Titanium dioxide / nano-diamond composite material and preparation method thereof

Abstract

The invention provides a titanium dioxide / nano-diamond composite material and a preparation method thereof. The titanium dioxide / nano-diamond composite material is obtained by gelatinizing a surface-modified nano-diamond dispersion mother solution, standing, drying, grinding and finally calcining, the surface modification of the surface-modified nano-diamond is realized through titanium tetraisopropylate. The prepared titanium dioxide / nano-diamond composite material is small and uniform in particle size and has good mechanical performance and optical and electrical characteristics, meanwhile, the deagglomeration of the nano-diamond is achieved, the performance of the nano-diamond is better played, and the titanium dioxide and the nano-diamond generate a synergistic effect.

Description

Technical Field

[0001] The invention relates to the technical field of nano-diamond composite materials, and in particular to a titanium dioxide / nano-diamond composite material and a preparation method thereof. Background Art

[0002] Titanium dioxide is the most widely used photocatalyst due to its wide band gap, good chemical stability, low price, good biocompatibility, good durability, high specific surface area, corrosion resistance and other characteristics. It can be used in antibacterial coatings, water treatment, cosmetics, energy storage, lithium batteries and other fields. However, due to its fast electron-hole recombination rate, its performance is limited. Therefore, the preparation of TiO 2 photocatalytic nanomaterials to improve the photogenerated charge transfer process.

[0003] Nanodiamonds were found in the carbon-containing smoke produced by explosions, and the average particle size of diamond powder is at the nanometer level. At present, the synthesis methods of nanodiamonds include detonation method, laser ablation method, high temperature and high pressure method, chemical vapor deposition method, etc. Because nanodiamonds have unique optical and electrical properties, they can interact with titanium dioxide and then regulate the recombination rate of electron-hole pairs. At the same time, nanodiamonds have low toxicity, large specific surface area, good biocompatibility, excellent mechanical properties, and surface functionalization properties, which are expected to give new properties or synergistic effects in the application field of titanium dioxide. Therefore, nano-titanium dioxide / nano-diamond composites have a very broad application prospect. However, the particle size of the composite material will affect its performance. Since nanodiamonds have a large surface energy and a large van der Waals force between particles, they are very easy to aggregate into agglomerates during application to form submicron particles. The particle size will be seriously affected during the synthesis of nano-titanium dioxide / nano-diamond composites, and the preparation method of the material will also affect the particle size.

[0004] Therefore, keeping the nano-diamond in a stable and uniform dispersion during the material preparation process and preparing a titanium dioxide / nano-diamond composite material with a smaller particle size is the key to its excellent performance. Therefore, finding a nano-diamond dispersion with good dispersibility, long-term stable dispersibility, and a green and simple manufacturing process and a method for preparing a nano-titanium dioxide / nano-diamond composite material with a smaller particle size will greatly enhance the application value of the composite material. In the prior art, the nano-diamond particles are given dispersibility by modifying the surface of the nano-diamond particles, thereby inhibiting aggregation.

[0005] Chinese patent CN 109071235 B discloses surface-modified nanodiamonds, organic solvent dispersions thereof and methods for preparing the same. The surface-modified nanodiamonds are obtained by reacting nanodiamonds with nitrile compounds in the presence of an acid catalyst. Since the generated -NHCOR groups have excellent affinity for organic solvents, the nanodiamonds can be easily dispersed in organic solvents.

[0006] Chinese patent CN 111683899 A discloses a nano-diamond particle dispersion, wherein the nano-diamond particle dispersion has nano-diamond particles with a silane compound (excluding a silane compound having a (meth)acryloyl group) bonded to the surface and a particle size (D50) in the range of 2 to 100 nm dispersed in a SP value of 8.0 to 14.0 (cal / cm 3 ) 1 / 2 The nano-diamond particle dispersion has a structure in which the surfaces of the nano-diamond particles contained therein are modified by a silane compound, and the surface modification portion becomes a steric hindrance, thereby suppressing the aggregation of the nano-diamond particles, and thus has high dispersibility. Summary of the invention

[0007] Aiming at a series of problems in the prior art, such as the high electron-hole recombination rate of nano titanium dioxide and the large particle size of the prepared composite material, the present application proposes a titanium dioxide / nano-diamond composite material and a preparation method thereof. In a mixed solution of ethanol and titanium tetraisopropoxide adjusted to a certain pH value by acetic acid, nano-diamond agglomerates are deagglomerated by cell crushing, and titanium tetraisopropoxide is chemically grafted to the surface of nano-diamonds, which provides a strong steric hindrance effect to hinder the agglomeration of nano-diamonds and forms a three-dimensional network structure with nano-diamonds to hinder the precipitation of nano-diamonds; acetic acid promotes the formation of the three-dimensional network structure to hinder the precipitation of nano-diamonds, thereby obtaining a nano-diamond fully suspended and dispersed mother liquor, and then the mother liquor is subjected to pH adjustment, gelation, drying, grinding, and calcination operations to obtain a titanium dioxide / nano-diamond composite material. The titanium dioxide / nano-diamond composite material has a small and uniform particle size, good mechanical properties, and optical and electrical properties, and at the same time, the deagglomeration of nano-diamonds is achieved, so that the performance of nano-diamonds can be better exerted, and the two can have a synergistic effect, and have a huge application prospect.

[0008] A titanium dioxide / nano-diamond composite material is obtained by gelling a surface-modified nano-diamond dispersed mother liquid, first standing and drying, then grinding, and finally calcining; the surface-modified nano-diamond is surface-modified by titanium tetraisopropoxide.

[0009] The particle size of the nano-diamond is 5 nm.

[0010] The particle size of the titanium dioxide / nano-diamond composite material is less than 20 nm. The particle size of the composite material obtained in the present application is better than that of the composite material in the prior art. Since the particle size of the composite material in the present application is small, the specific surface area will be large, and the active sites will be increased, so the application effect is more excellent.

[0011] A method for preparing a titanium dioxide / nano-diamond composite material comprises the following steps: (1) mixing titanium tetraisopropoxide and an ethanol solution and stirring them uniformly, and then dripping acetic acid until the pH value is 4-5; (2) adding nano-diamonds to the solution obtained in step (1), and then crushing the cells in an ice bath for 12-24 hours; (3) centrifuging the mixed liquid after the cell crushing in step (2) at a certain speed to obtain a uniform upper dispersion mother liquor after centrifugation; and (4) adding acid to the dispersion mother liquor obtained in step (3) to adjust the pH value, and drying, grinding, and calcining the dispersion mother liquor after standing at 40-50°C to form a gel to obtain the titanium dioxide / nano-diamond composite material.

[0012] In the above step (1), the volume ratio of titanium tetraisopropoxide to ethanol is 1:(6-8). The content of ethanol in the ethanol solution is 80-95%. Too high a content of titanium tetraisopropoxide will cause the system to easily form a gel, and the system may have gelled before the ultrasound reaches the expected effect.

[0013] In the above step (2), the concentration of nano-diamond in the solution is 0.1-2.0wt%.

[0014] The centrifugal speed of the above step (3) is 3000-9000r / min, and continuous long-term cell disruption can effectively disintegrate the agglomerates. The upper uniform suspension obtained in step (3) of the present application is dispersed in an organic solvent to obtain a nano-diamond fully suspended organic solvent dispersion; the organic solvent can be selected from any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and acetonitrile (ACN); the volume ratio of the suspension to the organic solvent is 1: (0.5-100).

[0015] In the above step (4), the pH is adjusted to 2.5-3.5, and the acid used can be common acids such as hydrochloric acid or nitric acid; the drying conditions are: baking at 70-90°C for 24-48h; the grinding time is 5-10min; and the calcination conditions are: heating at 400°C for 2-3h.

[0016] The specific operation of the above step (4) is as follows: after obtaining the nano-diamond dispersion mother solution, add an appropriate amount of hydrochloric acid to adjust the system pH to 2.5-3.5, stand the dispersion mother solution at 40-50°C until the system gels, and after the gel is formed, bake at 70-90°C for 24-48h until the system is completely dried, grind with an agate mortar for 5-10min, and heat at 400°C for 2-3h to obtain anatase TiO 2-ND composite material.

[0017] The titanium dioxide / nano-diamond composite material can be applied to the fields of membrane materials, lithium batteries, coating materials, cosmetics, photocatalysis, and lubrication and polishing.

[0018] Compared with the prior art, this application has the following advantages:

[0019] (1) The dispersion mother liquor can make nanodiamonds fully suspended and uniformly and stably dispersed in a variety of organic solvents; chemically grafted titanium tetraisopropoxide can provide a strong steric hindrance effect, which can effectively hinder the agglomeration of nanodiamonds; acetic acid slowly hydrolyzes titanium tetraisopropoxide to form a three-dimensional network structure with nanodiamonds, which can effectively hinder the sedimentation of nanodiamonds and provide excellent full suspension; the titanium dioxide / nanodiamond composite material prepared in this way has a small and uniform particle size, good mechanical properties and optical and electrical properties, and at the same time achieves the deagglomeration of nanodiamonds, so that the performance of nanodiamonds can be better exerted, so that the two have a synergistic effect.

[0020] (2) The preparation method is green, simple and low-cost.

[0021] Titanium tetraisopropoxide can be grafted onto the surface of nanodiamonds, thereby connecting the nanodiamonds after cell crushing and dispersion, and crosslinking them into a three-dimensional network in space, so that the nanodiamonds can be stably dispersed in the dispersion mother solution. At the same time, titanium tetraisopropoxide provides a strong steric hindrance effect to prevent the agglomeration of nanodiamonds, such as Figure 1 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of the mechanism of nanodiamond being fully suspended and evenly and stably dispersed in an organic solvent;

[0023] Figure 2 This is a comparison diagram of the nano-diamond fully suspended organic solvent dispersions of different volume ratios in Example 1 after being placed for 7 days;

[0024] Figure 3 This is a comparison diagram of the nano-diamond fully suspended organic solvent dispersions of different volume ratios in Example 2 after being placed for 7 days;

[0025] Figure 4 This is a comparison diagram of the nano-diamond fully suspended organic solvent dispersions of different volume ratios in Example 3 after being placed for 7 days;

[0026] Figure 5 This is a comparison diagram of the nano-diamond fully suspended organic solvent dispersions of different volume ratios in Example 4 after being placed for 7 days;

[0027] Figure 6This is a comparison diagram of the nano-diamond fully suspended organic solvent dispersions of different volume ratios in Example 5 after being placed for 7 days;

[0028] Figure 7 is a comparison diagram of the nano-diamond organic solvent dispersions with different volume ratios in Comparative Example 1 after being left for 7 days;

[0029] Figure 8 is a comparison diagram of the nano-diamond organic solvent dispersions with different volume ratios in Comparative Example 2 after being left for 7 days;

[0030] Fig. 9 According to the anatase TiO obtained in Example 1 2 -ND composite material, which can be compared with anatase TiO 2 The XRD of the standard card and ND corresponded, indicating that the composite material was successfully prepared;

[0031] Fig.10 The anatase TiO obtained in Comparative Example 3 2 -SEM image (a) and local magnified image (b) of ND composite material;

[0032] Fig.11 Anatase TiO obtained in Example 1 2 -SEM image (c) and local magnified image (d) of ND composite material;

[0033] Fig.12 40 mg of TiO prepared in Comparative Example 3 and Example 1 were respectively added. 2 -ND particle size distribution measured after 1h ultrasonic dispersion in 4ml of anhydrous ethanol;

[0034] Fig.13 This is a partial enlarged view of Example 1 ( Fig.11 d) The particle size statistics of 50 randomly selected particles and the partial enlarged image of comparative example 3 ( Fig.10 b) Particle size statistics obtained by randomly selecting 50 particles. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] A method for preparing a nano-diamond fully suspended organic solvent dispersion comprises the following steps:

[0038] (1) Take 4.6 mL of titanium tetraisopropoxide and 36.8 mL of 80% ethanol solution, mix and stir for 5 min until the solution is uniform and transparent; add 13.5 mL of acetic acid dropwise to the solution to make the pH value 4.0;

[0039] (2) adding 0.9842 g of 5 nm nanodiamond to the solution prepared in the first step, and disrupting the cells in an ice bath for 12 hours;

[0040] (3) centrifuging the mixed liquid obtained in the second step at 9000 r / min for 5 min, and taking the upper uniform suspension after centrifugation;

[0041] 3.5mL, 2mL, 1mL, 0.45mL, and 0.05mL of the upper uniform suspension after the third step of centrifugation were taken, respectively, and added to 1.75mL, 2mL, 5mL, 4.5mL, and 5mL of DMF, respectively, to prepare nanodiamond DMF dispersions with a volume ratio of nanodiamond upper uniform suspension to DMF of 2:1, 1:1, 1:5, 1:10, and 1:100. Figure 2 The glass bottles shown correspond from left to right.

[0042] (4) Take 5 mL of the upper uniform suspension after the third step of centrifugation, add an appropriate amount of hydrochloric acid to adjust the pH of the system to 3, and stand the dispersed mother liquor at 45°C until the system gels. After the gel is formed, bake at 80°C for 24 h until the system is completely dried. After grinding with an agate mortar for 10 min, heat at 400°C for 2 h to obtain anatase TiO 2 -ND composite material, particle size is 5.64nm, particle size distribution is as follows Fig.13 shown.

[0043] Example 2

[0044] A method for preparing a nano-diamond fully suspended organic solvent dispersion comprises the following steps:

[0045] (1) Take 5.1 mL of titanium tetraisopropoxide and 30.6 mL of 95% ethanol solution, mix and stir for 5 min until the solution is uniform and transparent; add 9 mL of acetic acid dropwise to the solution to make the pH value 4.5;

[0046] (2) adding 0.0390 g of 5 nm nanodiamond to the solution prepared in the first step, and disrupting the cells in an ice bath for 12 hours;

[0047] (3) centrifuging the mixed liquid obtained in the second step at 3000 r / min for 5 min, and taking the upper uniform suspension after centrifugation;

[0048] 3.5mL, 2mL, 1mL, 0.45mL, and 0.05mL of the upper uniform suspension after the third step of centrifugation were taken, respectively, and added to 1.75mL, 2mL, 5mL, 4.5mL, and 5mL of DMF, respectively, to prepare nanodiamond DMF dispersions with a volume ratio of nanodiamond upper uniform suspension to DMF of 2:1, 1:1, 1:5, 1:10, and 1:100. Figure 3 The glass bottles shown correspond from left to right.

[0049] (4) Take 5 mL of the upper uniform suspension after the third step of centrifugation, and after obtaining the nano-diamond dispersion mother solution, add an appropriate amount of hydrochloric acid to adjust the system pH to 2.5. At 40°C, the dispersion mother solution is allowed to stand until the system gels. After the gel is formed, it is dried at 90°C for 24 hours until the system is completely dried. After grinding with an agate mortar for 5 minutes, it is heated at 400°C for 2 hours to obtain anatase TiO 2 -ND composite material, with a particle size of 5.47 nm.

[0050] Example 3

[0051] A method for preparing a nano-diamond fully suspended organic solvent dispersion comprises the following steps:

[0052] (1) Take 4.6 mL of titanium tetraisopropoxide and 36.8 mL of 80% ethanol solution, mix and stir for 5 min until the solution is uniform and transparent; add 5.3 mL of acetic acid dropwise to the solution to make the pH value 5.0;

[0053] (2) adding 0.4060 g of 5 nm nanodiamond to the solution prepared in the first step, and disrupting the cells in an ice bath for 12 hours;

[0054] (3) centrifuging the mixed liquid obtained in the second step at 9000 r / min for 5 min, and taking the upper uniform suspension after centrifugation;

[0055] 3.5mL, 2mL, 1mL, 0.45mL, and 0.05mL of the upper uniform suspension after the third step of centrifugation were taken, respectively, and added to 1.75mL, 2mL, 5mL, 4.5mL, and 5mL of DMAC, respectively, to prepare nanodiamond DMAC dispersions with a volume ratio of nanodiamond upper uniform suspension to DMAC of 2:1, 1:1, 1:5, 1:10, and 1:100. Figure 4 The glass bottles shown correspond from left to right.

[0056] (4) Take 5 mL of the upper uniform suspension after the third step of centrifugation, add an appropriate amount of hydrochloric acid to adjust the pH of the system to 3.5, and stand the mother liquor at 50°C until the system gels. After the gel is formed, bake at 90°C for 24 h until the system is completely dried. After grinding with an agate mortar for 10 min, heat at 400°C for 3 h to obtain anatase TiO 2 -ND composite material, with a particle size of 5.89 nm.

[0057] Example 4

[0058] A method for preparing a nano-diamond fully suspended organic solvent dispersion comprises the following steps:

[0059] (1) Take 2.9 mL of titanium tetraisopropoxide and 20.3 mL of 95% ethanol solution, mix and stir for 10 min until the solution is uniform and transparent; add 3.4 mL of acetic acid dropwise to the solution to make the pH value 5.0;

[0060] (2) adding 0.1130 g of 5 nm nanodiamond to the dispersion prepared in the second step, and disrupting the cells in an ice bath for 12 hours;

[0061] (3) centrifuging the mixed liquid obtained in the second step at 9000 r / min for 5 min, and taking the upper uniform suspension after centrifugation;

[0062] 3.5mL, 2mL, 1mL, 0.45mL, and 0.05mL of the upper uniform suspension after the third step of centrifugation were taken and added to 1.75mL, 2mL, 5mL, 4.5mL, and 5mL of DMSO, respectively, to prepare nanodiamond DMSO dispersions with a volume ratio of 2:1, 1:1, 1:5, 1:10, and 1:100 between the upper uniform suspension of nanodiamond and DMSO. Figure 5 The glass bottles shown correspond from left to right.

[0063] (4) Take 5 mL of the upper uniform suspension after the third step of centrifugation, add an appropriate amount of hydrochloric acid to adjust the pH of the system to 3.5, and stand the mother liquor at 40°C until the system gels. After the gel is formed, bake at 70°C for 48 hours until the system is completely dried. After grinding with an agate mortar for 10 minutes, heat at 400°C for 3 hours to obtain anatase TiO 2 -ND composite material, with a particle size of 6.14 nm.

[0064] Example 5

[0065] A method for preparing a nano-diamond fully suspended organic solvent dispersion comprises the following steps:

[0066] (1) Take 2.4 mL of titanium tetraisopropoxide and 14.4 mL of 85% ethanol solution, mix and stir for 8 min until the solution is uniform; add 4.2 mL of acetic acid dropwise to the solution to make the pH value 4.5;

[0067] (2) adding 0.3709 g of 5 nm nanodiamond to the dispersion prepared in the second step, and disrupting the cells in an ice bath for 24 hours;

[0068] (3) centrifuging the mixed liquid obtained in the second step at 9000 r / min for 5 min, and taking the upper uniform suspension after centrifugation;

[0069] 3.5mL, 2mL, 1mL, 0.45mL, and 0.05mL of the upper uniform suspension after the third step of centrifugation were taken, respectively, and added to 1.75mL, 2mL, 5mL, 4.5mL, and 5mL of ACN, respectively, to prepare nanodiamond ACN dispersions with a volume ratio of nanodiamond upper uniform suspension to ACN of 2:1, 1:1, 1:5, 1:10, and 1:100. Figure 6 The glass bottles shown correspond from left to right.

[0070] (4) Take 5 mL of the upper uniform suspension after the third step of centrifugation, add an appropriate amount of hydrochloric acid to adjust the pH of the system to 2.5, and stand the mother liquor at 45°C until the system gels. After the gel is formed, bake at 80°C for 36 hours until the system is completely dried. After grinding with an agate mortar for 8 minutes, heat at 400°C for 2 hours to obtain anatase TiO 2 -ND composite material, with a particle size of 5.73 nm.

[0071] Comparative Example 1

[0072] The difference between Comparative Example 1 and Example 1 is that: in step (1) of Comparative Example 1, 4.6 mL of titanium tetraisopropoxide and 36.8 mL of 80% ethanol solution are respectively taken, mixed and stirred for 10 min until the solution is uniform and transparent; the other steps are the same as those of Example 1. Anatase TiO 2 -ND composite material.

[0073] Comparative Example 1 Figure 7 As shown in the figure, it can be seen that the nanodiamonds have sunk to the bottom of the bottle and failed to achieve full suspension. That is, without the effect of acetic acid, the sol is extremely unstable and quickly gels, and it is impossible to slowly hydrolyze titanium tetraisopropoxide and form a three-dimensional network structure with nanodiamonds. There is not enough time for the nanodiamonds to be suspended and stably dispersed in the system. Therefore, the anatase TiO 2 The particle size of the -ND composite material is obviously larger and more non-uniform than that of the example.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is that: in step (1) of Comparative Example 2, 36.8 mL of 80% ethanol solution is stirred for 5 min until the solution is uniform and transparent; 13.5 mL of acetic acid is added dropwise to the resulting solution to make the pH value 4.0; the other steps are the same as in Example 1.

[0076] Comparative Example 2 Figure 8 As shown, it can be seen from the figure that the nanodiamond has sunk to the bottom of the bottle and failed to achieve full suspension. Comparison of the results of Comparative Example 2 with Example 1 shows that titanium tetraisopropoxide can be grafted onto the surface of the nanodiamond, thereby connecting the nanodiamonds after cell crushing and dispersion, and crosslinking into a three-dimensional network in space, so that the nanodiamonds are fully suspended and stably dispersed in the organic solvent. At the same time, titanium tetraisopropoxide provides a strong steric hindrance effect to hinder the agglomeration of nanodiamonds. Therefore, Comparative Example 2 cannot form the composite material of the present application.

[0077] Comparative Example 3

[0078] The difference between Comparative Example 3 and Example 1 is that: in Comparative Example 3, tetrabutyl titanate is used to replace titanium tetraisopropoxide; the rest is the same as in Example 1. The particle size of the composite material is 7.52 nm, and the particle size distribution is as follows: Fig.13 shown.

[0079] like Fig.10 and Fig.11 As shown, TiO obtained using titanium tetraisopropoxide 2 -ND has a smaller and more concentrated average particle size, and the material morphology is more uniform. 2 They are often dispersed in anhydrous ethanol for subsequent application, so the dispersion of the two in ethanol was tested. Fig.12 As shown, it can be seen that TiO prepared using titanium tetraisopropoxide 2 -ND has a smaller particle size in anhydrous ethanol and has better dispersibility.

[0080] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A titanium dioxide / nano-diamond composite material, characterized in that: The titanium dioxide / nano-diamond composite material is obtained by gelling a surface-modified nano-diamond dispersed mother solution, first standing and drying, then grinding, and finally calcining; the surface-modified nano-diamond is surface-modified by titanium tetraisopropoxide.

2. The titanium dioxide / nano-diamond composite material according to claim 1, characterized in that: The nano-diamond particle size is 5 nm.

3. The titanium dioxide / nano-diamond composite material according to claim 1, characterized in that: The particle size of the titanium dioxide / nano-diamond composite material is less than 20 nm.

4. A method for preparing a titanium dioxide / nano-diamond composite material according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: (1) mixing titanium tetraisopropoxide and an ethanol solution and stirring them uniformly, and then dripping acetic acid until the pH value is 4-5; (2) adding nano-diamonds to the solution obtained in step (1), and then breaking the cells in an ice bath for 12-24 hours; (3) centrifuging the mixed liquid after the cell breaking in step (2) at a certain speed to obtain a uniform upper dispersion mother liquor after centrifugation; and (4) adding acid to the dispersion mother liquor obtained in step (3) to adjust the pH value, and drying, grinding, and calcining the mixture after standing at 40-50°C to form a gel to obtain a titanium dioxide / nano-diamond composite material.

5. The preparation method according to claim 4, characterized in that: In the step (1), the volume ratio of titanium tetraisopropoxide to ethanol is 1:(6-8).

6. The preparation method according to claim 4, characterized in that: In the step (2), the concentration of nano-diamond in the solution is 0.1-2.0 wt %.

7. The preparation method according to claim 4, characterized in that: The centrifugal speed in step (3) is 3000-9000 r / min.

8. The preparation method according to claim 4, characterized in that: In the step (4), the pH is adjusted to 2.5-3.5, and the acid used is hydrochloric acid or nitric acid.

9. The preparation method according to claim 4, characterized in that: The drying conditions of step (4) are: drying at 70-90° C. for 24-48 hours; the grinding time is 5-10 minutes; and the calcination conditions are: heating at 400° C. for 2-3 hours.

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