Gold-modified oxygen-rich vacancy zinc oxide nanosheet photocatalyst and preparation method thereof

Abstract

The application belongs to the technical field of photocatalytic methane conversion, and particularly relates to a gold-modified oxygen-enriched vacancy zinc oxide nanosheet photocatalyst and a preparation method thereof. x The photocatalyst has a structural formula of Au / ZnO; the specific steps of the preparation method are as follows: S1: zinc acetate and urea are respectively dissolved in deionized water and stirred to completely dissolve, the zinc acetate aqueous solution is added into the urea aqueous solution, polyether F127 is added, ultrasonic treatment is performed for 30 min, and then vigorous stirring is performed, the sample is transferred into a microwave reactor for heating, cooling and washing, after sample rotary evaporation drying is completed, the sample is placed into a tube furnace for high-temperature calcination under an argon atmosphere; S2: a gold precursor solution is added into a methanol aqueous solution in which the zinc oxide nanosheet obtained in step S1 is dissolved, ultrasonic treatment is performed for dissolution, photodeposition is performed after argon purging, centrifugal separation is performed, washing is performed, and rotary evaporation drying is performed to obtain Au / ZnO. x The photocatalyst obtained by the preparation method is used for oxidizing methanol to formaldehyde, the reaction condition is mild, the addition of gold is beneficial to the formation of oxygen vacancies, the separation efficiency of photo-generated carriers is improved, and the formaldehyde yield is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic methane conversion, and particularly relates to a gold-modified oxygen-enriched vacancy zinc oxide nanosheet photocatalyst and a preparation method thereof. BACKGROUND

[0002] Methane is the main component of natural gas and has abundant reserves on the earth. Methane conversion into high-value-added chemicals has been a core research topic in the fields of chemistry, energy and environment. Generally speaking, due to the inherent inertness of C-H bond and the high stability of tetrahedral structure, thermal catalytic methane conversion requires harsh reaction conditions. Unlike thermal catalytic systems, photocatalysis uses solar energy to provide Gibbs free energy for the reaction, and at the same time generates highly active free radicals, realizing the conversion of methane into value-added products (methanol, formaldehyde, formic acid, ethanol, etc.). Among these products, formaldehyde is a chemical with a wide range of uses, not only in daily life such as medical treatment, food, paint, etc., but also as an important intermediate for polyformaldehyde and polyols. Therefore, direct photocatalytic conversion of methane into formaldehyde is of great significance for sustainable development.

[0003] Chinese patent CN111701590A discloses an Au x / WO3 photocatalyst and its application in photocatalytic preparation of formaldehyde from methane. The Au-modified WO3 catalyst is used for photocatalytic direct conversion of methane into formaldehyde, but the yield of formaldehyde is low. ZnO is a typical ultraviolet light absorbing semiconductor and is commonly used as a catalyst in photocatalytic reactions, but it has the disadvantages of low separation efficiency of photo-generated carriers and insufficient active sites. SUMMARY

[0004] The application aims to provide a gold-modified oxygen-enriched vacancy zinc oxide nanosheet photocatalyst and a preparation method thereof, which solve the problem of low yield of photocatalytic direct conversion of methane into formaldehyde by existing catalysts,

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0006] A gold-modified oxygen-enriched vacancy zinc oxide nanosheet photocatalyst, having a structural formula of Au x / ZnO; wherein the gold loading is 0.05-1.0 wt%, and the ZnO is a porous zinc oxide nanosheet with abundant pore structure and oxygen vacancies.

[0007] The preparation method of the above-mentioned gold-modified oxygen-enriched vacancy zinc oxide nanosheet photocatalyst comprises the following steps:

[0008] S1: zinc acetate and urea were dissolved in deionized water respectively, and stirred to completely dissolve, the zinc acetate aqueous solution was added to the urea aqueous solution, polyether F127 was added, after ultrasonic for 30 min, it was stirred violently, transferred to a microwave reactor for heating, cooled, washed, after the sample was dried by rotary evaporation, the sample was placed in a tube furnace and calcined under argon atmosphere, due to the oxygen-poor environment, the lattice oxygen of zinc oxide overflowed to obtain vacancy oxygen, and oxygen vacancy-rich zinc oxide nanosheet was obtained;

[0009] S2: the gold precursor solution was added to the methanol aqueous solution containing the zinc oxide nanosheet obtained in step S1, ultrasonic was performed for dissolution, after argon purging for 15 min, photodeposition was performed, centrifugation, washing, after the reaction was completed, rotary evaporation was performed for drying, and Au / ZnO was obtained, due to the lattice disturbance and reconstruction caused by the addition of gold, the content of oxygen vacancy was increased, and the utilization rate of ultraviolet light was improved. x / ZnO, due to the lattice disturbance and reconstruction caused by the addition of gold, the content of oxygen vacancy was increased, and the utilization rate of ultraviolet light was improved.

[0010] Further, the molar ratio of urea, zinc acetate and polyether F127 in step S1 is (1-3.5):1:(0.00001-0.00007).

[0011] Further, the heating temperature in step S1 is 100-200 DEG C, the power is 300 W, and the heating time is 5-12 h.

[0012] Further, the high-temperature calcination temperature in step S1 is 400-700 DEG C, and the time is 5-10 h.

[0013] Further, the gold precursor solution in step S2 is tetrachloroauric acid solution.

[0014] Further, the time of photodeposition in step S2 is 0.5-2 h.

[0015] The application of the above gold-modified oxygen vacancy-rich zinc oxide nanosheet as a photocatalyst for photocatalytic methane oxidation reaction can effectively promote the separation of photo-generated carriers, improve the photocatalytic efficiency, and reduce the peroxidation of the product, and can be used for photocatalytic methane oxidation to prepare formaldehyde. The specific steps are as follows:

[0016] 5-30 mg of catalyst was dispersed in 10-30 mL of deionized water, the oxidant in the catalytic reaction process was selected as oxygen, the oxygen was filled to 0-1 MPa, the methane was filled to 0.1-3 MPa, the total pressure was normal pressure to 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was room temperature, and the reaction was carried out under light irradiation for 1-6 h, and the product content was detected.

[0017] The gas phase products and liquid phase products are detected by gas chromatography to detect CO, CO2, CH3OH, CH3CH2OH, CH3COOH, etc., by ion chromatography to detect HCOOH, etc., and by acetylacetone colorimetry to detect HCHO.

[0018] Further, the oxygen is filled to 0.1-0.8 MPa, and the methane is filled to 2-3 MPa.

[0019] Further, the volume ratio of methane to oxygen is 24:6.

[0020] When the gold nanoparticles are loaded on the surface of zinc oxide, the electrons of zinc oxide flow to the gold nanoparticles and occupy the low quantum state, and finally the Fermi level of zinc oxide and the Fermi level of gold nanoparticles reach equilibrium, improving the separation efficiency of photo-generated carriers of zinc oxide and increasing the number of active sites. At the same time, the conduction band and valence band of zinc oxide will bend at the interface of gold and zinc oxide, forming a Schottky barrier to inhibit the recombination of electrons and holes. In addition to charge dynamics, the chemical adsorption and activation of reactants are also important; the prepared porous sheet-like zinc oxide has a large specific surface area and more active sites, which can promote the activation of oxygen. At the same time, the addition of gold is more conducive to the formation of oxygen vacancies, which respectively act as hole and electron acceptors to improve the separation efficiency of photo-generated carriers. Based on these characteristics, gold-modified zinc oxide nanosheet with rich oxygen vacancies has the potential to synergistically trigger charge separation and reactant activation for photocatalytic methane conversion.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The preparation method adds polyether F127 and uses the zinc oxide nanosheet particles obtained by rotary evaporation drying, which are more uniform, have rich oxygen vacancies, have a higher specific surface area, can fully contact with reactants, promote the adsorption of oxygen, and improve the reaction activity;

[0023] (2) The photocatalyst prepared by the preparation method can catalyze the reaction of methane oxidation to formaldehyde at room temperature, and the conditions are mild; secondly, using oxygen as the oxygen source under light conditions, it is more green and economical;

[0024] (3) The preparation method composites gold with porous zinc oxide nanosheet with rich oxygen vacancies, the nanosheet structure of the catalyst shortens the carrier transport distance, making it easier to reach the catalyst surface, and the large surface area provides rich adsorption sites, and the addition of gold can improve the separation efficiency of carriers, and the synthesis method of the photocatalyst is simple, while increasing the formaldehyde yield, which is conducive to the popularization and application in the photocatalytic methane-to-formaldehyde reaction. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 XRD pattern of the photocatalyst of Example 1 and Comparative Example 1;

[0026] Figure 2 SEM image of the photocatalyst of Example 1, Comparative Example 1;

[0027] Figure 3 EPR spectrum of the photocatalyst of Example 1, Comparative Example 1;

[0028] Figure 4 Raman spectrum of the photocatalyst of Example 1, Comparative Example 1;

[0029] Figure 5 AC-STEM image of the photocatalyst of Example 1;

[0030] Figure 6 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 1, Example 2, Example 3, Example 4 with different loading ratios;

[0031] Figure 7 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 5, Example 6, Example 7, Example 8 with different gas ratios;

[0032] Figure 8 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 9, Example 10, Example 11, Example 12 with different total pressures;

[0033] Figure 9 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 13, Example 14, Example 15, Example 16 with different catalyst masses;

[0034] Figure 10 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 17, Example 18, Example 19, Example 20 with different water masses;

[0035] Figure 11 Comparative chart of the yield and selectivity of photocatalytic methane oxidation to formaldehyde of Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27 with different reaction times. DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with the accompanying drawings and examples. Example 1

[0037] Zinc acetate 3.4 g and urea 4.25 g were dissolved in 20 mL of deionized water separately with stirring to make them completely dissolved. Zinc acetate solution was added to the urea solution and then 0.332 g of polyether F127 was added. After ultrasonic treatment for 30 min, it was stirred vigorously and then transferred to a microwave reactor for heating. After the solution was cooled to room temperature, the precipitate was collected by centrifugation and washed with deionized water and ethanol three times each. Then the product was dissolved and dried by rotary evaporation at 50 °C for 1 h to obtain a solid mixture. The obtained solid mixture was placed in a tube furnace under an argon atmosphere and heated to 500 °C at a heating rate of 2 °C·min -1 -1, and then calcined at this temperature for 10 h to obtain zinc oxide nanosheets. 0.5 g of zinc oxide nanosheets was dissolved in 100 mL of a methanol aqueous solution, and then stirred after ultrasonic treatment. 2.5 mL of a gold precursor solution was added thereto. The solution was purged with argon, and then irradiated with a xenon lamp in a sealed environment for 1 h. After the reaction was completed, it was washed by centrifugation. The product was dissolved and dried by rotary evaporation at 50 °C for 1 h. The catalyst was named Au 0.05 / ZnO. 10 mg of the catalyst was dispersed in 30 mL of deionized water, and then charged with methane and oxygen at a ratio of 24:6. The total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25 °C, and the reaction was performed under light irradiation for 1 h. The formaldehyde yield was 7.48 μmol h -1 -1, and the formaldehyde selectivity was 80.60% (HCHO selectivity = yield of HCHO / (yield of HCHO + yield of HCOOH + yield of CO2). Example 2

[0038] Zinc acetate 3.4 g and urea 4.25 g were dissolved in 20 mL of deionized water separately with stirring to make them completely dissolved. Zinc acetate solution was added to the urea solution and then 0.332 g of polyether F127 was added. After ultrasonic treatment for 30 min, it was stirred vigorously and then transferred to a microwave reactor for heating. After the solution was cooled to room temperature, the precipitate was collected by centrifugation and washed with deionized water and ethanol three times each. Then the product was dissolved and dried by rotary evaporation at 50 °C for 1 h to obtain a solid mixture. The obtained solid mixture was placed in a tube furnace under an argon atmosphere and heated to 500 °C at a heating rate of 2 °C·min -1 -1, and then calcined at this temperature for 10 h to obtain zinc oxide nanosheets. 0.5 g of zinc oxide nanosheets was dissolved in 100 mL of a methanol aqueous solution, and then stirred after ultrasonic treatment. 5 mL of a gold precursor solution was added thereto. The solution was purged with argon, and then irradiated with a xenon lamp in a sealed environment for 1 h. After the reaction was completed, it was washed by centrifugation. The product was dissolved and dried by rotary evaporation at 50 °C for 1 h. The catalyst was named Au 0.1 / ZnO. The reaction conditions were the same as in Example 1. The reaction was performed under light irradiation for 1 h. The formaldehyde yield was 19.15 μmol h -1The formaldehyde selectivity was 87.97%.

[0039] Comparative Example 1

[0040] Zinc oxide nanosheets

[0041] 10 mg of zinc oxide nanosheet catalyst was dispersed in 30 mL of deionized water, and the mixture was charged with a methane-to-oxygen ratio of 24:6 at a total pressure of 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25 °C. After 1 h of irradiation, the formaldehyde yield was 8.36 μmol / h. -1 The formaldehyde selectivity was 86.07%.

[0042] Figure 1 The XRD patterns of the photocatalysts in Example 1 and Comparative Example 1 are shown below. Figure 1 As shown, XRD analysis of the catalyst's crystal structure revealed that all diffraction peaks of zinc oxide matched well with the standard diffraction pattern (JCPDS No. 36-1451), indicating that the product belongs to the hexagonal wurtzite structure. No characteristic peaks of Au were found in the XRD pattern because the loading was low and the dispersion on the zinc oxide surface was good.

[0043] Figure 2 These are SEM images of Example 1 and Comparative Example 1. The catalyst morphology was observed using SEM, such as... Figure 2 As shown, ZnO has a distinct porous lamellar structure, and Au did not alter the lamellar structure of the porous zinc oxide.

[0044] Figure 3 The EPR spectra of the photocatalysts in Example 1 and Comparative Example 1 are shown below. Figure 3 As shown, both samples exhibit a distinct characteristic peak at g=2.003, indicating that ZnO and Au... 0.1 Both ZnO and Au have oxygen vacancies because Au 0.1 The EPR peak of / ZnO is significantly higher than that of ZnO, therefore Au 0.1 The oxygen vacancy content of / ZnO is higher than that of ZnO. After photodeposition of Au, vacuum rotary drying is conducive to the formation of oxygen vacancies.

[0045] Figure 4 The Raman spectra of the photocatalysts in Example 1 and Comparative Example 1 are shown below. Figure 4 As shown, ZnO and Au 0.1 / ZnO at 580 cm −1 The E1(LO) peak position indicates the presence of oxygen vacancies, and Au 0.1 The E1(LO) peak of / ZnO is significantly stronger than that of ZnO.

[0046] Figure 5For the AC-STEM image of Example 1, as shown in Figure 5 Figure 1, the Au nanoparticles are uniformly dispersed on the surface of ZnO and the particle diameter of Au is 2-3 nm. Example 3

[0047] Zinc acetate 3.4 g and urea 4.25 g were dissolved in 20 mL of deionized water respectively, and stirred until completely dissolved. The zinc acetate solution was added to the urea solution, and then 0.332 g of polyether F127 was added. After ultrasonic treatment for 30 min, the solution was stirred vigorously, transferred to a microwave reactor for heating, and then the precipitate was collected by centrifugation after the solution was cooled to room temperature. The precipitate was washed with deionized water and ethanol three times respectively, and then the product was dissolved and dried by rotary evaporation at 50 °C for 1 h to obtain a solid mixture. The obtained solid mixture was placed in a tube furnace under an argon atmosphere, and heated to 500 °C at a heating rate of 2 °C·min -1 -1, and then kept at this temperature for 10 h to obtain zinc oxide nanosheets. 0.5 g of the zinc oxide nanosheets were dissolved in 100 mL of a methanol aqueous solution, and then stirred after ultrasonic treatment. 15 mL of a gold precursor solution was added to the solution. The solution was purged with argon, and then irradiated with a xenon lamp for 1 h in a sealed environment. After the reaction was completed, the product was washed by centrifugation, and then dissolved and dried by rotary evaporation at 50 °C for 1 h. The catalyst was named Au 0.3 / ZnO. The reaction conditions were the same as in Example 1. The formaldehyde production was 8.47 μmol h -1 -1, and the formaldehyde selectivity was 83.12% under irradiation of the light source for 1 h. Example 4

[0048] Zinc acetate 3.4 g and urea 4.25 g were dissolved in 20 mL of deionized water respectively, and stirred until completely dissolved. The zinc acetate solution was added to the urea solution, and then 0.332 g of polyether F127 was added. After ultrasonic treatment for 30 min, the solution was stirred vigorously, transferred to a microwave reactor for heating, and then the precipitate was collected by centrifugation after the solution was cooled to room temperature. The precipitate was washed with deionized water and ethanol three times respectively, and then the product was dissolved and dried by rotary evaporation at 50 °C for 1 h to obtain a solid mixture. The obtained solid mixture was placed in a tube furnace under an argon atmosphere, and heated to 500 °C at a heating rate of 2 °C·min -1 -1, and then kept at this temperature for 10 h to obtain zinc oxide nanosheets. 0.5 g of the zinc oxide nanosheets were dissolved in 100 mL of a methanol aqueous solution, and then stirred after ultrasonic treatment. 30 mL of a gold precursor solution was added to the solution. The solution was purged with argon, and then irradiated with a xenon lamp for 1 h in a sealed environment. After the reaction was completed, the product was washed by centrifugation, and then dissolved and dried by rotary evaporation at 50 °C for 1 h. The catalyst was named Au 0.6 / ZnO. The reaction conditions were the same as in Example 1. The formaldehyde production was 5.46 μmol h -1, and the formaldehyde selectivity was 83.12% under irradiation of the light source for 1 h.-1 The formaldehyde selectivity was 82.11%.

[0049] Comparative Example 2

[0050] Using data from Chinese patent CN111701590A, 10 mg of Au was taken. 0.3 The cubic WO3 catalyst was dispersed in 80 mL of H2O by stirring, then charged with methane at a methane-to-oxygen ratio of 19:1 at a total pressure of 2 MPa. The reaction was carried out under full-spectrum irradiation for 3 h at a maintained temperature of 25 °C, yielding 3.83 μmol / h of formaldehyde. -1 (11487.7 μmol g) -1 ×10mg×10 -3 ÷3h = 3.829μmolh -1 The selectivity is close to 100%.

[0051] Figure 6 This is a comparison chart showing the yield and selectivity of photocatalytic methane oxidation to formaldehyde with different loading ratios in Examples 1, 2, 3, and 4, as shown below. Figure 6 As shown, after being illuminated by light, Au 0.1 The highest formaldehyde yield was 19.14 μmol / h from ZnO. -1 The formaldehyde selectivity was 87.94%. Compared with Comparative Example 2, although the selectivity of the formaldehyde prepared by the method of the present invention was not high, the formaldehyde yield was high. Example 5

[0052] Take 10 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, and oxygen was introduced at 0.2 MPa, methane at 2.8 MPa, for a total pressure of 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25℃. After 1 h of reaction under the light source, the formaldehyde yield was 12.66 μmol / h. -1 The formaldehyde selectivity was 86.54%. Example 6

[0053] Take 10 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, and oxygen was introduced at 0.4 MPa, methane at 2.6 MPa, for a total pressure of 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25℃. After 1 h of reaction under light irradiation, the formaldehyde yield was 15.81 μmol / h. -1 The formaldehyde selectivity was 82.64%. Example 7

[0054] Take 10 mg Au 0.1ZnO was dispersed in 30 mL of deionized water, filled with oxygen 0.6 MPa, filled with methane 2.4 MPa, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25℃, and the formaldehyde yield was 19.15 μmol h under light source irradiation for 1 h -1 , the formaldehyde selectivity was 87.97%. Example 8

[0055] Take 10 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with oxygen 0.8 MPa, filled with methane 2.2 MPa, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25℃, and the formaldehyde yield was 13.89 μmol h under light source irradiation for 1 h -1 , the formaldehyde selectivity was 85.53%.

[0056] Figure 7 The yield and selectivity of photocatalytic oxidation of methane to formaldehyde with different gas ratios of Example 5, Example 6, Example 7, Example 8 are compared as shown in Figure 7 , due to the change of the partial pressure of methane and oxygen, the amount of CH4 and O2 dissolved in water is affected, and when the methane oxygen ratio is 24:6, the photocatalytic oxidation performance of methane is better, the yield is high, and the selectivity is high. Example 9

[0057] Take 10 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with methane oxygen ratio 24:6, the total pressure was 0.5 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25℃, and the formaldehyde yield was 7.68 μmol h under light source irradiation for 1 h -1 , the formaldehyde selectivity was 87.38%. Example 10

[0058] Take 10 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with methane oxygen ratio 24:6, the total pressure was 1 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25℃, and the formaldehyde yield was 9.14 μmol h under light source irradiation for 1 h -1 , the formaldehyde selectivity was 87.95%. Example 11

[0059] Take 10 mg Au 0.1ZnO was dispersed in 30 mL deionized water, filled with methane and oxygen in a ratio of 24:6, and the total pressure was 2 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the formaldehyde yield was 11.73 μmol h -1 with a formaldehyde selectivity of 85.08%. Example 12

[0060] 10 mg Au 0.1 ZnO was dispersed in 30 mL deionized water, filled with methane and oxygen in a ratio of 24:6, and the total pressure was 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the formaldehyde yield was 19.15 μmol h -1 with a formaldehyde selectivity of 87.97%.

[0061] Figure 8 The yield and selectivity of photocatalytic oxidation of methane to formaldehyde at different total pressures of Examples 9, 10, 11, and 12 are compared in the graph shown in Figure 8 As the partial pressure of methane and oxygen increases, the solubility of CH4 and O2 in water increases, so the yield of CH4 conversion to HCHO and HCOOH also increases, and the photocatalytic oxidation performance is better when the total pressure is 3 MPa. Example 13

[0062] 5 mg Au 0.1 ZnO was dispersed in 30 mL deionized water, filled with methane and oxygen in a ratio of 24:6, and the total pressure was 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the formaldehyde yield was 10.35 μmol h -1 with a formaldehyde selectivity of 83.02%. Example 14

[0063] 10 mg Au 0.1 ZnO was dispersed in 30 mL deionized water, filled with methane and oxygen in a ratio of 24:6, and the total pressure was 3 MPa. The light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the formaldehyde yield was 19.15 μmol h -1 with a formaldehyde selectivity of 87.97%. Example 15

[0064] 20 mg Au 0.1ZnO was dispersed in 30 mL of deionized water, and the mixture was charged with methane at a methane-to-oxygen ratio of 24:6. The total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25 °C. After 1 h of reaction under the light source, the formaldehyde yield was 14.14 μmol / h. -1 The formaldehyde selectivity was 85.93%. Example 16

[0065] Take 30 mg Au 0.1 ZnO was dispersed in 30 mL of deionized water, and the mixture was charged with methane at a methane-to-oxygen ratio of 24:6. The total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25 °C. After 1 h of reaction under the light source, the formaldehyde yield was 10.39 μmol / h. -1 The formaldehyde selectivity was 81.34%.

[0066] Figure 9 This is a comparison chart showing the yield and selectivity of photocatalytic methane oxidation to formaldehyde for Examples 13, 14, 15, and 16 with different catalyst masses. Figure 9 As shown, when the amount of catalyst is too small, fewer free radicals are generated during the reaction, resulting in low formaldehyde production; when the amount of catalyst is too large, the light transmittance of the reaction system decreases, leading to a decrease in the light absorption efficiency of the catalyst, and ultimately a low formaldehyde production. Among them, a catalyst mass of 10 mg has the best photocatalytic methane oxidation performance. Example 17

[0067] Take 10 mg Au 0.1 ZnO was dispersed in 10 mL of deionized water, and the mixture was charged with methane at a methane-to-oxygen ratio of 24:6. The total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25 °C. After 1 h of reaction under the light source, the formaldehyde yield was 7.27 μmol / h. -1 The formaldehyde selectivity was 82.16%. Example 18

[0068] Take 10 mg Au 0.1 ZnO was dispersed in 20 mL of deionized water, and the mixture was charged with methane at a methane-to-oxygen ratio of 24:6. The total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, and the reaction temperature was 25℃. After 1 h of reaction under the light source, the formaldehyde yield was 13.40 μmol / h. -1 The formaldehyde selectivity was 86.87%. Example 19

[0069] Take 10 mg Au 0.1ZnO was dispersed in 25 mL of deionized water, filled with methane / oxygen in a ratio of 24:6, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the reaction was carried out under light irradiation for 1 h, and the formaldehyde yield was 15.57 μmol h -1 , and the formaldehyde selectivity was 86.72%. Example 20

[0070] 10 mg of Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with methane / oxygen in a ratio of 24:6, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the reaction was carried out under light irradiation for 1 h, and the formaldehyde yield was 19.15 μmol h -1 , and the formaldehyde selectivity was 87.97%.

[0071] Figure 10 The yield and selectivity of the photocatalytic oxidation of methane to formaldehyde with different amounts of water in Example 17, Example 18, Example 19, and Example 20 are compared in the graph shown in Figure 10 As the amount of water increases, on the one hand, the mass transfer of the reaction increases, and on the other hand, it can prevent the overoxidation of the product, and when the amount of water is 30 mL, the photocatalytic oxidation performance is better. Example 21

[0072] 10 mg of Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with methane / oxygen in a ratio of 24:6, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the reaction was carried out under light irradiation for 0.5 h, and the formaldehyde yield was 4.06 μmol h -1 , and the formaldehyde selectivity was 74.50%. Example 22

[0073] 10 mg of Au 0.1 ZnO was dispersed in 30 mL of deionized water, filled with methane / oxygen in a ratio of 24:6, the total pressure was 3 MPa, the light source was a xenon lamp with a wavelength range of 400 nm, the reaction temperature was 25°C, and the reaction was carried out under light irradiation for 1 h, and the formaldehyde yield was 19.15 μmol h -1 , and the formaldehyde selectivity was 87.97%. Example 23

[0074] 10 mg of Au 0.1ZnO dispersed in 30 mL of deionized water, filled with methane oxygen ratio of 24:6, total pressure of 3 MPa, light source is a xenon lamp with wavelength range of 400 nm, reaction temperature is 25°C, under the light source irradiation for 2 h, formaldehyde production is 23.50 μmol h -1 , formaldehyde selectivity is 85.96%. Example 24

[0075] Take 10 mg Au 0.1 ZnO dispersed in 30 mL of deionized water, filled with methane oxygen ratio of 24:6, total pressure of 3 MPa, light source is a xenon lamp with wavelength range of 400 nm, reaction temperature is 25°C, under the light source irradiation for 3 h, formaldehyde production is 34.37 μmol h -1 , formaldehyde selectivity is 84.80%. Example 25

[0076] Take 10 mg Au 0.1 ZnO dispersed in 30 mL of deionized water, filled with methane oxygen ratio of 24:6, total pressure of 3 MPa, light source is a xenon lamp with wavelength range of 400 nm, reaction temperature is 25°C, under the light source irradiation for 4 h, formaldehyde production is 42.43 μmol h -1 , formaldehyde selectivity is 87.50%. Example 26

[0077] Take 10 mg Au 0.1 ZnO dispersed in 30 mL of deionized water, filled with methane oxygen ratio of 24:6, total pressure of 3 MPa, light source is a xenon lamp with wavelength range of 400 nm, reaction temperature is 25°C, under the light source irradiation for 5 h, formaldehyde production is 41.02 μmol h -1 , formaldehyde selectivity is 84.32%. Example 27

[0078] Take 10 mg Au 0.1 ZnO dispersed in 30 mL of deionized water, filled with methane oxygen ratio of 24:6, total pressure of 3 MPa, light source is a xenon lamp with wavelength range of 400 nm, reaction temperature is 25°C, under the light source irradiation for 6 h, formaldehyde production is 40.35 μmol h -1 , formaldehyde selectivity is 81.65%.

[0079] Figure 11 The production and selectivity of formaldehyde in the photocatalytic oxidation of methane to formaldehyde of different reaction times of Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, and Example 27 are compared in the following figures: Figure 11As shown, the product gradually increased with time, the yield and selectivity of the product were higher at 4 h, and the product was seriously peroxidized, the yield and selectivity decreased with the prolongation of time.

[0080] The preparation method reduces and loads gold on the surface of zinc oxide as a cocatalyst without adding a precipitant, catalyzes the efficient conversion of methane into formaldehyde through the synergistic effect of gold and oxygen vacancies, and the total yield of formaldehyde can reach 19.15 μmol·h -1 , and the selectivity of formaldehyde is 87.97%.

[0081] The above only describes the preferred embodiments of the present application, and does not limit the present application in any other form, and any modification or equivalent change made according to the technical essence of the present application still belongs to the scope of the present application.

Claims

1. An application of gold-modified oxygen-rich vacancy zinc oxide nanosheet photocatalyst in photocatalytic oxidation of methane to formaldehyde, characterized in that, The structural formula of the gold-modified oxygen-vacancy-rich zinc oxide nanosheet photocatalyst is Au x / ZnO, wherein the gold loading is 0.05-1.0 wt%, the ZnO is a porous zinc oxide nanosheet with rich pore structure and oxygen vacancies, the Au nanoparticles are uniformly dispersed on the surface of the ZnO, and the diameter of the Au nanoparticles is 2-3 nm. The preparation method of the gold-modified oxygen-vacancy-rich zinc oxide nanosheet photocatalyst comprises the following steps: S1: zinc acetate and urea were respectively dissolved in deionized water and stirred to completely dissolve, the zinc acetate aqueous solution was added to the urea aqueous solution, polyether F127 was added, after ultrasonic treatment for 30 min, it was stirred vigorously, transferred to a microwave reactor for heating, cooled, washed, after the sample was dried by rotary evaporation, the sample was placed in a tube furnace and calcined under argon atmosphere at high temperature, to obtain oxygen vacancy-rich zinc oxide nanosheets; S2: The gold precursor solution was added to the methanol aqueous solution of the zinc oxide nanosheets obtained in step S1, ultrasonically dissolved, and after argon purging for 15 min, photodeposition was performed, centrifuged, washed, and after reaction completion, rotary evaporated and dried to obtain Au / ZnO. x / ZnO.

2. The application of gold-modified oxygen-vacancy-rich ZnO nanosheets photocatalyst in photocatalytic oxidation of methane to formaldehyde according to claim 1, characterized in that, The molar ratio of urea, zinc acetate and polyether F127 in step S1 is (1-3.5):1:(0.00001-0.00007).

3. The application of gold-modified oxygen-vacancy-rich ZnO nanosheets photocatalyst in photocatalytic oxidation of methane to formaldehyde according to claim 1, characterized in that, The heating temperature in step S1 is 100-200 ℃, the power is 300 W, and the heating time is 5-12 h.

4. The application of gold-modified oxygen-vacancy-rich ZnO nanosheets photocatalyst in photocatalytic oxidation of methane to formaldehyde according to claim 1, characterized in that, The high-temperature calcination temperature in step S1 is 400-700 ℃, and the time is 5-10 h.

5. The application of gold-modified oxygen-vacancy-rich ZnO nanosheets photocatalyst in photocatalytic oxidation of methane to formaldehyde according to claim 4, characterized in that, The gold precursor solution in step S2 is tetrachloroauric acid solution.

6. The application of gold-modified oxygen-vacancy-rich ZnO nanosheets photocatalyst in photocatalytic oxidation of methane to formaldehyde according to claim 5, characterized in that, The time of photo-deposition in step S2 is 0.5-2 h.

7. The use of the gold-modified oxygen-vacancy-rich ZnO nanosheet photocatalyst according to claim 1 in photocatalytic oxidation of methane to formaldehyde, characterized in that, The specific steps are as follows: 5-30 mg of gold-modified oxygen vacancy-rich zinc oxide nanosheet photocatalyst was dispersed in 10-30 mL of deionized water, the oxidizing agent was oxygen, the oxygen was filled to 0.1-0.8 MPa and not 0 MPa, the methane was filled to 0.1-3 MPa, the total pressure was normal pressure to 3 MPa, the light source was a xenon lamp with a wavelength of 400 nm, the reaction temperature was room temperature, and the reaction was carried out under light irradiation for 1-6 h, and the product content was detected.

8. The use of the gold-modified oxygen-vacancy-rich ZnO nanosheet photocatalyst according to claim 7 in the photocatalytic oxidation of methane to formaldehyde, characterized in that, The oxygen was filled to 0.1-0.8 MPa, and the methane was filled to 2-3 MPa.

9. The use of the gold-modified oxygen-vacancy-rich ZnO nanosheet photocatalyst according to claim 8 in the photocatalytic oxidation of methane to formaldehyde, characterized in that, The volume ratio of methane to oxygen is 24:6.

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