A method for preparing high-purity titanium dioxide

Abstract

The application discloses a preparation method of high-purity titanium dioxide, which comprises the following steps: S1, titanium tetrachloride is slowly mixed with an aqueous hydrochloric acid solution to obtain a primary hydrolysis material containing titanium oxychloride and hydrochloric acid; S2, the primary hydrolysis material is mixed with water and subjected to secondary hydrolysis at 90-110 DEG C, and then solid-liquid separation is conducted after hydrolysis to obtain metatitanic acid precursor; and S3, the metatitanic acid precursor is calcined to obtain high-purity titanium dioxide. In the application, titanium tetrachloride is directly mixed with an aqueous hydrochloric acid solution under the conditions of a limited concentration and a limited amount at room temperature to generate a mixed solution of titanium oxychloride and hydrochloric acid, and then the mixed solution of titanium oxychloride and hydrochloric acid is subjected to secondary hydrolysis under the condition of a limited high temperature. Compared with direct hydrolysis of an aqueous titanium tetrachloride solution, the hydrolysis process does not need to be conducted under a low-temperature condition, there are less intermediate products, the reaction is easy to control, titanium oxychloride is fully hydrolyzed, and the hydrolysis rate is more than 99.0%.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide preparation technology, and specifically relates to a method for preparing high-purity titanium dioxide. Background Technology

[0002] Titanium dioxide, also known as titanium dioxide, is an important inorganic chemical raw material, known as the "king of white pigments". It mainly exists in three crystal forms: rutile, anatase, and brookite. It is non-toxic, has the best opacity, the best whiteness and gloss, and is considered to be the best performing white pigment in the world. It is widely used in coatings, plastics, papermaking, inks, chemical fibers, ceramics, daily chemicals, capacitors, photocatalysis and other fields.

[0003] Titanium dioxide can be divided into pigment grade and non-pigment grade. Pigment grade is mainly used for its white color, while non-pigment products are mainly used for their functionality and purity. Non-pigment grade titanium dioxide can be further divided into various types such as enamel grade titanium dioxide, welding rod grade titanium dioxide, ceramic grade titanium dioxide, and electronic grade titanium dioxide. High-purity titanium dioxide belongs to the non-pigment grade.

[0004] Titanium dioxide is an inorganic compound with stable physicochemical properties, exhibiting semiconductor characteristics, high dielectric constant and resistivity, and excellent mechanical and electrical properties. In recent years, titanium dioxide has gained increasing attention in high-end manufacturing, electronic components, and catalysts due to its superior photochemical properties. In these fields, high-purity titanium dioxide materials are widely used in electronic components such as resistors (thermometers, varistors, VDRs), capacitors (multilayer ceramic chip capacitors, MLCCs), inductors, piezoelectric materials (piezoelectric ceramics), circuit boards, and integrated circuits; battery materials such as lithium titanate anodes, lithium dioxide anodes, lithium cathode additives, sodium-ion battery anodes, fuel cell membranes, and solar cells; glass additives, glass colorants, optical glass, microcrystalline glass, and special glasses; and titanium dioxide thin films such as vacuum sputtering and vacuum evaporation coatings. Therefore, the preparation methods of higher-purity titanium dioxide are becoming a mainstream research focus, and demand has been increasing year by year.

[0005] High-purity TiO2 generally refers to TiO2 with a purity of 99.0% to 99.9%. The higher the purity of titanium dioxide, the better the performance and the more stable the quality of products made from it. Harmful impurities in titanium dioxide can have an adverse effect on subsequent finished products, especially elements such as silicon, aluminum, and iron, which have a fatal impact on the quality of finished products.

[0006] Currently, the main methods for producing high-purity titanium dioxide in China include the sulfuric acid process, the direct hydrolysis method using TiCl4, the chloride process, and the titanium alkoxide hydrolysis method. The sulfuric acid process for producing high-purity titanium dioxide has advantages such as simple and mature technology, readily available raw materials, low cost, and simple equipment. However, due to the high impurity content of the preparation system itself and the introduction of other impurities, the product purity is low. The direct hydrolysis method using titanium tetrachloride has a short process flow and good product quality, but it requires high-quality raw materials and has high production costs. Furthermore, it generates a large amount of acidic wastewater during production, posing a significant environmental burden. The chloride process has a short process flow, high automation, low waste, and good product quality, but it faces challenges such as high technical difficulty, high raw material quality requirements, and stringent equipment material requirements, making industrialization difficult. The titanium dioxide produced by the titanium alkoxide hydrolysis method has high purity, small particle size, and narrow particle size distribution, but the cost of titanium alkoxides is too high, making it only suitable for laboratory production.

[0007] Patent CN103073058A directly prepares a titanium tetrachloride solution by adding titanium tetrachloride to water. Then, hydrochloric acid and deionized water are added to the titanium tetrachloride solution to prepare a mixed solution. After hydrolysis, filtration, washing, and vacuum drying, rutile-type nano-titanium dioxide powder with a particle size of 15–30 nm is obtained. Because TiCl4 is extremely reactive and easily hydrolyzed, it reacts with water vapor in the air to form fumes. The reaction between TiCl4 and water is vigorous and complex. When TiCl4 is slowly added to water, a white suspension is initially formed. As TiCl4 is added further, the acidity in the reaction solution increases, and the suspension dissolves. Further addition of titanium tetrachloride yields a yellow-green liquid. The reaction is affected by temperature and the ratio of titanium tetrachloride to water. The ratio of titanium tetrachloride to water needs to be controlled within a certain range to obtain a solution. The reaction process is difficult to control. Furthermore, because this process does not include endpoint pH adjustment and calcination, the resulting titanium dioxide particles are hard and have mixed crystal forms.

[0008] The literature “Zhou Zhongcheng, et al. Direct preparation of rutile nano-titanium dioxide by low-temperature hydrolysis of titanium tetrachloride. [J] Rare Metals, 2006, 30(5):653-65” first prepared a mixture of isopropanol and water, then adjusted the pH value with hydrochloric acid, and then slowly added titanium tetrachloride solution, and added ammonia water to adjust the pH value. After that, it was hydrolyzed at 70℃ for 3h, aged for 24h, filtered, washed 2-3 times with anhydrous ethanol, and dried at 80℃ to obtain TiO2 powder. Then, it was calcined at 300 and 400℃ for 2h to obtain samples. This method hydrolyzes under alkaline conditions. The hydrolysis reaction is instantaneous and the reaction is not easy to control. The grain size and distribution of the prepared sample are not easy to control. The specific surface area is too large, and the reaction activity of downstream applications is not easy to control. Moreover, the purity of titanium dioxide is also low, which needs further improvement.

[0009] Therefore, developing a method for producing high-purity titanium dioxide that is easy to control is of great significance. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing high-purity titanium dioxide in order to overcome the shortcomings of the prior art.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for preparing high-purity titanium dioxide includes the following steps:

[0013] S1. Titanium tetrachloride is slowly mixed with hydrochloric acid aqueous solution to obtain a primary hydrolysate containing titanium oxychloride and hydrochloric acid; the mass fraction of the hydrochloric acid aqueous solution is 18-22%, and the mass ratio of titanium tetrachloride to the hydrochloric acid aqueous solution is (0.4-0.8):1;

[0014] S2. The primary hydrolysate is mixed with water and subjected to secondary hydrolysis at 90-110°C. After hydrolysis, solid-liquid separation is performed to obtain a metatitanic acid precursor. The volume ratio of the primary hydrolysate to the water is 1:(1.5-2.5).

[0015] S3. The metatitanic acid precursor is calcined to obtain high-purity titanium dioxide.

[0016] Preferably, the titanium tetrachloride has a purity of ≥99.99%.

[0017] Preferably, the titanium tetrachloride is crude titanium tetrachloride obtained by conventional chlorination process and condensation, and then purified by distillation; the distillation temperature is 130-160℃.

[0018] Preferably, after mixing in step S1, the mixture is allowed to stand for 0.5 to 1 hour, and the concentration of the primary hydrolysate, calculated as TiO2, is 250 to 450 g / L.

[0019] Preferably, in step S2, the primary hydrolysate is slowly added to water over a period of 2 to 5 hours, and then kept warm and homogenized for 0.5 to 2 hours after addition.

[0020] Preferably, the metatitanic acid precursor is prepared by the following method after hydrolysis in step S2:

[0021] First, a solid-liquid separation is performed. The filter cake is re-pulped with water, and the pH is adjusted to 6.0–8.0.

[0022] Then, a second solid-liquid separation was performed, followed by washing with water and alcohol in sequence to obtain the metatitanic acid precursor.

[0023] Preferably, the filtrate from the first solid-liquid separation is recycled in step S1.

[0024] Preferably, ammonia is used for pH adjustment.

[0025] Preferably, the calcination temperature in step S3 is 550–750°C, and the time is 2.0–5.0 h.

[0026] Preferably, in step S3, the metatitanic acid precursor is placed in a calcination furnace and then calcined under programmed temperature conditions, wherein the programmed temperature conditions are:

[0027] Phase 1: Raise the temperature from room temperature to 185-215℃ within 15-25 minutes;

[0028] Second stage: Increase the temperature from 185-215℃ to 550-750℃ in 50-60 minutes;

[0029] Third stage: Then keep warm at 550-750℃ for 2.0-5.0 hours.

[0030] This application first involves directly reacting titanium tetrachloride with an aqueous solution of hydrochloric acid at room temperature under specified concentration and dosage conditions to generate a mixed solution of titanium oxychloride and hydrochloric acid. Then, the titanium oxychloride and hydrochloric acid mixture is subjected to a second hydrolysis under specified high-temperature conditions, resulting in a one-time direct hydrolysis of titanium oxychloride to metatitanic acid. Compared to direct hydrolysis of titanium tetrachloride aqueous solution, this hydrolysis process does not require low-temperature reaction, produces fewer intermediate products, is easier to control, and achieves complete hydrolysis of titanium oxychloride, with a hydrolysis rate exceeding 99.0%. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of a commercially available brand of high-purity titanium dioxide;

[0032] Figure 2 This is a scanning electron microscope image of the high-purity titanium dioxide obtained in Example 3. Detailed Implementation

[0033] This invention provides a method for preparing high-purity titanium dioxide, comprising the following steps:

[0034] S1. Take titanium tetrachloride and slowly mix it with hydrochloric acid aqueous solution to obtain a primary hydrolysate containing titanium oxychloride and hydrochloric acid; the mass fraction of hydrochloric acid aqueous solution is 18-22%, and the mass ratio of titanium tetrachloride to hydrochloric acid aqueous solution is (0.4-0.8):1; when the amount of hydrochloric acid is too large, the acidity of the primary and secondary hydrolysates is too high, and too much alkali is required to neutralize the material before subsequent calcination; when the amount of hydrochloric acid is too small, a white precipitate will be generated in the primary hydrolysis, which will affect the subsequent hydrolysis.

[0035] If a white complex is produced by the first hydrolysis, and a second hydrolysis is performed, the white complex is equivalent to an added seed crystal. The hydrolysis process will cause the white complex to deposit, resulting in larger grain size and distribution in the prepared sample, which will affect the application performance of the sample in the later stages.

[0036] S2. The primary hydrolysate is mixed with water and subjected to secondary hydrolysis at 90-110℃. After hydrolysis, solid-liquid separation is performed to obtain the metatitanic acid precursor. The volume ratio of the primary hydrolysate to water is 1:(1.5-2.5).

[0037] Secondary hydrolysis ensures sufficient reactant water, which is beneficial for the reaction to proceed to the right, and the hydrolysis rate will increase accordingly.

[0038] S3. Calcining the metatitanic acid precursor yields high-purity titanium dioxide.

[0039] In existing technologies for preparing titanium dioxide by hydrolysis of titanium tetrachloride, titanium tetrachloride is first dissolved in water at a low temperature (<10℃) to prepare an aqueous solution. This aqueous solution is then mixed with hydrochloric acid for hydrolysis. However, titanium tetrachloride generally reacts readily with water, and the reaction is complex, producing numerous intermediate products. During the preparation of the aqueous solution, a white complex is easily formed. The reaction is affected by the ratio of titanium tetrachloride to water. The formation of this white complex makes it difficult to control the grain size and distribution of the hydrolyzed material, resulting in a product with a large specific surface area. Furthermore, insufficient water leads to a lower hydrolysis rate. Direct hydrolysis of titanium tetrachloride, with excessive water, will also result in the formation of white complexes. In contrast, the two-stage hydrolysis of titanium oxychloride, using sufficient water, will improve both the hydrolysis rate and the hydrolysis percentage.

[0040] This application first reacts titanium tetrachloride directly with hydrochloric acid aqueous solution under specified concentration and dosage conditions at room temperature to generate a mixed solution of titanium dichloride and hydrochloric acid. Experimental verification shows that under the conditions specified in this application, the reaction of titanium tetrachloride with hydrochloric acid aqueous solution directly generates a yellow-green mixture of titanium dichloride and hydrochloric acid, without forming a white complex. It is speculated that the presence of the initial hydrochloric acid aqueous solution prevents the formation of the complex. Then, the mixture of titanium dichloride and hydrochloric acid is subjected to a secondary hydrolysis under specified high-temperature conditions, directly hydrolyzing titanium dichloride into metatitanic acid in a single step. The main reaction formulas involved in the secondary hydrolysis are as follows:

[0041] TiOCl2+2H2O→TiO(OH)2↓+2HCl

[0042] Initially, the concentration of free acid in the solution is low, which, under high temperature conditions, favors the forward hydrolysis reaction, resulting in a faster hydrolysis rate. As the reaction proceeds, the free acidity in the hydrolysate increases, leading to a higher concentration of the product HCl, which in turn inhibits the forward reaction more effectively, thus controlling the reaction rate. This allows for the gradual and complete hydrolysis of titanium dichloride, resulting in the uniform precipitation of metatitanic acid, effective control of particle size and morphology, and improved hydrolysis rate. To prevent a slow reaction rate, sufficient water is required for the secondary hydrolysis, which accelerates the hydrolysis reaction, promotes TiOCl2 hydrolysis, and increases the hydrolysis rate.

[0043] Compared to direct hydrolysis of titanium tetrachloride aqueous solution, this hydrolysis process does not require reaction under low temperature conditions, produces fewer intermediate products, and is easier to control. Titanium oxychloride is fully hydrolyzed, with a hydrolysis rate of over 99.0%.

[0044] Using high-purity titanium tetrachloride can improve the purity of titanium dioxide. In this application, the titanium tetrachloride has a preferred purity of ≥99.99%. More preferably, crude titanium tetrachloride obtained by conventional chlorination process and condensation is purified by distillation to obtain high-purity titanium tetrachloride at a distillation temperature of 130-160℃.

[0045] Preferably, after mixing in step S1, the mixture is allowed to stand for 0.5 to 1 hour. During hydrolysis, titanium tetrachloride will volatilize to a certain extent, resulting in a lower amount of titanium in the primary hydrolysate compared to the initial amount of titanium tetrachloride. The concentration of the primary hydrolysate, calculated as TiO2, is 250 to 450 g / L.

[0046] Preferably, in step S2, the hydrolysate is slowly added to water over a period of 2 to 5 hours, and then kept warm and homogenized for 0.5 to 2 hours to make the reaction more thorough.

[0047] Preferably, the metatitanic acid precursor is prepared by the following method after hydrolysis in step S2:

[0048] First, a solid-liquid separation is performed, preferably by pressing. The filter cake is re-pulped with water, and the pH is adjusted to 6.0-8.0. Neutral conditions are conducive to calcination, and the calcined material is relatively loose. The filtrate from the solid-liquid separation is recycled to step S1 for reuse, and the hydrochloric acid can be recovered, saving production costs. Ammonia water is preferred for pH adjustment.

[0049] Then, a second solid-liquid separation is performed, followed by water washing and alcohol washing in sequence to obtain the metatitanic acid precursor. Alcohol washing after water washing can reduce surface tension and make the calcined material soft.

[0050] The calcination temperature in step S3 is 550–750℃, and the time is 2.0–5.0 h.

[0051] Step S3 involves placing the metatitanic acid precursor in a calcination furnace and then calcining it under programmed temperature conditions, wherein the programmed temperature conditions are:

[0052] Phase 1: Raise the temperature from room temperature to 185-215℃ within 15-25 minutes;

[0053] Second stage: Increase the temperature from 185-215℃ to 550-750℃ in 50-60 minutes;

[0054] Third stage: Then keep warm at 550-750℃ for 2.0-5.0 hours.

[0055] Titanium dioxide with different crystal forms and specific surface areas can be obtained by adjusting the calcination temperature and time. The appropriate calcination temperature and time can be selected according to the requirements of downstream customers. Generally, the higher the calcination temperature, the higher the rutile conversion rate.

[0056] The method provided by this invention has a short process, simple steps, low cost, and high production efficiency. It does not introduce any additional substances during the entire production process, resulting in titanium dioxide with low impurity content, high product purity (TiO2 ≥ 99.5%), and a BET of 15–25 mg / L. 2 / g, based on XRD analysis results, the average particle size calculated using the Scherrer equation is approximately 68 nm.

[0057] Example 1

[0058] Crude titanium tetrachloride, prepared by conventional chlorination and condensation of titanium-rich material and petroleum coke, was further purified by distillation at 140℃ to obtain high-purity titanium tetrachloride with a purity of 99.99%. A 1:1 hydrochloric acid solution was prepared by diluting 36% concentrated hydrochloric acid with water. The distilled titanium tetrachloride was then slowly added to the 1:1 hydrochloric acid solution over 3 hours. TiCl4 :m 1:1HCl溶液 =0.4:1, then let the reaction stand for 30 minutes to obtain the primary hydrolysate; then add the primary hydrolysate to boiling water within 2 hours for secondary hydrolysis, V 水 V 一次水解料 =1.7:1, and then kept at 100℃ for 0.5h to obtain secondary hydrolyzed material; after pressing the secondary hydrolyzed material, the filter cake is re-pulped with water, and ammonia is added to adjust the pH to 7.0; it is pressed a second time and washed with water until the conductivity is 50μs / cm, and then washed twice with ethanol; after flash drying the filter cake, it is placed in a clean sagger and calcined in air atmosphere at 600℃ for 2.5h, and then naturally cooled to room temperature, and pulverized to obtain high-purity titanium dioxide powder.

[0059] Example 2

[0060] Crude titanium tetrachloride, prepared by conventional chlorination and condensation of titanium-rich material and petroleum coke, was further purified by distillation at 150℃ to obtain high-purity titanium tetrachloride with a purity of 99.999%. A 1:1 hydrochloric acid solution was prepared by diluting 37% concentrated hydrochloric acid with water. The distilled titanium tetrachloride was then slowly added to the 1:1 hydrochloric acid solution over 2 hours. TiCl4 :m 1:1HCl溶液 =0.5:1, then let the reaction stand for 60 minutes to obtain the primary hydrolysate; then add the primary hydrolysate to boiling water within 3 hours for secondary hydrolysis, V 水 V 一次水解料= 2.0:1, and then kept at 105℃ for 1.0h to obtain secondary hydrolyzed material; after pressing the secondary hydrolyzed material, the filter cake is re-pulped with water, and ammonia is added to adjust the pH to 7.1; it is pressed a second time and washed with water until the conductivity is 45μs / cm, and then washed with ethanol 3 times; after flash drying the filter cake, it is placed in a clean sagger and calcined in air atmosphere at 650℃ for 3.0h, and then naturally cooled to room temperature. After pulverization, high-purity titanium dioxide powder is obtained.

[0061] Example 3

[0062] Crude titanium tetrachloride, prepared by conventional chlorination and condensation of titanium-rich material and petroleum coke, was further purified by distillation at 155℃ to obtain high-purity titanium tetrachloride with a purity of 99.9995%. A 1:1 hydrochloric acid solution was prepared by diluting 37% concentrated hydrochloric acid with water. The distilled titanium tetrachloride was then slowly added to the 1:1 hydrochloric acid solution over 2 hours. TiCl4 :m 1:1HCl溶液 =0.57:1, yielding a primary hydrolysate; then, the primary hydrolysate is added to boiling water within 3 hours for a secondary hydrolysis, V 水 V 一次水解料 = 2.5:1, and then kept at 105℃ for 1.0h to obtain secondary hydrolyzed material; after pressing the secondary hydrolyzed material, the filter cake is re-pulped with water and ammonia is added to adjust the pH to 7.2; it is pressed a second time and washed with water until the conductivity is 43μs / cm, and then washed 3 times with ethanol; after flash drying the filter cake, it is placed in a clean sagger and calcined in air atmosphere at 700℃ for 3.0h, and then naturally cooled to room temperature, and pulverized to obtain high-purity titanium dioxide powder.

[0063] Comparative Example 1

[0064] First, titanium tetrachloride was added to stirred deionized water at a rate of 40 ml / h at 10℃ to prepare a titanium tetrachloride solution with a concentration of 2 mol / L. Then, the temperature was raised to 100℃ and hydrolyzed for 3 hours to obtain metatitanic acid gel, which was then pumped into a filter press for filtration. The metatitanic acid filter cake obtained by filtration was placed in a kiln for calcination, and the calcination temperature was controlled at 650℃. After constant temperature calcination for 3 hours, it was taken out to obtain titanium dioxide powder.

[0065] Comparative Example 2

[0066] First, titanium tetrachloride was added to stirred deionized water at a rate of 40 mL / h at 10℃ to prepare a titanium tetrachloride solution with a concentration of 2 mol / L. Then, 950 mL of hydrochloric acid (hydrogen ion concentration of 6.3 mol / L) and deionized water were added to the titanium tetrachloride solution with a concentration of 2 mol / L and a volume of 50 mL to prepare a mixed solution with a titanium ion concentration of 0.1 mol / L and a hydrogen ion concentration of 6 mol / L. The mixed solution was then hydrolyzed at 110℃ for 3 h to obtain a precipitate. The precipitate was filtered, washed, dried, and calcined at 650℃ for 3 h to obtain rutile nano-titanium dioxide.

[0067] Table 1 compares some indicators of the titanium dioxide prepared in the embodiments of the present invention with a commercially available high-purity titanium dioxide of better quality and the titanium dioxide prepared in Comparative Examples 1-2. The particle morphology is as follows. Figure 1 and 2 As shown.

[0068] Table 1

[0069]

[0070] As can be seen from the above data, the titanium dioxide prepared by the present invention is better than commercially available products and comparative examples 1-2 in terms of TiO2%, BET, particle size, and impurity content. Furthermore, the product prepared by the present invention has a more uniform particle morphology.

[0071] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for producing high-purity titanium dioxide, characterized by, The method comprises the following steps: S1. Slowly mix titanium tetrachloride with an aqueous hydrochloric acid solution to obtain a primary hydrolysis material containing titanium oxychloride and hydrochloric acid at room temperature; The mass fraction of the aqueous hydrochloric acid solution is 18-22%, and the mass ratio of the titanium tetrachloride to the aqueous hydrochloric acid solution is (0.4-0.8):1; the concentration of the primary hydrolysis material is 250-450 g / L in terms of TiO2; S2. Slowly add the primary hydrolysis material to boiling water, and maintain the temperature at 90-110°C for 0.5-2h after the addition to homogenize the material, and then perform secondary hydrolysis, and then perform solid-liquid separation to obtain a metatitanic acid precursor; S3. Calcine the metatitanic acid precursor to obtain high-purity titanium dioxide.

2. The method according to claim 1, wherein the purity of the titanium tetrachloride is greater than or equal to 99.99%.

3. The method according to claim 2, wherein the titanium tetrachloride is obtained by condensation after chlorination by a conventional chlorination method, and then purified by rectification; and the rectification temperature is 130-160°C.

4. The method according to claim 1, wherein the mixture is allowed to stand for 0.5-1h after the mixing in step S1.

5. The method according to claim 1, wherein the metatitanic acid precursor is prepared after the hydrolysis in step S2 by the following method: firstly, perform a first solid-liquid separation, re-slurry the filter cake with water, and adjust the pH to 6.0-8.0; then, perform a second solid-liquid separation, and sequentially wash with water and alcohol to obtain the metatitanic acid precursor.

6. The method according to claim 5, wherein the filtrate of the first solid-liquid separation is recycled to step S1.

7. The method according to claim 5, wherein ammonia water is used to adjust the pH.

8. The method according to claim 1, wherein the calcination temperature in step S3 is 550-750°C, and the time is 2.0-5.0h.

9. The method according to claim 8, wherein the metatitanic acid precursor is placed in a calcination furnace, and then calcined under programmed temperature conditions, wherein the programmed temperature conditions are as follows: first stage: the temperature is raised from room temperature to 185-215°C within 15-25min; second stage: the temperature is raised from 185-215°C to 550-750°C within 50-60min; third stage: then maintain the temperature at 550-750°C for 2.0-5.0h. ​ ​ ​ ​ ​ ​ ​ ​

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