CN1994558A - Method for preparing unidimensional TiO2 hollow structured photocatalyst using vanadium oxide nanobelt as template - Google Patents

Abstract

The invention proposes a method for preparing a one-dimensional _TiO2 hollow structure photocatalyst by using vanadium oxide nanobelt as a template in one step. The method is to dissolve titanium tetrafluoride in deionized water, immerse the prepared vanadium oxide nanobelt in the solution, and treat it at a low temperature for a period of time to directly obtain a crystallized one-dimensional _TiO2 hollow structure photocatalyst. The basic principle of this preparation method is that the vanadium oxide nanoribbon template induces the deposition of _TiO2 nanoparticles on its surface to form a core-shell structure, while the vanadium oxide nanoribbon template is dissolved by HF in situ to form a hollow structure. The advantage of this method is to use the vanadium oxide nanobelt as a template to prepare a one-dimensional TiO ₂ hollow structure photocatalyst in one step, which simplifies the template method. In the preparation of a TiO ₂ hollow structure photocatalyst, the deposition (or growth) of TiO ₂ on the surface of the template and the template The complex process of removal, the obtained one-dimensional TiO ₂ hollow structure photocatalyst can overcome the problems of easy agglomeration and difficult separation of powder photocatalyst in the process of using the aqueous reaction system.

Description

One-step preparation method of one-dimensional TiO2 hollow structure photocatalyst using vanadium oxide nanobelt as template

technical field

The invention relates to a preparation method of an easy-to-separate one-dimensional _TiO2 hollow structure photocatalyst, and also relates to the technical field of simple template preparation of other oxide hollow structure materials.

technical background

In recent years, in order to solve the increasingly serious problem of environmental pollution, the research and development of heterogeneous photocatalytic materials has attracted extensive attention from governments and researchers all over the world, because this kind of photocatalytic materials can be widely used in air purification and water sterilization. Disinfection, degradation and removal of toxic and harmful pollutants in water, etc. Among all kinds of oxide semiconductor photocatalytic materials, practice has proved that titanium dioxide is the most suitable for a wide range of environmental applications, because titanium dioxide has biological and chemical inertness, very strong oxidation ability, strong resistance to light and chemical corrosion, etc. Powdered titanium dioxide photocatalyst, due to its high specific surface area, shows high photocatalytic efficiency in the degradation of pollutants in wastewater treatment and water purification. However, due to the small particle size of the powder photocatalyst, the photocatalyst is easy to agglomerate in the reaction system and difficult to separate and recover from the reaction mixture after the photocatalytic reaction, especially in the process of photocatalytic treatment of industrial wastewater. Difficulty in separation results in a high loss rate of powder photocatalysts, which severely limits the development of photocatalytic technology. Therefore, the preparation of one-dimensional _TiO2 photocatalysts with lengths in the micrometer scale that are easy to separate and recover has attracted extensive attention.

In the preparation process of one-dimensional _TiO2 hollow structure photocatalyst, the most commonly used method is the template synthesis method. The template synthesis method usually uses sol-gel, electrochemical deposition, and electrospray to deposit _TiO2 particles on the surface of the template (such as polymer fibers) or the inner wall of a tubular template (such as porous aluminum film). However, the structural materials prepared by the above method are usually amorphous TiO ₂ , so the template must be removed by high temperature heat treatment or dissolution and corrosion to form a hollow structure, which leads to the complexity of the template method in the process of preparing hollow materials . At the same time, the process of removing the template often leads to the destruction of the hollow structure, thus limiting the wide application of the template method. In order to simplify the template method in the preparation of TiO ₂ hollow structured photocatalysts, the complex process of TiO ₂ deposition (or growth) on the template surface and template removal must be experienced, and from the perspective of energy saving, the development of low-temperature crystallized one-dimensional TiO ₂ hollow structured photocatalysts A facile template preparation technique for catalysts is inevitable.

Contents of the invention

According to the current research status at home and abroad, considering the complexity of the usual template method in the process of preparing hollow structure materials and the shortcomings of titanium dioxide powder photocatalysts in the use process, the present invention proposes a vanadium oxide nanobelt as a template One-step method for preparing one-dimensional _TiO2 hollow structure photocatalyst. The method of the invention can prepare a one-dimensional _TiO2 hollow structure photocatalyst with a length of 5-400 microns, a specific surface area of 50-90 ^m2 /g, and _TiO2 nanoparticles with a diameter of 10-55 nm.

The basic principle of one-dimensional TiO ₂ hollow structure photocatalyst prepared in one step using vanadium oxide nanobelt as template: the hydrolysis reaction formula of titanium tetrafluoride in deionized water is: TiF ₄ +H ₂ O→Ti(OH) ₄ +4HF. Therefore, the hydrolysis of titanium tetrafluoride produces HF as a by-product while forming _TiO2 particles. Experiments have shown that when a certain amount of vanadium oxide nanobelts are added to the HF solution (pH 1.7), when the temperature is controlled at 25-60°C and kept for 3-6 hours, the vanadium oxide nanobelts can be completely dissolved to form a clear solution. Therefore, we proposed the formation process of one-dimensional TiO ₂ hollow structure photocatalyst: first, TiO ₂ nanoparticles undergo heterogeneous nucleation and growth on both sides of the vanadium oxide nanobelt surface (as shown in Figure 1A1), and then TiO ₂ nanoparticles from the nanobelt Both sides gradually grow towards the middle of the ribbon until the nanoribbon is completely covered by TiO ₂ nanoparticles to form a core-shell structure (as shown in Figure 1A2). At the same time, due to the continuous hydrolysis of titanium tetrafluoride, the concentration of HF in the reaction solution increased, so after the formation of the core-shell structure, the vanadium oxide nanoribbons were gradually dissolved by HF, resulting in the formation of a hollow structure (as shown in Figure 1A3).

According to above-mentioned analysis, the technical scheme that realizes the object of the present invention is:

A method for preparing a one-dimensional _TiO2 hollow structure photocatalyst using a vanadium oxide nanobelt as a template, which is characterized in that it is a low-temperature template preparation method, and the preparation steps are as follows:

1. The length of the vanadium oxide nanobelt template prepared by the hydrothermal method is 10-400 microns, the width is 100-300 nanometers, and the thickness is 20-50 nanometers;

The 2nd, dissolve titanium tetrafluoride in deionized water and stir to form a reaction solution evenly, adjust the pH value of the reaction solution with 1 mol/liter of hydrochloric acid and 1 mol/liter of sodium hydroxide to be 0-6, wherein the titanium tetrafluoride The molar concentration is 0.001-0.1 mol/liter;

3. Immerse 0.001 gram of vanadium oxide nanobelt prepared in step 1 into 60 ml of reaction solution prepared in step 2, seal it and put it in an oven with a temperature of 30-90 ° C for 8-20 hours to obtain a white precipitate substance solution;

4. Take out the reaction solution that has been heat-preserved in step 3, filter the white precipitate, rinse it with deionized water and absolute ethanol, and finally dry it in vacuum at 50-80°C to obtain a one-dimensional TiO ₂ hollow structured light catalyst.

The preferred preparation conditions of this method are: the concentration of titanium tetrafluoride in the reaction solution is 0.005-0.05 mol/liter; the pH of the solution is 1-3; the reaction temperature is 50-70°C; the reaction time is 10-15 hours; The white reaction product is washed with deionized water and absolute ethanol for 3-5 times respectively; the temperature of vacuum drying is 50-80° C.; the time of vacuum drying is 4-10 hours.

The preparation method step of described vanadium oxide nanobelt template is:

1. Add 0.01-0.1 grams of ammonium metavanadate and 0.1-0.5 grams of polyethylene glycol 400 into 30 ml of deionized water, and stir evenly;

The 2nd, be 2-4 with the pH of 1 mol/liter hydrochloric acid and 1 mol/liter sodium hydroxide regulation step 1 gained solution;

3rd, put the reaction solution obtained in step 2 into a 50 ml hydrothermal kettle, and keep it warm at 180-200° C. for 20-30 hours to generate vanadium oxide nanobelt precipitation;

4. After filtering the precipitate obtained in step 3, wash it with deionized water and absolute ethanol for 3-5 times respectively, and then vacuum dry it at 50-80° C. for 4-10 hours to obtain vanadium oxide nanobelts.

In addition to the vanadium oxide nanobelt, the template used to prepare the _TiO2 hollow structure in the present invention can also be a vanadium oxide nanostructure with other special shapes such as: nanorods, nanotubes, nanofibers, nanoneedles, and nanoparticles wait.

The photocatalytic activity of the 1D TiO hollow-structured photocatalyst was characterized by the photocatalytic degradation of methyl orange solution. The experimental procedure is as follows: Disperse 0.02 g of titanium dioxide photocatalyst in a quartz glass tank (52W×155L×20H mm) filled with 25 ml of methyl orange aqueous solution (3.1×10 ⁻⁵ mol/L). The UV light source (Cole-Parmer Instrument Co.) has a wavelength of 365 nm and a power of 15 W. The average light intensity irradiated on the methyl orange liquid surface is 112 microwatts/cm ² , which is measured by a UV radiometer produced by Beijing Normal University. Every 20 minutes, the reaction solution was separated by filtration, and then the concentration of methyl orange in the reaction solution was measured. The concentration of methyl orange in the degradation solution was determined by ultraviolet-visible absorption spectroscopy (UV-2550, SHIMADZU, Japan).

Description of drawings

Figure 1 The formation mechanism of the one-dimensional _TiO2 hollow structure (the lower part of the figure corresponds to the cross-section of the template at each stage): A1 is the heterogeneous nucleation and growth of _TiO2 nanoparticles on both sides of the vanadium oxide nanobelt surface; A2 is that TiO ₂ nanoparticles grow from both sides of the nanobelt to the middle of the ribbon, forming a core-shell structure; A3 is that the vanadium oxide nanobelt is gradually dissolved by HF, resulting in the formation of a hollow structure

The vanadium oxide nanoribbon template (B1, B2) and the one-dimensional _TiO2 hollow structure photocatalyst (B3, B4) FESEM picture that Fig. 2 embodiment 1 prepares

The XRD spectrum of the vanadium oxide nanoribbon template (C1) and one-dimensional TiO _hollow structure photocatalyst (C2) prepared in Fig. 3 embodiment 1

TEM (D1) and HRTEM (D2) pictures of the one-dimensional _TiO2 hollow structure photocatalyst prepared in Fig. 4 embodiment 1; Insert the corresponding electron diffraction pattern in Fig. D1

Fig. 5 Photocatalytic degradation of methyl orange by the one-dimensional TiO ₂ hollow structure photocatalyst prepared in Example 1: E1 is without adding photocatalyst; E2 is adding one-dimensional TiO ₂ hollow structure photocatalyst.

Detailed ways

Example 1:

Preparation of vanadium oxide nanobelt template: Add 0.06 g of ammonium metavanadate and 0.25 g of polyethylene glycol 400 into 30 ml of deionized water and stir evenly, adjust the above solution with 1 mol/L hydrochloric acid and 1 mol/L sodium hydroxide pH to 3. Then the reaction solution was transferred to a 50 ml hydrothermal kettle and kept at 190±2° C. for 24 hours. After the reaction is completed, the precipitate is separated by filtration, washed three times with deionized water and absolute ethanol, and finally vacuum-dried at 60±2° C. for 8 hours to obtain vanadium oxide nanobelts. Figures 2B1 and 2B2 show field emission SEM images of vanadium oxide nanoribbons. It can be seen from the figure that the products prepared by this hydrothermal method are nanoribbon structures with a length of 10-400 micrometers, a width of 100-300 nanometers, and a thickness of about 35 nanometers. Figure 3C1 shows the XRD pattern of the as-prepared nanoribbon structure, indicating that its crystal structure is layered vanadium oxide. According to the element composition analysis of XPS, the molecular formula of the nanobelt is VO _2.36 ·0.49H ₂ O.

Preparation of one-dimensional _TiO2 hollow structure photocatalyst: dissolve titanium tetrafluoride in deionized water and stir evenly to form a reaction solution, immerse 0.001 g of vanadium oxide nanoribbons into 60 ml of _TiF4 reaction solution with a concentration of 0.005 mol/L , the pH of the solution is about 1.9, the reaction solution is sealed and placed in an oven with a temperature of 60±2°C for heat preservation for 12 hours. The reaction solution was taken out, the white precipitate was filtered, washed three times with deionized water and absolute ethanol, and dried in vacuum at 60±2°C for 8 hours to obtain a one-dimensional _TiO2 hollow structure photocatalyst. Figure 2B3 and 2B4 show the field emission SEM pictures of the _1D TiO2 hollow structure photocatalyst. It can be seen from the figure that the as-prepared _TiO2 photocatalyst maintains the morphology of the nanoribbon template, whose length is generally greater than 5 μm. At the same time, this one-dimensional _TiO2 structure is composed of many small particles with a particle size of 10-55 nm. The XRD pattern of this sample (FIG. 3C2) shows that its crystal structure is pure anatase _TiO2 without the presence of vanadium oxide phase. The TEM in Figure 4D1 proves that the as-prepared _{1D TiO2} sample is a hollow structure. At the same time, HRTEM (Fig. 4D2) further proved that the crystal structure of the hollow structure is anatase phase.

Figure 5 is the degradation curve of the one-dimensional _TiO2 hollow structure photocatalyst to the methyl orange solution. It can be seen from Fig. 5E1 that when no photocatalyst was added, UV light did not cause a decrease in the concentration of methyl orange. On the contrary, the concentration of methyl orange increased slightly, which was mainly due to the increase of the concentration of methyl orange due to the evaporation of a small amount of water under light. When the as-prepared _1D TiO2 hollow photocatalyst was added (Figure 5E2), the concentration of methyl orange decreased rapidly with the prolongation of the illumination time, indicating that methyl orange was effectively degraded by the photocatalyst.

For practical application of _TiO2 photocatalyst, in addition to having high photocatalytic activity, the preparation process of the catalyst should be as simple as possible, especially the catalyst used is easy to separate from the solution after photocatalytic wastewater treatment and water purification Can be reused. Nano-powder titanium dioxide photocatalysts such as P25 show high photocatalytic efficiency for the degradation of various pollutants due to their high specific surface area. However, due to the small particle size of the powder photocatalyst, the photocatalyst is easy to agglomerate in the reaction system and difficult to separate and recover from the reaction mixture after the photocatalytic reaction. The length of the one-dimensional _TiO2 photocatalyst prepared by the invention is in the range of microns, so after the photocatalytic degradation of organic pollutants, it is easy to separate from the reaction solution and enter the next cycle. At the same time, the wall shell of the photocatalyst prepared by this method has a mesoporous structure, which can effectively transport the organic reactants and degradation products in the shell through the mesoporous channels between the pore walls, thereby increasing the efficiency of the photocatalytic reaction. .

Example 2:

In order to examine the effect of the concentration of titanium tetrafluoride on the morphology of the one-dimensional _TiO2 hollow structure, in addition to the concentration of titanium tetrafluoride, other reaction conditions such as: the pH value of the reaction solution, the reaction temperature of the solution, and the reaction time of the solution Etc. are identical with embodiment 1. The results show that when the concentration of titanium tetrafluoride is higher than 0.1 mol/liter, because the shell layer of the prepared _TiO2 hollow structure is very thick, it is difficult to see its hollow structure with TEM; when the concentration of titanium tetrafluoride is low At 0.001 mol/L, due to the low content of _TiO2 in the system, the surface of the vanadium oxide nanobelts cannot be completely covered, resulting in an uneven hollow structure. At the same time, the decrease in the concentration of titanium tetrafluoride leads to The template cannot be completely dissolved by HF. The optimum concentration of titanium tetrafluoride is 0.005-0.05 mol/liter.

Example 3:

In order to examine the effect of the pH value of the reaction solution on the morphology of the one-dimensional _TiO2 hollow structure, except for the pH value of the reaction solution, other reaction conditions such as: the concentration of the reaction solution, the reaction temperature of the solution, and the reaction time of the solution were all compared with Example 1 is exactly the same. The results show that when the pH value of the reaction solution is higher than 6, the solution has an obvious white precipitate, which is deposited on the bottom of the container but not on the surface of the template, and it is difficult to obtain a hollow structure of one-dimensional TiO ₂ . The increase in the hydrolysis rate of titanium fluoride leads to a decrease in the crystallization degree of titanium dioxide particles; when the H ⁺ ions in the reaction solution are very high (pH<0), since the presence of H ⁺ ions will inhibit the hydrolysis of titanium tetrafluoride, it takes longer processing time. The pH value of the optimal reaction solution is 1-3.

Example 4:

In order to examine the effect of the reaction temperature of the solution on the morphology of the one-dimensional _TiO2 hollow structure, except for the different reaction temperatures of the solutions, other reaction conditions such as: the concentration of titanium tetrafluoride, the pH value of the reaction solution, and the reaction time of the solution were all the same. Exactly the same as Example 1. The results show that when the reaction temperature of the solution is lower than 30±2°C, the hydrolysis reaction rate of titanium tetrafluoride is too slow, the deposition rate of titanium dioxide particles is too low, and a long reaction time is required; when the reaction temperature is higher than 90±2 At 2°C, the hydrolysis reaction rate of titanium tetrafluoride is too fast, and titanium dioxide directly forms powder and deposits at the bottom of the container, which affects the number of particles deposited on the surface of the vanadium oxide nanoribbon template. The optimal reaction temperature of the reaction solution is 50-70°C.

Example 5:

In order to test the effect of the reaction time of the solution on the morphology of the one-dimensional _TiO2 hollow structure, except for the different reaction time of the solution, other reaction conditions such as: concentration of titanium tetrafluoride, pH value of the reaction solution, reaction temperature of the solution, etc. Exactly the same as Example 1. The results show that when the reaction time of the solution is less than 8 hours, titanium tetrafluoride is not completely hydrolyzed and forms titanium dioxide particles and deposits on the surface of the vanadium oxide nanobelt template, which will cause waste of raw materials, and the vanadium oxide nanobelt template cannot be completely removed ; When the reaction time is longer than 20 hours, the impact on the morphology of the one-dimensional TiO ₂ hollow structure is very small, and from the perspective of energy saving, it will cause waste of energy. The optimal reaction time of the reaction solution is 10-15 hours.

Claims (8)

1. A method for preparing one-dimensional TiO _hollow structure photocatalyst with vanadium oxide nanobelt as a template, characterized in that the steps of the method are as follows: 1. The vanadium oxide nanobelt prepared by the hydrothermal method is used as a template, the length of the template is 10-400 microns, the width is 100-300 nanometers, and the thickness is 20-50 nanometers; The 2nd, dissolve titanium tetrafluoride in deionized water and stir to form a reaction solution evenly, adjust the pH value of the reaction solution with 1 mol/liter of hydrochloric acid and 1 mol/liter of sodium hydroxide to be 0-6, wherein the titanium tetrafluoride The molar concentration is 0.001-0.1 mol/liter; 3. Immerse 0.001 gram of vanadium oxide nanobelt prepared in step 1 into 60 ml of reaction solution prepared in step 2, seal it and put it in an oven with a temperature of 30-90 ° C for 8-20 hours to obtain a white precipitate substance solution; 4. Take out the reaction solution that has been heat-preserved in step 3, filter the white precipitate, rinse it with deionized water and absolute ethanol, and finally dry it in vacuum at 50-80°C to obtain a one-dimensional _TiO2 hollow structure photocatalyst . 2. The method for preparing a one-dimensional _TiO2 hollow structure photocatalyst according to claim 1, characterized in that the molar concentration of titanium tetrafluoride in the reaction solution is 0.005-0.05 mol/liter. 3. The method for preparing one-dimensional _TiO2 hollow structure photocatalyst according to claim 1, characterized in that the pH value of the reaction solution is 1-3. 4. The method for preparing a one-dimensional TiO ₂ hollow structure photocatalyst as claimed in claim 1, characterized in that the reaction temperature of the reaction solution is 50-70°C. 5. The method for preparing a one-dimensional _TiO2 hollow structure photocatalyst as claimed in claim 1, characterized in that the reaction time of the reaction solution is 10-15 hours. 6. The method for preparing a one-dimensional _TiO2 hollow photocatalyst as claimed in claim 1, characterized in that the obtained white reaction product is washed with deionized water and absolute ethanol for 3-5 times respectively. 7. The method for preparing one-dimensional TiO ₂ hollow photocatalyst according to claim 1, characterized in that the vacuum drying temperature is 50-80°C; the vacuum drying time is 4-10 hours. 8. The hydrothermal preparation method of the vanadium oxide nanobelt used in claim 1, characterized in that the steps of the preparation method are: 1. Add 0.01-0.1 grams of ammonium metavanadate and 0.1-0.5 grams of polyethylene glycol 400 into 30 ml of deionized water, and stir evenly; The 2nd, be 2-4 with the pH of 1 mol/liter hydrochloric acid and 1 mol/liter sodium hydroxide regulation step 1 gained solution; 3rd, put the reaction solution obtained in step 2 into a 50 ml hydrothermal kettle, and keep it warm at 180-200° C. for 20-30 hours to generate vanadium oxide nanobelt precipitation; 4. After filtering the precipitate obtained in step 3, wash it with deionized water and absolute ethanol for 3-5 times respectively, and then vacuum dry it at 50-80° C. for 4-10 hours to obtain vanadium oxide nanobelts.

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