RU2408427C1 - Method of producing titanium dioxide-based photocatalyst - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to production of photocatalysts. Proposed method consists in preparing water solution of titanyl sulphate with concentration of 0.1-1.0 mol/l, adding acid thereto obtain concentration of 0.15-1 mol/l, hydrolysis of obtained solution in hydrothermal conditions at 100-250°C for 0.5-24 h, and drying of produced suspension of porous titanium dioxide.

EFFECT: production of porous photocatalyst with high specific surface and photocatalytic ctivity.

5 cl, 5 tbl, 8 dwg, 5 ex

Description

The invention relates to the composition and structure of porous dispersed materials based on titanium dioxide, as well as to methods and compositions of intermediates for obtaining such materials. Porous dispersed materials can be used as catalysts for photochemical reactions in chemical plants, in particular, for the production of molecular hydrogen as a fuel for vehicles, for the purification of air and water from harmful organic compounds by heterogeneous photocatalytic oxidation of these compounds to form products that are safe for human health.

It is known [1] that photocatalysts consisting of crystalline particles with a high specific surface (small particle size) possess the highest catalytic activity.

A known method of producing titanium dioxide by hydrolysis of TiOSO ₄ [2-4]. This method leads to the production of non-porous particles ranging in size from 300 nm to 8.5 μm, unsuitable for use as photocatalysts.

A known method of producing particles of TiO _{2 with a} size of less than 100 nm for photocatalytic processes from titanium alkoxides [5-6]. However, their receipt is a separate task, and storage requires special conditions. In addition, the content of the crystalline phase in the resulting product is about 50%, which leads to a loss of photocatalytic activity.

A known method of producing sols based on TiO ₂ [7] by hydrolysis of TiOSO ₄ . This method consists in the hydrolysis of TiOSO ₄ using 10-200 mol of water per mol of TiOSO ₄ , adding acid to pH 0.1-2.5, growing TiO ₂ crystals under hydrothermal conditions at 80-210 ° C for 1-48 hours, adding non-volatile organic solvent and water removal using a Dean-Stark nozzle. This method was selected as a prototype.

The disadvantage of the prototype is to obtain particles of titanium oxide with a size of 80-200 nm, which does not significantly increase the photocatalytic activity compared to traditional photocatalysts based on titanium dioxide. In addition, the conditions of hydrothermal treatment (up to 48 hours) proposed in the prototype are economically inefficient.

The claimed invention allows to reduce the size of the resulting particles to 10-60 nm without loss of crystallinity and, thus, the technical result of the invention is to obtain a more efficient photocatalyst.

The specified technical result is achieved by the fact that in the inventive method, on the basis of the preparation of an aqueous solution of titanyl sulfate and its hydrothermal treatment in accordance with the invention, the concentration of titanyl sulfate in an aqueous solution is 0.1-1.0 mol / l, acid is added to the solution to obtain a concentration 0.15-1 mol / L, the solution is hydrolyzed under hydrothermal conditions at a temperature in the range of 100-250 ° C for 0.5-24 hours, after which the resulting suspension of porous titanium dioxide is dried.

In addition, the indicated technical result is achieved in that a solution of sulfuric acid is used as the acid.

In addition, this technical result is achieved in that the porous titanium dioxide is isolated by centrifugation.

In addition, the specified technical result is achieved in that the porous titanium dioxide is purified from the mother liquor using distilled water.

In addition, this technical result is achieved in that the porous titanium dioxide is dried in air at 60-70 ° C.

A titanium dioxide based photocatalyst is obtained by hydrolysis of an acidified titanyl sulfate solution under hydrothermal conditions. To do this, prepare an aqueous solution containing 0.1-1 mol / L TiOSO ₄ and 0.15-1 mol / L acid, and then carry out hydrothermal treatment at a temperature of 100-250 ° C for 0.5-24 hours.

In addition, an increase in the photocatalytic activity of the obtained material is achieved by increasing the surface area caused by the formation of pores of 1-4 nm in size under conditions of production.

On the basis of St. Petersburg State University, studies were conducted in different modes and based on them specific examples of implementation are given below.

Example 1

Obtaining porous titanium oxide from a solution of titanyl sulfate stabilized by the addition of sulfuric acid.

A solution of TiOSO ₄ (1M) was prepared by dissolving titanyl sulfate in distilled water with the addition of a significant amount of sulfuric acid (4M). The solution was diluted with distilled water to predetermined concentrations and subjected to hydrothermal treatment. Sulfuric acid has a stabilizing effect on solutions of titanyl sulfate - they become more stable, and for a long time hydrated titanium dioxide does not precipitate from them.

The hydrothermal synthesis of nanocrystalline oxide powders was carried out by the method of high-temperature hydrolysis of aqueous solutions of titanyl sulfate. Hydrothermal synthesis was carried out in isothermal mode at a temperature of 250 ° C for 6 hours at a pressure of saturated steam of water. During the synthesis, the degree of filling of the cell was 75%. At the end of the experiment, the autoclave was removed from the furnace and cooled to room temperature. After cooling, a Teflon cell was removed from the autoclave, at the bottom of which there was a precipitate of the synthesis product. The resulting product was isolated by centrifugation, washed repeatedly with distilled water, and then dried in air at a temperature of 60 ° C.

According to x-ray phase analysis, all samples contained only a crystalline metastable anatase phase with a CSR size of 15 to 60 nm. Figure 1 shows typical x-ray diffraction patterns for samples synthesized by the hydrothermal method from a TiOSO ₄ solution previously stabilized with sulfuric acid: 1 - 0.25 M; 2 - 0.5M; 3 - 0.25 M + 0.5 M H ₂ SO ₄ ; 4 - 0.5 M + 0.5 M H ₂ SO ₄ ; 5 - 0.25M + 1M H ₂ SO ₄ ; 6 - 0.5M + 1M H ₂ SO ₄ .

According to the results of determining the CSR sizes of samples synthesized from a TiOSO ₄ solution, previously stabilized with sulfuric acid, a sample obtained by hydrothermal synthesis from a 0.5 M TiOSO ₄ solution is characterized by a CSR size of 60 ± 6 nm. When synthesizing from a more diluted (0.25 M) TiOSO ₄ solution, the CSR sizes of the obtained sample practically do not change and amount to 54 ± 5 nm. With a further decrease in the concentration of titanyl sulfate solution to 0.15 M, the CSR sizes of the obtained sample decrease to 22 ± 2 nm.

When various amounts of sulfuric acid are added to the initial stabilized TiOSO ₄ solution (the concentration of added H ₂ SO ₄ is 0.5 M and 1 M) and subsequent hydrothermal synthesis under similar conditions, in the case of a 0.5 M TiOSO ₄ solution, no change in the size of the CSR samples is detected . The CSR sizes for these samples turned out to be 57 ± 6 nm (see Table 1). A similar situation is observed in the synthesis of nanocrystalline titanium dioxide from a 0.25 M TiOSO ₄ solution with the addition of various amounts of sulfuric acid: in both cases, the CSR sizes of the obtained samples are 55 ± 5 nm (Table 1).

In the synthesis from a more dilute (0.15 M) TiOSO ₄ solution, with an increase in the concentration of added sulfuric acid from 0.5 M to 1 M, an increase in CSR sizes from 43 ± 4 to 54 ± 5 nm occurs (Table 1).

According to transmission electron microscopy, the obtained TiO ₂ samples are completely crystallized, while in contrast to the prototype, the particles contain pores from 1 to 4 nm in size, which leads to an increase in the specific surface area of the photocatalyst. Figure 2 presents microphotographs of samples synthesized by the hydrothermal method from a 0.25M solution No. 1 (A), with the addition of 0.5M (B) and 1M (C) sulfuric acid, (D) - increase.

Table 1. Sample Description Phase composition CSR size, nm (± 10%) Stable solution 0.5M Anataz - 100% 60 The stabilized solution of 0.5 M + 0.5 M H ₂ SO ₄ Anataz - 100% 57 The stabilized solution of 0.5M + 1M H ₂ SO ₄ Anataz - 100% 57 The stabilized solution of 0.25M Anataz - 100% 54 The stabilized solution of 0.25M + 0.5M H ₂ SO ₄ Anataz - 100% 56 The stabilized solution of 0.25M + 1M H ₂ SO ₄ Anataz - 100% 56 Stable Solution 0.15M Anataz - 100% 22 The stabilized solution of 0.15M + 0.5M H ₂ SO ₄ Anataz - 100% 43 Stable Solution 0.15M + 1M H ₂ SO ₄ Anataz - 100% 54

Separately, it should be noted that the particles with the smallest sizes and the largest surface area are formed at a low concentration of a solution of titanyl sulfate, thus, the concentration range proposed in the prototype (up to 5 mol / l) is unreasonable.

Example 2

Obtaining porous titanium oxide from an unstabilized solution of titanyl sulfate.

A solution of TiOSO ₄ (1M) was prepared by dissolving titanyl sulfate in distilled water. The solution was diluted with distilled water to predetermined concentrations and subjected to hydrothermal treatment.

The hydrothermal synthesis of nanocrystalline oxide powders was carried out by the method of high-temperature hydrolysis of aqueous solutions of titanyl sulfate. Hydrothermal synthesis was carried out in isothermal mode at a temperature of 250 ° C for 6 hours at a pressure of saturated steam of water. During the synthesis, the degree of filling of the cell was 75%. At the end of the experiment, the autoclave was removed from the furnace and cooled to room temperature. After cooling, a Teflon cell was removed from the autoclave, at the bottom of which there was a precipitate of the synthesis product. The resulting product was isolated by centrifugation, washed repeatedly with distilled water, and then dried in air at a temperature of 60 ° C.

Figure 3 shows the characteristic x-ray for the obtained samples (1 - 0.25 M; 2 - 0.5 M; 3 - 0.15 M + 0.5 M H ₂ SO ₄ ). The CSR sizes of the samples obtained by hydrothermal treatment of solutions not stabilized by sulfuric acid turn out to be significantly smaller than by the synthesis of samples from solutions stabilized by sulfuric acid of similar concentrations. With a decrease in the concentration of titanyl sulfate in the treated unstabilized solution from 0.5 M to 0.25 M and 0.15 M, there is an additional decrease in the CSR sizes of the obtained TiO ₂ particles from 27 ± 3 to 21 ± 2 nm and 15 ± 2 nm, respectively (Table 2 )

According to transmission microscopy (Figure 4), samples obtained from an unstabilized solution of titanyl sulfate also represent porous nanocrystalline titanium dioxide with a particle size of from 20 to 40 nm. Electron diffraction data confirm the formation of a pure anatase phase.

Thus, in the synthesis of a solution that was not initially stabilized by sulfuric acid, it is possible to obtain nanocrystalline powders with smaller particles, which should positively affect the photocatalytic activity of these samples.

Table 2. Solution without stabilization 0,5M Anataz - 100% 21 Solution without stabilization 0.25M Anataz - 100% 27 Solution without stabilization 0.15M Anataz - 100% fifteen Solution without stabilization 0.15M + 0.5M H ₂ SO ₄ Anataz - 100% 35

Example 3

Obtaining porous titanium oxide from an unstabilized solution of titanyl sulfate with the addition of nitric acid.

A solution of TiOSO ₄ (1M) was prepared by dissolving titanyl sulfate in distilled water. The solution was diluted with distilled water to predetermined concentrations, the required amount of nitric acid was added, and subjected to hydrothermal treatment.

The hydrothermal synthesis of nanocrystalline oxide powders was carried out by the method of high-temperature hydrolysis of aqueous solutions of titanyl sulfate. Hydrothermal synthesis was carried out in isothermal mode at a temperature of 250 ° C for 6 hours at a pressure of saturated steam of water. During the synthesis, the degree of filling of the cell was 75%. At the end of the experiment, the autoclave was removed from the furnace and cooled to room temperature. After cooling, a Teflon cell was removed from the autoclave, at the bottom of which there was a precipitate of the synthesis product. The resulting product was isolated by centrifugation, washed repeatedly with distilled water, and then dried in air at a temperature of 60 ° C.

According to x-ray phase analysis of samples synthesized by the hydrothermal method from solutions of titanyl sulfate, with the addition of nitric acid (Figure 5: (1) 0.1 M + 0.5 M HNO ₃ ; 2) 0.1 M + 1 M HNO ₃ ; 3) 0.3 M + 0.25 M HNO ₃ ; 4) 0.3 M + 0.5 M HNO ₃ ; 5) 0.3 M + 1 M HNO ₃ ; 6) - 0.5 M + 1 M HNO ₃ ; 7) 0.5 M + 1 M HNO ₃ ; 8) 1M + 1M HNO ₃ ), during hydrothermal synthesis of titanium dioxide from a solution of titanyl sulfate with the addition of nitric acid, anatase also crystallizes with CSR sizes from 20 to 40 nm (Figure 5, Table 3). These results are confirmed by transmission microscopy data presented in Fig.6 (0.25M (A), 0.5M (B) and 1M (C) nitric acid). Electron diffraction data confirm the formation of a pure anatase phase.

Table 3. Sample Description Phase composition CSR size, nm (± 10%) Unstabilized solution 1M TiOSO ₄ + 1M HNO ₃ Anataz - 100% 38 Non-stabilized solution 0.5M TTiOSO ₄ + 0.5M HNO ₃ Anataz - 100% thirty Non-stabilized solution 0.5M TiOSO ₄ + 1M HNO ₃ Anataz - 100% 28 Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ Anataz - 100% 21 Non-stabilized solution 0.3 M TiOSO ₄ + 0.5 M HMO ₃ Anataz - 100% 24 Non-stabilized solution 0.3M TiOSO ₄ + 1M HNO ₃ Anataz - 100% 24 Non-stabilized solution 0.1 M TiOSO ₄ + 0.5 M HNO ₃ Anataz - 100% twenty Non-stabilized solution 0.1 M TiOSO ₄ + 1 M HNO ₃ Anataz - 100% 22

Example 4

Obtaining porous titanium oxide from an unstabilized solution of titanyl sulfate with the addition of nitric acid at various times of hydrothermal treatment.

A solution of TiOSO ₄ (1M) was prepared by dissolving titanyl sulfate in distilled water. The solution was diluted with distilled water and the required amount of nitric acid was added to obtain a TiOSO ₄ concentration _of 0.3 M and a HNO ₃ concentration of 0.25 M.

The hydrothermal synthesis of nanocrystalline oxide powders was carried out by the method of high-temperature hydrolysis of aqueous solutions of titanyl sulfate. Hydrothermal synthesis was carried out in isothermal mode at a temperature of 250 ° C, for 3-24 hours at a pressure of saturated steam of water. During the synthesis, the degree of filling of the cell was 75%. At the end of the experiment, the autoclave was removed from the furnace and cooled to room temperature. After cooling, a Teflon cell was removed from the autoclave, at the bottom of which there was a precipitate of the synthesis product. The resulting product was isolated by centrifugation, washed repeatedly with distilled water, and then dried in air at a temperature of 60 ° C.

According to x-ray phase analysis, during hydrothermal synthesis of titanium dioxide from a solution of 0.3 M TiOSO ₄ solution with the addition of 0.25 M HNO ₃ for: 1) 3 hours; 2) 6 hours; 3) 12 hours; 4) for 24 hours, a metastable phase also crystallizes - nanocrystalline anatase with CSR sizes from 20 to 40 nm (Fig. 7, Table 4). These results are confirmed by transmission microscopy (Fig. 8): A) 3 h; B) 6 hours; B) 12 hours; D) 24 h

Table 4. Sample Description Hydrothermal treatment time, h Phase composition CSR size, nm (± 10%) Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HMO ₃ 3 Anataz - 100% twenty Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HMO ₃ 6 Anataz - 100% 21 Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ 12 Anataz - 100% 22 Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ 24 Anataz - 100% 23

Example 5

Obtaining porous titanium oxide from an unstabilized solution of titanyl sulfate with the addition of nitric acid at various temperatures of hydrothermal treatment.

A solution of TiOSO ₄ (1M) was prepared by dissolving titanyl sulfate in distilled water. The solution was diluted with distilled water and the required amount of nitric acid was added to obtain a TiOSO ₄ concentration _of 0.3 M and a HNO ₃ concentration of 0.25 M.

The hydrothermal synthesis of nanocrystalline oxide powders was carried out by the method of high-temperature hydrolysis of aqueous solutions of titanyl sulfate. Hydrothermal synthesis was carried out in isothermal mode at a temperature of 100, 150 and 250 ° C, for 6 hours at a pressure of saturated steam of water. During the synthesis, the degree of filling of the cell was 75%. At the end of the experiment, the autoclave was removed from the furnace and cooled to room temperature. After cooling, a Teflon cell was removed from the autoclave, at the bottom of which there was a precipitate of the synthesis product. The resulting product was isolated by centrifugation, washed repeatedly with distilled water, and then dried in air at a temperature of 60 ° C.

According to the X-ray phase analysis, during hydrothermal synthesis of titanium dioxide from a solution of titanyl sulfate with the addition of nitric acid, anatase also crystallizes with CSR sizes from 20 to 25 nm and a slight admixture of the amorphous phase (Table 5).

Table 5. Sample Description Hydrothermal treatment temperature, ° C Phase composition CSR size, nm (± 10%) Unstabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ one hundred Anataz - 100% 25 Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ 150 Anataz - 100% 21 Non-stabilized solution 0.3 M TiOSO ₄ + 0.25 M HNO ₃ 250 Anataz - 100% 22

The results of the study of the formation of particles of titanium dioxide at different processing times show that it is possible to significantly reduce the processing time proposed in the prototype (up to 48 hours).

Based on the studies, the above examples clearly confirm the possibility of obtaining the proposed method of particles of titanium oxide is significantly smaller (20-60 nm) than other methods, and all particles are completely crystallized. This leads to the fact that the specific surface area of the material increases, which enhances its photocatalytic properties. In addition, titanium dioxide is formed in the form of mesoporous particles, which further increases the surface area available for catalysis.

The claimed invention, as shown by the results of numerous studies, can increase the efficiency of water and air purification from organic pollutants, effectively carry out air disinfection in medical institutions, conduct photocatalytic decomposition of water in order to obtain molecular hydrogen and its further use as a fuel. In addition, the achieved mesoporosity of the obtained material makes it possible to use it in other industries, for example, to obtain white pigment in paints, plastics, in the pulp and paper, textile, food industries, in leather processing, in pharmaceuticals, and cosmetics.

Information sources

1. M. Kaneko, I. Okura, Photocatalysis: Science and Technology. Springer, 2002, 356 p.

2. Patent of the Russian Federation No. 2315123.

3. Patent of the Russian Federation No. 2315818.

4. Patent of the Russian Federation No. 2317345.

5. Patent of the Russian Federation No. 2291839.

6. German patent No. 102006035755.

7. Korean Patent No.20020043133 is a prototype.

Claims (5)

1. A method of producing a titanium dioxide-based photocatalyst, which consists in preparing an aqueous solution of titanyl sulfate and its hydrothermal treatment, characterized in that the concentration of titanyl sulfate in the aqueous solution is 0.1-1.0 mol / l, acid is added to the solution until concentration of 0.15-1 mol / l, the solution is subjected to hydrolysis under hydrothermal conditions at a temperature in the range of 100-250 ° C for 0.5-24 hours, after which the resulting suspension of porous titanium dioxide is dried. 2. The method according to claim 1, characterized in that a solution of sulfuric acid is used as the acid. 3. The method according to claim 1, characterized in that the porous titanium dioxide is isolated by centrifugation. 4. The method according to claim 3, characterized in that the porous titanium dioxide is purified from the mother liquor using distilled water. 5. The method according to claim 4, characterized in that the porous titanium dioxide is dried in air at 60-70 ° C.

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