Zinc oxide / polyacid nanocomposite for photocatalytic production of hydrogen peroxide and preparation method thereof

Abstract

The application discloses a zinc oxide / polyoxometalate nanocomposite for photocatalytic production of hydrogen peroxide and a preparation method thereof. The ZnO nanomaterial with uniform size is prepared by using a hydrothermal-calcination method, and the ZnO nanomaterial is compounded with POMs through hydrothermal impregnation, so that the zinc oxide / polyoxometalate nanocomposite with uniform morphology and pure phase is obtained. In the preparation process, the specific reaction temperature and the mass ratio of reactants and other conditions can optimize the influence of polyoxometalate on the growth of ZnO crystals, so that the size and morphology of ZnO can be best controlled. Meanwhile, through the synthesis process of hydrothermal-calcination-heat bath impregnation, the synthesized composite material can compensate for the defects of nano-zinc oxide, introduce more photochemical active sites, effectively reduce the electron-hole recombination, accelerate the generation and transfer rate of photo-generated electrons, promote the catalytic activity of zinc oxide nanomaterial, and obtain a hydrogen peroxide production rate of 700 muM per hour and excellent cycle stability.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation and photocatalytic hydrogen peroxide production technology, and particularly to a zinc oxide / polyacid nanocomposite material for photocatalytic hydrogen peroxide production and its preparation method. Background Technology

[0002] Hydrogen peroxide (H2O2), as a multifunctional green catalyst, has been widely used in pharmaceutical disinfection, environmental remediation, chemical synthesis, and automotive batteries. Traditional hydrogen peroxide production uses the anthraquinone process (AQ), which has limitations such as environmental pollution, high energy consumption, and low economic efficiency. Therefore, photocatalytic hydrogen peroxide production has attracted widespread attention as a green and sustainable production method.

[0003] Photocatalytic generation of hydrogen peroxide mainly utilizes the electrons and holes generated by a photocatalyst under light irradiation to react with oxygen and water to produce hydrogen peroxide. Currently reported photocatalysts include metal oxides such as TiO2 and ZnO, carbon nitride (g-C3N4), and covalent organic frameworks (COFs). Among these, ZnO has attracted industry attention due to its low cost, high stability, and high carrier fractionation efficiency. Existing methods for synthesizing ZnO, including sol-gel methods, hydrothermal methods, and vapor deposition methods, cannot precisely control the size and morphology of ZnO particles and are difficult to regulate the active sites on the crystal faces, resulting in limited photocatalytic performance.

[0004] Polyoxometalates (POMs) have been widely used in photoelectrocatalysis due to their unique redox activity, excellent photochemical activity, reversible multi-electron transfer capability, good chemical stability, and tunability. However, to date, there are no reports on the preparation of zinc oxide / polyoxometalate nanocomposites by incorporating polyoxometalates onto nano-ZnO and applying them to the photocatalytic production of hydrogen peroxide. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing a zinc oxide / polyacid nanocomposite material for photocatalytic hydrogen peroxide production and its preparation method.

[0006] The technical solution of the present invention is: a zinc oxide / polyoxometalate nanocomposite material for photocatalytic hydrogen peroxide production, which is prepared by placing ZnO powder and polyoxometalates in deionized water and stirring in a hot bath. The morphology is cotton-like and the size is 30-130 nm.

[0007] A method for preparing the above-mentioned zinc oxide / polyacid nanocomposite material for photocatalytic hydrogen peroxide production is carried out according to the following steps: Step 1. Dissolve zinc salt and ammonium salt in deionized water at a mass ratio of 0.5-30:1 to form a mixed solution. Stir the mixed solution in a 40-100℃ hot bath and then transfer it to an autoclave and heat it at 90-180℃ for 4-36 h. Wash and dry the reaction product and then heat it in a muffle furnace at a heating rate of 5℃ / min to 300-900℃ and hold it for 1-5 h to obtain white ZnO powder. Step 2. Add ZnO powder and polyoxometalate at a mass ratio of 1:0.25 ~ 40 to deionized water and stir in a hot bath at 50-100℃ to obtain the composite material POMs@ZnO.

[0008] The preferred technical solution is that the zinc salt is zinc sulfate or zinc sulfide, the ammonium salt is ammonium chloride or ammonium carbonate, and the polyoxometalate is tungboronic acid (BW). 12 ), tungstic acid (SiW) 12 ) or tungsten phosphate (PW) 12 ).

[0009] A further preferred technical solution is that the zinc salt is zinc sulfate, the ammonium salt is ammonium carbonate, and the polyoxometalate is BW. 12 The mass ratio of ZnO powder to polyoxometalate is 1:1.

[0010] This invention utilizes a hydrothermal-calcination method to prepare uniformly sized ZnO nanomaterials, and then combines these ZnO nanomaterials with polyoxometalates (POMs) via hydrothermal impregnation to obtain a zinc oxide / polyoxometalate nanocomposite material with uniform morphology and pure phase. The specific reaction temperature and reactant mass ratios used in the preparation process optimize the influence of polyoxometalates on ZnO crystal growth, thereby achieving optimal control over ZnO size and morphology. Simultaneously, the hydrothermal-calcination-hot bath impregnation synthesis process compensates for the defects of nano-zinc oxide, introduces more photochemical active sites, effectively reduces electron-hole recombination, accelerates photogenerated electron generation and transfer rates, promotes the catalytic activity of the zinc oxide nanomaterials, and achieves a hydrogen peroxide yield of 700 μM per hour and excellent cycling stability. Attached Figure Description

[0011] Figure 1 The embodiments of the present invention are ZnO and BW 12 SEM image of @ZnO.

[0012] Figure 2 The embodiments of this invention are ZnO and BW. 12 BW 12 Fourier transform infrared spectrum and 400-1800 cm⁻¹ of ZnO -1 A magnified view of a portion of the image.

[0013] Figure 3 The embodiments of this invention are ZnO and BW. 12 BW 12 XRD pattern of ZnO.

[0014] Figure 4 The embodiments of this invention are ZnO and BW. 12 @ZnO、BW 12 0.5BW 12 @ZnO、2BW 12 The yield of H2O2 produced by photocatalysis of ZnO.

[0015] Figure 5 This is embodiment BW of the present invention. 12 Cyclic test diagram of ZnO photocatalytic hydrogen peroxide production. Detailed Implementation

[0016] All raw materials used in the embodiments of this invention are not particularly limited in their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0017] There are no particular restrictions on the purity of all raw materials used in the embodiments of this invention, but analytical grade is preferred.

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example 1

[0019] The preparation method of the zinc oxide / polyacid nanocomposite material for photocatalytic hydrogen peroxide production of the present invention is carried out in sequence according to the following steps: Step 1. Dissolve 2.87 g ZnSO4·7H2O and 0.567 g (NH4)2·CO3 in deionized water to form a mixed solution. Stir the mixed solution in a 40°C hot bath for 30 min. While hot, transfer it to a polytetrafluoroethylene liner and seal it in an autoclave. Then place it in an oven and heat it at 100°C for 5 h. Wash the reaction product, dry it at 60°C, and place it in a muffle furnace. Heat it to 700°C at a heating rate of 5°C / min and hold it for 2 h to obtain white ZnO powder. Step 2. Mix ZnO powder with BW 12 Add the mixture to 30 mL of deionized water at a mass ratio of 1:1 and stir at 80 °C for 24 h to obtain BW. 12 @ZnO; The polyacid BW used 12 (K5BW) 12 O 40 xH2O was prepared using the following method: Dissolve 100 g Na₂WO₄·2H₂O and 5 g H₃BO₃ sequentially in 100 mL of water, stirring vigorously. Then add 60 mL of 6 mol / L HCl solution, making the pH of the mixed solution 6. Boil for several hours, continuously adding water, to remove the solid Na₂WO₄·2H₂O. 10 W 12 O 41 The xH2O (byproduct) was filtered off, and the filtrate was acidified to pH=2 with 6 mol / L HCl solution and boiled for half an hour. 20 g of solid KCl was added to obtain a white precipitate, which was washed with ether to obtain 71 g of crude product. The product was recrystallized in 50 mL of 60 ℃ aqueous solution, yielding 57 g.

[0020] ZnO and BW prepared in Example 1 12 @ZnO's SEM image is as follows: Figure 1 As shown in a and b, through Figure 1 Uniformly sized ZnO nanomaterials can be observed through... Figure 1 b shows that after ZnO is loaded with polyacids, its morphology changes from granular to cotton-like, with a size of 30-130 nm, indicating that BW 12 It plays a role in morphology control throughout the entire synthesis process.

[0021] ZnO and BW in Example 1 12 BW 12 Fourier transform infrared spectrum and 400-1800 cm⁻¹ of ZnO -1 A magnified view of the part is as follows Figure 2 As shown in a and b. Through Figure 2 It can be seen that in BW 12 @ZnO belongs to BW 12 The characteristic absorption peaks of BW still exist and have shifted significantly, indicating that... 12 Successfully loaded onto the ZnO surface and tightly bonded.

[0022] ZnO and BW in Example 1 12 BW 12 @ZnO's XRD pattern is as follows Figure 3 As shown. Comparing with Jade database ZnO-PDF #99-0111, it can be seen that the XRD characteristic peaks of the synthesized sample correspond to the standard ZnO card, indicating the successful synthesis of ZnO and loading of BW. 12 The diffraction peak curve of the original ZnO at 2 θ = No BW appeared at 10 ~ 15° 12 The diffraction peaks, but in BW 12 The enhanced diffraction peaks belonging to ZnO in @ZnO indicate that BW 12 It is uniformly dispersed on ZnO and loaded with BW.12 The ZnO did not change the original crystal form of the sample, which corresponds to the infrared results. Example 2

[0023] Steps 1 and 2 are the same as in Example 1, except that in step 3, the ZnO powder and BW... 12 At a mass ratio of 1:2, 2BW is obtained. 12 @ZnO. Example 3

[0024] Steps 1 and 2 are the same as in Example 1, except that in step 3, the ZnO powder and BW... 12 A mass ratio of 1:0.5 yields 0.5 BW. 12 @ZnO.

[0025] Comparative Example 1: ZnO prepared in Examples 1-3 of this invention.

[0026] Comparative Example 2: The polyacid BW used in Examples 1-3 of this invention 12 (K5BW) 12 O 40 ·xH2O).

[0027] Examples 1-3 and Comparative Examples 1 and 2 of this invention were used as photocatalysts in a quartz reactor for the photocatalytic synthesis of hydrogen peroxide. The specific operations were as follows: The quartz reactor was placed in an ice-water bath, and the reaction system was maintained at approximately 10 °C; 50 mg of photocatalyst was dispersed in 90 mL of distilled water, and 10 mL of ethanol was added as a hole sacrificial agent; the mixture was sonicated for 5 min; after a dark reaction of 30 min, a 300 W xenon lamp (λ ≥ 320 nm) was used as the photocatalytic reaction light source, and O2 was continuously introduced during the reaction. Samples were taken every 30 min, and the concentration of H2O2 produced was determined by iodometric titration. The yield of H2O2 produced by photocatalysis is shown in the figure below. Figure 4 As shown. The results indicate that ZnO and BW 12 @ZnO、BW 12 0.5BW 12 @ZnO、2BW 12 Of the five materials in ZnO, BW 12 @ZnO has the best photocatalytic performance in producing H2O2.

[0028] The cyclic test diagram of photocatalytic hydrogen peroxide production by the zinc oxide / polyacid nanocomposite material in Example 1 of this invention is shown below. Figure 5 As shown, after 5 hours, its H2O2 production decreased from 100% to 92.8%, indicating that it has good stability.

Claims

1. The application of a zinc oxide / polyacid nanocomposite material in photocatalytic hydrogen peroxide production, characterized in that: The zinc oxide / polyoxometalate nanocomposite material is prepared by placing ZnO powder and polyoxometalates in deionized water and stirring in a hot bath. It has a cotton-like morphology and a size of 30-130 nm. The polyoxometalates are tungboronic acid, tungstic silicic acid, or tungstic phosphoric acid.

2. The application of the zinc oxide / polyacid nanocomposite material as described in claim 1 in photocatalytic hydrogen peroxide production, characterized in that... The zinc oxide / polyacid nanocomposite material was prepared according to the following steps: Step 1. Dissolve zinc salt and ammonium salt in deionized water at a mass ratio of 0.5-30:1 to form a mixed solution. Stir the mixed solution in a 40-100℃ hot bath and then transfer it to an autoclave and heat it at 90-180℃ for 4-36 hours. Wash and dry the reaction product and then heat it in a muffle furnace at a heating rate of 5℃ / min to 300-900℃ and hold it for 1-5 hours to obtain white ZnO powder. Step 2. Add ZnO powder and polyoxometalate at a mass ratio of 1:0.25 ~ 40 to deionized water and stir in a hot bath at 50-100℃ to obtain the composite material POMs@ZnO.

3. The application of the zinc oxide / polyacid nanocomposite material according to claim 2 in photocatalytic hydrogen peroxide production, characterized in that: The zinc salt is zinc sulfate, the ammonium salt is ammonium carbonate, and the polyoxometalate is BW. 12 The mass ratio of ZnO powder to polyoxometalate is 1:1.

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