Titanium dioxide materials, their preparation methods, applications, and photodegradation methods

Abstract

This invention relates to a titanium dioxide material, its preparation method, uses, and photodegradation method. The preparation method of the titanium dioxide material includes the following steps: (1) stirring the compound shown in formula (I) and the compound shown in formula (II) in a molar ratio of (1-4):1 at 60-110°C to obtain a eutectic solvent; wherein R1 and R2 are independently selected from OH, halogen, and hydroxyl-substituted C, respectively. 1‑6 Alkyl or C 1‑6 (1) Halogenated alkyl group; (2) The eutectic solvent and water are stirred for the first time to obtain a microemulsion; then titanate ester is added dropwise to the microemulsion and stirred for the second time to obtain a titanium-containing mixture; (3) The titanium-containing mixture is washed and centrifuged; the precipitate obtained by centrifugation is dried and then calcined to obtain titanium dioxide material. The titanium dioxide material prepared by this method can be used as a photocatalyst to improve the degradation efficiency of pollutants.

Description

Technical Field

[0001] This invention relates to a titanium dioxide material, its preparation method and uses, and also to a photodegradation method. Background Technology

[0002] Photocatalytic degradation is a process in which organic pollutants are gradually oxidized and decomposed into harmless small molecules (such as CO2 and H2O) by photocatalysts excited to generate free radicals and active substances under light irradiation. Among these, photocatalytic oxidation technology is widely used in water treatment, air purification, and organic pollutant remediation due to its advantages such as mild reaction conditions, thorough degradation, and environmental friendliness.

[0003] Semiconductor titanium dioxide (TiO2) is a photocatalyst with broad application prospects, possessing advantages such as non-toxicity, non-polluting nature, good chemical stability, and high photocatalytic activity. Studies have shown that the physicochemical properties of TiO2, such as crystal form, surface structure, and particle size, significantly affect its photocatalytic performance. However, TiO2 still faces some limitations in practical applications, such as a narrow light absorption range (mainly ultraviolet light), high recombination rate of photogenerated carriers, relatively low reaction efficiency, and the tendency of nanoparticles to aggregate and be difficult to recycle, which limits its long-term application in complex environments.

[0004] CN101637719A discloses a method for preparing a titanium dioxide photocatalyst. The method involves assembling a silica template, filling the template pores with a carbon precursor, carbonizing at high temperature, removing the template to obtain ordered macroporous carbon, and then loading a TiO2 precursor onto the ordered macroporous carbon in sol or suspension form, followed by calcination. This patented preparation process involves multiple steps, is complex, and requires strict control over temperature, atmosphere, and other conditions.

[0005] CN108772052A discloses a method for preparing titanium dioxide-based porous blocks. The method involves preparing a sol system using N,N-dimethylacetamide, chitin, and lithium chloride; blending nano-titanium dioxide, carbon materials, and a low-melting-point metal with the sol system; adding a pore-forming agent to obtain a gel block; dissolving the pore-forming agent from the gel block using a pore-forming solvent; and then preparing the final product through drying and sintering. This patented method requires specific sol systems and pore-forming agents, and may require re-optimization of process conditions for different raw material combinations, thus its applicability is relatively narrow. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide a method for preparing titanium dioxide material, wherein the titanium dioxide material obtained by the preparation method has good photocatalytic performance and improves the degradation efficiency of pollutants.

[0007] Another object of the present invention is to provide the above-mentioned titanium dioxide material.

[0008] Another object of the present invention is to provide the use of the above-mentioned titanium dioxide material, which can improve the degradation efficiency of pollutants.

[0009] Another object of the present invention is to provide a method for photodegradation of benzoyl carmine.

[0010] The present invention achieves the above objectives using the following technical solutions.

[0011] This invention provides a method for preparing titanium dioxide material, comprising the following steps:

[0012] (1) The compound shown in formula (I) and the compound shown in formula (II) with a molar ratio of (1~4):1 are stirred at 60~110℃ to obtain a eutectic solvent;

[0013]

[0014] R1 and R2 are independently selected from C-substituted OH, halogen, and hydroxyl groups, respectively. 1-6 Alkyl or C 1-6 Halogenated alkyl groups;

[0015] (2) The eutectic solvent and water are stirred for the first time to obtain a microemulsion; then titanate is added dropwise to the microemulsion and stirred for the second time to obtain a titanium-containing mixture; the titanate is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetran-n-propyl titanate or tetraoctyl titanate.

[0016] (3) Wash the titanium-containing mixture and centrifuge it; dry the precipitate obtained by centrifugation and then calcine it to obtain titanium dioxide material.

[0017] According to the preparation method of the present invention, preferably, R1 and R2 are independently selected from OH, F, Cl, and hydroxyl-substituted C. 1-3 Alkyl or C 1-3 Halogenated alkyl groups.

[0018] According to the preparation method of the present invention, preferably, the volume ratio of the eutectic solvent to water in step (2) is (3-25):1; and the volume ratio of the eutectic solvent to titanate is (2-10):1.

[0019] According to the preparation method of the present invention, preferably, the first stirring time in step (2) is 10-35 min; the second stirring time is 7-30 min.

[0020] According to the preparation method of the present invention, preferably, the solvent used for washing in step (3) is selected from one or more of methanol, ethanol, n-propanol or isopropanol.

[0021] According to the preparation method of the present invention, preferably, the centrifugation speed in step (3) is 8000-15000 rpm; the centrifugation time is 5-25 min; the drying temperature is 60-150℃; and the drying time is 1-4 h.

[0022] According to the preparation method of the present invention, preferably, the calcination temperature in step (3) is 300-900℃ and the calcination time is 1-5h.

[0023] On the other hand, the present invention also provides a titanium dioxide material, which is obtained by the above-described preparation method.

[0024] Furthermore, the present invention provides the use of the above-mentioned titanium dioxide material as a photocatalyst in the degradation of pollutants.

[0025] In another aspect, the present invention also provides a photodegradation method for benzoxanthin, using the aforementioned titanium dioxide material as a photocatalyst to photodegrade the benzoxanthin solution.

[0026] The titanium dioxide material prepared by the method of this invention has good photocatalytic performance and can improve the degradation efficiency of pollutants. Attached Figure Description

[0027] Figure 1 Scanning electron microscope (SEM) image of titanium dioxide material in Example 1.

[0028] Figure 2 Example 1: X-ray diffraction pattern of titanium dioxide material.

[0029] Figure 3 UV-Vis absorption spectra of titanium dioxide material in Example 1 and Comparative Example 2. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] <Preparation Method>

[0032] The method for preparing the titanium dioxide material of the present invention includes the following steps:

[0033] (1) Preparation of eutectic solvent; (2) Preparation of titanium-containing mixture; (3) Preparation of titanium-containing mixture into titanium dioxide material.

[0034] Preparation of eutectic solvent

[0035] The compound shown in formula (I) and the compound shown in formula (II) are stirred at a certain temperature to obtain a eutectic solvent;

[0036]

[0037] R1 and R2 are independently selected from C-substituted OH, halogen, and hydroxyl groups, respectively. 1-6 Alkyl or C 1-6 Halogenated alkyl groups.

[0038] C 1-6 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, tert-pentyl, neopentyl, or n-hexyl.

[0039] C 1-6 Examples of alkyl halogens include, but are not limited to, monofluoromethyl, difluoromethyl, trifluoromethyl, monochloromethyl, dichloromethyl, trichloromethyl, monobromomethyl, dibromomethyl, tribromomethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, monochloroethyl, dichloroethyl, trichloroethyl, monobromoethyl, dibromoethyl, tribromoethyl, propyl halogen, isopropyl halogen, butyl halogen, or isobutyl halogen.

[0040] The compound shown in formula (I) can be represented as in formula (I-1):

[0041]

[0042] R1 is defined as described above.

[0043] The compound shown in formula (I) can be represented as in formula (I-2):

[0044]

[0045] R1 is defined as described above.

[0046] R1 is selected from C-substituted with OH, halogen, or hydroxyl groups. 1-3 Alkyl or C 1-3 The alkyl group is a haloalkyl group; preferably, R1 is selected from OH, F, Cl, CH3OH or CH3Cl; more preferably, R1 is OH.

[0047] The compound shown in formula (II) can be represented as in formula (II-1).

[0048]

[0049] R2 is defined as described above.

[0050] R2 is selected from C-substituted OH, halogen, or hydroxyl groups. 1-3 Alkyl or C 1-3 The alkyl halogroup is preferably selected from OH, F, Cl, CH3OH or CH3Cl; more preferably, R2 is OH.

[0051] According to one embodiment of the present invention, the compound represented by formula (I) is menthol; the compound represented by formula (II) is 1-naphthol.

[0052] The molar ratio of the compound shown in formula (I) to the compound shown in formula (II) is (1 to 4):1, preferably (1.5 to 3):1, and more preferably (2 to 2.5):1.

[0053] The stirring temperature is 60–110°C, preferably 70–90°C, and more preferably 75–85°C. Oil bath heating can be used.

[0054] The stirring time can be 20 to 50 minutes, preferably 25 to 40 minutes.

[0055] Magnetic stirring can be used.

[0056] After stirring, the temperature was lowered to room temperature to obtain a eutectic solvent.

[0057] Preparation of titanium-containing mixtures

[0058] The eutectic solvent and water were stirred for the first time to obtain a microemulsion; then titanate was added dropwise to the microemulsion and stirred for the second time to obtain a titanium-containing mixture.

[0059] The volume ratio of the eutectic solvent to water can be (3-25):1, preferably (4-20):1, and more preferably (5-16):1. In some embodiments, the volume ratio of the eutectic solvent to water is (9-14):1.

[0060] The volume ratio of the eutectic solvent to the titanate can be (2-10):1; preferably, the volume ratio of the eutectic solvent to the titanate is (3.75-7.5):1; more preferably, the volume ratio of the eutectic solvent to the titanate is (4-6):1.

[0061] The microemulsion is of the water-in-oil (W / O) type.

[0062] The first stirring time can be 10 to 35 minutes, preferably 15 to 25 minutes, and more preferably 18 to 22 minutes.

[0063] The second stirring time can be 7 to 30 minutes, preferably 10 to 20 minutes; more preferably 12 to 17 minutes.

[0064] Magnetic stirring can be used.

[0065] The titanate is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetra-n-propyl titanate, or tetraoctyl titanate; preferably, the titanate is selected from one or more of tetrabutyl titanate or tetra-n-propyl titanate; more preferably, the titanate is tetrabutyl titanate.

[0066] Preparation of titanium dioxide materials from titanium-containing mixtures

[0067] The titanium-containing mixture was washed and centrifuged; the precipitate obtained by centrifugation was dried and then calcined to obtain titanium dioxide material.

[0068] The solvent used for washing is selected from alcohol solvents; preferably, the solvent used for washing is selected from one or more of methanol, ethanol, n-propanol, and isopropanol; more preferably, the solvent used for washing is ethanol.

[0069] The centrifugation speed can be 8000-15000 rpm; preferably, the centrifugation speed is 10000-14000 rpm; more preferably, it is 11000-13000 rpm.

[0070] The centrifugation time can be 5 to 25 minutes; preferably, the centrifugation time is 10 to 20 minutes; more preferably, it is 15 to 18 minutes.

[0071] The drying temperature can be 60–150°C; preferably, the drying temperature is 80–120°C; more preferably, it is 90–110°C.

[0072] The drying time can be 1 to 4 hours; preferably, the drying time is 1.5 to 2.5 hours.

[0073] The calcination temperature can be 300–900℃, preferably 350–800℃, more preferably 380–750℃, and even more preferably 400–550℃.

[0074] The calcination time can be 1 to 5 hours; preferably, the calcination time is 1.5 to 4 hours; more preferably, it is 2 to 3 hours.

[0075] <Titanium Dioxide Materials>

[0076] The titanium dioxide material of the present invention is prepared by the above-described preparation method.

[0077] The particle size of the titanium dioxide material is 100–450 nm; preferably 200–400 nm; more preferably 250–350 nm.

[0078] The titanium dioxide material exhibits diffraction peaks at 25.4±3°, 37.2±3°, 48.5±3°, 54.1±3°, and 55.5±3°. Specifically, the titanium dioxide material also exhibits diffraction peaks at 27.8±3°, 41.3±3°, and 64.2±3°.

[0079] Titanium dioxide materials have the following properties: Figure 2 The X-ray diffraction pattern shown.

[0080] <Applications>

[0081] The titanium dioxide material of the present invention exhibits excellent photocatalytic activity. Therefore, the present invention provides the use of the above-mentioned titanium dioxide material as a photocatalyst.

[0082] Titanium dioxide materials can be used as photocatalysts to degrade pollutants.

[0083] <Photodegradation Methods>

[0084] The photodegradation method of benzoxanthin of the present invention includes the following steps: using the above-mentioned titanium dioxide material as a photocatalyst to photodegrade the benzoxanthin solution.

[0085] The concentration of the benzoyl carmine solution can be 10–80 mg / L; preferably 20–50 mg / L; more preferably 30–40 mg / L.

[0086] The mass-to-volume ratio of titanium dioxide material to benzoyl carmine solution can be 1:(1-6) mg / mL, preferably 1:(2-5) mg / mL, and more preferably 1:(2-4) mg / mL.

[0087] Xenon lamps can be used as a light source for degradation.

[0088] A dark reaction can be carried out before the photodegradation reaction. The dark reaction time can be 5 to 40 minutes; preferably 10 to 30 minutes.

[0089] The photodegradation time can be 100-180 min; preferably 120-160 min; more preferably 130-150 min.

[0090] Preparation Example 1

[0091] Menthol and 1-naphthol were added to the reactor at a molar ratio of 2:1, followed by the addition of a magnetic stir bar. The reactor was then placed in an 80°C oil bath and stirred with the magnetic stir bar for 30 minutes. After stirring, the magnetic stir bar was removed from the reactor, and the reactor was cooled to room temperature to obtain a eutectic solvent.

[0092] Example 1

[0093] 10 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0094] The obtained titanium dioxide material was characterized by field emission scanning electron microscopy (FEM), and the scanning electron microscopy spectra are shown in the figure. Figure 1 It can be seen that the titanium dioxide material presents as spherical particles with a particle size of approximately 300 nm, and some of the spherical particles have agglomerated.

[0095] The obtained titanium dioxide material was characterized by crystal form using X-ray diffraction. The X-ray diffraction pattern is shown in the figure. Figure 2 The diffraction peaks with 2θ values ​​of 25.4°, 37.2°, 48.5°, 54.1°, and 55.5° correspond to the (101), (103), (200), (105), and (211) crystal planes of anatase titanium dioxide. There are also weaker diffraction peaks with 2θ values ​​of 27.8°, 41.3°, and 64.2°, corresponding to the (110), (111), and (310) crystal planes of rutile titanium dioxide.

[0096] Example 2

[0097] Add 5 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water to a beaker, and stir magnetically for 20 min to uniformly disperse the distilled water in the eutectic solvent, obtaining a water-in-oil (W / O) microemulsion. Then, uniformly add 2 mL of tetrabutyl titanate to the microemulsion, and continue magnetic stirring for 15 min to obtain a titanium-containing mixture. After thoroughly washing the titanium-containing mixture with anhydrous ethanol, centrifuge at 12000 rpm for 15 min. Dry the precipitate obtained by centrifugation at 100 °C for 2 hours, and then calcine it in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0098] Example 3

[0099] 7.5 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0100] Example 4

[0101] 15 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0102] Example 5

[0103] 15 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 400 °C for 2 hours to obtain titanium dioxide material.

[0104] Example 6

[0105] 15 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 600 °C for 2 hours to obtain titanium dioxide material.

[0106] Example 7

[0107] 15 mL of the eutectic solvent obtained in Preparation Example 1 and 0.9 mL of distilled water were added to a beaker, and the mixture was magnetically stirred for 20 min to uniformly disperse the distilled water in the eutectic solvent, resulting in a water-in-oil (W / O) microemulsion. Then, 2 mL of tetrabutyl titanate was uniformly added dropwise to the microemulsion, and the mixture was magnetically stirred for another 15 min to obtain a titanium-containing mixture. The titanium-containing mixture was thoroughly washed with anhydrous ethanol and centrifuged at 12000 rpm for 15 min. The precipitate obtained by centrifugation was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 700 °C for 2 hours to obtain titanium dioxide material.

[0108] Comparative Example 1

[0109] Add 0.9 mL of distilled water to a beaker, then add 2 mL of tetrabutyl titanate dropwise, and stir magnetically for 15 min to obtain a titanium-containing mixture. Wash the titanium-containing mixture thoroughly with anhydrous ethanol, and centrifuge at 12000 rpm for 15 min. Dry the precipitate obtained by centrifugation at 100 °C for 2 hours, and then calcine it in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0110] Comparative Example 2

[0111] 10 mL of anhydrous ethanol and 7 mL of distilled water were mixed and magnetically stirred to obtain mixed solution A. 10 mL of tetrabutyl titanate was added to a solution of 12 mL glacial acetic acid and 30 mL anhydrous ethanol to obtain mixed solution B. Mixed solution A was added to mixed solution B, and the mixture was stirred for 2 hours and allowed to stand to obtain a gel mixture. The gel mixture was dried at 100 °C for 2 hours and then calcined in a muffle furnace at 500 °C for 2 hours to obtain titanium dioxide material.

[0112] The titanium dioxide materials of Comparative Example 2 and Example 1 were subjected to UV-Vis absorption spectroscopy measurements, and the spectra are shown below. Figure 3 .Depend on Figure 3 It can be seen that, compared with the titanium dioxide material of Comparative Example 2, the titanium dioxide material of Example 1 has enhanced absorption of visible light across the entire wavelength range.

[0113] Experimental Example

[0114] The performance of titanium dioxide materials was tested by simulating pollutants using the benzoyl carmine experiment.

[0115] 90 mL of benzoyl carmine solution (concentration 30 mg / L) and 30 mg of titanium dioxide material prepared in the examples or comparative examples were placed in a degradation device. After a 20-minute dark reaction under stirring, adsorption equilibrium was reached in the degradation device. Then, the degradation experiment was carried out by a xenon lamp with a fixed current intensity for 140 minutes.

[0116] Every 20 minutes, the solution in the degradation device was aspirated using a pipette. The aspirated solution was then passed through a needle filter and the absorbance was measured using a UV-Vis spectrophotometer.

[0117] The maximum absorption wavelength of benzoyl carmine is 526 nm.

[0118] Formula for calculating degradation rate:

[0119] (A0: initial absorbance of the solution; A: absorbance of the solution after degradation)

[0120] The degradation effect on benzoyl carmine is shown in Table 1.

[0121] Table 1. Degradation effect of titanium dioxide materials on benzodiazepines

[0122] Example 1 86.8 Example 2 65.6 Example 3 77.5 Example 4 80.1 Example 5 73.7 Example 6 71.2 Example 7 61.2 Comparative Example 1 53.6

[0123] As shown in Table 1, compared with Comparative Example 1 without eutectic solvent, Examples 1-7 showed a significant increase in the degradation rate of benzoyl carmine, from 53.6% to 61.2%-86.8%, demonstrating superior photocatalytic performance.

[0124] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing titanium dioxide material, characterized in that, Includes the following steps: (1) The compounds shown in formula (I) and formula (II) with a molar ratio of (1-4):1 are stirred at 60-110 °C to obtain a eutectic solvent; Equation (I) Equation (II) R1 and R2 are independently selected from C-substituted OH, halogen, and hydroxyl groups, respectively. 1-6 Alkyl or C 1-6 Halogenated alkyl groups; (2) The eutectic solvent and water are stirred for the first time to obtain a microemulsion; then titanate is added dropwise to the microemulsion and stirred for the second time to obtain a titanium-containing mixture; the titanate is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetran-n-propyl titanate or tetraoctyl titanate; wherein the volume ratio of the eutectic solvent to water is (9-14):1, and the volume ratio of the eutectic solvent to titanate is (4-6):1; (3) Wash the titanium-containing mixture and centrifuge it; dry the precipitate obtained by centrifugation and then calcine it to obtain titanium dioxide material.

2. The preparation method according to claim 1, characterized in that, R1 and R2 are independently selected from OH, F, Cl, and C with hydroxyl substitution, respectively. 1-3 Alkyl or C 1-3 Halogenated alkyl groups.

3. The preparation method according to claim 1, characterized in that, The first stirring time in step (2) is 10 to 35 minutes; the second stirring time is 7 to 30 minutes.

4. The preparation method according to claim 1, characterized in that, The solvent used for washing in step (3) is selected from one or more of methanol, ethanol, n-propanol or isopropanol.

5. The preparation method according to claim 1, characterized in that, In step (3), the centrifugation speed is 8000-15000 rpm; the centrifugation time is 5-25 min; the drying temperature is 60-150℃; and the drying time is 1-4 h.

6. The preparation method according to claim 1, characterized in that, The calcination temperature in step (3) is 300–900℃; the calcination time is 1–5h.

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