalytic degradation of pollutants, photoelectric conversion, antibacterial and anti-corrosion, and solar energy utilization due to its strong chemical stability, non-toxicity, and low cost. The performance of TiO2 is closely related to its crystal structure, among which rutile and anatase are the two most common and valuable crystal forms, which exhibit significant differences in physicochemical properties.

[0003] Rutile is the most thermodynamically stable crystalline form of TiO2, possessing excellent thermal stability, mechanical strength, and electron transport efficiency. Its dense crystal structure serves as a powder core, ensuring structural integrity under complex operating conditions. However, it has few surface active sites and a relatively low specific surface area, resulting in relatively limited photocatalytic activity. Its band gap is approximately 3.0 eV, with a low conduction band level, weak photogenerated electron reduction ability, and a relatively fast electron-hole recombination rate. Anatase, although a metastable structure, exhibits superior photocatalytic performance—its higher conduction band position endows it with stronger photogenerated electron reduction ability; simultaneously, its slower carrier recombination rate facilitates charge separation. Furthermore, it typically exists as high-specific-surface-area nanoparticles with numerous surface active sites, thus demonstrating excellent photocatalytic efficiency. However, the anatase phase has significant shortcomings in terms of structural stability and mechanical properties: its crystal structure is relatively loose, with low density (about 3.84 g / cm³), poor thermal stability, and it can undergo an irreversible phase transformation into the rutile phase at temperatures above 600~700℃; in addition, anatase phase particles are prone to sintering and agglomeration during high-temperature or long-term use, resulting in a significant decrease in effective specific surface area and surface active sites, and insufficient mechanical strength to support long-term stable use under complex working conditions. When used alone as a functional powder, it is difficult to simultaneously ensure structural integrity and continuous high-efficiency photocatalytic performance.

[0004] Combining anatase and rutile phases can leverage the heterojunction formed between them to promote the separation of photogenerated electron-hole pairs, significantly enhancing the overall photocatalytic performance of the material. Constructing a core-shell structure TiO2 powder with a rutile core and anatase shell, achieving functional complementarity through the structural stability of the core and the high surface activity of the shell, is an effective strategy to overcome the limitations of a single crystal form. The applicant previously developed "A method for preparing TiO2 powder with a rutile@anatase core-shell structure" (application number: CN202511776848.8), which uses a three-step method of "alkali treatment-acid treatment-heat treatment" to construct an active anatase shell in situ on the surface of rutile TiO2 particles, combining core structural stability with high surface activity.

[0005] However, the photoresponse of the undoped core-shell TiO2 powder is still limited to the ultraviolet region (λ<387 nm), and can only utilize less than 5% of the ultraviolet component in the solar spectrum, which seriously restricts its practical application efficiency under visible light conditions. To extend light absorption to the visible light region, element doping is a recognized effective strategy. However, traditional doping methods have the following drawbacks: (1) Bulk doping, which is carried out simultaneously with powder synthesis, is prone to forming carrier recombination centers inside the lattice, which reduces photocatalytic activity; (2) Although the post-modification impregnation method can achieve surface doping, the doping element and the TiO2 matrix are mostly physically adsorbed, with weak binding force, which makes it easy to fall off and be lost during use, and it is difficult to ensure the uniformity of particle surface doping; (3) High-temperature doping process may cause irreversible phase transition from anatase to rutile phase, destroying the constructed core-shell structure. In addition, existing TiO2 surface modification technologies are mostly concentrated on nano or submicron-sized powders, and there is still a lack of effective means for the precise construction and doping control of micron-sized and even centimeter-sized particles. This limits the widespread use of core-shell TiO2 materials in applications requiring specific particle sizes, such as the need for millimeter / centimeter-scale supports in packed bed reactors.

[0006] Currently, there are no reported technologies that directly introduce dopant precursors into alkaline or acidic solutions to simultaneously construct powder core-shell structures and modulate surface band structures. How to precisely control the type, concentration, and spatial distribution of dopants without interfering with the formation kinetics of titanates / hydrotitanic acid, so that dopants selectively accumulate in the anatase shell rather than the bulk phase, remains a long-standing technical challenge in this field. Summary of the Invention

[0007] The objective of this invention is to provide an in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its applications. This application utilizes the processes of alkali treatment to generate titanate (Na2Ti3O7) and acid treatment to generate hydrotitanic acid (H2Ti3O7·nH2O), during which the surface of the rutile phase TiO2 powder is in a highly active reconstructed state: the former possesses interlayer cation exchange capacity, while the latter is rich in substituted -OH groups. This application achieves selective enrichment of dopant elements in the anatase shell by introducing dopant sources in situ during the alkali and acid treatment processes, thereby significantly improving the visible light photocatalytic performance of the material while retaining all the advantages of the core-shell structure.

[0008] To achieve the above objectives, this application adopts the following technical solution:

[0009] This application provides an in-situ doped TiO2 core-shell structured powder with a wide particle size range, its preparation method, and its application. The preparation method includes the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0010] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0011] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0012] In step S2, the concentration of the cation doping source and the concentration of the anion doping precursor in step S3 are independently adjustable and both are ≥0, but they are not both zero at the same time; that is, the three schemes of cation (containing rare earth ions) doping, anion doping and synergistic co-doping are all within the scope of protection of this application.

[0013] Further, in step S1, the D of the rutile phase TiO2 powder 50 The range is 20 nm-2 cm, preferably 0.5 μm-1 mm; The alkaline solution is composed of an alkaline substance and water, and the mass ratio of the rutile TiO2 powder, the alkaline substance and water is 1:(5-25):(15-100). The alkaline solution is prepared from at least one of sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and cesium hydroxide (CsOH), preferably NaOH; Furthermore, in step S2, 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 any one or more soluble inorganic salts 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), 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 salt includes 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 salt includes any one or more of nitrates, chlorides, sulfates, or their hydrates. The total concentration of the cation dopant source in the TiO2 alkaline slurry is 0.001-0.5 mol / L, preferably 0.005-0.2 mol / L; When the dopant element belongs to the following easily hydrolyzable type, its single element concentration preferably does not exceed 0.1 mol / L, and a pre-complexation process is required. The dopant source and complexing agent are pre-mixed to form a homogeneous and transparent complexation precursor solution, which is then added to an alkaline solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The easily hydrolyzable metal cation includes: Be² + Mg² + ,Sc³ + Y³ + Al³ + Ti³ + Zr 4+ Hf 4+ V³ + VO² + VO2 + 、Nb 5+ Ta 5+ Cr³ + Mn² + Mn³ + Fe² + Fe³ + Co² + Ni² + Cu + Cu² + Ag + Au³ + Zn² + Cd² + Hg² + Hg2² + Ga³ + In³ + 、Tl + 、Tl³ + Ge² + 、Ge 4+ Sn² + Pb² + Sb³ + Bi³+ And all lanthanide rare earth trivalent ions La³ + Ce³ + Ce 4+ Pr³ + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + platinum group metal ions Ru³ + 、Rh³ + Pd² + Os 4+ 、Ir³ + Ir 4+ Pt² + Pt 4+ Mo 5+ Mo 6+ W 6+ Re 4+ Re 7+ ; 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 ions is 1-15:1; When dopants exist stably in a strongly alkaline medium as soluble oxyanions, including VO4³ - VO3 - NbO3 - TaO3 - CrO4² - MoO4² - WO4² - MnO4² - MnO4 - ReO4 -GeO3² - Sn(OH)6² - SnO3² - Pb(OH)6² - PbO3² - SbO3 - Sb(OH)6 - Al(OH)4 - AlO2 - Ga(OH)4 - In(OH)4 - Zn(OH)4² - ZnO2² - Its single element concentration can reach up to 0.3 mol / L, and it can be directly introduced into TiO2 alkaline slurry without pre-complexation treatment; The reactor and liner used for the hydrothermal reaction are commercially available reactors and liners, which can be stainless steel reactors, nickel-based alloy reactors, or carbon manganese steel reactors. 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 80-250°C, preferably 100-160°C; the time is 2-200 hours, preferably 10-50 hours; the stirring speed is 10-1000 r / min; the liquid-to-solid ratio of the hydrothermal reaction is 5-80 mL / g, preferably 10-30 mL / g. The solid-liquid separation is performed by vacuum filtration. The material of the vacuum filtration membrane is selected from one or more of mixed cellulose ester (MCE), polyethersulfone (PES), nylon, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polycarbonate track etching (PCTE / PETE), preferably a PES membrane with a pore size of ≤1 μm. 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 temperature is 30-150°C, the heating rate is 1-20°C / min, and the holding time is 0.5-24 hours; The average thickness of the obtained cation-doped alkali metal titanate shell is 50 nm-2 mm.

[0014] Further, in step S3, the acidic 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 HCl or HNO3; The concentration of the acidic solution is 0.01-12 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 (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. The concentration of organic precursors (such as glucose, urea, and citric acid) is preferably no more than 0.5 mol / L to avoid excessive complexation or adsorption of high-concentration organic matter on the titanate surface in acidic media, which could interfere with the ion exchange process and the uniform transformation of the shell structure. The concentration of sulfur-containing precursors is preferably no more than 0.3 mol / L to suppress the decomposition of sulfur-containing components under acidic conditions, releasing gaseous byproducts such as H2S. The concentration of phosphorus-containing precursors is preferably no more than 0.3 mol / L to prevent excessive deposition of phosphate ions on the particle surface, forming a titanium phosphate precipitate phase and affecting doping uniformity. The ratio of the alkaline-treated product to the acidic solution is at least 30 mL of acidic solution per gram of alkaline-treated product, preferably a solid-liquid ratio of 1 g:(30-120) mL. The acid treatment temperature is 5-95°C, preferably 20-60°C; the treatment time is 0.1-48 hours; for heat-sensitive precursors (such as ammonia, L-cysteine), in order to suppress their decomposition and inactivation at higher temperatures and ensure effective doping, the temperature is preferably controlled at 20-50°C. The stirring speed for acid treatment is 10-1000 r / min; The solid-liquid separation is performed by vacuum filtration. The material of the vacuum filtration membrane is selected from one or more of mixed cellulose ester (MCE), polyethersulfone (PES), nylon, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polycarbonate track etching (PCTE / PETE), preferably a PES membrane with a pore size of ≤1 μm. The drying temperature is 30-150°C, the heating rate is 1-20°C / min, and the holding time is 0.5-24 hours; The final pH of the wash is controlled at 6.0-7.0; 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 anion-doped amorphous hydrogen titanate shell is 30 nm to 1.5 mm.

[0015] Furthermore, in step S4: The sagger is made of an inert material that can be used stably under the calcination atmosphere, and is selected from any one of corundum crucibles, quartz crucibles, silicon carbide crucibles and boron nitride crucibles, preferably corundum crucibles; wherein, silicon carbide crucibles are only suitable for inert or reducing atmospheres and must not be used in oxygen-containing atmospheres to avoid oxidation loss of the crucible. In the calcination process, for D 50 For fine particle samples <1 mm, the powder spreading thickness is 0.5-30 mm, preferably 1-10 mm; for D 50 For coarse particle samples ≥1 mm, the spreading thickness is 30-50 mm, that is, the upper limit of the spreading thickness can be appropriately relaxed to 50 mm, but the constant temperature time needs to be extended accordingly to ensure the uniformity of heat treatment. The calcination atmosphere is selected from air, nitrogen (N2), argon (Ar), helium (He), ammonia (NH3), a mixture of hydrogen and nitrogen (H2 / N2, H2 volume fraction ≤10%), or any combination of the above gases; the specific selection principles are as follows: (1) Nitrogen (N) doped samples are preferably calcined in an NH3 or NH3 / N2 mixed atmosphere (NH3 volume fraction 5-100%), using NH3 to provide a reducing nitrogen source simultaneously, which can improve the Ti-N bond formation rate and nitrogen retention. (2) Sulfur (S) and carbon (C) doped samples are preferably calcined under an inert atmosphere (N2 or Ar) to suppress the oxidative decomposition of sulfur- and carbon-containing components; (3) Samples doped with fluorine (F), phosphorus (P) and boron (B) can be calcined in air or an inert atmosphere; if a fluorine precursor is used, the calcination tail gas may contain trace amounts of HF volatiles, and an alkaline tail gas absorption device should be configured. (4) For samples containing precious metals (Ag, Au, Pt, Pd), it is preferred to calcine them at low temperature in an air atmosphere to maintain the high dispersion of metal nanoparticles; When using an inert or reducing atmosphere, the gas purity should be no less than 99.99%, the flow rate should be 10-2000 mL / min, and the furnace pressure should be maintained at atmospheric pressure or slightly positive pressure (50-1000 Pa gauge pressure) to effectively isolate external oxygen and moisture. The calcination temperature is 200-750°C, preferably 350-600°C, and is set according to the type of doped element. (1) For samples containing volatile anionic dopants such as nitrogen (N), sulfur (S), and carbon (C), the calcination temperature is preferably not more than 500°C to suppress the thermal decomposition loss of the above elements; (2) Contains fluorine (F), phosphorus (P), boron (B) or high-valence cations (W) 6+ Mo 6+ 、Nb 5+ Samples doped with elements have high thermal stability and can be calcined up to 600°C. (3) For samples containing noble metal (Ag, Au, Pt, Pd) dopants, the preferred calcination temperature is 350-500°C to avoid the metal nanoparticles from sintering and agglomerating at high temperatures, which would reduce the number of active sites. (4) For multi-element co-doped samples, the calcination temperature is taken as the lowest value of the upper limit of the temperature of each doping element; The calcination heating rate is 1-20°C / min, preferably 5°C / min; the isothermal time is 5-500 min, preferably 30-120 min; for D 50 For coarse particle samples ≥100 μm, the isothermal time is preferably not less than 60 min to ensure uniform temperature inside and outside the particles. After calcination, the cooling method is selected from natural cooling with the furnace or programmed cooling (cooling rate 0.5-10°C / min); for samples containing precious metals, programmed cooling is preferred to reduce the impact of rapid cooling stress on the shell structure. This application also provides in-situ doped TiO2 powder with a rutile@anatase core-shell structure prepared by the above preparation method: The core-shell structured TiO2 powder D 50 The range is 100 nm to 20 mm, which corresponds to the particle size range of the initial rutile phase TiO2 powder. The core phase of the core-shell structured TiO2 powder is rutile TiO2, and the shell phase is doped anatase TiO2. XRD characterization showed that the characteristic diffraction peaks of both the rutile and anatase phases were detectable. The mass fraction of the rutile phase was 10-75 wt.%; the thickness of the anatase shell layer was 4 nm-1.2 mm. The doping elements are mainly concentrated in the anatase shell, and XPS depth analysis or TOF-SIMS confirms that they exist stably in the form of chemical bonding (such as Ti-N, Ti-F, Ti-S, Ti-P, Ti-B or MO-Ti, where M is the doped metal). The specific surface area of ​​the core-shell structured TiO2 powder is 0.1-80 m² / g; UV-Vis DRS showed that, compared with the undoped core-shell sample, the absorption intensity in the visible region (420-800 nm) of the doped sample was significantly enhanced, and the absorption edge was red-shifted to 450-800 nm. Under visible light (λ≥420 nm) irradiation, the degradation rate constant of methylene blue (10 mg / L) is 1.5-15 times that of undoped core-shell structure samples, and the activity retention rate is ≥90% after 5 cycles.

[0016] This application also provides the application of in-situ doped TiO2 powder with rutile@anatase core-shell structure prepared by the above preparation method in water treatment or photocatalytic degradation of organic pollutants.

[0017] This application also provides the application of an in-situ doped TiO2 powder with a wide particle size range and a rutile@anatase core-shell structure prepared by the above preparation method in the preparation of water treatment devices or devices for degrading organic pollutants.

[0018] The in-situ doped core-shell structured TiO2 powder exhibits a photocatalytic degradation rate of ≥80% for organic pollutants in water under visible light irradiation.

[0019] 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 (PFOA) 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.

[0020] The preparation method provided in this application utilizes the "surface dynamic reconstruction window" formed by alkali and acid treatments to simultaneously achieve in-situ co-doping of cations and anions during the sequential formation of titanate and hydrogen titanate. This precisely transforms the surface layer of rutile TiO2 powder into a doped anatase shell, constructing an integrated core-shell structure of "rutile core – doped anatase shell," applicable to particle sizes ranging from nanometers to centimeters. This preparation method and the resulting material possess the following core technical characteristics: Firstly, the synergistic activation of surface function by components and performance. The surface anatase phase not only provides a high specific surface area and abundant active sites, but also precisely modulates 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 or MO-Ti chemical bonds (X = N, F, S, P, B, etc.; M is the doping metal), which redshifts the light absorption edge to 450-800 nm, significantly improving the visible light photocatalytic activity; at the same time, the introduction of heterogeneous elements can optimize the chemical affinity of the adsorption sites on the TiO2 surface, enhancing the targeted adsorption and directional degradation of specific pollutant molecules (including PFAS, antibiotics and other recalcitrant organics).

[0021] Secondly, interface-carrier synergistic enhancement of energy utilization. An atomically tight heterojunction interface is formed between the rutile core and the doped anatase shell, creating a built-in electric field that facilitates the directional migration of photogenerated electrons from the anatase shell to the rutile core. Simultaneously, the dopant element introduces intermediate energy levels or defect states (such as oxygen vacancies, N-doped N 2p states, and F-doped surface Ti³ states) into the shell. + Together with other components, a triple charge regulation mechanism of "band gradient – ​​interface electric field – doped energy level" is constructed, which significantly promotes the cross-interface separation of photogenerated electron-hole pairs, suppresses bulk recombination, and prolongs carrier lifetime, thereby achieving multi-dimensional global optimization of "structural stability – photoresponse width – charge utilization efficiency".

[0022] Third, the doping space selectivity is precise and the functional positioning is clear. Leveraging the alkali metal titanates (with layered structures and exchangeable cation sites between layers) generated during the alkali treatment stage and the amorphous hydrogen titanates (with abundant –OH active groups) formed during the acid treatment stage, dopant elements are selectively enriched in the shell layer that will eventually transform into the anatase phase, rather than being uniformly distributed in the bulk powder phase. This "surface-confined doping" strategy maximizes the efficiency of dopant elements in controlling surface bands and interface charges, completely avoiding the problem of deep-level carrier recombination centers induced by bulk doping, while fully preserving the high density, high thermal stability, and intrinsic electron transport advantages of the rutile core layer.

[0023] Fourth, wide particle size compatibility enables the material to be applied across various scenarios. This application achieves D by systematically controlling the concentration of alkali solution, hydrothermal temperature and time, type of acid solution, and solid-liquid ratio. 50 Uniform and controllable core-shell structure construction and in-situ doping have been achieved on rutile TiO2 powders ranging from nanometer to centimeter scale (20 nm-2 cm), breaking through the limitation of existing technologies that are only applicable to nanometer or submicron powders. This provides a material basis for engineering applications that require specific particle sizes, such as packed bed reactors and photocatalytic foam ceramic carriers.

[0024] Compared with the prior art, this application has the following significant advantages and beneficial effects: 1) Highly integrated processes, green and efficient This application innovatively embeds elemental doping into the "surface reconstruction window" of alkali treatment (step S2) and acid treatment (step S3), realizing the integrated process of "surface activation → cation doping integration → anion doping integration → low-temperature crystallization". Compared with the traditional two-stage process of "independent impregnation doping + high-temperature heat treatment", this application eliminates redundant steps such as independent impregnation and multiple calcinations, shortens the preparation cycle, reduces energy consumption, and fundamentally avoids the anatase phase transformation and doping unevenness problems caused by multiple high-temperature treatments. It significantly improves the economics of the process and batch consistency, making it suitable for large-scale production.

[0025] 2) The doping is firmly bonded and exhibits excellent environmental stability. Dopant elements are deeply integrated into the material structure through a three-pronged mechanism: ion exchange (e.g., La³⁺) + Intercalation sites in titanate layers), lattice substitution (such as W) 6+ Replace Ti 4+ In situ bonding (such as in-situ formation of Ti-N, Ti-F, Ti-S, Ti-P, and Ti-B bonds); after the above chemically bonded dopants are solidified by subsequent low-temperature calcination, the doping retention rate in a simulated water treatment environment (pH 3-11, continuous operation) is significantly higher than that of physically adsorbed or post-impregnated doped materials, and the doping resistance is excellent.

[0026] 3) The spectral response range is significantly broadened, and the catalytic efficiency is doubled. By precisely controlling the electronic structure of the anatase shell through in-situ doping, the absorption intensity in the visible light region (420-800 nm) was significantly improved, and the absorption of the tailed state was extended to the near-infrared region. Under visible light irradiation, the degradation rate constant of methylene blue was 1.5-10 times that of the undoped sample. It also showed broad-spectrum and efficient degradation capabilities for a variety of recalcitrant organic pollutants (including antibiotics, PFAS, bisphenol A and other emerging pollutants), and the carrier lifetime (characterized by time-resolved photoluminescence) was significantly extended, confirming that doping effectively suppressed electron-hole recombination.

[0027] 4) Dual uniform control of shell thickness and doping distribution Thanks to the uniform molecular-level dispersion of the dopant source in alkaline / acidic solutions, the anatase shell thickness in the resulting core-shell structure is uniformly distributed (coefficient of variation CV≤15%), with no local overthickness or missing parts; the heterojunction interface layer has a consistent width and continuous transition (CV≤10%), and the gradient distribution of dopant element concentration in the shell and core layers is clear and controllable (shell / core layer concentration ratio≥5:1), effectively overcoming structural defects such as uneven shell, blurred interface, or dopant agglomeration in traditional methods.

[0028] 5) Applicable to a wide particle size range, with broad prospects for engineering applications. The preparation method has no strict limitations on the particle size of the starting rutile phase TiO2 powder, and its application range covers nanoparticles to millimeter / centimeter-scale particles. It can be directly used in different reactor forms such as photocatalytic foam ceramics, packed beds, and suspension systems, which significantly expands the engineering application space of core-shell structured TiO2 materials and fills the technical gap in the field of surface doping modification of large-particle-size photocatalytic materials.

[0029] 6) The doping system is highly flexible and has strong functional customization capabilities. It is compatible with single or arbitrary combination co-doping schemes of non-rare earth cations (26 selectable elements), rare earth ions (15 selectable elements), and six major classes of anionic precursors (N, C, S, F, P, B). The doping combination can be adjusted as needed according to the type of target pollutant and degradation mechanism to precisely match the application scenario. The entire preparation process does not require template agents, high-pressure fluorine-containing gases, or harsh reaction conditions. The process is green, simple, and has excellent repeatability, and has good industrialization prospects. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process flow for the preparation method proposed in this application. Detailed Implementation

[0031] To make the technical solution of this application clearer and easier to understand, the preferred embodiments are described in detail below with reference to the accompanying drawings.

[0032] Unless otherwise specified, the test methods or experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources.

[0033] This application provides a method for preparing in-situ doped TiO2 powder with a rutile@anatase core-shell structure over a wide particle size range. The preparation process is as follows: Figure 1 As shown, the specific steps include the following: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0034] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0035] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0036] The following description, in conjunction with specific embodiments, illustrates this point.

[0037] Example 1 An in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its application, specifically including the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0038] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0039] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0040] This embodiment provides a method for preparing Fe / N co-doped rutile@anatase core-shell structured TiO2 powder. The specific process conditions and parameters for each step are as follows: Step S1: Preparation of TiO2 alkaline slurry Rutile TiO2 powder (D 50 = 1.0 μm, rutile phase purity ≥98%, XRD detection) added to NaOH alkaline solution according to the predetermined solid-liquid ratio to prepare a uniformly dispersed TiO2 alkaline slurry.

[0041] Among them, the D of the rutile phase TiO2 powder 50 It is 1.0 μm; The alkaline solution was prepared from NaOH and deionized water, with a concentration of 10 mol / L. The mass ratio of the rutile TiO2 powder, NaOH and deionized water is 1:10:40. The dispersion method is ultrasonic dispersion, with an ultrasonic power of 400 W and an ultrasonic time of 30 min, to ensure that the powder is fully wetted and the particles are uniformly suspended. Step S2: In-situ doping alkali treatment process The TiO2 alkaline slurry obtained in step S1 was thoroughly mixed with the cation doping source and then transferred to a stainless steel reactor (with a polytetrafluoroethylene liner) for hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially undergoes a topochemical reaction with the surface of the TiO2 particles, converting the surface TiO2 in situ into Fe-containing particles. 3+ The reaction involves doping with alkali metal titanates, while the rutile phase core inside the particles is preserved due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and Fe-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the product is repeatedly washed with deionized water until the washing solution is neutral. After drying, the intermediate product with a rutile core-Fe-doped alkali metal titanate shell core-shell structure is obtained.

[0042] The cation doping source is ferric nitrate (Fe(NO3)3·9H2O), which is an easily hydrolyzable dopant element and requires a pre-complexation process: Fe(NO3)3·9H2O is pre-mixed with the complexing agent trisodium citrate to prepare a homogeneous and transparent complexation precursor solution, which is then introduced into an alkaline solution to avoid Fe from being absorbed into the strongly alkaline environment. 3+ Instantaneous hydrolysis precipitation; The complexing agent is trisodium citrate, and trisodium citrate reacts with Fe³⁺. + The molar ratio of the ions is 5:1; The concentration of the cation dopant source in the alkaline solution is 0.05 mol / L; The hydrothermal reaction temperature was 120°C; the reaction time was 18 hours; and the stirring speed was 200 r / min. The liquid-to-solid ratio of the hydrothermal reaction is 15 mL / g; The solid-liquid separation is performed by vacuum filtration, and the filter membrane is made of polyethersulfone (PES) with a pore size ≤1 μm. The washing process begins with a thorough rinse with deionized water for 5 minutes, followed by another rinse with deionized water for 1 minute, until the washing solution is neutral. The drying temperature is 90°C, and the constant temperature time is 2 hours; The average thickness of the shell of the obtained alkali metal titanate intermediate product was 80 nm. XRD analysis showed that the shell had a Na2Ti3O7 layered structure, and Fe element had been embedded in the interlayer of titanate through ion exchange. Step S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring conditions. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, converting Na... + Gradually replace with H + Simultaneously, nitrogen (N) dopant is introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing N dopant. After acid treatment, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a rutile core-N doped amorphous hydrogen titanate shell-shell structure is obtained.

[0043] The acidic solution is an aqueous solution of hydrochloric acid (HCl) with a concentration of 3 mol / L; The anion-doped precursor is urea (a thermosensitive nitrogen-containing organic precursor) at a concentration of 0.25 mol / L; The acid treatment temperature is 40°C (to suppress the decomposition and deactivation of urea at higher temperatures and ensure effective N doping, the temperature is controlled within the range of 20–50°C); the treatment time is 4 hours. The liquid-to-solid ratio of the acid treatment was 50 mL / g; the stirring speed was 300 r / min. The final pH of the washing process is controlled at 6.5–7.0; the drying temperature is 80°C and the drying time is 2 hours. The obtained amorphous hydrogen titanate intermediate has chemically bonded N dopant elements (Ti–N bonds) derived from urea in its structure. XPS detection confirmed that the N 1s binding energy peak is located at 396.2 eV, corresponding to a lattice-substituted N–Ti–O structure. The average thickness of the shell of the obtained hydrotitanic acid intermediate was 60 nm; Step S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a corundum crucible and calcined to a thickness of 3 mm to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, generating an in-situ N-doped anatase phase coating layer. Fe elements simultaneously enter the anatase lattice, and the rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core – Fe / N co-doped anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain Fe / N in-situ co-doped rutile@anatase core-shell structure TiO2 powder.

[0044] The calcination process is carried out in a programmable temperature controlled tube furnace. The calcination atmosphere is N2 (gas purity ≥ 99.99%, flow rate 400 mL / min, furnace pressure maintained at a slightly positive pressure of 1 kPa gauge pressure) to suppress the oxidative decomposition loss of N doped elements; The calcination temperature is 480°C (for elements doped with N, the calcination temperature is ≤500°C); the heating rate is 5°C / min; and the holding time is 60 min. After calcination, the cooling method is natural cooling with the furnace. Characterization of the obtained products The obtained product is Fe / N in-situ co-doped TiO2 powder with a rutile@anatase core-shell structure, and its main performance indicators are as follows: ① Particle size: D of the obtained core-shell structured TiO2 powder 50 The particle size is 1.2 μm, which is similar to that of the initial rutile phase TiO2 powder, and the powder morphology is well maintained. ② Phase composition: XRD patterns simultaneously detected characteristic diffraction peaks of rutile and anatase phases, with the rutile phase mass fraction being approximately 82 wt% and the anatase phase approximately 18 wt%, confirming the formation of a core-shell structure; ③ Core-shell structure: TEM observation shows that the thickness of the anatase shell is about 50 nm, with a thickness variation coefficient CV of 11% (≤15%); the thickness of the heterojunction interface layer between the core and shell phases is about 8 nm, with a CV of 7% (≤10%). ④ Distribution of doping elements: XPS depth analysis confirmed that Fe and N elements are mainly enriched in the anatase shell, with a shell / core doping element concentration ratio of approximately 7:1 (≥5:1); Fe is mainly enriched in Fe... 3+ –O–Ti bonds exist, and N exists as Ti–N bonds (lattice substitution type); ⑤ Specific surface area: determined by the BET method, the specific surface area is 18.5 m². 2 / g; ⑥ Optical properties: UV-Vis DRS showed that, compared with the undoped core-shell structure sample, the absorption intensity in the visible light region (420–800 nm) of the Fe / N co-doped sample was significantly enhanced, and the absorption edge was redshifted to about 560 nm, indicating that the visible light response was significantly broadened. ⑦ Photocatalytic performance: Under visible light (λ ≥ 420 nm, 300 W xenon lamp + filter) irradiation, the first-order degradation rate constant of methylene blue (10 mg / L, 50 mL) is k = 0.0412 min. -1 The sample was an undoped core-shell TiO2 sample (k = 0.0105 min). -1 3.9 times that of ) ⑧ Cyclic stability: After 5 cycles, the visible light photocatalytic activity retention rate is ≥93%, and XPS detection shows that the doping retention rates of Fe and N are 97% and 91%, respectively, confirming that the chemically bonded doping is firmly bonded; ⑨ Degradation Application: Under xenon lamp irradiation, the photocatalytic degradation rate of bisphenol A (BPA, 20 mg / L) in water is ≥82%, and the degradation rate of tetracycline (TC, 20 mg / L) is ≥82%, demonstrating a broad-spectrum degradation ability for emerging organic pollutants.

[0045] Example 2 An in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its application, specifically including the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0046] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0047] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0048] This embodiment provides a method for preparing La / F co-doped rutile@anatase core-shell structured TiO2 powder. This embodiment uses D... 50 = 500 μm coarse-grained rutile TiO2 powder was used as raw material, and the doping system selected was rare earth cation La 3+ (Cation doping) and F (Anion doping) is used to demonstrate the universal applicability of the preparation method of this application to powders with a wide particle size range (nanometer to millimeter scale), and the synergistic effect of rare earth ion doping and inorganic anion doping. Specific process conditions and parameters are as follows: Step S1: Preparation of TiO2 alkaline slurry Rutile TiO2 powder (D 50= 500 μm, rutile phase purity ≥ 98%) is added to NaOH alkaline solution at a predetermined solid-liquid ratio, and mechanical stirring (300 r / min, 30 min) is used to prepare a uniformly dispersed TiO2 alkaline slurry.

[0049] Among them, the D of the rutile phase TiO2 powder 50 It is 500 μm; The alkaline solution was prepared from NaOH and deionized water, with a concentration of 8 mol / L. The mass ratio of the rutile TiO2 powder, NaOH and deionized water is 1:8:35. The dispersion method is mechanical stirring at a speed of 300 r / min for 30 min; for D 50 For powders with a coarse particle size of ≥100 μm, mechanical stirring is more suitable than ultrasonic dispersion for maintaining particle integrity while ensuring uniform suspension of the slurry. Step S2: In-situ doping alkali treatment process The TiO2 alkaline slurry obtained in step S1 was thoroughly mixed with the cation doping source and then transferred to a stainless steel reactor (with a polytetrafluoroethylene liner) for hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacted with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 into La-containing particles in situ. 3+ The reaction involves doping with alkali metal titanates, while the rutile phase core inside the particles is preserved due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and La-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the product is repeatedly washed with deionized water until the washing solution is neutral. After drying, the intermediate product with a rutile core-La-doped alkali metal titanate shell core-shell structure is obtained.

[0050] The cation doping source is lanthanum nitrate (La(NO3)3·6H2O), La 3+ La (NO3)3·6H2O is a rare earth ion and an easily hydrolyzable dopant, requiring a pre-complexation process: La(NO3)3·6H2O is pre-mixed with the complexing agent EDTA-2Na (disodium ethylenediaminetetraacetate) to prepare a homogeneous and transparent complexation precursor solution. This precursor solution is then introduced into an alkaline solution to prevent La from being absorbed into the strongly alkaline environment. 3+ Instantaneous hydrolysis precipitation; The complexing agent is EDTA-2Na, and EDTA-2Na reacts with La³⁺. + The molar ratio of the ions is 3:1; The concentration of the cation dopant source in the alkaline solution is 0.02 mol / L; The hydrothermal reaction temperature was 130°C; the reaction time was 24 hours; and the stirring speed was 150 r / min. The liquid-to-solid ratio of the hydrothermal reaction is 20 mL / g; for D 50 For coarse-grained powders with a diameter of 500 μm, appropriately increasing the liquid-solid ratio is beneficial to ensuring sufficient contact and uniform reaction of the alkali solution on the particle surface. The solid-liquid separation is performed by vacuum filtration, and the filter membrane is made of nylon with a pore size ≤1 μm. The washing process begins with a thorough rinse with deionized water for 10 minutes, followed by another rinse with deionized water for 2 minutes until the washing solution is neutral. The drying temperature is 100°C, and the constant temperature time is 3 hours; The average thickness of the shell of the obtained alkali metal titanate intermediate was 350 nm (the surface area of ​​the coarse-grained raw material was larger, and the absolute thickness of the shell increased accordingly); XRD detection showed that the shell had a Na2Ti3O7 layered structure, and the La element had been embedded in the interlayer of titanate through ion exchange. Step S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring conditions. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, converting Na... + Gradually replace with H + At the same time, F The dopant element is introduced in situ into the titanate framework, and the shell structure is transformed into amorphous hydrogen titanate containing F dopant. After acid treatment, solid-liquid separation is performed, and the product is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a rutile core-F doped amorphous hydrogen titanate core-shell structure is obtained.

[0051] The acidic solution is an aqueous solution of nitric acid (HNO3) with a concentration of 2 mol / L. The anion-doped precursor is ammonium bifluoride (NH4HF2) at a concentration of 0.15 mol / L; NH4HF2 can simultaneously provide F in acidic media. With HF, it is beneficial for F element to pass through Ti–OH + F → Ti–F + OH The mechanism replaces surface hydroxyl groups, enabling in-situ formation of Ti–F bonds; The fluorine-containing precursor is an inorganic fluoride, which has better thermal stability than nitrogen-containing organic precursors, and the acid treatment temperature can be appropriately increased; the acid treatment temperature is 30°C; the treatment time is 6 hours. Note: A small amount of HF may volatilize during acid treatment of fluorine-containing precursors. The operation must be carried out in a fume hood, and an appropriate amount of sodium carbonate aqueous solution should be prepared as the tail gas absorbent. The liquid-to-solid ratio of the acid treatment was 60 mL / g; the stirring speed was 200 r / min. The final pH of the washing process is controlled at 6.5–7.0; the drying temperature is 100°C and the drying time is 3 hours. The obtained amorphous hydrogen titanate intermediate has chemically bonded F dopant elements derived from NH4HF2 (Ti–F bonds) in its structure. XPS analysis confirmed that the F 1s binding energy peak is located at 684.5 eV, corresponding to the surface Ti–F structure; a small amount of Ti was also detected. 3+ Signal (Ti 2p) 3 / 2 The peak is located at 458.1 eV, indicating that F doping is accompanied by the formation of oxygen vacancies; The average thickness of the shell of the obtained hydrotitanic acid intermediate was 280 nm; Step S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was evenly spread in a corundum crucible and calcined to a thickness of 8 mm (corresponding to D). 50 = 500 μm coarse particles, with the thickness appropriately increased to 8 mm and the isothermal time extended accordingly to ensure heat treatment uniformity, to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, generating an in-situ F-doped anatase phase coating layer. La element simultaneously enters the anatase lattice, and the rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core – La / F co-doped anatase shell". After calcination, the powder is cooled to room temperature in the furnace to obtain La / F in-situ co-doped rutile@anatase core-shell structure TiO2 powder.

[0052] The calcination process is carried out in a programmable temperature controlled box furnace. The calcination atmosphere is air (containing F dopant, allowing calcination in an air atmosphere; the calcination tail gas contains trace amounts of HF volatiles, and a sodium carbonate solution tail gas absorption device is installed at the furnace outlet). Calcination temperature was 550°C (for F dopant, which has high thermal stability, the calcination temperature can be up to 600°C); heating rate was 5°C / min; isothermal time was 90 min (for coarse particle sample D). 50 = 500 μm, isothermal time not less than 60 min); After calcination, the cooling method is natural cooling with the furnace. Characterization of the obtained products The obtained product is a La / F in-situ co-doped TiO2 powder with a rutile@anatase core-shell structure, and its main performance indicators are as follows: ① Particle size: D of the obtained core-shell structured TiO2 powder 50The particle size was 530 μm, which is basically consistent with the particle size of the initial rutile phase TiO2 powder, indicating that the alkali treatment and acid treatment processes have no significant effect on the overall particle size of the coarse-sized powder and the particle morphology remains intact. ② Phase composition: XRD patterns simultaneously detected characteristic diffraction peaks of both rutile and anatase phases, with the rutile phase mass fraction being approximately 79 wt% and the anatase phase approximately 21 wt%. ③ Core-shell structure: TEM / SEM cross-sectional observations show that the thickness of the anatase shell is approximately 220 nm, with a thickness variation coefficient CV of 12% (≤15%); the thickness of the heterojunction interface layer between the core and shell phases is approximately 15 nm, with a CV of 8% (≤10%). ④ Distribution of doped elements: TOF-SIMS in-depth analysis confirmed that La and F elements are mainly enriched in the anatase shell, with a shell / core doping element concentration ratio of approximately 6:1 (≥5:1); La is predominantly found in the anatase shell. 3+ –O–Ti (M–O–Ti) bonds exist, and F exists in the form of Ti–F bonds. Simultaneously, oxygen vacancies (V0) introduced by F doping are detected. O ); ⑤ Specific surface area: determined by the BET method, the specific surface area is 3.2 m². 2 / g (The specific surface area of ​​coarse-grained powder is lower than that of fine powder, which is within the normal range); ⑥ Optical properties: UV-Vis DRS showed that, compared to the undoped core-shell sample, the La / F co-doped sample exhibited significantly enhanced absorption intensity in the visible light region (420–800 nm), with the absorption edge red-shifted to approximately 490 nm; the oxygen vacancies introduced by F doping and the Ti 3+ Defect states further broaden the visible light response range; ⑦ Photocatalytic performance: Under visible light (λ ≥ 420 nm, 300 W xenon lamp + filter) irradiation, the first-order degradation rate constant k for methylene blue (10 mg / L, 50 mL) is 0.0278 min. -1 The sample was undoped core-shell TiO2 powder (same particle size, k = 0.0089 min). -1 5.1 times that of ) ⑧ Cyclic stability: After 5 cycles, the visible light photocatalytic activity retention rate is ≥91%, and XPS detection shows that the doping retention rates of La and F are 98% and 94%, respectively, confirming that the chemically bonded dopants La–O–Ti and Ti–F are firmly bonded in the actual application environment. ⑨ Comparison with Example 1: This example (D) 50 = 500 μm coarse grain size, La / F doped) and Example 1 (D 50The successful preparation of 1.0 μm fine powder (Fe / N doped) together confirms that the preparation method of this application has good universality and applicability to rutile phase TiO2 powder with particle sizes spanning three orders of magnitude (1 μm to 500 μm), and the core-shell structure construction and in-situ co-doping effect both meet the design specifications.

[0053] Example 3 An in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its application, specifically including the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0054] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0055] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0056] This embodiment provides a method for preparing W / S co-doped rutile@anatase core-shell structured TiO2 powder. This embodiment uses D... 50 = 50 nm nanoscale rutile phase TiO2 powder was used as raw material, and the doping system selected was oxyanion-stabilized cation W 6+ (with WO4) 2 Formal introduction (no pre-complexation required) and S 2 (Anion doping, thiourea as precursor). This embodiment focuses on demonstrating: (1) the construction of the core-shell structure of nano-sized powder; (2) the simplified process advantage of directly introducing the oxyanion-stable cation doping source into the alkaline slurry without pre-complexation; and (3) the effective retention of the sulfur-containing precursor under low-temperature calcination in an inert atmosphere. The specific process conditions and parameters are as follows: Step S1: Preparation of TiO2 alkaline slurry Rutile TiO2 nanoparticles (D 50 = 50 nm, rutile phase purity ≥97%, BET specific surface area approximately 45 m² 2 / g) is added to NaOH alkaline solution according to the predetermined solid-liquid ratio, and ultrasonic dispersion (power 500 W, time 45 min) is combined with mechanical stirring (200 r / min) to prepare a uniformly dispersed TiO2 alkaline slurry.

[0057] Among them, the D of the rutile phase TiO2 powder 50 50 nm; The alkaline solution is prepared by NaOH and deionized water with a concentration of 12 mol / L. For nanoparticles, appropriately increasing the NaOH concentration helps to complete the topological chemical transformation of the surface TiO2 to alkali metal titanate in a shorter time, while avoiding excessive dissolution. The mass ratio of the rutile TiO2 powder, NaOH and deionized water is 1:12:45. The dispersion method is ultrasonic-assisted mechanical stirring with an ultrasonic power of 500 W and a time of 45 min. Nanoparticles have a large specific surface area and strong van der Waals forces between particles, so ultrasonic-assisted dispersion is particularly important for ensuring that nanoparticles are fully dispersed and avoiding agglomeration. Step S2: In-situ doping alkali treatment process The TiO2 alkaline slurry obtained in step S1 was thoroughly mixed with the cation doping source and then transferred to a stainless steel reactor (with a polytetrafluoroethylene liner) for hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially undergoes a topochemical reaction with the surface of the TiO2 nanoparticles, converting the surface TiO2 in situ into a W-containing layer. 6+ The rutile phase core inside the particles is retained due to diffusion restriction, forming a core-shell structure intermediate with rutile as the core and W-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the particles are repeatedly washed with deionized water until the washing solution is neutral. After drying, the intermediate product with a rutile core-W-doped alkali metal titanate shell core-shell structure is obtained.

[0058] The cation doping source is sodium tungstate (Na2WO4·2H2O); W 6+ It belongs to the oxyanion-stabilized doping type, and in strongly alkaline media, it exists as the soluble oxyanion anion WO4. 2 It exists stably in the form of Na2WO4·2H2O without hydrolysis or precipitation, and does not require pre-complexation treatment. Na2WO4·2H2O can be directly added to TiO2 alkaline slurry, which significantly simplifies the process. The concentration of the cation dopant source in the alkaline solution is 0.10 mol / L; W is an oxyanion-stabilized element, and the concentration of a single element can be up to 0.3 mol / L. In this embodiment, 0.10 mol / L is selected to obtain a suitable doping amount. The hydrothermal reaction temperature was 110°C; for nanoparticles, appropriately lowering the hydrothermal temperature (110°C vs. 120–130°C) can slow down the topological chemical reaction rate, which is beneficial to obtaining an ultrathin shell with more uniform thickness; the reaction time was 12 hours; the stirring speed was 400 r / min; The liquid-to-solid ratio of the hydrothermal reaction is 25 mL / g; the nanoparticles have a large specific surface area, and increasing the liquid-to-solid ratio helps to ensure sufficient contact between the dopant source and the particle surface. The solid-liquid separation is performed by vacuum filtration, and the filter membrane material is polyethersulfone (PES) with a pore size ≤0.22 μm; since the nanoparticles are small, a filter membrane with an even smaller pore size must be selected to avoid powder penetration loss. The washing process begins with a thorough rinse with deionized water for 3 minutes, followed by another rinse with deionized water for 1 minute, until the washing solution is neutral. The drying temperature is 80°C, and the constant temperature time is 1.5 hours. The nanoparticles have good thermal conductivity and fast drying speed. The drying temperature should not be too high to avoid aggravated agglomeration due to local overheating. The average thickness of the shell of the obtained alkali metal titanate intermediate was 8 nm. The nanoparticles have a large specific surface area, and less TiO2 can be reacted per unit area under the same liquid-solid ratio. The absolute thickness of the shell is correspondingly thinner, but the shell / core ratio is within a reasonable range. XRD detection shows that the shell has a Na2Ti3O7 layered structure, and W element has been embedded into the titanate framework through lattice substitution. Step S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring conditions. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, converting Na... + Gradually replace with H + Simultaneously, sulfur (S) dopant is introduced in situ into the titanate framework, transforming the shell structure into an amorphous hydrogen titanate containing S dopant. After acid treatment, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a rutile core-S doped amorphous hydrogen titanate shell-shell structure is obtained.

[0059] The acidic solution is an aqueous solution of hydrochloric acid (HCl) with a concentration of 2 mol / L; The anion-doped precursor is thiourea ((NH2)2CS) at a concentration of 0.20 mol / L (the concentration of sulfur-containing precursor is ≤0.3 mol / L to suppress the decomposition of sulfur-containing components and the release of gaseous byproducts such as H2S under acidic conditions); thiourea hydrolyzes slowly in acidic solutions and can continuously release S in solution. 2 This facilitates the uniform incorporation of S elements into the hydrotitanic acid shell through Ti–S bonds. The acid treatment temperature is 25°C; the treatment time is 8 hours; low temperature and long time acid treatment is conducive to the uniform and slow hydrolysis of thiourea, and avoids the excessive decomposition of thiourea at high temperature, which leads to uneven doping. Note: Thiourea hydrolysis under acidic conditions may produce trace amounts of H2S gas; therefore, the operation must be carried out in a fume hood. The liquid-to-solid ratio of the acid treatment is 80 mL / g; the stirring speed is 500 r / min; the nanoparticles have a large specific surface area, so a sufficiently large liquid-to-solid ratio and stirring speed must be ensured to ensure full and uniform contact between the acid solution and the particle surface. The final pH of the washing process is controlled at 6.5–7.0; the drying temperature is 70°C and the drying time is 2 hours. The resulting amorphous hydrogen titanate intermediate contains chemically bonded S-doped elements derived from thiourea (Ti–S bonds). XPS analysis confirmed that the S 2p binding energy peak is located at 161.8 eV (corresponding to S…). 2 –Ti structure) and 163.5 eV (corresponding to S–S or bridged S structure). The average thickness of the shell of the obtained hydrotitanic acid intermediate was 6 nm; Step S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a corundum crucible and calcined to a thickness of 2 mm (the nanoparticles have low packing density, and a thickness of 2 mm corresponds to a large number of actual particle layers, which is conducive to uniform contact with the atmosphere) to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, generating an in-situ S-doped anatase phase coating layer. W element simultaneously enters the anatase lattice, and the rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core – W / S co-doped anatase shell". After calcination, the powder was cooled to room temperature with the furnace to obtain W / S in-situ co-doped rutile@anatase core-shell structure TiO2 nanoparticles.

[0060] The calcination process is carried out in a programmable temperature controlled tube furnace. The calcination atmosphere is Ar (gas purity ≥ 99.99%, flow rate 500 mL / min, furnace pressure maintained at a slightly positive pressure of 1 kPa gauge pressure); for sulfur dopant, an inert Ar atmosphere is selected to suppress the oxidative decomposition loss of sulfur-containing components; The calcination temperature is 450°C (for S-doped elements, which are volatile anions, the preferred calcination temperature is ≤500°C); the heating rate is 5°C / min; and the isothermal time is 45 min (for nanoparticles, which have fast heat transfer and small particle size, the isothermal time can be appropriately shortened compared to coarser particle size samples). After calcination, the cooling method is programmed cooling, with a cooling rate of 5°C / min to 200°C, followed by natural cooling with the furnace. Nanoparticles experience significant shell stress during rapid cooling at high temperatures, and programmed cooling helps reduce the generation of microcracks in the shell. Characterization of the obtained products The obtained product is a W / S in-situ co-doped TiO2 nanoparticle with a rutile@anatase core-shell structure, and its main performance indicators are as follows: ①Particle size: D of the obtained core-shell structured TiO2 nanoparticles 50 The thickness is 65 nm, which is slightly larger than the initial rutile phase TiO2 powder (50 nm). The increase corresponds to the thickness of the anatase phase shell, and the powder as a whole still maintains the nanoscale scale. ②Phase composition: XRD patterns simultaneously detected characteristic diffraction peaks of both rutile and anatase phases, with the rutile phase mass fraction being approximately 76 wt% and the anatase phase approximately 24 wt%. ③ Core-shell structure: HRTEM observations showed that the thickness of the anatase shell was about 5 nm, with a thickness variation coefficient CV of 10% (≤15%); the thickness of the heterojunction interface layer between the core and shell phases was about 2 nm, with a CV of 7% (≤10%); the core-shell interface was clear, and the lattice fringes were continuous, confirming the formation of an atomically compact heterojunction interface; ④ Distribution of doping elements: XPS depth analysis confirmed that W and S elements are mainly enriched in the anatase shell, with a shell / core doping element concentration ratio of approximately 8:1 (≥5:1); W is predominantly W 6+ –O–Ti (lattice substitution Ti) 4+ S exists in the form of Ti–S bonds (lattice substitution of O). 2 It exists in the form of ); W 6+ Replace Ti 4+ Introducing additional electrons (n-type doping), with S 2 Replace O 2 A synergistic bandgap modulation effect is formed; ⑤ Specific surface area: determined by the BET method, the specific surface area is 52.3 m². 2 / g (Nano powders have a high specific surface area, which is significantly better than coarse-particle-size samples, and is conducive to providing more surface active sites); ⑥ Optical properties: UV-Vis DRS showed that the absorption intensity in the visible light region (420–800 nm) of the W / S co-doped sample was significantly enhanced, with the absorption edge red-shifted to approximately 620 nm; W 6+ The introduced donor level and S 2 The synergistic effect of the introduced acceptor energy level compresses the effective band gap from 3.0 eV (undoped rutile) to about 2.0 eV, achieving a significant extension of the response in the visible and even near-infrared regions; ⑦ Photocatalytic performance: Under visible light (λ ≥ 420 nm, 300 W xenon lamp + filter) irradiation, the first-order degradation rate constant k for methylene blue (10 mg / L, 50 mL) is 0.0631 min. -1 The sample is undoped core-shell structured TiO2 nanoparticles (same particle size, k = 0.0148 min). -1 7.3 times that of ) ; benefiting from the high specific surface area of ​​the nanoparticles, its absolute photocatalytic rate constant was the highest in the four examples; ⑧ Cyclic stability: After 5 cycles, the visible light photocatalytic activity retention rate is ≥92%, and XPS detection shows that the doping retention rates of W and S are 99% and 89%, respectively, confirming that low-temperature inert atmosphere calcination effectively retains S-doped elements. ⑨ Comprehensive comparison with the first two embodiments: The particle sizes of the three embodiments are D 50 = 50 nm (nanometer scale), 1.0 μm (submicron / micron scale) and 500 μm (coarse particle size), spanning four orders of magnitude, collectively demonstrating the broad applicability of the preparation method of this application across a wide particle size range; the doping systems cover three types of cation doping sources: oxyanion-stable (W, no pre-complexation required), transition metal easily hydrolyzable (Fe, pre-complexed), and rare earth ion easily hydrolyzable (La, pre-complexed), as well as three types of anion doping precursors: S-containing organic (thiourea), N-containing organic (urea), and F-containing inorganic (NH4HF2), comprehensively verifying the universality and technical feasibility of this application in multi-component doping systems and across a wide particle size range.

[0061] Example 4 An in-situ doped TiO2 core-shell structure powder with a wide particle size range, its preparation method, and its application, specifically including the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder is added to an alkaline solution at a predetermined solid-liquid ratio to prepare a uniformly dispersed alkaline TiO2 slurry; if necessary, ultrasonic dispersion or mechanical stirring is used to ensure that the powder is fully wetted and the particles are uniformly suspended.

[0062] S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it was transferred to a high-pressure reactor and subjected to a hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially reacts with the surface of the TiO2 particles in a topological chemical reaction, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation-doped alkali metal titanate as the shell. After the reaction is complete, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a "rutile core – cation-doped alkali metal titanate shell" core-shell structure is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, gradually replacing alkali metal ions with hydrogen ions. Simultaneously, the anion dopant element was introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing anion dopant. After acid treatment, solid-liquid separation was performed, and the product was repeatedly washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core – anion-doped amorphous hydrogen titanate shell" was obtained.

[0063] S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was uniformly spread in a crucible and calcined to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, forming an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core-anatase shell". After calcination, the powder was cooled to room temperature in the furnace to obtain in-situ co-doped rutile@anatase core-shell structure TiO2 powder with a wide particle size range.

[0064] This embodiment provides a method for preparing Ce / P co-doped rutile@anatase core-shell structured TiO2 powder. This embodiment uses D... 50 = 2 mm millimeter-sized rutile phase TiO2 powder was used as raw material, and the doping system selected was rare earth cation Ce. 3+ (Cation doping, citric acid pre-complexation) and P (anion doping, ammonium dihydrogen phosphate as precursor). This embodiment focuses on demonstrating: (1) the construction of core-shell structure and in-situ co-doping of millimeter-sized large-particle-size powder, further verifying the wide particle size applicable upper limit of the preparation method of this application; (2) rare earth Ce 3+ / Ce 4+ Redox pairs synergistically enhance photocatalytic performance with P doping; (3) Engineering feasibility of direct loading of millimeter-sized powders into a fixed-bed reactor. Specific process conditions and parameters are as follows: Step S1: Preparation of TiO2 alkaline slurry Rutile TiO2 powder (D 50 = 2 mm, rutile phase purity ≥98%, particles are nearly spherical, aspect ratio ≤1.5) are added to NaOH alkaline solution according to the predetermined solid-liquid ratio, and low-speed mechanical stirring (100 r / min, 60 min) is used to prepare a uniformly dispersed TiO2 alkaline slurry.

[0065] Among them, the D of the rutile phase TiO2 powder 50 It is 2 mm; The alkaline solution was prepared from NaOH and deionized water, with a concentration of 10 mol / L. The mass ratio of the rutile TiO2 powder, NaOH and deionized water is 1:10:40. The dispersion method is low-speed mechanical stirring, at a speed of 100 r / min, for 60 min; for D 50 = 2 mm millimeter-sized particles, slow stirring at low speed can ensure particle suspension and slurry uniformity, while avoiding particle breakage caused by high-speed mechanical force; Step S2: In-situ doping alkali treatment process The TiO2 alkaline slurry obtained in step S1 was thoroughly mixed with the cation doping source and then transferred to a stainless steel reactor (with a polytetrafluoroethylene liner) for hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal process, the alkaline solution preferentially undergoes a topochemical reaction with the surface of the TiO2 particles, converting the surface TiO2 in situ into Ce-containing particles. 3+ The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and Ce-doped alkali metal titanate as the shell. After the reaction is completed, solid-liquid separation is performed, and the particles are repeatedly washed with deionized water until the washing solution is neutral. After drying, the intermediate product with a rutile core-Ce-doped alkali metal titanate shell core-shell structure is obtained.

[0066] The cation doping source is cerium nitrate (Ce(NO3)3·6H2O); Ce 3+ As a rare earth ion, Ce(NO3)3·6H2O is an easily hydrolyzable dopant element, requiring a pre-complexation process: Ce(NO3)3·6H2O is pre-mixed with the complexing agent citric acid to prepare a homogeneous and transparent complexation precursor solution. This precursor solution is then introduced into an alkaline solution to prevent Ce from being absorbed into the strongly alkaline environment. 3+ Instantaneous hydrolysis precipitation; Ce 3+ It has a 4f electron orbital, which can introduce Ce into the anatase shell. 3+ / Ce 4+ Redox pairs form intermediate energy levels that can capture photogenerated holes, effectively suppressing electron-hole recombination; The complexing agent is citric acid, and citric acid reacts with Ce³ + The molar ratio of the ions is 4:1; The concentration of the cation dopant source in the alkaline solution is 0.03 mol / L; The hydrothermal reaction temperature is 140°C; for D 50= 2 mm millimeter-sized particles, appropriately increasing the hydrothermal temperature (140°C) is beneficial for the alkaline solution to fully penetrate and complete the topological chemical transformation of the surface; the time is 36 hours; for large-diameter powders, extending the hydrothermal time is beneficial for ensuring that the shell layer at each position on the particle surface is formed completely and uniformly; the stirring speed is 80 r / min. The liquid-to-solid ratio of the hydrothermal reaction is 30 mL / g; the surface area per unit mass of millimeter-sized large particles is small, so appropriately increasing the liquid-to-solid ratio ensures a sufficient supply of dopant source. The solid-liquid separation is first pre-separated using a stainless steel screen with a pore size ≤ 0.5 mm, and then thoroughly rinsed with deionized water. The washing process begins with a thorough rinse with deionized water for 15 minutes, followed by another 3 minutes of washing with deionized water until the washing solution is neutral. The drying temperature is 110°C, and the constant temperature time is 4 hours; The average thickness of the shell of the obtained alkali metal titanate intermediate product was 1.2 μm; the millimeter-sized coarse particles had the largest amount of alkali solution per unit area under the same liquid-solid ratio conditions, and the absolute thickness of the shell was the thickest among the four examples; XRD detection showed that the shell had a Na2Ti3O7 layered structure, and Ce element had been embedded in the interlayer of titanate through ion exchange. Step S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring conditions. The acid solution underwent an ion exchange reaction with the shell alkali metal titanate, converting Na... + Gradually replace with H + Simultaneously, P-doped elements are introduced in situ into the titanate framework, transforming the shell structure into amorphous hydrogen titanate containing P-doped elements. After acid treatment, solid-liquid separation is performed, and the mixture is repeatedly washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a rutile core-P-doped amorphous hydrogen titanate shell-shell structure is obtained.

[0067] The acidic solution is an aqueous solution of nitric acid (HNO3) with a concentration of 3 mol / L; The anion-doped precursor is ammonium dihydrogen phosphate (NH4H2PO4) at a concentration of 0.10 mol / L (preferably ≤0.3 mol / L to prevent excessive deposition of phosphate ions on the particle surface, forming a titanium phosphate precipitate phase that affects doping uniformity); NH4H2PO4 has good solubility in acidic solutions and can stably provide H2PO4. The P element is embedded in the hydrotitanic acid framework through Ti–O–P bonds; The acid treatment temperature is 50°C; NH4H2PO4 has good thermal stability and is not a heat-sensitive precursor, so the acid treatment temperature can be selected in the range of 20–60°C. 50°C is selected to accelerate the ion exchange rate; the treatment time is 12 hours; for large particles in the millimeter size, the acid treatment time is appropriately extended to ensure complete alkali ion replacement and uniform P element insertion. The liquid-to-solid ratio of the acid treatment was 40 mL / g; the stirring speed was 100 r / min. The final pH of the washing process is controlled at 6.5–7.0; the drying temperature is 110°C and the drying time is 4 hours. The obtained amorphous hydrogen titanate intermediate has a chemically bonded P dopant element (Ti–O–P bond) derived from NH4H2PO4 in its structure. XPS detection confirmed that the P 2p binding energy peak is located at 133.2 eV, corresponding to the Ti–O–P–O bridged phosphate ester structure. The average thickness of the shell layer of the obtained hydrotitanic acid intermediate was 0.9 μm; Step S4: Heat treatment process The core-shell structure intermediate product obtained in step S3 was evenly spread in a corundum crucible and calcined to a thickness of 20 mm (corresponding to D). 50 = 2 mm-sized particles, with the thickness increased to 20 mm and the isothermal time extended accordingly to ensure heat treatment uniformity, to prevent particle agglomeration and ensure sufficient contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, generating a P-doped anatase phase coating layer in situ. Ce element simultaneously enters the anatase lattice, and the rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a heterostructure of "rutile core – Ce / P co-doped anatase shell". After calcination, the powder is cooled to room temperature in the furnace to obtain Ce / P in-situ co-doped rutile@anatase core-shell structure TiO2 powder.

[0068] The calcination process is carried out in a programmable temperature controlled box furnace. The calcination atmosphere is air (containing P dopant, which has high thermal stability and can be calcined in air atmosphere; containing Ce, Ce in air atmosphere). 3+ It can be partially oxidized to Ce 4+ , forming Ce 3+ / Ce 4+ Mixed valence states are beneficial for constructing redox active centers. The calcination temperature is 580°C (containing P and Ce dopants, both thermally stable; calcination temperatures can reach 600°C, but 580°C is chosen to ensure complete shell crystallization while allowing for a safety margin); the heating rate is 5°C / min; the isothermal time is 120 min (D 50= 2 mm coarse-grained particles, isothermal time not less than 60 min, 120 min selected to ensure uniform temperature of the particles and full crystallization of the shell). After calcination, the cooling method is programmed cooling, with a cooling rate of 2°C / min to 300°C, followed by natural cooling with the furnace. The millimeter-sized particles have a large heat capacity, and programmed cooling can effectively avoid shell cracking or peeling caused by thermal stress due to the temperature difference between the inside and outside. Characterization of the obtained products The obtained product is a Ce / P in-situ co-doped TiO2 powder with a rutile@anatase core-shell structure, and its main performance indicators are as follows: ① Particle size: D of the obtained core-shell structured TiO2 powder 50 The particle size is 2.1 mm, which is basically consistent with the starting rutile phase TiO2 powder (2 mm). The particle morphology is intact and there is no obvious breakage, which makes it easy to directly fill and use in packed bed or fixed bed reactors. ② Phase composition: XRD patterns simultaneously detected characteristic diffraction peaks of rutile and anatase phases. The mass fraction of rutile phase was approximately 83 wt%, and that of anatase phase was approximately 17 wt%. The proportion of rutile phase was the highest in the four examples, reflecting the structural characteristics of large rutile core volume and thin shell coverage in millimeter-sized large-diameter particles. ③ Core-shell structure: SEM cross-sectional observation showed that the thickness of the anatase shell was about 0.8 μm, with a thickness variation coefficient CV of 13% (≤15%); the thickness of the heterojunction interface layer between the core and shell phases was about 50 nm, with a CV of 9% (≤10%); the shell was continuous and uniform, with no local detachment. ④ Distribution of doped elements: XPS depth profiling and EDS surface scanning confirmed that Ce and P elements are mainly enriched in the anatase shell, with a shell / core doping element concentration ratio of approximately 6:1 (≥5:1); Ce is predominantly found in the anatase shell. 3+ / Ce 4+ Ce–O–Ti bonds exist in mixed valence states, while P exists in Ti–O–P bonds; Ce 3+ / Ce 4+ Redox pairs can serve as hole trapping centers, effectively extending the lifetime of photogenerated carriers; ⑤ Specific surface area: determined by the BET method, the specific surface area is 1.4 m². 2 / g; The specific surface area of ​​the millimeter-sized powder is the lowest in the four examples, but its single particle mechanical strength is high, making it suitable for direct filling into a fixed bed reactor without the need for granulation, thus avoiding the separation and recovery problems of nano / micro powders in engineering applications. ⑥ Optical properties: UV-Vis DRS showed that the Ce / P co-doped sample exhibited significantly enhanced absorption intensity in the visible region (420–800 nm), with the absorption edge red-shifted to approximately 510 nm; Ce3+ The 4f→5d transition produces additional absorption at about 350 nm, which, combined with the modulation of the electronic structure by P doping, extends the visible light response range. ⑦ Photocatalytic performance: Under visible light (λ ≥ 420 nm, 300 W xenon lamp + filter) irradiation, the first-order degradation rate constant k for methylene blue (10 mg / L, 50 mL) is 0.0198 min. -1 The sample was undoped core-shell TiO2 powder (same particle size, k = 0.0065 min). -1 3.0 times that of ) ⑧ Cyclic stability: After 5 cycles, the visible light photocatalytic activity retention rate is ≥95% (millimeter-sized particles are easy to recover, there is no powder loss during the cycle, and the activity retention rate is the highest among the four examples); XPS detection shows that the Ce and P doping retention rates are 98% and 97%, respectively; ⑨ Engineering application verification: The obtained Ce / P co-doped millimeter-sized TiO2 powder was directly packed into a quartz tube fixed bed reactor with an inner diameter of 25 mm and a filling height of 100 mm. Tetracycline (TC, 20 mg / L) wastewater was introduced at a flow rate of 1.0 L / h. Under visible light (λ ≥ 420 nm) lateral irradiation, the steady-state degradation rate of TC reached 71%, and the catalyst activity showed no significant decay after 72 hours of operation. ⑩ Comprehensive comparison of four embodiments: The preparation method of this application covers particle sizes spanning D 50 Under the conditions of a particle size distribution ranging from 50 nm to 2 mm (spanning five orders of magnitude), cations including stable oxyanions (W, requiring no pre-complexation), easily hydrolyzable transition metals (Fe), and easily hydrolyzable rare earth ions (La, Ce), and anions including N-containing organics (urea), S-containing organics (thiourea), F-containing inorganics (NH4HF2), and P-containing inorganics (NH4H2PO4), the obtained products successfully achieved rutile@anatase core-shell structure construction and in-situ co-doping. The shell CV was ≤15%, the interface CV was ≤10%, the shell / core doping concentration ratio was ≥5:1, the visible light degradation rate constant was more than 3.0 times that of the undoped sample, and the activity retention rate was ≥91%. This fully demonstrates the wide particle size universality, doping system flexibility, and product performance stability of the preparation method proposed in this application.

[0069] 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 in-situ doped TiO2 core-shell structured powder with a wide particle size range, characterized in that, The preparation method includes the following steps: S1: Preparation of TiO2 slurry Rutile TiO2 powder was added to an alkaline solution to prepare a uniformly dispersed TiO2 alkaline slurry. S2: In-situ doping alkali treatment process After thoroughly mixing the TiO2 alkaline slurry obtained in step S1 with the cation doping source, it is transferred to a high-pressure reactor and subjected to hydrothermal reaction under constant temperature and stirring conditions. During the hydrothermal reaction, the alkaline solution preferentially undergoes a topological chemical reaction with the surface of the TiO2 particles, converting the surface TiO2 in situ into alkali metal titanates containing cation doped elements. The rutile phase core inside the particles is retained due to diffusion restriction, thus forming a core-shell structure intermediate with rutile as the core and cation doped alkali metal titanate as the shell. After the reaction is completed, solid-liquid separation is performed, and the product is washed with deionized water until the washing solution is neutral. After drying, an intermediate product with a core-shell structure of "rutile core – cation doped alkali metal titanate shell" is obtained. S3: In-situ doping acid treatment process The core-shell intermediate product obtained in step S2 was immersed in an acidic solution containing anion-doped precursor and subjected to acid treatment under constant temperature and stirring conditions. The acid solution and the shell alkali metal titanate underwent an ion exchange reaction, gradually replacing the alkali metal ions with hydrogen ions. At the same time, the anion doping element was introduced in situ into the titanate framework, and the shell structure was transformed into amorphous hydrogen titanate containing anion doping element. After the acid treatment was completed, solid-liquid separation was performed, and the product was washed with deionized water until the washing solution was neutral. After drying, an intermediate product with a core-shell structure of "rutile core-anion-doped amorphous hydrogen titanate shell" was obtained. S4: Heat treatment process The core-shell structured intermediate product obtained in step S3 was evenly spread in a sagger and calcined to prevent particle agglomeration and ensure full contact between the powder and the calcining atmosphere. During calcination, the amorphous hydrogen titanate in the shell undergoes a crystallization transformation, generating an anatase phase coating layer in situ. The rutile phase core is stably retained under heat treatment conditions, ultimately forming TiO2 powder with a "rutile core-anatase shell" heterostructure. After calcination, the powder is cooled to room temperature to obtain in-situ co-doped rutile@anatase core-shell structured TiO2 powder with a wide particle size range. In step S2, the concentration of the cation doping source and the concentration of the anion doping precursor in step S3 are adjusted independently, and both are ≥0, but they are not both zero at the same time; that is, cation doping, anion doping or synergistic co-doping of the two are formed.

2. The preparation method according to claim 1, characterized in that, In step S1, the D of the rutile phase TiO2 powder 50 The range is 20 nm - 2 cm; The alkaline solution is composed of an alkaline substance and water, and the mass ratio of the rutile TiO2 powder, the alkaline substance and water is 1:(5-25):(15-100). The alkaline substance is selected from at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, and cesium hydroxide.

3. The preparation method according to claim 1, characterized in that, In step S2, 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, zirconium, hafnium, tin, antimony, silver, gold, platinum, palladium, aluminum, gallium, indium, and bismuth; the soluble inorganic salt includes 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, yttrium, and soluble salts of lanthanides (excluding promethium), wherein the lanthanides include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium; 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 slurry is 0.001-0.5 mol / L; when the dopant element belongs to the following easily hydrolyzable type, its single element concentration does not exceed 0.1 mol / L, and a pre-complexation process is required. The dopant source and complexing agent are pre-mixed to form a uniform and transparent complexation precursor solution, and then the precursor solution is added to the alkaline solution to avoid instantaneous hydrolysis and precipitation in a strongly alkaline environment. The easily hydrolyzable metal cations include: Be² + Mg² + ,Sc³ + Y³ + Al³ + Ti³ + Zr 4+ Hf 4+ V³ + VO² + VO2 + 、Nb 5+ Ta 5+ Cr³ + Mn² + Mn³ + Fe² + Fe³ + Co² + Ni² + Cu + Cu² + Ag + Au³ + Zn² + Cd² + Hg² + Hg2² + Ga³ + In³ + 、Tl + 、Tl³ + Ge² + 、Ge 4+ Sn² + Pb² + Sb³ + Bi³ + And all lanthanide rare earth trivalent ions La³ + Ce³ + Ce 4+ Pr³ + 、Nd³ + Sm³ + Eu³ + Gd³ + Tb³ + Dy³ + Ho³ + Er³ + Tm³ + Yb³ + Lu³ + platinum group metal ions Ru³ + 、Rh³ + Pd² + Os 4+ 、Ir³ + Ir 4+ Pt² + Pt 4+ Mo 5+ Mo 6+ W 6+ Re 4+ Re 7+ ; 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, disodium ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trisodium diethylenetriaminepentaacetic acid, aminotriacetic acid; 3) High molecular weight polymers: low molecular weight polyacrylic acid and ammonium polyacrylate with molecular weights of 1,000-10,000; The molar ratio of the complexing agent to the cation is 1-15:1; When dopants exist stably in a strongly alkaline medium as soluble oxyanions, including VO4³ - VO3 - NbO3 - TaO3 - CrO4² - MoO4² - WO4² - MnO4² - MnO4 - ReO4 - GeO3² - Sn(OH)6² - SnO3² - Pb(OH)6² - PbO3² - SbO3 - Sb(OH)6 - Al(OH)4 - AlO2 - Ga(OH)4 - In(OH)4 - Zn(OH)4² - ZnO2² - Its single element concentration can reach up to 0.3 mol / L, and it can be directly introduced into TiO2 alkaline slurry without pre-complexation treatment.

4. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the hydrothermal reaction is 80-250°C; the time is 2-200 hours; the stirring speed is 10-1000 r / min; and the liquid-to-solid ratio of the hydrothermal reaction is 5-80 mL / g. The solid-liquid separation is performed by vacuum filtration. The filter membrane material for vacuum filtration is selected from one or more of mixed cellulose ester, polyethersulfone, nylon, polytetrafluoroethylene, polyvinylidene fluoride, and polycarbonate track etching, and the pore size of the filter membrane is ≤1 μm. 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 temperature is 30-150°C, the heating rate is 1-20°C / min, and the holding time is 0.5-24 hours; The average thickness of the shell of the obtained intermediate product was 50 nm-2 mm.

5. The preparation method according to claim 1, characterized in that, In step S3, the acidic 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; The concentration of the acidic solution is 0.01-12 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 acidic solution is 0.01–5 mol / L; wherein, the concentration of organic precursor does not exceed 0.5 mol / L to avoid excessive complexation or adsorption of high-concentration organic matter with the titanate surface in the acidic medium, which would interfere with the ion exchange process and the uniform transformation of the shell structure; the concentration of sulfur-containing precursor does not exceed 0.3 mol / L to suppress the decomposition of sulfur-containing components and the release of gaseous byproducts under acidic conditions; and the concentration of phosphorus-containing precursor does not exceed 0.3 mol / L to prevent excessive deposition of phosphate ions on the particle surface to form a titanium phosphate precipitate phase, which would affect the doping uniformity. The ratio of the intermediate product with a core-shell structure of "rutile core-cation-doped alkali metal titanate shell" obtained in step S2 to the acidic solution is no less than 30 mL of acidic solution per gram of alkali-treated core-shell structure intermediate product.

6. The preparation method according to claim 1, characterized in that, In step S3, the acid treatment temperature is 5-95°C; the treatment time is 0.1-48 hours; for heat-sensitive precursors, in order to suppress their decomposition and deactivation at higher temperatures and ensure effective doping, the temperature is controlled at 20-50°C. The stirring speed for acid treatment is 10-1000 r / min; The solid-liquid separation is performed by vacuum filtration. The material of the vacuum filtration membrane is selected from one or more of mixed cellulose ester, polyethersulfone, nylon, polytetrafluoroethylene, polyvinylidene fluoride, and polycarbonate track etching, and the pore size of the membrane is ≤1 μm. The drying temperature is 30-150°C, the heating rate is 1-20°C / min, and the holding time is 0.5-24 hours; The final pH of the wash is controlled at 6.0-7.0; 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 intermediate product with a core-shell structure of "rutile core-anion-doped amorphous hydrogen titanate shell" has an average shell thickness of 30 nm-1.5 mm.

7. The preparation method according to claim 1, characterized in that, In step S4, during the calcination treatment, for D 50 For fine particle samples <1mm, the powder spreading thickness is 0.5-30 mm; for D 50 For coarse particle samples ≥1 mm, the thickness of the spread should be 30-50 mm, but the isothermal time needs to be extended accordingly to ensure uniform heat treatment. The calcination atmosphere is selected from air, nitrogen, argon, helium, ammonia, or a mixture of hydrogen and nitrogen (H2 / N2, H2 volume fraction ≤10%), or any combination of the above gases; the specific selection principles are as follows: 1) Nitrogen-doped samples are calcined in an NH3 or NH3 / N2 mixed atmosphere (NH3 volume fraction 5-100%) to utilize NH3 to simultaneously provide a reducing nitrogen source, thereby improving the Ti-N bond formation rate and nitrogen retention. 2) Sulfur- and carbon-doped samples are calcined under an inert atmosphere of N2 or Ar to suppress the oxidative decomposition of sulfur- and carbon-containing components. 3) Samples doped with fluorine, phosphorus, or boron are calcined in air or an inert atmosphere; 4) Samples containing precious metals (Ag, Au, Pt, Pd) are calcined in air to maintain the high dispersion of metal nanoparticles. When using an inert or reducing atmosphere, the gas purity should be no less than 99.99%, the flow rate should be 10-2000 mL / min, and the furnace pressure should be maintained at a slight positive pressure of 50-1000 Pa gauge pressure to effectively isolate external oxygen and moisture. The calcination temperature is 200-750°C, and is set in different ranges according to the type of doped element: 1) For samples containing volatile anionic dopants 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 the above elements; 2) Contains fluorine (F), phosphorus (P), boron (B), or high-valence cations (W). 6+ Mo 6+ 、Nb 5+ Samples doped with elements have high thermal stability and can be calcined up to 600°C. 3) For samples containing noble metal dopants Ag, Au, Pt, and Pd, the calcination temperature is 350-500°C to avoid the metal nanoparticles from sintering and agglomerating at high temperatures, which would reduce the number of active sites. 4) For multi-element co-doped samples, the calcination temperature is taken as the lowest value of the upper limit of the temperature of each doping element; The calcination heating rate is 1-20°C / min; the isothermal time is 5-500 min; for D 50 For coarse particle samples ≥100 μm, the isothermal time should be no less than 60 min to ensure uniform temperature inside and outside the particles.

8. The in-situ doped TiO2 powder with a rutile@anatase core-shell structure prepared by the preparation method according to any one of claims 1-7.

9. The application of the in-situ doped TiO2 powder with a rutile@anatase core-shell structure prepared by the preparation method according to any one of claims 1-7 in water treatment or photocatalytic degradation of organic pollutants.

10. The application of an in-situ doped TiO2 powder with a wide particle size range and a rutile@anatase core-shell structure prepared by the preparation method according to any one of claims 1-7 in the preparation of water treatment devices or devices for degrading organic pollutants.

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