Gold nanoparticle loaded polycrystal face zinc oxide photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a gold nanoparticle loaded polycrystal face zinc oxide photocatalyst as well as a preparation method and application thereof, and relates to the technical field of catalyst preparation and photocatalysis. A hydrothermal method is combined with calcination treatment, and ZnO nanorods and ZnO nanosheets with different exposed crystal faces are prepared by controlling the use amount of a surfactant; and finally, loading the gold nanoparticles on ZnO through a photo-reduction method to construct the Au-ZnO material. According to the preparation method disclosed by the invention, high-efficiency and high-selectivity photocatalytic CH4 oxidative coupling preparation of C2H6 can be realized at normal temperature and normal pressure, the requirement of sustainable development energy strategy is met, and the preparation method has a wide application prospect. According to the method, the ZnO nanorods mainly exposed on the 0110 / 1010 crystal face and the ZnO nanosheets mainly exposed on the 0001 crystal face are synthesized, performance optimization is achieved through specific crystal face regulation and control, and the methane oxidative coupling efficiency is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation and photocatalysis, and in particular to a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, a preparation method and an application thereof. Background Art

[0002] CH4 is the main component of natural gas, shale gas and combustible ice, and its reserves are abundant. As crude oil resources are becoming increasingly depleted, CH4, as a potential chemical raw material, its resource utilization not only has economic value, but also has environmental significance, and can reduce the chemical industry's dependence on crude oil. Directly converting CH4 into high-value-added multi-carbon (C 2+ ) compounds, such as ethane and ethylene, is a promising method for synthesizing fuels and chemicals, which can improve the utilization efficiency and economic value of CH4.

[0003] However, the high symmetry of the CH4 molecule, its high CH bond energy (435-439 kJ / mol), and its extremely stable chemical properties make its activation and conversion thermodynamically unfavorable, often requiring a large amount of additional energy. Photocatalytic technology, using solar energy as a driving force, provides a mild pathway for CH4 conversion, breaking the theoretical limitations of steady-state thermodynamic equilibrium and avoiding the high energy consumption and harsh reaction conditions of traditional thermal catalytic methods.

[0004] Research has found that nano-zinc oxide can efficiently photocatalyze the oxidative coupling of CH4, surpassing most known photocatalysts in performance. In addition to its nontoxicity, low cost, and diverse surface chemical properties, its use in gas-phase photocatalysis can also inhibit persistent photocorrosion. These advantages make zinc oxide a promising candidate for cost-effective photocatalytic oxidative coupling of CH4. The photocatalytic activity of catalysts can be highly dependent on the growth orientation of specific crystal facets, making it crucial to investigate the performance differences of gold nanoparticle-supported polycrystalline zinc oxide photocatalysts for the photocatalytic oxidative coupling of CH4. Summary of the Invention

[0005] The purpose of the present invention is to provide a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst and its preparation method and application to solve the above-mentioned problems. By selecting the zinc oxide morphology (nanorods or nanosheets) that exposes specific crystal faces, the photogenerated charge separation ability of the catalyst can be directionally controlled, providing a direct basis for the design of an efficient methane photocatalytic system.

[0006] The invention discloses a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, comprising zinc oxide and gold nanoparticles loaded on the zinc oxide through a photoreduction method. The gold nanoparticles construct gold particle active sites.

[0007] Preferably, the zinc oxide is either a zinc oxide nanorod mainly exposing a 0110 / 1010 non-polar crystal face or a zinc oxide nanosheet mainly exposing a 0001 polar crystal face.

[0008] Preferably, the specific surface area of ​​the zinc oxide nanorods is 15-20 m 2 / g; the specific surface area of ​​the zinc oxide nanosheets is 5-10m 2 / g.

[0009] Preferably, the gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst has a surface plasmon resonance effect.

[0010] The present invention also provides a method for preparing the gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, comprising the following steps:

[0011] Step (1), preparing zinc oxide;

[0012] Step (2): dispersing the prepared zinc oxide in anhydrous ethanol containing gold salt and stirring; placing the solution under a xenon lamp while stirring and irradiating it with light by a photoreduction method; centrifuging after stirring and drying to obtain a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst.

[0013] Preferably, the preparation of zinc oxide nanosheets in step (1) comprises the following steps: dissolving zinc acetate, sodium hydroxide and cetyltrimethylammonium bromide in deionized water and performing a hydrothermal reaction, collecting the precursor powder, and calcining the precursor powder at a high temperature to obtain zinc oxide nanosheets;

[0014] The concentrations of zinc acetate, sodium hydroxide and cetyltrimethylammonium bromide are 3-4 mg / mL, 5-7 mg / mL and 18-20 mg / mL, respectively; the temperature of the hydrothermal reaction is 130-180° C., and the reaction time is 14-18 hours; and the temperature of the high-temperature calcination is 300-400° C., and the time is 3-5 hours.

[0015] Preferably, the preparation of zinc oxide nanorods in step (1) comprises the following steps: dissolving zinc acetate and sodium hydroxide in anhydrous ethanol and performing a solvothermal reaction, collecting the precursor powder, and calcining at a high temperature to obtain zinc oxide nanorods;

[0016] The concentrations of zinc acetate and sodium hydroxide are 9-10 mg / mL and 17-18 mg / mL, respectively; the temperature of the solvent thermal reaction is 130-180° C., and the reaction time is 22-26 hours; and the temperature of the high-temperature calcination is 250-350° C., and the time is 1-2 hours.

[0017] Preferably, in step (2), the concentration of zinc oxide in ethanol is 1-3 mg / mL; the mass percentage of gold and zinc oxide is 0.5%-3%; the light source is a 300W xenon lamp, and the light intensity is 200-400mW / cm 2 , wavelength range is 200-1100nm, and illumination time is 1-2 hours.

[0018] The gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst provided by the present invention is used in photocatalytic CH4 oxidative coupling.

[0019] Therefore, the present invention adopts the above-mentioned gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst and its preparation method and application, which has the following beneficial effects:

[0020] (1) The present invention provides a catalyst for photocatalytic CH4 oxidative coupling, which is composed of zinc oxide nanorods / nanosheets loaded with gold nanoparticles. Performance optimization is achieved through specific crystal face regulation. The catalyst uses zinc oxide nanorods (ZnO NRs) with (0110) or (1010) non-polar crystal faces and zinc oxide nanosheets (ZnONSs) with (0001) polar crystal faces as carriers. Due to the significant difference in the surface electron-hole separation ability of the two, the loaded gold nanoparticles (Au NPs) directly form a photocatalytic system with very different performance. At the same time, the methane oxidative coupling efficiency is greatly improved. The crystal face-dependent carrier separation characteristics make the photocatalytic methane oxidative coupling performance of Au-ZnO NRs (non-polar crystal face-dominated) reach four times that of Au-ZnONSs (polar crystal face-dominated), significantly improving the production efficiency of the target product.

[0021] (2) The gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst prepared by the present invention can achieve efficient and highly selective photocatalytic oxidative coupling of CH4 to C2H6 at room temperature and pressure, meeting the requirements of sustainable energy strategies and having broad application prospects. In addition, the catalyst synthesis process is simple and easy, the raw materials are low-cost and abundant in storage, and it has excellent stability and is recyclable. These characteristics make it an ideal choice for replacing rare precious metal catalysts, improving CH4 utilization efficiency and economic value, and it has important application value in the field of energy conversion.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are scanning electron micrographs of the samples synthesized in Examples 1-2 of the present invention, wherein a is a scanning electron micrograph of the ZnO nanorods prepared in Example 1, and b is a scanning electron micrograph of the ZnO nanosheets prepared in Example 2;

[0024] Figure 2 Transmission electron microscopy images of samples synthesized in Example 3 of the present invention, wherein a is a transmission electron microscopy image of 1% Au-ZnO NRs prepared in Example 3, and b is a transmission electron microscopy image of 1% Au-ZnO NSs prepared in Example 3;

[0025] Figure 3 The UV-visible-near-infrared diffuse reflectance spectra of the synthetic samples of Examples 1-3 of the present invention are shown;

[0026] Figure 4 The X-ray diffraction pattern of the synthetic sample of Example 1-2 of the present invention;

[0027] Figure 5 This is a performance diagram of the photocatalytic oxidative coupling of CH4 to C2H6 and C3H8 of the synthetic samples of Examples 1-6 in Application Example 1 of the present invention;

[0028] Figure 6 This is a performance diagram of four photocatalytic CH4 oxidative coupling cycles of the 1% Au-ZnO NRs sample synthesized in Example 3 in Application Example 2 of the present invention. DETAILED DESCRIPTION

[0029] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0030] Furthermore, it should be understood that although this specification describes the embodiments, not every embodiment includes only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in the various embodiments may also be appropriately combined to form other embodiments that are understandable to those skilled in the art. These other embodiments are also encompassed within the scope of protection of the present invention.

[0031] The present invention provides a method for preparing zinc oxide nanorods, comprising dissolving zinc acetate and sodium hydroxide in anhydrous ethanol and performing a solvent thermal reaction, collecting the precursor powder, and calcining the precursor powder at a high temperature to obtain ZnO nanorods having a specific surface area of ​​about 15-20 m 2 / g.

[0032] In the above-mentioned method for preparing zinc oxide nanorods, the concentrations of zinc acetate and sodium hydroxide are 9-10 mg / mL and 17-18 mg / mL, respectively; the temperature of the solvothermal reaction is 130-180°C, and the reaction time is 22-26 hours; the temperature of the high-temperature calcination is 250-350°C, and the calcination time is 1-2 hours.

[0033] The present invention provides a method for preparing zinc oxide nanosheets. The preparation of ZnO nanosheets comprises dissolving zinc acetate, sodium hydroxide and cetyltrimethylammonium bromide in deionized water and performing a hydrothermal reaction, collecting the precursor powder, and calcining the precursor powder at a high temperature to obtain ZnO nanosheets having a specific surface area of ​​about 5-10 m 2 / g.

[0034] In the above-mentioned method for preparing zinc oxide nanosheets, the concentrations of zinc acetate, sodium hydroxide, and cetyltrimethylammonium bromide are 3-4 mg / mL, 5-7 mg / mL, and 18-20 mg / mL, respectively; the hydrothermal reaction temperature is 130-180°C, and the reaction time is 14-18 hours; the high-temperature calcination temperature is 300-400°C, and the calcination time is 3-5 hours.

[0035] The present invention also provides a method for preparing a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, comprising dispersing the prepared ZnO nanorods / nanosheets in anhydrous ethanol containing a gold salt and stirring the solution. The solution is placed under a xenon lamp and irradiated with light while stirring using a photoreduction method. After stirring, the solution is centrifuged and dried to obtain gold nanoparticle-loaded zinc oxide.

[0036] In the above-mentioned method for preparing a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, the concentration of ZnO nanorods / nanosheets in ethanol is 1-3 mg / mL; the mass percentage of gold and ZnO nanorods / nanosheets added to the gold salt is 0.5%-3%; the light source is a 300W xenon lamp with a light intensity of 200-400mW / cm 2 , wavelength range is 200~1100nm, and illumination time is 1-2 hours.

[0037] The gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst obtained by the above preparation method has elemental gold loaded on the surface of ZnO nanorods / nanosheets in the form of dispersed nanoparticles, and the formed zinc oxide-loaded gold nanoparticles have a surface plasmon resonance effect.

[0038] The gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst is used in photocatalytic CH4 oxidative coupling. There is a four-fold gap in photocatalytic CH4 oxidative coupling performance between Au-ZnONRs and Au-ZnO NSs.

[0039] The specific method of the photocatalytic CH4 oxidative coupling experiment is as follows: ultrasonically disperse the catalyst in water to obtain a uniform dispersion, coat the obtained catalyst dispersion on a glass sheet and dry it, place the glass sheet covered with the catalyst in a reactor and seal it, and perform the photocatalytic CH4 oxidative coupling experiment using a xenon lamp as simulated sunlight in an atmosphere containing high-purity CH4 and a certain amount of oxygen.

[0040] In the application of the above-mentioned gold nanoparticle-supported polycrystalline zinc oxide photocatalyst in the photocatalytic CH4 oxidative coupling, the amount of photocatalyst used is 4-6 mg, and the area of ​​the glass sheet is 8-12 cm 2 , the volume of oxygen is 0.1-0.3mL.

[0041] The light source is a 300W xenon lamp with a wavelength range of 200-1100nm and an intensity of 200-400mW / cm 2 .

[0042] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0043] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0044] Furthermore, it should be understood that although this specification describes the embodiments, not every embodiment includes only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in the various embodiments may also be appropriately combined to form other embodiments that are understandable to those skilled in the art. These other embodiments are also encompassed within the scope of protection of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for preparing zinc oxide nanorods, which specifically includes the following steps:

[0047] 650 mg of zinc acetate powder was thoroughly dispersed in 20 mL of anhydrous ethanol under vigorous stirring (800 rpm). Separately, 1.2 g of sodium hydroxide powder was ultrasonically dispersed in 50 mL of anhydrous ethanol. The sodium hydroxide solution was then slowly dripped into the zinc acetate solution to form a precursor solution. The precursor solution was then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and solvothermally reacted at 160°C for 24 hours. After the reaction, the product was cooled to room temperature, and the resulting precipitate was washed several times with anhydrous ethanol and dried in a vacuum oven at 60°C for 3 hours to obtain ZnO nanorods.

[0048] Example 2

[0049] This example provides a method for preparing zinc oxide nanosheets, comprising the following steps: 210 mg of zinc acetate, 300 mg of sodium hydroxide, and 1.2 g of cetyltrimethylammonium bromide are thoroughly dispersed in 60 mL of ultrapure water under vigorous stirring (800 rpm). After stirring for 2 hours, the solution is transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and subjected to a hydrothermal reaction at 160°C for 15 hours. After the reaction is completed, the mixture is cooled to room temperature, the resulting precipitate is washed multiple times with anhydrous ethanol, and dried in a vacuum drying oven at 60°C for 3 hours to obtain ZnO nanosheets.

[0050] Example 3

[0051] This embodiment provides a method for preparing a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst, comprising the following steps:

[0052] 20 mg of zinc oxide powder was ultrasonically dispersed in 15 mL of anhydrous ethanol, and then 14 μL of 0.092 M chloroauric acid solution was added dropwise to the zinc oxide dispersion. The mixed solution was illuminated under a xenon lamp with an intensity of 300 mW / cm 2 The reaction mixture was stirred and irradiated for 2 hours. The precipitate was collected by multiple centrifugation and washing, and dried at 60°C for 3 hours to obtain a zinc oxide-supported gold nanoparticle photocatalyst. Based on the mass ratio of gold nanoparticles to zinc oxide, it was named 1% Au-ZnO.

[0053] In this example, the zinc oxide nanorods prepared in Example 1 and the zinc oxide nanosheets prepared in Example 2 were used to prepare the catalysts, respectively. According to the different types of zinc oxide, they were named 1% Au-ZnO NRs and 1% Au-ZnO NSs, respectively.

[0054] Example 4

[0055] This example provides a method for preparing a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst. The steps are identical to those in Example 3, differing only in that the mass ratio of gold nanoparticles to zinc oxide in this example is 0.5%, i.e., 0.5% Au-ZnO. The catalysts were prepared using the zinc oxide nanorods prepared in Example 1 and the zinc oxide nanosheets prepared in Example 2. Based on the type of zinc oxide used, these catalysts are designated 0.5% Au-ZnO NRs and 0.5% Au-ZnO NSs, respectively.

[0056] Example 5

[0057] This example provides a method for preparing a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst. The steps are identical to those in Example 3, differing only in that the mass ratio of gold nanoparticles to zinc oxide in this example is 2%, i.e., 2% Au-ZnO. The catalysts were prepared using the zinc oxide nanorods prepared in Example 1 and the zinc oxide nanosheets prepared in Example 2. Based on the type of zinc oxide used, they are designated 2% Au-ZnO NRs and 2% Au-ZnO NSs, respectively.

[0058] Example 6

[0059] This example provides a method for preparing a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst. The steps are identical to those in Example 3, differing only in that the mass ratio of gold nanoparticles to zinc oxide in this example is 3%, i.e., 3% Au-ZnO. The catalysts were prepared using the zinc oxide nanorods prepared in Example 1 and the zinc oxide nanosheets prepared in Example 2. Based on the type of zinc oxide used, they are designated 3% Au-ZnO NRs and 3% Au-ZnO NSs, respectively.

[0060] The ZnO nanorods and ZnO nanosheets synthesized in Example 1-2 were characterized by scanning electron microscopy. Figure 1 As shown in a, the morphology of ZnO nanorods is composed of nanorods with a length of 1-3 μm and a diameter of about 20-50 nm. Figure 1 As shown in b, the morphology of ZnO nanosheets is composed of irregular nanosheets with a size of about 0.2-2 μm stacked together.

[0061] In addition, the 1% Au-ZnO NRs and 1% Au-ZnO NSs synthesized in Example 3 were characterized by transmission electron microscopy, and the results were as follows: Figure 2 a and Figure 2 As shown in b. Figure 2 As shown in a, the surface of ZnO nanorods is loaded with gold nanoparticles with a diameter of 10-40 nm. Figure 2 As shown in b, the surface of ZnO nanosheets is loaded with gold nanoparticles with a diameter of 10-40 nm.

[0062] The ZnO nanorods, ZnO nanosheets, 1% Au-ZnO NRs and 1% Au-ZnO NSs synthesized in Examples 1-3 were analyzed by UV-visible-near-infrared diffuse reflectance spectroscopy. Figure 3 As shown in the figure, the absorption band edge of ZnO nanorods and ZnO nanosheets is around 400nm; 1% Au-ZnO NRs and 1% Au-ZnO NSs both show the absorption characteristics of both ZnO and Au, and exhibit SPR absorption at 500-600nm.

[0063] The ZnO nanorods and ZnO nanosheets synthesized in Example 1-2 were subjected to X-ray diffraction analysis. Figure 4 As shown, the synthesized ZnO nanorods and ZnO nanosheets have good crystallinity. The diffraction peaks of both correspond to the standard diffraction pattern JCPDS:89-1397 (ZnO), indicating the successful preparation of the materials. In the XRD pattern, the zinc oxide nanorods show obvious characteristic peaks at the 0110 and 1010 crystal planes. The zinc oxide nanosheets have a clear diffraction peak near the 0001 crystal plane.

[0064] Application Example 1

[0065] This application example provides an application of a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst in photocatalytic CH4 oxidative coupling, specifically comprising the following steps:

[0066] 5 mg of ZnO nanorods, ZnO nanosheets and Au-ZnO photocatalysts with different gold nanoparticle loadings prepared in Examples 1-6 were ultrasonically dispersed in 0.4 mL of deionized water and uniformly coated on an area of ​​9.61 cm 2 After drying, the glass sheet coated with the photocatalyst was placed in a 200 mL reactor, which was then sealed with a thick quartz cover and treated under vacuum for 15 minutes to remove oxygen. Before the reaction, 159 mL of methane and 3 mL of oxygen were added to the reactor. The reaction was carried out using a 300 W xenon lamp as a simulated sunlight light source (wavelength 200-1100 nm, light intensity 300 mW / cm 2 ), a photocatalytic CH4 oxidative coupling experiment was carried out by top irradiation. The reaction time was 180 minutes, during which the gas reaction products were collected every 30 minutes and monitored and analyzed by gas chromatography.

[0067] The yields of photocatalytic oxidative coupling of CH4 to C2H6 and C3H8 are as follows: Figure 5 As shown, neither ZnO nanorods nor ZnO nanosheets generate any product. Only when gold nanoparticles are loaded on the zinc oxide surface does a product form. With increasing gold nanoparticle loading on zinc oxide, the C2H6 yield of Au-ZnO first increases and then decreases, with 1% Au-ZnO exhibiting the highest C2H6 yield. Furthermore, a four-fold difference in photocatalytic CH4 oxidative coupling performance exists between 1% Au-ZnO NRs and 1% Au-ZnO NSs.

[0068] Application Example 2

[0069] This application example provides a cyclic experiment using a gold nanoparticle-supported polycrystalline zinc oxide photocatalyst in the photocatalytic oxidative coupling of CH₄. Following the experimental protocol described in Application Example 1, the 1% Au-ZnO NRs prepared in Example 3 were first subjected to a single photocatalytic oxidative coupling of CH₄. After 180 minutes of reaction, the reactor was purged with high-purity N₂ gas for 15 minutes and then vacuum-treated for 15 minutes to remove the reduction products produced in the first reaction. The protocol described in Application Example 1 was repeated for a total of four photocatalytic oxidative coupling experiments.

[0070] The curve of C2H6 production over time under four cycles collected is as follows Figure 6 As shown in the figure, it can be seen that the catalyst has good stability in photocatalytic CH4 oxidative coupling and can be repeatedly recycled.

[0071] In summary, the present invention provides a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst, its preparation method, and application. The photocatalyst is constructed by loading gold nanoparticles onto zinc oxide surfaces with different crystal faces via a photoreduction method. ZnO nanorods are primarily characterized by 0110 / 1010 crystal faces, while ZnO nanosheets are primarily characterized by 0001 crystal faces. The varying electron-hole separation capabilities of zinc oxide with different crystal faces result in a fourfold difference in photocatalytic CH4 oxidative coupling performance between Au-ZnO NRs and Au-ZnO NSs. Therefore, this catalyst has significant application value in CH4 oxidative coupling and solar energy utilization.

[0072] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific implementation method of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Gold nanoparticle-supported polycrystalline zinc oxide photocatalyst, characterized in that: The invention comprises zinc oxide and gold nanoparticles loaded on the zinc oxide by a photoreduction method, wherein the gold nanoparticles construct gold particle active sites.

2. The gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 1, characterized in that: The zinc oxide is either a zinc oxide nanorod mainly exposing a 0110 / 1010 non-polar crystal face or a zinc oxide nanosheet mainly exposing a 0001 polar crystal face.

3. The gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 2, characterized in that: The specific surface area of ​​the zinc oxide nanorods is 15-20 m 2 / g; the specific surface area of ​​the zinc oxide nanosheets is 5-10m 2 / g.

4. The gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 2, characterized in that: The gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst has a surface plasmon resonance effect.

5. A method for preparing the gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step (1), preparing zinc oxide; Step (2): dispersing the prepared zinc oxide in anhydrous ethanol containing gold salt and stirring; placing the solution under a xenon lamp while stirring and irradiating it with light by a photoreduction method; centrifuging after stirring and drying to obtain a gold nanoparticle-loaded polycrystalline zinc oxide photocatalyst.

6. The method for preparing the gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 5, characterized in that: The preparation of zinc oxide nanosheets in step (1) comprises the following steps: dissolving zinc acetate, sodium hydroxide and hexadecyltrimethylammonium bromide in deionized water and performing a hydrothermal reaction, collecting the precursor powder, and calcining at a high temperature to obtain zinc oxide nanosheets; The concentrations of zinc acetate, sodium hydroxide and cetyltrimethylammonium bromide are 3-4 mg / mL, 5-7 mg / mL and 18-20 mg / mL, respectively; the temperature of the hydrothermal reaction is 130-180° C., and the reaction time is 14-18 hours; and the temperature of the high-temperature calcination is 300-400° C., and the time is 3-5 hours.

7. The method for preparing the gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 5, characterized in that: The preparation of zinc oxide nanorods in step (1) comprises the following steps: dissolving zinc acetate and sodium hydroxide in anhydrous ethanol and performing a solvothermal reaction, collecting the precursor powder, and calcining at a high temperature to obtain zinc oxide nanorods; The concentrations of zinc acetate and sodium hydroxide are 9-10 mg / mL and 17-18 mg / mL, respectively; the temperature of the solvent thermal reaction is 130-180° C., and the reaction time is 22-26 hours; and the temperature of the high-temperature calcination is 250-350° C., and the time is 1-2 hours.

8. The method for preparing the gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to claim 5, characterized in that: In step (2), the concentration of zinc oxide in ethanol is 1-3 mg / mL; the mass percentage of gold and zinc oxide is 0.5%-3%; the light source is a 300W xenon lamp with a light intensity of 200-400 mW / cm 2 , wavelength range is 200-1100nm, and illumination time is 1-2 hours.

9. Use of the gold nanoparticle-supported polycrystalline zinc oxide photocatalyst according to any one of claims 1 to 4, characterized in that: Gold nanoparticle-loaded polycrystalline zinc oxide photocatalysts are used in photocatalytic CH4 oxidative coupling.

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