A method for preparing hollow spherical inorganic oxides based on self-assembly

Abstract

The application discloses a preparation method of hollow spherical inorganic oxide based on self-assembly, which comprises the following steps: (1) mixing a passivator with an inorganic oxide precursor, passivating and protecting the inorganic oxide precursor through an ester exchange or chelation reaction, adding water or an aqueous solution with a pH of 4-14 to pre-crosslink, and obtaining a solution A containing a composite precursor with amphiphilic properties; (2) mixing the solution A with a non-polar compound to prepare a solution B, dispersing the solution B in water or an aqueous solution with a pH of 4-14 to form an oil-in-water structure, stirring for more than 6 hours, and then washing and drying to obtain a hollow spherical oxide precursor; and (3) calcining the hollow spherical oxide precursor to obtain a hollow spherical inorganic oxide. The method does not need an interface agent, a hard template or a high-temperature and high-pressure environment, and has the advantages of low cost, expandability, simple preparation and green safety.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for preparing self-assembled, surfactant-free hollow spherical inorganic oxides. Background Technology

[0002] Hollow spherical inorganic oxides have shown great potential in applications such as optoelectronics, catalysis, energy storage, biomedicine, and dyes due to their unique structural characteristics (high specific surface area, low density, and hollow structure).

[0003] Traditional preparation methods include hard template methods (such as using polystyrene microspheres as templates), soft template methods (requiring the addition of surfactants, etc.), and solvothermal methods. However, these methods often have the following problems: removing hard templates may require etching with chemical reagents or high-temperature calcination, which can easily lead to material structure collapse and is a complex process; the presence of surfactants and other interfacial agents can easily introduce impurities that are difficult to remove; and solvothermal methods require a high-temperature and high-pressure environment. These drawbacks significantly limit the application and development of hollow inorganic oxides. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing hollow inorganic oxides that does not require complex preparation processes such as interface agents, hard templates, or high temperature and high pressure, and has a wide range of applications.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing hollow spherical inorganic oxides based on self-assembly, wherein the inorganic oxides are inorganic metal oxides or silicon oxides, and the preparation method includes the following steps: (1) First, the passivating agent is mixed with the inorganic oxide precursor, and the inorganic oxide precursor is passivated and protected by transesterification or chelation reaction. The passivating agent and the inorganic oxide precursor are fed in a ratio of 10%-100% to achieve the theoretical passivation ratio of hydrolyzable functional groups of the inorganic oxide precursor. Then, water or an aqueous solution with a pH of 4-14 is added for pre-crosslinking. The molar amount of water added is 0%-100% of the molar amount of hydrolyzable functional groups in the inorganic oxide precursor (when it is 0%, that is, no pre-crosslinking is performed after passivation, and step (2) is performed directly), to obtain a solution A containing an amphiphilic composite precursor. The passivating agent is selected from at least one of β-dicarbonyl compounds, ester compounds, acetal compounds, and ketal compounds. The inorganic oxide precursor is selected from at least one of alkoxide compounds and β-diketone compounds. At least one of the passivating agent and the inorganic oxide precursor is a liquid at room temperature. (2) Solution A is mixed with a nonpolar compound in a volume ratio of 1:0.1-1:10 to prepare solution B. Solution B is then dispersed in water or an aqueous solution with a pH of 4-14 to form an oil-in-water structure. The reaction is stirred for more than 6 hours, and then washed and dried to obtain a hollow spherical oxide precursor. The nonpolar compound is selected from one or more of benzene compounds, alkane compounds or ester compounds, and the volume ratio of solution B to water or an aqueous solution with a pH of 4-14 is 1:0.1-1:100. (3) The hollow spherical oxide precursor is calcined to promote further dehydration and condensation of the hollow spherical oxide precursor, and at the same time remove the residual passivating agent. After calcination, hollow spherical inorganic oxide is obtained.

[0006] In this invention, the inorganic oxide is an inorganic metal oxide or silicon oxide. In some embodiments, the inorganic metal oxide is titanium oxide, zirconium oxide, aluminum oxide, niobium oxide, tantalum oxide, vanadium oxide, tin oxide, or cobalt oxide.

[0007] In this invention, the inorganic oxide precursor is selected from at least one of alkoxide compounds and β-diketone compounds. In some embodiments, the alkoxide compound may be at least one of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetrabutyl zirconate, tetraethyl zirconate, aluminum sec-butoxide, aluminum isopropoxide, aluminum n-butoxide, tetraethyl orthosilicate, hyperbranched polyethoxysiloxane, pentaethyl niobate, pentabutyl tantalate, triisopropoxide, and tetrabutyl stannate. In some embodiments, the β-diketone compound may be at least one of zirconium acetylacetonate, vanadium diacetylacetonate, aluminum acetylacetonate, cobalt acetylacetonate, and titanium diisopropoxybisacetylacetonate.

[0008] In this invention, the passivating agent is selected from at least one of β-dicarbonyl compounds, ester compounds, acetal compounds, and ketal compounds. In some embodiments, the β-dicarbonyl compound may be at least one of acetylacetone, benzoylacetone, ethyl acetoacetate, isobutyl acetoacetate, and ethyl trifluoroacetoacetate; the ester compound may be at least one of diethyl malonate and methyl benzoate; the acetal compound may be at least one of 1,3-dioxolane, formaldehyde dimethyl acetal, and acetaldehyde diethanolyl acetal; and the ketal compound may be at least one of acetone dimethyl acetal and cyclohexanone ethylene glycol acetal. Preferably, the passivating agent is acetylacetone, diethyl malonate, methyl benzoate, or 1,3-dioxolane.

[0009] In step (1) of this invention, the passivating agent is mixed with the inorganic oxide precursor, and the inorganic oxide precursor is passivated and protected by transesterification or chelation reaction, so that the passivation ratio of the hydrolyzable functional groups of the inorganic oxide precursor is 10%-100%. In some embodiments, the feed ratio of the passivating agent to the inorganic oxide precursor is controlled so that the passivation ratio of the hydrolyzable functional groups of the inorganic oxide precursor is 50%-100%, preferably 50-75%. In some embodiments, after the passivating agent and the inorganic oxide precursor are mixed, the transesterification or chelation reaction between the passivating agent and the inorganic oxide precursor can be promoted by stirring at room temperature to achieve passivation protection of the inorganic oxide precursor. The stirring time at room temperature is 0-72 h, preferably 20-30 h.

[0010] In step (1) of this invention, after passivation, step (2) can be performed directly, or water or an aqueous solution with a pH of 4-14 can be added for pre-crosslinking. The molar amount of water added is 0%-100% of the molar amount of hydrolyzable functional groups in the inorganic oxide precursor, resulting in a solution A containing an amphiphilic composite precursor. In some embodiments, the water or aqueous solution with a pH of 4-14 can be water, a NaOH aqueous solution with a pH below 14, or an HCl solution with a pH above 4. In some embodiments, the molar amount of water added is 0%-50% of the molar amount of hydrolyzable functional groups in the inorganic oxide precursor, preferably 0-30%. In some embodiments, the pre-crosslinking temperature is room temperature, and the pre-crosslinking time does not exceed 48 h, preferably 1-15 h, more preferably 8-15 h, and most preferably 12 h.

[0011] In step (2) of this invention, the nonpolar compound is selected from one or more mixtures of benzene compounds, alkane compounds, and ester compounds. In some embodiments, the benzene compounds may be at least one of benzene, toluene, ethylbenzene, xylene, dodecylbenzene, and hexadecylbenzene; the alkane compounds may be at least one of n-pentane, n-hexane, n-heptane, n-octane, n-decane, n-dodecane, n-hexadecane, white oil, and liquid paraffin; and the ester compounds may be at least one of ethyl acetate, butyl acetate, ethyl propionate, methyl butyrate, isooctyl acetate, and dioctyl adipate.

[0012] In step (2) of this invention, the water or aqueous solution with a pH of 4-14 can be water, NaOH aqueous solution with a pH below 14, or HCl solution with a pH above 4.

[0013] In step (2) of the present invention, the volume ratio of solution A to nonpolar compound is 1:0.1-1:10, preferably 1:0.5-1.5, and more preferably 1:1.

[0014] In step (2) of the present invention, the volume ratio of solution B to water or aqueous solution with pH 4-14 is 1:0.1-1:100, preferably 1:10-30, and more preferably 1:20.

[0015] In step (2) of this invention, solution B is dispersed in water or an aqueous solution with a pH of 4-14 to form an oil-in-water structure. In some embodiments, solution B is dispersed in water or an aqueous solution with a pH of 4-14. The dispersion method can be a homogenizer or ultrasound. The homogenizer speed can be above 10,000 rpm, and the homogenization time can be 10 s-20 min. The ultrasound dispersion power can be 100 W-1200 W, preferably 500-1000 W, and the ultrasound time can be 3 min-20 min, preferably 5-15 min.

[0016] In step (2) of this invention, the stirring reaction process can be magnetic stirring or mechanical stirring, with a rotation speed of 100 rpm or more and a stirring time of 6 hours or more.

[0017] In step (2) of the present invention, the washing process can be water or ethanol.

[0018] In step (2) of this invention, the drying can be blower drying or vacuum drying, and the temperature is above room temperature.

[0019] In step (3) of this invention, hollow inorganic oxides are obtained by calcining to remove hydroxyl groups and passivating agents from the hollow spherical oxide precursor. During the calcination process, the hollow structure is maintained. In some embodiments, the calcination temperature is 300-800℃ and the calcination time is 1-6 h.

[0020] The main mechanism of this invention is to first passivate and protect the inorganic oxide precursor through transesterification or chelation reaction, thereby generating an amphiphilic (hydrophilic and lipophilic) composite precursor. This precursor is then mixed with a nonpolar compound, and under external energy input, forms an oil-in-water structure. The final reaction results in a stable hollow spherical oxide precursor. This hollow spherical oxide precursor is then calcined at high temperature to remove most of the hydroxyl groups and passivating agent, yielding hollow inorganic oxides. This invention modifies the inorganic oxide precursor to acquire amphiphilicity, allowing the method to be extended to the preparation of numerous inorganic oxides, demonstrating significant application potential.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes a self-assembly preparation method for hollow spherical inorganic oxides without the need for interfacial agents. Since this method does not require interfacial agents, hard templates, or high temperature and high pressure environments, it has the advantages of low cost, scalability, simple preparation, and green safety.

[0022] 2. This invention modifies inorganic oxide precursors to be amphiphilic, making the method universal and thus applicable to the preparation of many inorganic oxides. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required in the embodiments will be briefly introduced below. The following drawings only show some embodiments and comparative examples of the present invention, and therefore should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 (a) Transmission scanning electron microscope (TEM) image of hollow spherical alumina prepared in Example 1, (b) Fourier transform infrared spectrum comparison of hollow spherical alumina prepared in Example 1 before and after calcination, (c) Physical image of hollow spherical alumina prepared in Example 1 before calcination, (d) Physical image of hollow spherical alumina prepared in Example 1 after calcination. Figure 2 SEM image of the hollow spherical titanium dioxide prepared in Example 2; Figure 3 SEM image (a) and TEM image (b) of the hollow spherical zirconia prepared in Example 3; Figure 4 SEM image of the hollow spherical titanium dioxide prepared in Example 4; Figure 5 SEM image of alumina prepared in Comparison Example 1; Figure 6 SEM image of titanium oxide prepared in Comparative Example 2. Detailed Implementation

[0025] The present invention is further described below through specific embodiments, but these specific embodiments should not be considered as limitations on the present invention, but are only for further illustrating the features and properties of the present invention.

[0026] Example 1

[0027] (1) Preparation of passivated pre-crosslinked alumina precursor

[0028] First, diethyl malonate and aluminum isopropoxide were mixed at a molar ratio of 2:1 (the theoretical passivation ratio of hydrolyzable functional groups in aluminum isopropoxide is 67%) and stirred at 500 rpm for 24 h to protect aluminum isopropoxide by chelation. Then, an aqueous solution of NaOH with pH=10 (the molar amount of water is 22% of the molar amount of hydrolyzable functional groups in aluminum isopropoxide) was added at a molar ratio of aluminum isopropoxide to water of 1.5:1 and stirred again for 12 h to obtain solution A containing the passivated pre-crosslinked alumina precursor.

[0029] (2) Solution A was mixed with xylene at a volume ratio of 1:1 to obtain solution B. Finally, solution B and a NaOH aqueous solution with pH=10 were mixed at a volume ratio of 1:20 by ultrasonication. The ultrasonic power was 700 W, and the ultrasonication time was 10 min. Then, the mixture was stirred at 500 rpm for 12 h. After washing with ethanol, the mixture was then subjected to a 60°C solution. o Hollow spherical active alumina (incompletely hydrolyzed and condensed) was obtained by drying in a C-type forced-air oven for 24 h, and then further dried at 800 °C. o Hollow spherical alumina was obtained by calcination at C for 4 h, and its TEM image is shown below. Figure 1 .

[0030] Example 2

[0031] (1) Preparation of passivated titanium oxide precursor

[0032] First, methyl benzoate and tetraethyl titanate were mixed at a molar ratio of 3:1 (the theoretical passivation ratio of hydrolyzable groups in tetraethyl titanate is 75%) and stirred at 500 rpm for 24 h. Tetraethyl titanate was protected by transesterification to obtain solution A containing the passivated tetraethyl titanate precursor.

[0033] (2) Solution A was mixed with toluene at a volume ratio of 1:1 to obtain solution B. Finally, solution B and a pH=4 HCl aqueous solution were mixed by ultrasonication at a volume ratio of 1:20. The ultrasonic power was 700 W and the ultrasonication time was 10 min. Then, the mixture was stirred at 500 rpm for 12 h. After washing with ethanol, the mixture was then subjected to a 60°C solution. o Dry in a forced-air oven at C for 24 hours, then further dry at 800°C. o Hollow spherical titanium oxide was obtained by calcination at C for 4 h, and its SEM image is shown below. Figure 2 .

[0034] Example 3

[0035] (1) Preparation of passivated pre-crosslinked zirconia precursor

[0036] First, 1,3-dioxolane and tetrabutyl zirconate were mixed at a molar ratio of 3:1 (the theoretical passivation ratio of hydrolyzable groups in tetrabutyl zirconate is 75%) and stirred for 24 h at 500 rpm. Then, an aqueous solution of NaOH with pH=10 was added at a molar ratio of 2:1 (tetrabutyl zirconate:water) and stirred again for 12 h to obtain solution A containing the passivated pre-crosslinked zirconium oxide precursor.

[0037] (2) Solution A was mixed with xylene at a volume ratio of 1:1 to prepare solution B. Finally, solution B and a NaOH aqueous solution with pH=10 were mixed by ultrasonication at a volume ratio of 1:20. The ultrasonic power was 700 W and the ultrasonication time was 10 min. Then, the mixture was stirred at 500 rpm for 12 h. After washing with ethanol, the mixture was then subjected to a 60°C solution. o Dry in a forced-air oven at C for 24 hours, then further dry at 800°C. o Hollow spherical zirconium oxide was obtained by calcination at C for 4 h. Its SEM and TEM images are shown below. Figure 3 .

[0038] Example 4

[0039] (1) Preparation of passivated titanium oxide precursor

[0040] First, trifluoroacetylacetone and titanium acetylacetone were mixed at a molar ratio of 1:1 (the theoretical passivation ratio of hydrolyzable groups in titanium acetylacetone is 50%) and stirred at 500 rpm for 24 h to prepare solution A containing the passivated zirconium oxide precursor.

[0041] (2) Solution A was mixed with ethyl acetate at a volume ratio of 1:1 to prepare solution B. Finally, solution B and a NaOH aqueous solution with pH=13 were mixed at a volume ratio of 1:20 using a homogenizer at 20,000 rpm for 3 minutes. The mixture was then stirred at 500 rpm for 12 hours. After washing with ethanol, the solution was heated to 60 °C. o Dry in a C-type forced-air oven for 24 hours, then at 800°C. o Hollow spherical titanium oxide was obtained by calcination in a muffle furnace of C for 4 hours. Its SEM image is shown below. Figure 4 .

[0042] Compare with Example 1

[0043] It prepares alumina using the same method, but without adding a passivating agent.

[0044] (1) Preparation of pre-crosslinked alumina precursor

[0045] First, aluminum isopropoxide and a NaOH aqueous solution with pH=10 were mixed at a molar ratio of 1.5:1 and stirred for 12 h to prepare solution A containing a pre-crosslinked alumina precursor. The stirring speed was 500 rpm.

[0046] (2) Solution A was mixed with xylene at a volume ratio of 1:1 to prepare solution B. Finally, solution B and a NaOH aqueous solution with pH=10 were mixed by ultrasonication at a volume ratio of 1:20. The ultrasonic power was 700 W and the ultrasonication time was 10 min. Then, the mixture was stirred at 500 rpm for 12 h. After washing with ethanol, the mixture was then subjected to a 60°C solution. o Dry in a forced-air oven at C for 24 hours, then further dry at 800°C. o Alumina calcined at C for 4 h, its SEM image is shown below. Figure 5 .

[0047] Compare with Example 2

[0048] Titanium oxide was prepared using the same method, but without the addition of a passivating agent.

[0049] Tetraethyl titanate and toluene were mixed at a volume ratio of 1:1, and then this mixture was combined with an aqueous HCl solution at pH 4 at a volume ratio of 1:20 by ultrasonication at a power of 700 W for 10 min. The mixture was then stirred at 500 rpm for 12 h. After washing with ethanol, the mixture was further mixed at 60 °C. o Dry in a forced-air oven at C for 24 hours, then further dry at 800°C. o Titanium oxide was obtained by calcination at C for 4 hours, and its SEM image is shown below. Figure 6 .

[0050] The accompanying drawings show chromatograms of the products prepared according to the embodiments and comparative examples of the present invention.

[0051] from Figure 1 As can be seen, in the preparation of hollow alumina based on diethyl malonate and aluminum isopropoxide, uniform hollow alumina with a diameter of approximately 1 μm can be clearly formed. Furthermore, Fourier transform infrared spectroscopy shows that after calcination, impurity peaks such as -OH and C=O disappear, leaving only obvious Al-O bond peaks, representing the formation of pure alumina. In addition, from... Figure 1 According to the CD, the product is whiter after calcination, which further indicates the formation of pure alumina.

[0052] from Figure 2 As can be seen, hollow titanium dioxide with a wide particle size distribution can be clearly formed in the preparation of hollow titanium dioxide based on methyl benzoate and tetraethyl titanate.

[0053] from Figure 3As can be seen, in the preparation of hollow zirconium oxide based on 1,3-dioxolane and tetrabutyl zirconate, uniform hollow zirconium oxide with a diameter of about 1 μm can be clearly formed.

[0054] from Figure 4 As can be seen, in the preparation of hollow titanium oxide based on trifluoroacetylacetone and acetylacetone titanium, uniform hollow titanium oxide with a diameter of about 10-20 μm can be clearly formed.

[0055] from Figure 5 and Figure 6 As can be seen, in Comparative Example 1 and Comparative Example 2, alumina and titanium oxide were prepared using the same method, but no passivating agent was added, and stable hollow alumina and titanium oxide could not be formed at all.

Claims

1. A method for preparing hollow spherical inorganic oxides based on self-assembly, wherein the inorganic oxide is an inorganic metal oxide or silicon oxide, characterized in that: The preparation method includes the following steps: (1) First, the passivating agent is mixed with the inorganic oxide precursor, and the inorganic oxide precursor is passivated and protected by transesterification or chelation reaction. The feed ratio of the passivating agent to the inorganic oxide precursor is controlled so that the theoretical passivation ratio of the hydrolyzable functional groups of the inorganic oxide precursor is 10%-100%. Then, water or an aqueous solution with a pH of 4-14 is added for pre-crosslinking. The molar amount of water added is 0%-100% of the molar amount of the hydrolyzable functional groups in the inorganic oxide precursor, to obtain a solution A containing an amphiphilic composite precursor. The passivating agent is selected from at least one of β-dicarbonyl compounds, ester compounds, acetal compounds, and ketal compounds. The inorganic oxide precursor is selected from at least one of alkoxide compounds and β-diketone compounds. At least one of the passivating agent and the inorganic oxide precursor is a liquid at room temperature. (2) Solution A is mixed with a nonpolar compound in a volume ratio of 1:0.1-1:10 to prepare solution B. Solution B is then dispersed in water or an aqueous solution with a pH of 4-14 to form an oil-in-water structure. The reaction is stirred for more than 6 hours, and then washed and dried to obtain a hollow spherical oxide precursor. The nonpolar compound is selected from one or more of benzene compounds, alkane compounds or ester compounds, and the volume ratio of solution B to water or an aqueous solution with a pH of 4-14 is 1:0.1-1:

100. (3) The hollow spherical oxide precursor is calcined to promote further dehydration and condensation of the hollow spherical oxide precursor, and at the same time remove the residual passivating agent. After calcination, hollow spherical inorganic oxide is obtained.

2. The preparation method according to claim 1, characterized in that: The inorganic metal oxide is titanium oxide, zirconium oxide, aluminum oxide, niobium oxide, tantalum oxide, vanadium oxide, tin oxide, or cobalt oxide.

3. The preparation method according to claim 1, characterized in that: The alkoxide compound is at least one of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetrabutyl zirconate, tetraethyl zirconate, aluminum sec-butoxide, aluminum isopropoxide, aluminum n-butoxide, tetraethyl orthosilicate, hyperbranched polyethoxysiloxane, pentaethyl niobate, pentabutyl tantalate, triisopropoxide, and tetrabutyl stannate; the β-diketone compound is at least one of zirconium acetylacetonate, vanadium diacetylacetonate, aluminum acetylacetonate, cobalt acetylacetonate, and titanium diisopropoxybisacetylacetonate; the β-dicarbonyl compound is at least one of acetylacetone, benzoylacetone, ethyl acetoacetate, isobutyl acetoacetate, and ethyl trifluoroacetoacetate; the ester compound is at least one of diethyl malonate and methyl benzoate; the acetal compound is at least one of 1,3-dioxolane, formaldehyde diethanoloxide, and acetaldehyde diethanoloxide; and the ketal compound is at least one of acetone diethanoloxide and cyclohexanone ethylene glycol condensate.

4. The preparation method according to claim 1, characterized in that: In step (1), the ratio of passivating agent to inorganic oxide precursor is controlled so that the passivation ratio of hydrolyzable functional groups of inorganic oxide precursor is 50%-100%.

5. The preparation method according to claim 4, characterized in that: In step (1), the ratio of passivating agent to inorganic oxide precursor is controlled so that the passivation ratio of hydrolyzable functional groups of inorganic oxide precursor is 50-75%.

6. The preparation method according to claim 1, characterized in that: In step (1), the passivating agent is mixed with the inorganic oxide precursor and stirred at room temperature for 0-72 h to passivate and protect the inorganic oxide precursor.

7. The preparation method according to claim 6, characterized in that: In step (1), the passivating agent is mixed with the inorganic oxide precursor and stirred at room temperature for 20-30 h to passivate and protect the inorganic oxide precursor.

8. The preparation method according to claim 1, characterized in that: In step (1), the water or aqueous solution with a pH of 4-14 is water, NaOH aqueous solution with a pH below 14 or HCl solution with a pH above 4, the molar amount of water added is 0%-50% of the molar amount of hydrolyzable functional groups in the inorganic oxide precursor, the pre-crosslinking temperature is room temperature, and the pre-crosslinking time does not exceed 48 h.

9. The preparation method according to claim 8, characterized in that: In step (1), the molar amount of water added is 0-30% of the molar amount of hydrolyzable functional groups in the inorganic oxide precursor, the pre-crosslinking temperature is room temperature, and the pre-crosslinking time is 1-15 h.

10. The preparation method according to claim 1, characterized in that: In step (2), the benzene compound is at least one of benzene, toluene, ethylbenzene, xylene, dodecylbenzene, and hexadecylbenzene; the alkane compound is at least one of n-pentane, n-hexane, n-heptane, n-octane, n-decane, n-dodecane, n-hexadecane, white oil, and liquid paraffin; and the ester compound is at least one of ethyl acetate, butyl acetate, ethyl propionate, methyl butyrate, isooctyl acetate, and dioctyl adipate.

11. The preparation method according to claim 1, characterized in that: In step (2), solution B is dispersed in water or an aqueous solution with a pH of 4-14. The dispersion method is homogenization or ultrasound. The homogenization speed is above 10,000 rpm and the homogenization time is 10s-20min. The ultrasound dispersion power is 100W-1200W and the ultrasound time is 3min-20min.

12. The preparation method according to claim 1, characterized in that: In step (2), the stirring reaction is carried out by magnetic stirring or mechanical stirring, with a speed of more than 100 rpm and a stirring time of more than 6 hours.

13. The preparation method according to claim 1, characterized in that: In step (3), the calcination temperature is 300-800℃ and the calcination time is 1-6 h.

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