A method for preparing titanium dioxide with high photocatalytic activity

Abstract

The present invention discloses a method for preparing titanium dioxide with high photocatalytic activity, comprising the following steps: S1. taking a metatitanic acid slurry, adding a salt treatment agent, and calcining at high temperature to obtain a primary titanium dioxide product; the salt treatment agent comprises a magnesium source, a potassium source, and a phosphorus source; S2. preparing the primary titanium dioxide product into a slurry; S3. adding a titanium source, a nitrogen source, and a magnesium source to the titanium dioxide-based material slurry, and reacting at 180-220°C to form a nitrogen- and magnesium-doped titanium dioxide film layer. The present invention adopts a magnesium source, a potassium source, and a phosphorus source as salt treatment agents, and doping Mg and N into a conventional titanium dioxide film layer, wherein Mg 2+ Doping reduces the bandwidth of TiO2 to reduce the recombination of electron-hole pairs. N doping can effectively reduce the band gap of TiO2, enhance the absorption of visible light, and further improve the photocatalytic activity, thereby obtaining titanium dioxide with high photocatalytic activity.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium dioxide preparation, and particularly relates to a method for preparing titanium dioxide with high photocatalytic activity. Background Art

[0002] TiO2 is a non-toxic, chemically stable, and catalytically active semiconductor material that is widely used in electronics, ceramics, coatings, and other fields. However, it has a wide photocatalytic band gap and can only absorb ultraviolet light with a wavelength less than 380nm, and cannot fully absorb visible light from 400 to 750nm. So far, there are three main approaches to improve the photocatalytic activity of TiO2: (1) modifying nano-TiO2 by doping; (2) modifying nano-TiO2 by doping; (3) modifying nano-TiO2 by doping; (4) modifying nano-TiO2 by doping; (5) modifying nano-TiO2 by doping; (6) modifying nano-TiO2 by doping; (7) modifying nano-TiO2 by doping; (8) modifying nano-TiO2 by doping; (9) modifying nano-TiO2 by doping; (10) modifying nano-TiO2 by doping; (11) modifying nano- 20 , narrowing the band gap, expanding the spectral response range, and broadening the light response to the visible light region; (2) adding electron or hole scavengers to inhibit the recombination of photogenerated electron-hole pairs to improve the quantum efficiency; (3) preparing TiO2 assemblies with special morphology to improve the physical utilization efficiency of incident light.

[0003] Some literature summarizes the effects of the melting point, ionic radius, doping ion concentration, and doping ion valence of metal doping ions on the crystal transformation of TiO2; some literature studies the preparation method and visible light catalytic activity of TiO2 doped with non-metallic elements (N, C, S, F), discusses the relationship between the preparation process and the visible light catalytic activity of doped TiO2, and deeply analyzes the induction mechanism of non-metallic elements on the visible light catalytic activity of TiO2.

[0004] For a long time, precious metal-doped TiO2 has shown good catalytic activity, but precious metals are expensive and the research cost is high. Therefore, this application intends to provide a method for preparing titanium dioxide with low production cost and good photocatalytic activity. Summary of the Invention

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

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A method for preparing titanium dioxide with high photocatalytic activity comprises the following steps:

[0008] S1. Take metatitanic acid slurry, add salt treatment agent, and obtain titanium dioxide primary product after high temperature calcination; the salt treatment agent includes a magnesium source, a potassium source and a phosphorus source;

[0009] S2. The titanium dioxide primary product is prepared into a slurry;

[0010] S3. Add a titanium source, a nitrogen source, and a magnesium source to the titanium dioxide-based material slurry, and react at 180 to 220° C. to form a nitrogen- and magnesium-doped titanium dioxide film layer.

[0011] Preferably, the added amounts of the magnesium source, potassium source and phosphorus source are 0.2-0.5% of the mass of titanic acid respectively; the added amount of the magnesium source is calculated as MgO, the amount of the potassium source is calculated as K2O, the amount of the phosphorus source is calculated as P2O5, and the mass of the titanic acid is calculated as TiO2.

[0012] Preferably, the calcination temperature in step S1 is 500-600° C., and the calcination time is 6-8 hours.

[0013] Preferably, the titanium source in step S3 is metatitanic acid, and the amount added is 3-4% of the mass of the titanium dioxide substrate in the slurry, calculated as titanium dioxide.

[0014] Preferably, the nitrogen source and magnesium source are magnesium nitrate, and the amount of magnesium nitrate used is 0.3-0.5% of the mass of the titanium dioxide substrate in the slurry.

[0015] Preferably, a boehmite alumina coating step is further included after step S3.

[0016] Preferably, the boehmite alumina coating step is:

[0017] The titanium dioxide-based material slurry coated with a titanium dioxide film layer is adjusted to a temperature of 50-60°C, and an acidic aluminum source and an alkaline aluminum source are added simultaneously. The aluminum source is added for 20-40 minutes, and the pH is maintained at 8.5-9.0. After aging for 90-150 minutes, a loose boehmite aluminum oxide film layer is formed.

[0018] Preferably, the total amount of the aluminum source is 2.0 to 4.0% of the total mass of the titanium dioxide substrate calculated as Al2O3.

[0019] A titanium dioxide with high photocatalytic activity, prepared by the method according to any one of claims 1 to 7, comprises a titanium dioxide substrate and a coating layer located on the surface of the titanium dioxide substrate, wherein the coating layer comprises at least a nitrogen- and magnesium-doped titanium dioxide film layer.

[0020] Preferably, the coating layer further comprises a boehmite aluminum oxide film layer located on the outer surface of the nitrogen and magnesium doped titanium dioxide film layer.

[0021] The present invention adopts magnesium source, potassium source and phosphorus source as salt treatment agent, wherein the magnesium source has Mg with smaller ion radius. 2+ Entering the lattice, thereby introducing new charges in the lattice and forming defects, which can improve the photocatalytic activity of TiO2 and doping Mg and N in the conventional titanium dioxide film layer, where Mg 2+Doping reduces the wide band of TiO2 to reduce the recombination of electron-hole pairs. N doping can effectively reduce the band gap of TiO2, enhance the absorption of visible light, and further improve the photocatalytic activity, thereby obtaining titanium dioxide with high photocatalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a graph showing the results of a rhodamine photocatalytic degradation experiment on the titanium dioxide obtained in Examples 1 to 4 and Comparative Examples 1 to 4 of the present application. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing titanium dioxide with high photocatalytic activity, comprising the following steps:

[0024] S1. Take titanate slurry, add salt treatment agent, and obtain titanium dioxide primary product after high temperature calcination; the salt treatment agent includes a magnesium source, a potassium source and a phosphorus source;

[0025] S2. Preparing the primary titanium dioxide into a slurry;

[0026] S3. Add a titanium source, a nitrogen source, and a magnesium source to the titanium dioxide-based material slurry and react at 180-220°C to form a nitrogen- and magnesium-doped titanium dioxide film. Under high temperature and high energy conditions, magnesium and nitrogen easily enter the crystal lattice due to their smaller atomic radius. Mg replaces tetravalent titanium, and nitrogen is located in the lattice gaps, causing lattice changes, thereby reducing the band gap and improving photocatalytic activity.

[0027] The coated slurry is then washed with water to remove the flash powder and obtain titanium dioxide.

[0028] The salt treatment agent of the present application includes a magnesium source, a potassium source and a phosphorus source, wherein the magnesium source used has a smaller ionic radius of Mg 2+ The magnesium source enters the crystal lattice, thereby introducing new charges and forming defects in the lattice, which can improve the photocatalytic activity of TiO2. Furthermore, as a crystal form promoter, it can also reduce the calcination temperature, improve the hue of titanium dioxide, and reduce the energy consumption of calcination and grinding. The calcination temperature of this application is 500-600°C (the conventional calcination temperature is generally around 950°C), and the calcination time is 6-8 hours.

[0029] The inorganic coating process of this application is to dope Mg and N into the conventional titanium dioxide film layer, wherein Mg 2+Doping reduces the bandwidth of TiO2 to reduce the recombination of electron-hole pairs. N doping can effectively reduce the band gap of TiO2, enhance the absorption of visible light, and improve photocatalytic activity. If doping is not used and a composite coating of titanium oxide and magnesium oxide is used, the main function of the titanium oxide and magnesium oxide film layer is to block the surface defects of the titanium dioxide substrate particles and improve light resistance, rather than photocatalytic activity. However, the present application uses nitrogen and magnesium doping to cause changes in the titanium dioxide lattice, narrow the band gap, make it easier for electrons or holes to migrate to the conduction band, and reduce the carrier recombination rate, thereby further improving the visible light photocatalytic activity, thereby obtaining titanium dioxide with high photocatalytic activity.

[0030] The amount of the magnesium source, potassium source, and phosphorus source added is 0.2-0.5% of the mass of the metatitanic acid, respectively; the amount of the magnesium source added is calculated as MgO, the amount of the potassium source is calculated as K2O, the amount of the phosphorus source is calculated as P2O5, and the mass of the metatitanic acid is calculated as TiO2. The salt treatment agents are all added in the form of solutions, and the concentration of the solutions is preferably 100-120 g / L, calculated as the respective oxides.

[0031] Preferably, the titanium dioxide-based material slurry is obtained by pulping and grinding a primary titanium dioxide product. The pulping and grinding process follows industry standard operations to achieve a particle size that meets the required particle size for coating, specifically PS = 0.285 ± 0.005 μm, PSD ≤ 1.420. The primary titanium dioxide product is obtained by adding a salt treatment agent to a metatitanic acid slurry, filtering, and calcining the filter cake at high temperature. The metatitanic acid slurry concentration is preferably 300-500 g / L.

[0032] Preferably, the concentration of the titanium dioxide-based material slurry is 300 to 350 g / L, calculated as titanium dioxide.

[0033] Preferably, the titanium source is metatitanic acid, and the amount added is 3-4% of the mass of the titanium dioxide substrate in the slurry, calculated as titanium dioxide.

[0034] Preferably, in order to reduce the interference of other ions that affect the doping effect, magnesium nitrate is used as the nitrogen source and magnesium source, and the amount of magnesium nitrate used is 0.3-0.5% of the mass of the titanium dioxide substrate in the slurry. The reaction time is 6-8 hours, and the reaction is carried out in a high-temperature and high-pressure polytetrafluoroethylene reactor.

[0035] Preferably, the titanium oxide coating further includes a loose boehmite alumina coating to improve the dispersibility of titanium dioxide. The alumina coating step is as follows:

[0036] A titanium dioxide-based material slurry coated with a titanium oxide film is adjusted to a temperature of 50-60°C, and an acidic aluminum source and an alkaline aluminum source are added simultaneously. The aluminum source addition time is 20-40 minutes, and the pH is maintained at 8.5-9.0. After aging for 90-150 minutes, a loose boehmite aluminum oxide film is formed. The acidic aluminum source is preferably Al2(SO4)3, and the alkaline aluminum source is preferably NaAlO2. The addition is performed in the form of a solution, and the concentration of the solution is 100-180 g / L, calculated as Al2O3. The total amount of the aluminum source, calculated as Al2O3, is 2.0-4.0% of the total mass of the titanium dioxide substrate.

[0037] Example 1

[0038] (1) Preparation of coating base material

[0039] Titanate was slurried to a concentration of 400 g / L, 0.3% magnesium sulfate, 0.2% potassium chloride, and 0.43% phosphoric acid were added, and the mixture was filtered. The filter cake after filtration was calcined at 550°C for 6.5 h. The calcined sample was pulped and ground to a particle size of PS = 0.287 μm and PSD = 1.411.

[0040] (2) Encapsulation

[0041] The concentration of the ground titanium dioxide slurry is 317g / L, which is transferred to a polytetrafluoroethylene high-temperature and high-pressure reactor, and 4% titanic acid and 0.5% magnesium nitrate are added to the reactor, mixed evenly, and reacted at 200°C for 8h; the slurry in the reactor is transferred to a coating tank and cooled to 53°C, and 1.9% NaAlO2 and 1.1% Al2(SO4)3 are added to the coating tank at the same time, the parallel flow pH is 8.7, the parallel flow addition time is 33min, and homogenization is carried out for 2h; the product is obtained by water washing, flash evaporation, and steam powder.

[0042] Example 2

[0043] (1) Preparation of coating base material

[0044] Titanate was slurried to a concentration of 300 g / L, 0.35% magnesium sulfate, 0.3% potassium chloride, and 0.35% phosphoric acid were added, and the mixture was filtered. The filter cake after filtration was calcined at 600°C for 7 hours. The calcined sample was pulped and ground to a particle size of PS = 0.284 μm and PSD = 1.406.

[0045] (2) Encapsulation

[0046] The concentration of the ground titanium dioxide slurry is 342g / L, which is transferred to a polytetrafluoroethylene high-temperature and high-pressure reactor, and 3.5% of titanic acid and 0.4% of magnesium nitrate are added to the reactor, mixed evenly, and reacted at 200°C for 6h; the slurry in the reactor is transferred to a coating tank and cooled to 57°C, and 1.9% of NaAlO2 and 1.1% of Al2(SO4)3 are added to the coating tank at the same time, with a parallel flow pH of 8.6, the addition time is 36min, and the homogenization is 2h; the product is obtained by water washing, flash evaporation, and steam powder.

[0047] Example 3

[0048] (1) Preparation of coating base material

[0049] Titanic acid was slurried to a concentration of 443 g / L, 0.2% magnesium sulfate, 0.4% potassium chloride, and 0.48% phosphoric acid were added, and the mixture was filtered. The filter cake after filtration was calcined at 500°C for 7.5 hours. The calcined sample was pulped and ground to a particle size of PS = 0.281 μm and PSD = 1.402.

[0050] (2) Encapsulation

[0051] The titanium dioxide slurry after grinding has a concentration of 329 g / L, which is transferred to a polytetrafluoroethylene high-temperature and high-pressure reactor, and 3% of titanic acid and 0.3% of magnesium nitrate are added to the reactor, mixed evenly, and reacted at 200°C for 6.5 hours; the slurry in the reactor is transferred to a coating tank and cooled to 55°C, and 1.9% of NaAlO2 and 1.1% of Al2(SO4)3 are added to the coating tank at the same time, with a parallel flow pH of 8.6, a parallel flow addition time of 35 minutes, and homogenization for 2 hours; the product is obtained by water washing, flash evaporation, and steam powdering.

[0052] Example 4

[0053] (1) Preparation of coating base material

[0054] Titanate was slurried to a concentration of 379 g / L, 0.28% magnesium sulfate, 0.35% potassium chloride, and 0.23% phosphoric acid were added, and the mixture was filtered. The filter cake after filtration was calcined at 570°C for 6.5 hours. The calcined sample was pulped and ground to a particle size of PS = 0.285 μm and PSD = 1.413.

[0055] (2) Encapsulation

[0056] The concentration of the ground titanium dioxide slurry is 329g / L, which is transferred to a polytetrafluoroethylene high-temperature and high-pressure reactor, and 4% titanic acid and 0.5% magnesium nitrate are added to the reactor, mixed evenly, and reacted at 200°C for 7.5h; the slurry in the reactor is transferred to a coating tank and cooled to 58°C, and 1.9% NaAlO2 and 1.1% Al2(SO4)3 are added to the coating tank at the same time, with a parallel flow pH of 8.7, a parallel flow addition time of 32min, and homogenization for 2h; the product is obtained by water washing, flash evaporation, and steam powdering.

[0057] Comparative Example 1 (non-magnesium salt treatment)

[0058] Titanium dioxide that has not been treated with magnesium salt (other salt treatment agents are the same as in Example 1) is crushed, wet-ground, sand-milled, and diluted, and then transferred to a polytetrafluoroethylene high-temperature and high-pressure reactor. 4% of metatitanic acid and 0.5% of magnesium nitrate are added to the reactor, mixed evenly, and reacted at 200°C for 8 hours; the slurry in the reactor is transferred to a coating tank and cooled to 53°C, and 1.9% of NaAlO2 and 1.1% of Al2(SO4)3 are added to the coating tank at the same time, with a parallel flow pH of 8.7, a parallel flow addition time of 33 minutes, and homogenization for 2 hours; the product is obtained by water washing, flash evaporation, and steam powder.

[0059] Comparative Example 2 (Non-Mg-N-doped TiO2 Coating)

[0060] (1) Preparation of coating base material

[0061] Titanate was slurried to a concentration of 300 g / L, 0.35% magnesium sulfate, 0.3% potassium chloride, and 0.35% phosphoric acid were added, and the mixture was filtered. The filter cake after filtration was calcined at 600°C for 7 hours. The calcined sample was pulped and ground to a particle size of PS = 0.284 μm and PSD = 1.406.

[0062] (2) Encapsulation

[0063] A. Normal silicon-aluminum coated product.

[0064] B. Titanium aluminum coating: The concentration of the ground titanium dioxide slurry is 279g / L, and it is heated to 85°C; 0.8% TiOCl2 is added, and the addition time is 40 minutes, and the homogenization time is 20 minutes; the pH value is adjusted to 8.0 with NaOH, and the addition time is 20 minutes, and the homogenization time is 20 minutes; 1.8% NaAlO2 and 1.2% Al2(SO4)3 are added in parallel, and the parallel flow pH value is 8, and the parallel flow time is 60 minutes, and the homogenization time is 30 minutes; H2SO4 is added to adjust the pH value to 6.3-6.5, and the adjustment time is 60 minutes; the product is obtained by water washing, flash evaporation, and steam powder.

[0065] Comparative Example 4

[0066] Foreign standard S.

[0067] The titanium dioxide obtained in Examples 1 to 2 and Comparative Examples 1 to 4 of the present application was subjected to a rhodamine photocatalytic degradation experiment using conventional methods. The results are shown in Tables 1 and Figure 1 shown.

[0068] Table 1

[0069] Sample / degradation rate% 0h 12h 24h 30h 36h Example 1 0 65.4 91.9 96.6 98.5 Example 2 0 67.0 94.3 98.1 99.4 Example 3 0 63.2 88.9 93.6 96.9 Example 4 0 70.1 92.9 94.9 99.0 Comparative Example 1 0 17.4 29.3 37.2 48.5 Comparative Example 2A 0 12.4 21.0 22.8 44.3 Comparative Example 2B 0 15.7 20.1 26.5 46.2 Comparative Example 4 0 25.8 39.2 47.9 62.7

[0070] From Table 1 and Figure 1 It is obvious that the photocatalytic effect of the embodiment is better than that of the comparative example. In comparative example 1, magnesium salt treatment was not used during salt treatment. In comparative example 2, although magnesium salt treatment was used for the two conventional silicon-aluminum coatings and titanium-aluminum coatings during salt treatment, nitrogen and magnesium doping were not performed, and the degradation effect of rhodamine was poor. This proves that magnesium salt treatment and nitrogen- and magnesium-doped titanium dioxide coatings have a good synergistic effect, which can significantly improve the photocatalytic degradation effect.

[0071] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the invention. Thus, the present invention is intended to include such changes and modifications as fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing titanium dioxide with high photocatalytic activity, characterized in that: The following steps are involved: S1. Take a metatitanic acid slurry, add a salt treatment agent, and calcine at high temperature to obtain a primary titanium dioxide; the salt treatment agent includes a magnesium source, a potassium source, and a phosphorus source; the calcination temperature is 500 to 600 ° C, and the calcination time is 6 to 8h; S2. The titanium dioxide primary product is prepared into a slurry; S3. Add a titanium source, a nitrogen source, and a magnesium source to the titanium dioxide-based material slurry, and react at 180-220° C. to form a nitrogen- and magnesium-doped titanium dioxide film layer.

2. The method for preparing titanium dioxide with high photocatalytic activity according to claim 1, wherein: The added amounts of the magnesium source, potassium source and phosphorus source are respectively 0.2-0.5% of the mass of the titanic acid; the added amount of the magnesium source is calculated as MgO, the amount of the potassium source is calculated as K2O, the amount of the phosphorus source is calculated as P2O5, and the mass of the titanic acid is calculated as TiO2.

3. The method for preparing titanium dioxide with high photocatalytic activity according to claim 1, wherein: The titanium source in step S3 is metatitanic acid, and the amount added is 3-4% of the mass of the titanium dioxide substrate in the slurry, calculated as titanium dioxide.

4. The method for preparing titanium dioxide with high photocatalytic activity according to claim 1, wherein: The nitrogen source and magnesium source are magnesium nitrate, and the amount of the magnesium nitrate is 0.3-0.5% of the mass of the titanium dioxide substrate in the slurry.

5. The method for preparing titanium dioxide with high photocatalytic activity according to claim 1, wherein: After step S3, a boehmite alumina coating step is also included.

6. The method for preparing titanium dioxide with high photocatalytic activity according to claim 5, wherein: The boehmite alumina coating step is: The titanium dioxide-based material slurry coated with a titanium dioxide film layer is adjusted to a temperature of 50-60°C, and an acidic aluminum source and an alkaline aluminum source are added simultaneously. The aluminum source is added for 20-40 minutes, and the pH is maintained at 8.5-9.

0. After aging for 90-150 minutes, a loose boehmite aluminum oxide film layer is formed.

7. The method for preparing titanium dioxide with high photocatalytic activity according to claim 6, wherein: The total amount of the aluminum source used is 2.0 to 4.0% of the total mass of the titanium dioxide substrate calculated as Al2O3.

8. A titanium dioxide with high photocatalytic activity, characterized in that: It is prepared by the method according to any one of claims 1 to 7, and comprises a titanium dioxide substrate and a coating layer located on the surface of the titanium dioxide substrate, wherein the coating layer comprises at least a nitrogen- and magnesium-doped titanium dioxide film layer.

9. The titanium dioxide with high photocatalytic activity according to claim 8, characterized in that: The coating layer further includes a boehmite aluminum oxide film layer located on the outer surface of the nitrogen and magnesium doped titanium dioxide film layer.

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