Tungsten trioxide containing surface oxygen vacancies, preparation thereof and application thereof in photocatalytic oxidation of acetonitrile

Abstract

The application belongs to the technical field of photocatalytic materials, and particularly relates to a surface oxygen vacancy-containing tungsten trioxide and a preparation method and photocatalytic acetonitrile oxidation application thereof. The application adds a sodium tungstate solution dropwise into a hydrochloric acid solution under stirring, stirs after the dropwise addition is completed, centrifuges, washes and dries the precipitate after the reaction is completed, and obtains monoclinic tungsten trioxide; the obtained monoclinic tungsten trioxide is annealed to obtain the surface oxygen vacancy-containing tungsten trioxide. The surface oxygen vacancy-containing tungsten trioxide prepared by the application can photocatalyze the selective oxidation of acetonitrile to formic acid with high activity and high selectivity, realizes efficient degradation of acetonitrile and conversion into formic acid product which also has economic value. The application can degrade acetonitrile wastewater by means of photocatalysis, obtain formic acid product with high added value at the same time, greatly reduce the treatment cost, and the catalyst does not decrease in performance in a catalytic test of five cycles for 30 hours, and has wide application prospects in practical application.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a tungsten trioxide containing surface oxygen vacancies, its preparation, and its application in photocatalytic oxidation of acetonitrile. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention.

[0003] Acetonitrile (CH3CN), a stable organic substance, is widely used in industry, pharmaceuticals, and laboratories as a solvent and extractant. Consequently, the production of acetonitrile-containing wastewater is enormous. Acetonitrile is a highly toxic substance, and its (-CN) group possesses strong biotoxicity, posing a significant potential threat to the environment and ecosystem. Furthermore, acetonitrile is highly volatile and extremely difficult to degrade, making the treatment of acetonitrile-containing wastewater extremely challenging. Currently, besides using reflux methods to treat wastewater containing high concentrations of acetonitrile, common methods for acetonitrile wastewater degradation are limited to thermocatalysis and electrochemical oxidation. Both methods are relatively expensive and only completely mineralize acetonitrile into carbon dioxide. Current acetonitrile wastewater treatment methods still suffer from drawbacks such as high degradation costs, long degradation processes, and the lack of usable degradation products. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide tungsten trioxide with surface oxygen vacancies, its preparation method, and its application in photocatalytic acetonitrile oxidation.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing tungsten trioxide containing surface oxygen vacancies, comprising the following steps:

[0007] S1. Add sodium tungstate solution dropwise to hydrochloric acid solution with stirring. After the addition is complete, stir the reaction. After the reaction is complete, centrifuge, wash and dry the precipitate to obtain monoclinic tungsten trioxide.

[0008] S2. Anneal the monoclinic tungsten trioxide obtained in step S1 to obtain tungsten trioxide with surface oxygen vacancies.

[0009] Preferably, in step S1, the concentration of sodium tungstate solution is 0.9-1.1 mol / L, the concentration of hydrochloric acid solution is 2.9-3.1 mol / L, the volume ratio of sodium tungstate solution to hydrochloric acid solution is 1:6-12, and the stirring reaction time is 1-2 h.

[0010] Preferably, in step S2, the annealing reaction temperature is 350-600 °C, the time is 2-6 h, and the annealing atmosphere is air, argon, or nitrogen. By adjusting the annealing time, atmosphere, and temperature, tungsten trioxide nanomaterials with different oxygen vacancy concentrations can be obtained.

[0011] In a second aspect, the present invention provides tungsten trioxide containing surface oxygen vacancies, which is obtained by the preparation method described in the first aspect.

[0012] Thirdly, the present invention provides the application of tungsten trioxide containing surface oxygen vacancies as described in the second aspect in the photocatalytic oxidation of acetonitrile.

[0013] Fourthly, the present invention provides a method for photocatalytic oxidation of acetonitrile, comprising the following steps:

[0014] Tungsten trioxide containing surface oxygen vacancies, as described in the second aspect, is dispersed in an aqueous solution of acetonitrile and subjected to a photocatalytic reaction under illumination.

[0015] Preferably, the ratio of tungsten trioxide containing surface oxygen vacancies to acetonitrile is 2-3 mg:1 mL.

[0016] Preferably, the volume ratio of acetonitrile to water in the acetonitrile aqueous solution is 1:0.5-59.

[0017] Preferably, the light used for illumination is ultraviolet light, visible light, or full-spectrum light.

[0018] Preferably, the atmosphere of the reaction system during the photocatalytic reaction is one or more of argon, oxygen, carbon dioxide and air.

[0019] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0020] (1) This invention can conveniently and efficiently synthesize a large amount of monoclinic tungsten trioxide material through a simple tungstic acid precipitation method. The subsequent argon annealing generates effective oxygen vacancies on the material surface, which serve as effective sites for the adsorption and activation of acetonitrile and water molecules, without causing the material to generate too many bulk oxygen vacancies that induce the recombination of photogenerated carriers. The material synthesis method is simple and controllable as a whole, and is suitable for large-scale industrialization.

[0021] (2) In the photocatalytic reaction of acetonitrile selective oxidation to formic acid, the tungsten trioxide material with oxygen vacancies on its surface exhibits amazing high activity (~8 mmol / g catalyst per hour formic acid yield) and high selectivity (>85%), achieving efficient degradation of acetonitrile without complete mineralization. Instead, it is highly selectively converted into formic acid, which is also economically valuable. Therefore, by means of photocatalysis, acetonitrile wastewater is degraded while obtaining formic acid with high added value, which can significantly reduce treatment costs. Moreover, the performance of the catalyst did not decrease in the catalytic test of five cycles for a total of 30 h, and it has broad prospects in practical applications.

[0022] (3) In the photocatalytic reaction of acetonitrile selective oxidation to formic acid by tungsten trioxide material rich in oxygen vacancies on the surface, stable acetonitrile molecules were successfully activated by photocatalysis and tungsten trioxide material, and the carbon-carbon bond and carbon-nitrogen bond in acetonitrile molecules were broken at the same time. Its internal mechanism is worth further exploration. Moreover, compared with other wide bandgap semiconductors, the high selectivity of tungsten trioxide for formic acid products is very attractive, which also opens up a new path for the photocatalytic activation of stable cyano and methyl groups.

[0023] (4) In the photocatalytic reaction of selective oxidation of acetonitrile to formic acid by tungsten trioxide material with oxygen vacancies on its surface, the catalyst can be directly added to the acetonitrile aqueous solution and placed under light to carry out the catalytic reaction efficiently. This simple and conventional catalytic reaction condition ensures the feasibility and convenience of large-scale application and proves its practical application value. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 These are scanning electron microscope images of tungsten trioxide containing surface oxygen vacancies obtained in Examples 1 and 2 of this invention;

[0026] Figure 2 This is a transmission electron microscope image of tungsten trioxide containing surface oxygen vacancies from Example 1;

[0027] Figure 3 The image shows an X-ray diffraction pattern of tungsten trioxide containing surface oxygen vacancies from Example 1.

[0028] Figure 4 These are diffuse reflectance images of tungsten trioxide containing surface oxygen vacancies in Examples 1 and 2;

[0029] Figure 5Electron paramagnetic resonance (EPR) images of tungsten trioxide containing surface oxygen vacancies in Examples 1 and 2;

[0030] Figure 6 The graphs show the performance of tungsten trioxide photocatalytic oxidation of acetonitrile with surface oxygen vacancies in Examples 1 and 2.

[0031] Figure 7 The time-resolved performance diagrams of tungsten trioxide photocatalytic oxidation of acetonitrile with surface oxygen vacancies in Examples 1 and 2 are shown.

[0032] Figure 8 The graph shows the yield and selectivity of tungsten trioxide and anatase TiO2 containing surface oxygen vacancies in Example 1. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0034] Example 1

[0035] (1) Dissolve 1.65 g of sodium tungstate dihydrate in 5 mL of deionized water to obtain a 1 mol / L sodium tungstate aqueous solution.

[0036] (2) 11.25 mL of 37% concentrated hydrochloric acid was added dropwise to 33.75 mL of deionized water to obtain 45 mL of hydrochloric acid aqueous solution of about 3 mol / L.

[0037] (3) Add sodium tungstate aqueous solution slowly dropwise into hydrochloric acid aqueous solution, while the hydrochloric acid aqueous solution is continuously and rapidly stirred. Tungstic acid precipitate will be generated immediately during the dropwise addition. After the dropwise addition is completed, continue stirring for 1 h.

[0038] (4) Centrifuge and wash the precipitate, then wash it several times with deionized water and anhydrous ethanol until the pH is neutral. Then place it in an oven to dry.

[0039] (5) After the dried sample is preliminarily ground, it is placed in a porcelain boat and then placed in a tube furnace. After the furnace is installed, argon gas is purged for 1 h and then annealed. The specific conditions are 500 ℃ for 3 h. Argon gas is kept flowing continuously throughout the annealing process. After natural cooling, tungsten trioxide rich in surface oxygen vacancies is obtained, denoted as Ov-R-WO3.

[0040] Example 2

[0041] Unlike Example 1, air was used in the annealing process in step (5), while the other conditions remained the same. Tungsten trioxide containing a small number of surface oxygen vacancies was obtained, denoted as Ov-P-WO3.

[0042] like Figure 1 As shown, the two types of tungsten trioxide containing surface oxygen vacancies prepared in Examples 1 and 2 have uniform nanosheet morphologies with an overall size of approximately 200~400 nm.

[0043] like Figure 3 As shown, the X-ray diffraction image confirms that the synthesized tungsten trioxide with surface oxygen vacancies is a monoclinic crystal.

[0044] like Figure 4 As shown in the diffuse reflection absorption diagram, the Ov-R-WO3 of Example 1 exhibits an absorption tail in the visible light band based on local surface plasmon resonance (LSPR), which proves the presence of more oxygen vacancies.

[0045] like Figure 5 As shown in the electron paramagnetic resonance (EPR) spectrum, the signal at g=2.003 is an oxygen vacancy signal, and the signal intensity of Ov-R-WO3 in Example 1 is higher than that of Ov-P-WO3 in Example 2, which proves that it has a higher oxygen vacancy concentration.

[0046] Example 3

[0047] Weigh 5 mg of the Ov-R-WO3 sample synthesized in Example 1 and add it to an acetonitrile aqueous solution obtained by mixing 4 mL of acetonitrile with 2 mL of deionized water. After thorough ultrasonic dispersion, place the solution in a sealed quartz reaction vessel and connect the exhaust gas line to exhaust the gas using argon gas for 1 hour. After exhausting the gas, seal the vessel and extract a certain amount of gas from the vessel using a disposable syringe. Then, inject an equal volume of oxygen, with the oxygen to reaction vessel volume ratio being approximately 1:5 (i.e., the atmosphere inside the vessel is 80% argon gas by volume + 20% oxygen gas by volume). After the gas inside the vessel is evenly mixed, place the reactor under a 300-watt xenon lamp for photocatalytic reaction, maintaining a constant temperature of 25°C during the reaction.

[0048] Example 4

[0049] The Ov-P-WO3 tungsten trioxide nanomaterials prepared in Example 2 were subjected to catalytic oxidation of acetonitrile. Except for the catalyst used, the other conditions were the same as in Example 3.

[0050] Comparative Example 1

[0051] Unlike Example 3, a commercial anatase titanium dioxide sample was used as the catalyst, while the other conditions remained the same.

[0052] like Figure 6As shown in the performance graph of photocatalytic conversion of acetonitrile to formic acid, the Ov-R-WO3 sample with a higher surface oxygen vacancy concentration exhibits a superior formic acid yield compared to the Ov-P-WO3 sample with a lower surface oxygen vacancy concentration, with a yield of up to 8.8 mmol / g catalyst per hour.

[0053] like Figure 7 As shown, the production of formic acid continued to rise within a 6-hour cycle, exhibiting a good time-dependent effect.

[0054] like Figure 8 As shown, the prepared tungsten trioxide nanomaterials have high selectivity for photocatalytic oxidation of acetonitrile, while commercially available anatase titanium dioxide mineralizes in large quantities to produce carbon dioxide products, and its overall activation efficiency for acetonitrile is far inferior to that of Ov-R-WO3 prepared in Example 1.

[0055] Example 5

[0056] Unlike Example 1, in step (5) of the annealing process, the annealing temperature was 600 °C, and the other conditions were the same, resulting in tungsten trioxide with surface oxygen vacancies.

[0057] Example 6

[0058] Unlike Example 1, in step (5) of the annealing process, the annealing temperature was 350 °C, and the other conditions were the same, resulting in tungsten trioxide with surface oxygen vacancies.

[0059] Example 7

[0060] Unlike Example 1, in step (5) annealing, the annealing time was 2 h, and the other conditions were the same, resulting in tungsten trioxide with surface oxygen vacancies.

[0061] Example 8

[0062] Unlike Example 1, in step (5) annealing, the annealing time was 6 h, and the other conditions were the same, resulting in tungsten trioxide with surface oxygen vacancies.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of tungsten trioxide containing surface oxygen vacancies in the photocatalytic oxidation of acetonitrile, characterized in that, The method for preparing tungsten trioxide containing surface oxygen vacancies includes the following steps: S1. Add sodium tungstate solution dropwise to hydrochloric acid solution with stirring. After the addition is complete, stir the reaction. After the reaction is complete, centrifuge, wash and dry the precipitate to obtain monoclinic tungsten trioxide. S2. Anneal the monoclinic tungsten trioxide obtained in step S1 to obtain tungsten trioxide with surface oxygen vacancies. In step S2, the annealing reaction temperature is 350-600 ℃, the time is 2-6 h, and the annealing atmosphere is argon or nitrogen. In step S1, the concentration of sodium tungstate solution is 0.9-1.1 mol / L, the concentration of hydrochloric acid solution is 2.9-3.1 mol / L, the volume ratio of sodium tungstate solution to hydrochloric acid solution is 1:6-12, and the stirring reaction time is 1-2 h.

2. The application as described in claim 1, characterized in that, Includes the following steps: The tungsten trioxide containing surface oxygen vacancies was dispersed in an aqueous acetonitrile solution and subjected to a photocatalytic reaction under illumination.

3. The application as described in claim 2, characterized in that, The ratio of tungsten trioxide containing surface oxygen vacancies to acetonitrile is 2-3 mg: 1 mL.

4. The application as described in claim 2, characterized in that, The volume ratio of acetonitrile to water in an aqueous acetonitrile solution is 1:0.5-59.

5. The application as described in claim 2, characterized in that, The light used for illumination is ultraviolet light, visible light, or full-spectrum light.

6. The application as described in claim 2, characterized in that, The atmosphere of the reaction system during the photocatalytic reaction is one or more of argon, oxygen, carbon dioxide and air.

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