A method for preparing titanium dioxide with high photocatalytic activity

Abstract

This invention discloses a method for preparing titanium dioxide with high photocatalytic activity. First, a metatitanic acid slurry is salt-treated and calcined to prepare a titanium dioxide base material. Then, the titanium dioxide base material is slurried and coated. The salt treatment agent used includes zinc and magnesium salts. An organic dispersant is added during the slurry preparation of the titanium dioxide base material. The coating process sequentially includes zinc titanate coating and magnesium titanate coating. After coating, the method further includes a step of calcining the coated material to decompose the organic dispersant. This application introduces magnesium and zinc ions into both the base material preparation and the post-coating treatment, allowing these ions to enter both the interior of the titanium dioxide crystal lattice and exist on the surface of the titanium dioxide particles. Titanates are introduced into the zinc and magnesium particles on the surface of the titanium dioxide particles. Combined with the use of an organic dispersant during calcination, the surface of the titanium dioxide particles becomes loose and porous, significantly improving the photocatalytic activity of the titanium dioxide.

Description

Technical Field

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

[0002] Solar energy is a highly efficient yet inexpensive renewable energy source, making its development and effective utilization of significant importance. Applications in photocatalysis are also a research focus. A photocatalyst is a catalyst capable of utilizing light energy to initiate chemical reactions. It can absorb light energy, excite electrons, and promote chemical reactions. Photocatalysts have been widely used in environmental remediation, energy storage and conversion, and organic synthesis.

[0003] Catalysts are mostly transition metal oxides such as TiO2, ZnO, CdS, and Fe2O3, but their catalytic efficiency is greatly reduced due to factors such as band gap, specific surface area, and reaction rate.

[0004] Titanium dioxide, as an excellent photocatalytic material, mainly improves its photocatalytic activity through doping and modification, and performs outstandingly in applications. However, the energy transfer efficiency of titanium dioxide catalysts is relatively low, and they are prone to forming short-lived electron-hole pairs, resulting in low catalytic efficiency under light. Furthermore, in practical applications, they are easily affected by environmental factors such as light, oxygen, water, and acids and alkalis, and may lose their catalytic performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing titanium dioxide with high photocatalytic activity in order to overcome the shortcomings of the prior art.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing highly photocatalytically active titanium dioxide involves first salting and calcining a metatitanic acid slurry to prepare a titanium dioxide base material, and then slurrying and coating the titanium dioxide base material.

[0008] The salt treatment agent used in the salt treatment includes zinc salt and magnesium salt;

[0009] An organic dispersant is added during the slurry preparation process of the titanium dioxide base material;

[0010] The coating comprises, in sequence, a zinc titanate coating and a magnesium titanate coating;

[0011] Following the coating process, the method further includes a step of calcining the coating material to decompose the organic dispersant.

[0012] Preferably, the amounts of zinc salt and magnesium salt, calculated as ZnO and MgO respectively, are 0.2-0.4% of the dry weight of the metatitanic acid slurry; the dry weight of the metatitanic acid slurry is calculated as titanium dioxide.

[0013] The salt treatment agent also includes phosphate salts, the amount of which, calculated as P2O5, is 0.2 to 0.4% of the dry basis mass of the metatitanic acid slurry; the dry basis mass of the metatitanic acid slurry is calculated as titanium dioxide.

[0014] Preferably, the calcination temperature after salt treatment is 600-700℃, the calcination time is 6-8h, and the grain size is controlled to be 0.19-0.22μm after calcination.

[0015] Preferably, the organic dispersant is selected from one or more of monoisopropanolamine and citric acid, and the amount of the organic dispersant is 0.1-2% of the titanium dioxide base material by mass based on titanium dioxide. After adding the organic dispersant, the mixture is ground until the slurry particle size is <0.3μm.

[0016] Preferably, the zinc titanate coating step is as follows:

[0017] A titanium source, a zinc source, and a pH adjuster are added concurrently to a titanium dioxide-based slurry with a pH of 8.5–9.5, maintaining the concurrent pH at 8.5–9.5. After curing, a zinc titanate coating layer is obtained.

[0018] Preferably, the amount of titanium source added, calculated as titanium dioxide, is 5-6% of the mass of titanium dioxide base material in the titanium dioxide base slurry; the amount of zinc source added, calculated as zinc oxide, is 6.5-8% of the mass of titanium dioxide base material in the titanium dioxide base slurry.

[0019] Preferably, the magnesium titanate coating step is as follows:

[0020] Titanium source, magnesium source and pH adjuster are added concurrently to titanium dioxide base material slurry coated with zinc titanate film at pH 9.5 to 12.0, and the concurrent pH is maintained at 9.5 to 12.0. After aging, magnesium titanate film is obtained.

[0021] Preferably, the amount of titanium source added, calculated as titanium dioxide, is 5-6% of the mass of titanium dioxide base material in the titanium dioxide base slurry; the amount of magnesium source added, calculated as magnesium oxide, is 6.5-8% of the mass of titanium dioxide base material in the titanium dioxide base slurry.

[0022] Preferably, the calcination temperature after coating is 500-600℃ and the calcination time is 2-3 hours.

[0023] Preferably, the concentration of the titanium dioxide base slurry is 500-600 g / L.

[0024] In this application, magnesium and zinc ions are introduced during the preparation of the base material and the post-coating process, so that the magnesium and zinc ions can enter the interior of the titanium dioxide lattice and exist on the surface of the titanium dioxide particles. Titanates are introduced into the zinc and magnesium particles on the surface of the titanium dioxide particles. Combined with the use of organic dispersants for calcination, the surface of the titanium dioxide particles becomes loose and porous, which greatly improves the photocatalytic activity of titanium dioxide. Attached Figure Description

[0025] Figure 1 These are the results of the Rhodamine photocatalytic degradation experiments on titanium dioxide obtained from Examples 1-3 and Comparative Examples 1-4 of this application. Detailed Implementation

[0026] This invention provides a method for preparing titanium dioxide with high photocatalytic activity. First, a metatitanic acid slurry is salted and calcined to prepare a titanium dioxide base material. Then, the titanium dioxide base material is slurried and coated using conventional methods to obtain titanium dioxide.

[0027] The salt treatment agents used include zinc salts and magnesium salts. In the salt treatment stage of titanium dioxide base material preparation, zinc salts and magnesium salts are used as salt treatment agents. Zinc ions and magnesium ions can enter the TiO2 lattice, introduce impurity state energy levels, narrow the band gap and energy level spacing, and improve photocatalytic activity. In addition, the introduction of magnesium ions and zinc ions promotes the formation of rutile grains at low temperature, increases the specific surface area, and improves photocatalytic activity.

[0028] Organic dispersants are added during the slurry preparation of titanium dioxide base material; after coating, the process also includes a step of calcining the coated material to decompose the organic dispersants and volatilize them in the form of CO2 and H2O, making the titanium dioxide loose and porous, and further improving its photocatalytic activity.

[0029] The coatings consist of zinc titanate coating and magnesium titanate coating. Compared to conventional zinc oxide and magnesium oxide coatings, zinc and magnesium titanate coatings can introduce defects and distortions into the intact crystal form, increasing the system energy and disorder, forming doped energy levels. This is beneficial for light absorption and the separation of photogenerated electron pairs, resulting in better catalytic performance compared to zinc oxide and magnesium oxide coatings. Furthermore, calcination after coating can improve the crystallinity of zinc and magnesium titanates, reduce the probability of electron-hole recombination, and after absorbing light energy, the excited and generated photogenerated electrons and holes will generate highly oxidizing free radicals, which oxidize organic matter and generate small molecules, thereby improving photocatalytic performance.

[0030] Therefore, in the preparation of the base material and the post-coating process, magnesium and zinc ions are introduced into the titanium dioxide lattice and exist on the surface of the titanium dioxide particles. Titanates are introduced into the zinc and magnesium particles on the surface of the titanium dioxide particles. Combined with calcination using an organic dispersant, the surface of the titanium dioxide particles becomes loose and porous, which greatly improves the photocatalytic activity of titanium dioxide.

[0031] Preferably, the amounts of zinc salt and magnesium salt in the salt treatment agent, calculated as ZnO and MgO respectively, are 0.2 to 0.4% of the dry basis mass (calculated as titanium dioxide) of the metatitanic acid slurry.

[0032] The salt treatment agent also includes phosphate salts, the amount of which, calculated as P2O5, is 0.2-0.4% of the dry weight (based on titanium dioxide) of the metatitanic acid slurry. Phosphate salts can promote rutile conversion and mask the color development of the impurity element iron.

[0033] The preferred concentration of metatitanic acid slurry is 600–800 g / L. The salt treatment agent is added in solution form with a concentration of 100–120 g / L. Magnesium salts can be magnesium chloride, magnesium sulfate, magnesium nitrate, etc., zinc salts can be zinc chloride, zinc sulfate, zinc nitrate, etc., and phosphate salts can be phosphoric acid, etc.

[0034] Preferably, the calcination temperature after salt treatment is 600-700℃, the calcination time is 6-8h, and the grain size is controlled to be 0.19-0.22μm after calcination.

[0035] Preferably, the organic dispersant is selected from one or more of monoisopropanolamine and citric acid, and the amount of organic dispersant is 0.1 to 2% of the mass of titanium dioxide base material (calculated as titanium dioxide). After adding the organic dispersant, the material is ground until the slurry particle size is <0.3μm.

[0036] Preferably, the zinc titanate coating process is as follows:

[0037] A titanium source, a zinc source, and a pH adjuster are added concurrently to a titanium dioxide-based slurry with a pH of 8.5–9.5, maintaining the concurrent pH at 8.5–9.5. After curing, zinc titanate particles precipitate and gradually deposit on the surface of the titanium dioxide-based slurry, forming a zinc titanate coating layer. The preferred concurrent addition time of the titanium source, zinc source, and pH adjuster is 20–40 min, and the preferred curing time is 5–15 min. Preferably, the amount of titanium source added, calculated as titanium dioxide, is 5–6% of the mass of titanium dioxide-based material in the titanium dioxide-based slurry; the amount of zinc source added, calculated as zinc oxide, is 6.5–8% of the mass of titanium dioxide-based material in the titanium dioxide-based slurry.

[0038] Preferably, the magnesium titanate coating process is as follows:

[0039] A titanium source, a magnesium source, and a pH adjuster are added concurrently to a titanium dioxide-based slurry with a pH of 9.5–12.0, maintaining the concurrent pH at 9.5–12.0. After curing, a magnesium titanate coating layer is obtained. The concurrent addition time of the titanium source, magnesium source, and pH adjuster is preferably 20–40 min, and the curing time is preferably 5–15 min. Preferably, the amount of titanium source added, calculated as titanium dioxide, is 5–6% of the mass of titanium dioxide-based material in the titanium dioxide-based slurry; and the amount of magnesium source added, calculated as magnesium oxide, is 6.5–8% of the mass of titanium dioxide-based material in the titanium dioxide-based slurry.

[0040] Preferably, the titanium source in the zinc titanate and magnesium titanate coatings can be TiOCl2 or TiOSO4, the zinc source can be zinc chloride, zinc sulfate, zinc nitrate, etc., and the magnesium source can be magnesium chloride, magnesium sulfate, magnesium nitrate, etc.

[0041] Preferably, the concentration of the titanium dioxide base slurry is 500-600 g / L, and the zinc titanate coating and magnesium titanate coating are carried out at 80-90°C.

[0042] Preferably, the calcination temperature after coating is 500–600℃, and the calcination time is 2–3 hours. Within this range, the organic dispersant decomposes and the crystallinity of the film is improved. Before calcination, the coated slurry is first filtered and washed with water, and then preliminarily dried at 100–110℃. After calcination, it is pulverized until the titanium dioxide particle size is <0.3μm.

[0043] Processes not limited in this invention, such as grinding and pulverizing, are all carried out using conventional methods in the art.

[0044] Example 1

[0045] (1) Preparation of coating base material

[0046] Metatitanic acid was pulped to a concentration of 600 g / L. 0.3% magnesium sulfate, 0.25% zinc chloride, and 0.4% phosphoric acid were added, and the mixture was then filtered. The filter cake was calcined in a kiln at 700℃ for 6.5 h. After calcination, a sample was taken and the particle size (CS) was measured to be 0.205 μm. 0.1% monoisopropanolamine was added to the calcined sample for dispersion and pulping. After grinding, a sample was taken and the particle size was measured to be 0.297 μm.

[0047] (2) Encapsulation

[0048] The concentration of the ground titanium dioxide slurry was adjusted to 535 g / L. Stirring was started, and the temperature was raised to 85℃. The pH of the slurry was adjusted to 9.0. At the same time, 5% TiOCl2 (as TiO2) solution, 6.5% ZnCl2 (as ZnO) solution and NaOH solution were added to the solution. The pH was maintained at 9.0 in parallel flow for 20 min, and the solution was allowed to mature for 10 min. Then, the pH of the slurry was adjusted to 10.0. At the same time, 6% TiOCl2 (as TiO2) solution, 8% MgCl2 (as MgO) solution and NaOH solution were added to the solution. The pH was maintained at 10.0 in parallel flow for 40 min, and the solution was allowed to mature for 10 min.

[0049] (3) Calcination and pulverization

[0050] The coated slurry was filtered and washed with water, and then dried at 105℃ for 6 hours. The dried sample was calcined in a muffle furnace at 600℃ for 2 hours, and then pulverized to a particle size of <0.3μm.

[0051] Example 2

[0052] (1) Preparation of coating base material

[0053] Metatitanic acid was pulped to a concentration of 600 g / L. 0.3% magnesium sulfate, 0.25% zinc chloride, and 0.4% phosphoric acid were added, and the mixture was then filtered. The filter cake was calcined in a kiln at 700℃ for 6.5 h. After calcination, the sample was taken and the particle size (CS) was measured to be 0.212 μm. 0.1% monoisopropanolamine was added to the calcined sample for dispersion and pulping. After grinding, the sample was taken and the particle size was measured to be 0.286 μm.

[0054] (2) Encapsulation

[0055] The concentration of the ground titanium dioxide slurry was 535 g / L. Stirring was started and the temperature was raised to 80℃. The pH of the slurry was adjusted to 9.5. At the same time, 6% TiOCl2 (as TiO2) solution, 8% ZnCl2 (as ZnO) solution and NaOH solution were added to the solution. The pH was maintained at 9.5 in parallel flow for 40 min, and the solution was allowed to mature for 10 min. The pH of the slurry was then adjusted to 11.5. At the same time, 5% TiOCl2 (as TiO2) solution, 6.5% MgCl2 (as MgO) solution and NaOH solution were added to the solution in parallel flow for 20 min, and the solution was allowed to mature for 10 min.

[0056] (3) Calcination and pulverization

[0057] The coated slurry was filtered and washed with water, and then dried at 105℃ for 6 hours. The dried sample was calcined in a muffle furnace at 500℃ for 3 hours, and then pulverized to a particle size of <0.3μm.

[0058] Example 3

[0059] (1) Preparation of coating base material

[0060] Metatitanic acid was pulped to a concentration of 600 g / L. 0.2% magnesium sulfate, 0.4% zinc chloride, and 0.3% phosphoric acid were added, and the mixture was then filtered. The filter cake was calcined in a kiln at 600℃ for 8 hours. After calcination, the sample was taken and the particle size (CS) was measured to be 0.199 μm. After calcination, 0.3% citric acid was added to the sample to disperse and pulp it. The sample was then ground and the particle size was measured to be 0.293 μm.

[0061] (2) Encapsulation

[0062] The concentration of the ground titanium dioxide slurry was 554 g / L. Stirring was started and the temperature was raised to 90℃. The pH of the slurry was adjusted to 8.5. At the same time, 6% TiOCl2 (as TiO2) solution, 8% ZnCl2 (as ZnO) solution and NaOH solution were added to the solution. The pH was maintained at 8.5 in parallel flow for 40 min, and the solution was allowed to mature for 10 min. The pH of the slurry was then adjusted to 12. At the same time, 5% TiOCl2 (as TiO2) solution, 6.5% MgCl2 (as MgO) solution and NaOH solution were added to the solution. The pH was maintained at 12 in parallel flow for 20 min, and the solution was allowed to mature for 10 min.

[0063] (3) Calcination and pulverization

[0064] The coated slurry was filtered and washed with water, and then dried at 105℃ for 6 hours. The dried sample was calcined in a muffle furnace at 500℃ for 3 hours, and then pulverized to a particle size of <0.3μm.

[0065] Comparative Example 1 (Conventional Base Material)

[0066] (1) Preparation of coating base material

[0067] Conventional aluminum salts are used as salt treatment agents to treat substrates.

[0068] (2) Encapsulation

[0069] The concentration of the ground titanium dioxide slurry was 554 g / L. Stirring was started and the temperature was raised to 90℃. The pH of the slurry was adjusted to 8.5. At the same time, 6% TiOCl2 (as TiO2) solution, 8% ZnCl2 (as ZnO) solution and NaOH solution were added to the solution. The pH was maintained at 8.5 in parallel flow for 40 min, and the solution was allowed to mature for 10 min. The pH of the slurry was then adjusted to 12.0. At the same time, 5% TiOCl2 (as TiO2) solution, 6.5% MgCl2 (as MgO) solution and NaOH solution were added to the solution. The pH was maintained at 12.0 in parallel flow for 20 min, and the solution was allowed to mature for 10 min.

[0070] (3) Calcination and pulverization

[0071] The coated slurry was filtered and washed with water, and then dried at 105℃ for 6 hours. The dried sample was calcined in a muffle furnace at 500℃ for 3 hours, and then pulverized to a particle size of <0.3μm.

[0072] Comparative Example 2 (Magnesium and zinc salt treated substrate, conventional coating)

[0073] (1) Preparation of coating base material

[0074] Metatitanic acid was pulped to a concentration of 600 g / L, and 0.2% magnesium sulfate, 0.4% zinc chloride, and 0.3% phosphoric acid were added. The mixture was then filtered. The filter cake was calcined in a kiln at 600°C for 8 hours. After calcination, 0.3% citric acid was added to disperse the pulp and then it was ground.

[0075] (2) Encapsulation

[0076] General-purpose silicon-aluminum coating.

[0077] (3) Calcination and pulverization

[0078] The coated slurry was filtered and washed with water, and then dried at 105℃ for 6 hours. The dried sample was calcined in a muffle furnace at 500℃ for 3 hours, and then pulverized to a particle size of <0.3μm.

[0079] Comparative Example 3 (without calcination)

[0080] (1) Preparation of coating base material

[0081] Metatitanic acid was pulped to a concentration of 600 g / L, and 0.2% magnesium sulfate, 0.4% zinc chloride and 0.3% phosphoric acid were added and then filtered. The filter cake after filtration was calcined in a kiln at 600℃ for 8 hours. After calcination, 0.3% citric acid was added to disperse the pulp and then ground.

[0082] (2) Encapsulation

[0083] The concentration of the ground titanium dioxide slurry was 554 g / L. Stirring was started and the temperature was raised to 90℃. The pH of the slurry was adjusted to 8.5. At the same time, 6% TiOCl2 (as TiO2) solution, 8% ZnCl2 (as ZnO) solution and NaOH solution were added to the solution. The pH was maintained at 8.5 in parallel flow for 40 min, and the solution was allowed to mature for 10 min. The pH of the slurry was then adjusted to 12.0. At the same time, 5% TiOCl2 (as TiO2) solution, 6.5% MgCl2 (as MgO) solution and NaOH solution were added to the solution. The pH was maintained at 12.0 in parallel flow for 20 min, and the solution was allowed to mature for 10 min.

[0084] (3) Crushing

[0085] The sample was directly crushed to a particle size of <0.3μm.

[0086] Comparative Example 4 (Standard Sample)

[0087] Foreign standard sample S.

[0088] Rhodamine photocatalytic degradation experiments were conducted on the titanium dioxide obtained in Examples 1-3 and Comparative Examples 1-4 of this application using conventional methods. The results are shown in Table 1 and 2. Figure 1 As shown.

[0089] Table 1

[0090]

[0091] From Table 1 and Figure 1 It is evident that the photocatalytic effect of the embodiment is superior to that of the comparative example.

[0092] 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 preparing titanium white powder with high photocatalytic activity, characterized in that firstly metatitanic acid slurry is subjected to salt treatment and calcination to prepare titanium white powder base material, and then the titanium white powder base material is slurried and coated, wherein the salt treatment agent used in the salt treatment comprises zinc salt and magnesium salt; the amount of the zinc salt and the magnesium salt is 0.2-0.4% of the dry basis mass of the metatitanic acid slurry, calculated as ZnO and MgO respectively; the dry basis mass of the metatitanic acid slurry is calculated as titanium dioxide; an organic dispersant is added during the slurring of the titanium white powder base material; the coating comprises zinc titanate coating and magnesium titanate coating in sequence; and after the coating, the coated material is calcined to decompose the organic dispersant.

2. The method for preparing titanium white powder with high photocatalytic activity according to claim 1, characterized in that the salt treatment agent further comprises phosphorus salt, and the amount of the phosphorus salt added is 0.2-0.4% of the dry basis mass of the metatitanic acid slurry, calculated as P2O5.

3. The method for preparing titanium white powder with high photocatalytic activity according to claim 1, characterized in that the calcination temperature after the salt treatment is 600-700℃, the calcination time is 6-8h, and the grain size after the calcination is controlled to be 0.19-0.22μm.

4. The method for preparing titanium white powder with high photocatalytic activity according to claim 1, characterized in that the organic dispersant is selected from one or more of monoisopropanolamine and citric acid, the amount of the organic dispersant is 0.1-2% of the mass of the titanium white powder base material, calculated as titanium dioxide, and the slurry particle size is ground to be <0.3μm after the addition of the organic dispersant.

5. The method for preparing titanium white powder with high photocatalytic activity according to claim 1, characterized in that the zinc titanate coating step is as follows: the titanium source, the zinc source and the pH regulator are added into the titanium white powder base slurry with pH of 8.5-9.5 in parallel flow, the parallel flow pH is maintained at 8.5-9.5, and the zinc titanate coating layer is obtained after maturation.

6. The method for preparing titanium white powder with high photocatalytic activity according to claim 5, characterized in that the amount of the titanium source added is 5-6% of the mass of the titanium dioxide base material in the titanium white powder base slurry, calculated as titanium dioxide; and the amount of the zinc source added is 6.5-8% of the mass of the titanium dioxide base material in the titanium white powder base slurry, calculated as zinc oxide.

7. The method for preparing titanium white powder with high photocatalytic activity according to claim 1, characterized in that the magnesium titanate coating step is as follows: the titanium source, the magnesium source and the pH regulator are added into the titanium white powder base slurry with zinc titanate coating layer and pH of 9.5-12.0 in parallel flow, the parallel flow pH is maintained at 9.5-12.0, and the magnesium titanate coating layer is obtained after maturation.

8. The method for preparing titanium white powder with high photocatalytic activity according to claim 7, characterized in that the amount of the titanium source added is 5-6% of the mass of the titanium dioxide base material in the titanium white powder base slurry, calculated as titanium dioxide; and the amount of the magnesium source added is 6.5-8% of the mass of the titanium dioxide base material in the titanium white powder base slurry, calculated as magnesium oxide. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 9. The method for preparing titanium white powder having high photocatalytic activity according to claim 1, wherein the calcination temperature after the coating is 500 to 600°C and the calcination time is 2 to 3 hours.

10. The method for preparing titanium white powder having high photocatalytic activity according to claim 5, wherein the concentration of the titanium white powder base slurry is 500 to 600 g / L. ​ ​

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