MOF (Cu, Fe)-CdS catalyst, preparation method and application thereof

Abstract

The invention discloses an MOF (Cu, Fe)-CdS catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts.The novel MOF (Cu, Fe)-CdS material is obtained by preparing MOF (Cu, Fe) catalyst powder and MOF (Cu, Fe)-CdS catalyst powder step by step and used for preparing methyl alcohol through photocatalytic oxidation of methane, the catalytic efficiency of MOF (Cu, Fe)-CdS is two times that of MOF (Cu, Fe), and the catalytic efficiency of MOF (Cu, Fe)-CdS is higher than that of MOF (Cu, Fe). The invention also provides a new thought for the photocatalytic conversion of methane, and provides important theoretical basis and practical guidance for the design and synthesis of a high-efficiency catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a MOF(Cu,Fe)-CdS catalyst, its preparation method, and its application. Background Technology

[0002] Methane, a major component of natural gas, shale gas, and coalbed methane, is considered a high-potential energy resource. Currently, methane is mainly used for heating, power generation, and a small amount as vehicle fuel. As an important hydrocarbon feedstock, methane also plays a central role in the production of high-quality fuels and high-value-added chemicals. However, methane extraction sites are often remote and have low boiling points, making liquefied transportation inconvenient. Therefore, on-site conversion into high-value-added chemicals and fuels is crucial. Methanol, as an ideal product, can be stored and transported, and can also serve as a common structural unit in chemicals. However, the CH bond in methane is highly stable, and activation requires stringent conditions. Traditional industrial conversion relies on high-temperature steam reforming, which is energy-intensive and produces large amounts of CO2 emissions. In recent years, the direct conversion of methane to methanol at room temperature has attracted much attention. Among these technologies, photocatalytic oxidation, as a green and sustainable catalytic technology, utilizes clean and renewable solar energy to drive the activation and conversion of methane, demonstrating broad application prospects.

[0003] In recent years, traditional oxide semiconductor materials have still faced some limitations in practical applications. For example, the high recombination rate of photogenerated electron-hole pairs and the typically small specific surface area lead to insufficient exposure of active sites, limiting the adsorption and activation of reactant molecules on the catalyst surface. Furthermore, many metal oxides exhibit uneven distribution of surface acidic sites and poor chemical stability, making them prone to structural collapse or loss of active components in strongly oxidizing environments (such as the H₂O₂ system). In contrast, metal-organic frameworks (MOFs) have become ideal candidate materials for photocatalytic methane conversion due to their unique structural characteristics. Among numerous MOF materials, Fe-based MOFs demonstrate significant advantages in the photocatalytic conversion of methane to methanol due to their unique magnetic properties, low synthesis cost, and low toxicity.

[0004] Although bimetallic MOF materials have a large specific surface area and ordered porous structure, which are beneficial for photon capture and transmission, their narrow light absorption range and low efficiency of photogenerated electron-hole pair separation limit their photocatalytic performance. Summary of the Invention

[0005] In view of this, the present invention discloses a MOF(Cu,Fe)-CdS catalyst, its preparation method and its application.

[0006] The present invention adopts the following technical solution: A method for preparing a MOF(Cu,Fe)-CdS catalyst, the method comprising the following steps: S1 is used to prepare MOF(Cu) catalyst powder; S2 Preparation of MOF(Cu,Fe) catalyst powder: Using the MOF(Cu) catalyst powder as raw material, further prepare MOF(Cu,Fe) catalyst powder; Preparation of MOF(Cu,Fe)-CdS catalyst powder by S3: MOF(Cu,Fe)-CdS was synthesized by photodeposition. The MOF(Cu,Fe) catalyst powder was uniformly dispersed in anhydrous ethanol to form a suspension. S8 and CdCl2·5H2O were added to the suspension, and nitrogen gas was introduced in the dark. The suspension was irradiated with a xenon arc lamp. After the reaction was completed, the powder was recovered by centrifugation. The recovered powder was dried in an oven to obtain the MOF(Cu,Fe)-CdS catalyst.

[0007] Furthermore, the mass-to-volume ratio of the MOF (Cu,Fe) catalyst powder to anhydrous ethanol in step S3 is 4:1.

[0008] Furthermore, in step S3, the amount of S8 added is 1 / 42 to 1 / 38 of the mass of the MOF (Cu,Fe) catalyst powder, and the amount of CdCl2·5H2O added is 7 to 8 times the amount of S8 added.

[0009] Furthermore, the nitrogen gas is introduced for 30 minutes in step S3.

[0010] Furthermore, in step S3, the power of the xenon arc lamp is 300W, the wavelength of the incident light is ≥420nm, and the irradiation time is 4h.

[0011] Further, the preparation of MOF(Cu) catalyst powder in step S1 includes: preparing MOF(Cu) catalyst powder using a hydrothermal method, mixing DMF, ethanol and distilled water to obtain a mixture, adding BTA and BTC while sonicating the mixture, then adding CuCl2·2H2O, and then magnetically stirring and sonicating the mixture to obtain a uniform colloidal suspension; transferring the colloidal suspension to a polytetrafluoroethylene container and reacting it in a closed environment for 10 hours to obtain a reaction mixture; after cooling the reaction mixture, recovering the powder by filtration, and drying the recovered powder in an oven to obtain MOF(Cu) catalyst powder.

[0012] Further, the preparation of MOF(Cu,Fe) catalyst powder in step S2 includes: dissolving FeCl3·6H2O in DMF, then dispersing MOF(Cu) in the solution and sonicating it to obtain a mixture suspension; sealing the mixture suspension in a high-pressure reactor containing polytetrafluoroethylene and reacting it for 10 hours to obtain a reaction mixture; after cooling the reaction mixture, recovering the powder by filtration; and drying the recovered powder in an oven to obtain MOF(Cu,Fe) catalyst powder.

[0013] A MOF(Cu,Fe)-CdS catalyst, wherein the MOF(Cu,Fe)-CdS catalyst is prepared by the method described above.

[0014] Furthermore, the outer layer of the MOF(Cu,Fe)-CdS catalyst has a (100) crystal plane of CdS, a lattice spacing of d=0.37nm, and elements such as Fe, Cu, Cd and S are uniformly distributed in the MOF(Cu,Fe)-CdS. The XRD pattern of the MOF(Cu,Fe)-CdS catalyst showed no obvious CdS characteristic peaks. The C1s XPS spectrum of the MOF(Cu,Fe)-CdS catalyst showed three characteristic peaks at 284.80, 285.62, and 288.50 eV; The O1s spectrum of the MOF(Cu,Fe)-CdS catalyst shows three characteristic peaks at 529.81, 531.00, 532.03 and 533.36 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst Cu2p shows three characteristic peaks centered at 932.30 eV, 952.07 eV, and 953.87 eV. The XPS spectrum of the Fe2p catalyst of the MOF(Cu,Fe)-CdS catalyst shows three characteristic peaks centered at 710.08, 723.95 eV and 711.67 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst Cd3d shows two characteristic peaks centered at 11.91 eV and 405.10 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst S2p contains two characteristic peaks centered at 161.33 and 162.45 eV. The band gap of the MOF(Cu,Fe)-CdS catalyst is 3.88 eV; The specific surface area of ​​the MOF(Cu,Fe)-CdS catalyst is 19.71 m². 2 / g.

[0015] An application of the above-mentioned MOF(Cu,Fe)-CdS catalyst, wherein the MOF(Cu,Fe)-CdS catalyst is used for photocatalytic conversion of methane to methanol.

[0016] The beneficial effects of this invention are: The present invention has the following beneficial effects: This invention develops a novel strategy for the efficient photocatalytic oxidation of methane to methanol under mild conditions. The MOF(Cu,Fe)-CdS catalyst synthesized using hydrothermal and photochemical deposition methods exhibits superior catalytic performance, significantly increasing methanol yield to 31.86 μmol·g. -1 Compared to a single MOF (Cu,Fe) catalyst, the yield was increased by 2 times.

[0017] In the MOF(Cu,Fe)-CdS catalyst, the copper-iron bimetallic centers achieve dynamic regeneration of Fe(III) / Fe(II) through an efficient redox cycle system combined with an optimized electron transfer pathway, significantly improving the separation efficiency of photogenerated electron-hole pairs. Specifically, Fe(II) and Cu(I) act as key active sites, significantly enhancing the generation efficiency of hydroxyl radicals (·OH) (confirmed by ESR testing), thereby efficiently activating the CH bond in methane.

[0018] Furthermore, the introduction of CdS into the catalyst of this invention significantly narrows the band gap of MOF(Cu,Fe) (from 4.13 eV to 3.88 eV), broadens the photoresponse range, and improves the light harvesting efficiency by 58.4%. In addition, the construction of the MOF(Cu,Fe)-CdS heterojunction electric field improves the transient photocurrent response by 1.1 times (to 1.05 mA cm⁻¹). -2 EIS testing showed that the semi-circle radius was significantly reduced, indicating that the charge transfer rate was accelerated and electron-hole recombination was effectively suppressed, thereby significantly improving the photocatalytic activity.

[0019] Photodeposition replaces high-temperature calcination, avoiding MOF framework collapse; the three-step process eliminates the need for precious metals, significantly reducing raw material costs.

[0020] This invention not only provides new ideas and methods for the photocatalytic conversion of methane, but also provides important theoretical basis and practical guidance for the design and synthesis of efficient catalysts. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 : Schematic diagram of the preparation process of MOF(Cu,Fe)-CdS catalyst of the present invention; Figure 2 : Schematic diagram of the photocatalytic experimental apparatus of this invention; Figure 3 Schematic diagram of scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the MOF(Cu,Fe)-CdS catalyst of this invention; Figure 4 Schematic diagram of XRD patterns of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS samples of this invention; Figure 5 Schematic diagram of the XPS spectrum of MOF(Cu,Fe)-CdS of this invention; Figure 6 : Schematic diagram of UV-Vis absorption spectrum and Tauc of the MOF catalyst material of this invention; Figure 7 : Schematic diagram of the low-temperature N2 adsorption-desorption isotherm and pore size distribution curve of the MOF catalyst of this invention; Figure 8 Schematic diagram comparing methanol production (a), methane conversion (b), and methanol selectivity (c) of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS in this invention; Figure 9 : A schematic diagram of the J-t curve of MOF(Cu,Fe)-CdS of the present invention after continuous irradiation at a potential of 0.5V (relative to RHE) for 1h (3600s); Figure 10 The present invention includes the linear sweep voltammetry (LSV) curves (a) of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS photoanodes under saturated methane, the Ampere Jt curves (b) of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS at a potential of 1V (relative to RHE), and the electrochemical impedance spectra (c) of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS under simulated sunlight irradiation. Figure 11 The present invention utilizes 10 mV s on MOF(Cu,Fe) and MOF(Cu,Fe)-CdS. -1 Schematic diagrams of CV curves at different scan rates, corresponding to (a) and (b) respectively; Schematic diagram of Cdl scan rate of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS of the present invention (c); Figure 12: Schematic diagram (a) showing the change in the intensity of the electron spin resonance signal of the ·OH free radical captured by DMPO after the MOF(Cu,Fe)-CdS composite material of the present invention was exposed to a methane atmosphere for 1.5 hours; Schematic diagram (b) showing the change in the intensity of the electron spin resonance signal of the ·CH3 free radical captured by TEMPO of the present invention. Detailed Implementation

[0023] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] Example 1 A method for preparing a MOF(Cu,Fe)-CdS catalyst, such as... Figure 1 As shown, the method includes the following steps: S1 is used to prepare MOF(Cu) catalyst powder; S2 Preparation of MOF(Cu,Fe) catalyst powder: Using the MOF(Cu) catalyst powder as raw material, further prepare MOF(Cu,Fe) catalyst powder; Preparation of MOF(Cu,Fe)-CdS catalyst powder by S3: MOF(Cu,Fe)-CdS was synthesized by photodeposition. The MOF(Cu,Fe) catalyst powder was uniformly dispersed in anhydrous ethanol to form a suspension. S8 and CdCl2·5H2O were added to the suspension, and nitrogen gas was introduced in the dark. The suspension was irradiated with a xenon arc lamp. After the reaction was completed, the powder was recovered by centrifugation. The recovered powder was dried in an oven to obtain the MOF(Cu,Fe)-CdS catalyst.

[0026] Furthermore, in step S3, the mass-to-volume ratio of the MOF (Cu,Fe) catalyst powder to anhydrous ethanol is 4:1. This ratio helps the catalyst powder to be fully dispersed to form a stable suspension, avoiding agglomeration and ensuring uniform subsequent CdS loading, thereby significantly improving the exposure of photocatalytic active sites.

[0027] Furthermore, in step S3, the amount of S8 added is 1 / 42 to 1 / 38 of the mass of the MOF (Cu,Fe) catalyst powder, and the amount of CdCl2·5H2O added is 7 to 8 times the amount of S8 added.

[0028] Furthermore, the nitrogen introduction time in step S3 is 30 minutes. This controlled introduction time completely eliminates oxygen, prevents sulfur source oxidation and CdS photocorrosion, ensures catalyst stability, and improves preparation efficiency.

[0029] Furthermore, in step S3, the xenon arc lamp has a power of 300W, the incident light wavelength is ≥420nm, and the irradiation time is 4h. Studies have found that controlling the irradiation time to 4h is significantly effective in maintaining the CdS nanoparticle size at 8-16nm.

[0030] Further, the preparation of MOF(Cu) catalyst powder in step S1 includes: preparing MOF(Cu) catalyst powder using a hydrothermal method, mixing DMF, ethanol and distilled water to obtain a mixture, adding BTA and BTC while sonicating the mixture, then adding CuCl2·2H2O, and then magnetically stirring and sonicating the mixture to obtain a uniform colloidal suspension; transferring the colloidal suspension to a polytetrafluoroethylene container and reacting it in a closed environment for 10 hours to obtain a reaction mixture; after cooling the reaction mixture, recovering the powder by filtration, and drying the recovered powder in an oven to obtain MOF(Cu) catalyst powder.

[0031] Further, the preparation of MOF(Cu,Fe) catalyst powder in step S2 includes: dissolving FeCl3·6H2O in DMF, then dispersing MOF(Cu) in the solution and sonicating it to obtain a mixture suspension; sealing the mixture suspension in a high-pressure reactor containing polytetrafluoroethylene and reacting it for 10 hours to obtain a reaction mixture; after cooling the reaction mixture, recovering the powder by filtration; and drying the recovered powder in an oven to obtain MOF(Cu,Fe) catalyst powder.

[0032] A MOF(Cu,Fe)-CdS catalyst, wherein the MOF(Cu,Fe)-CdS catalyst is prepared by the method described above.

[0033] Furthermore, the outer layer of the MOF(Cu,Fe)-CdS catalyst has a (100) crystal plane of CdS, a lattice spacing of d=0.37nm, and elements such as Fe, Cu, Cd and S are uniformly distributed in the MOF(Cu,Fe)-CdS. The XRD pattern of the MOF(Cu,Fe)-CdS catalyst showed no obvious CdS characteristic peaks. The C1s XPS spectrum of the MOF(Cu,Fe)-CdS catalyst showed three characteristic peaks at 284.80, 285.62, and 288.50 eV; The O1s spectrum of the MOF(Cu,Fe)-CdS catalyst shows three characteristic peaks at 529.81, 531.00, 532.03 and 533.36 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst Cu2p shows three characteristic peaks centered at 932.30 eV, 952.07 eV, and 953.87 eV. The XPS spectrum of the Fe2p catalyst of the MOF(Cu,Fe)-CdS catalyst shows three characteristic peaks centered at 710.08, 723.95 eV and 711.67 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst Cd3d shows two characteristic peaks centered at 11.91 eV and 405.10 eV. The XPS spectrum of the MOF(Cu,Fe)-CdS catalyst S2p contains two characteristic peaks centered at 161.33 and 162.45 eV. The band gap of the MOF(Cu,Fe)-CdS catalyst is 3.88 eV; The specific surface area of ​​the MOF(Cu,Fe)-CdS catalyst is 19.71 m². 2 / g.

[0034] An application of the above-mentioned MOF(Cu,Fe)-CdS catalyst, wherein the MOF(Cu,Fe)-CdS catalyst is used for photocatalytic conversion of methane to methanol.

[0035] Example 2 Experiments on the preparation of MOF(Cu,Fe)-CdS catalyst materials, such as Figure 1 As shown.

[0036] The composite MOF catalyst was prepared using a typical hydrothermal method. DMF (90 mL), ethanol (6 mL), and distilled water (30 mL) were mixed. 0.5 mmol of BTA and BTC were added to the solution under ultrasonication. Subsequently, 0.2 mmol of CuCl2·2H2O was added. The solution was then magnetically stirred for 10 min and continuously sonicated for 30 min to obtain a homogeneous colloidal suspension. Finally, the mixture was transferred to a polytetrafluoroethylene container and reacted at 180 °C for 10 h in a sealed environment. After cooling, the reaction mixture was filtered and dried in a 60 °C oven to obtain MOF(Cu) catalyst powder.

[0037] 1.082 g of FeCl3·6H2O was dissolved in 50 mL of LMF. 400 mg of MOF(Cu) was dispersed in the above solution and sonicated for 30 min. The resulting mixture suspension was sealed in a high-pressure reactor containing polytetrafluoroethylene and reacted at 150 °C for 10 h. After the reaction mixture was cooled, the powder was filtered and recovered. The recovered powder was dried in an oven at 60 °C to obtain MOF(Cu,Fe) catalyst powder.

[0038] MOF(Cu,Fe)-CdS was synthesized by photodeposition.

[0039] (1) 400 mg of MOF(Cu,Fe) was uniformly dispersed in 25 mL of anhydrous ethanol. Then, 9.5 mg of S8 and 66.5 mg of CdCl2·5H2O were added, and nitrogen gas was introduced in the dark for 30 min. Finally, the suspension was irradiated with a 300 W xenon arc lamp with an incident light wavelength ≥420 nm for 4 h. After the reaction was completed, the powder was recovered by centrifugation, and the recovered powder was dried in an oven at 60 °C to obtain MOF(Cu,Fe)-CdS catalyst powder.

[0040] (2) 400 mg of MOF(Cu,Fe) was uniformly dispersed in 25 mL of anhydrous ethanol. Then, 10.6 mg of S8 and 84.8 mg of CdCl2·5H2O were added, and nitrogen gas was introduced in the dark for 30 min. Finally, the suspension was irradiated with a 300 W xenon arc lamp with an incident light wavelength ≥420 nm for 4 h. After the reaction was completed, the powder was recovered by centrifugation, and the recovered powder was dried in an oven at 60 °C to obtain MOF(Cu,Fe)-CdS catalyst powder.

[0041] (3) 400 mg of MOF(Cu,Fe) was uniformly dispersed in 25 mL of anhydrous ethanol. Then, 10 mg of S8 and 78 mg of CdCl2·5H2O were added, and nitrogen gas was introduced in the dark for 30 min. Finally, the suspension was irradiated with a 300 W xenon arc lamp with an incident light wavelength ≥420 nm for 4 h. After the reaction was completed, the powder was recovered by centrifugation, and the recovered powder was dried in an oven at 60 °C to obtain MOF(Cu,Fe)-CdS catalyst powder.

[0042] All three schemes mentioned above can achieve the preparation of MOF(Cu,Fe)-CdS catalyst powder. Experimental results show that when the amount of S8 added is 1 / 40 of the mass of the MOF(Cu,Fe) catalyst powder, and the amount of CdCl2·5H2O added is 7.8 times the amount of S8 added, the catalyst prepared has a better catalytic effect. The following examples are the performance tests and studies of the catalyst powder prepared by (3).

[0043] Example 3 The morphology of the synthesized catalyst was examined using an AJSM-F100 field emission scanning electron microscope (FESEM), while the surface features and crystal structure were carefully examined using a Titan ETEM G2 ambient atmosphere aberration-corrected transmission electron microscope (ETEM). X-ray diffraction (XRD) analysis was performed using Cu Kα radiation (40 kV, 150 mA) on a Rigaku SmartLab X-ray diffractometer. The UV-Vis-NIR absorption characteristics of the samples were measured using a Varian Cary 7000 spectrophotometer. The elemental composition and oxidation states were determined by X-ray photoelectron spectroscopy (XPS) on an AXIS Ultra DLD system with Al Kα radiation. Active radical species were detected using a JEOL FA 200 electron paramagnetic resonance (ESR). The specific surface area and pore size distribution of the catalyst were determined using a Micron ASAP2460 surface area and porosity analyzer (BET).

[0044] Catalytic performance testing of MOF(Cu,Fe)-CdS catalyst, such as Figure 2 As shown.

[0045] The photocatalytic oxidation of methane was conducted in a photocatalytic reactor. First, 50 mg of MOF(Cu,Fe) / MOF(Cu,Fe)-CdS catalyst was ultrasonically dispersed in 80 ml of deionized water until homogeneous. Then, 13 μL of hydrogen peroxide was added. The prepared solution was poured into the photocatalytic reactor. During illumination, a 300 W Xe lamp (PLSSXE300, PerfectLight Co., China) equipped with an AM1.5G filter was used to irradiate the top of the sample at a light intensity of 100 mW·cm⁻¹. -2 Connect all reaction instruments and begin the experiment. Purge the reactor with methane for 5 minutes under no-light conditions to remove air interference. Initiate illumination. After illumination, take samples from the gas and liquid valves of the reactor every 30 minutes using a syringe. Detect the methane oxidation products using a gas chromatograph (SHIMADZU GC-2014).

[0046] The photoelectrochemical performance of the MOF(Cu,Fe)-CdS catalyst was tested in a 100 mL glass electrolytic cell equipped with a three-electrode system connected to an electrochemical workstation (CHI 660E, CH Instruments Inc., USA). The three-electrode system consisted of a saturated Ag / AgCl reference electrode (0.197 V), a Pt wire pair electrode, and a working electrode. The working electrode was an FTO glass coated with MOF(Cu,Fe) and MOF(Cu,Fe)-CdS, with its edges and back sealed with polyacrylate adhesive. The electrolyte was an aqueous solution of 0.35 mol / L Na2SO3 and 0.25 mol / L Na2S. The photoelectrocatalytic experiments were conducted at room temperature and atmospheric pressure. The experimental procedure is as follows: First, nitrogen gas was continuously introduced into the electrolytic cell at a flow rate of 100 mL / min for 10 min to remove air from the electrolyte. Then, using an electrochemical workstation, linear voltammetry (LSV), current density-time (J / t) curves, and electrochemical impedance spectroscopy (EIS) of the sample were acquired under both dark and light conditions. Under light conditions, a 300W Xe lamp (PLSSXE300, PerfectLight Co., China) equipped with an AM1.5G filter was used to illuminate the front of the sample at a light intensity of 100 mW·cm². -2 .

[0047] Morphology and structure analysis of MOF(Cu,Fe)-CdS catalyst.

[0048] The prepared material was analyzed in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, and the results are as follows: Figure 3 As shown. Specifically, Figure 3 (a) shows a SEM image of the MOF(Cu,Fe) compound, from which it can be observed that the sample has a microstructure with nanopetal stacking characteristics, with the size of a single petal being around 0.4 μm. Figure 3 (b) SEM images of the MOF(Cu,Fe)-CdS sample are presented. It can be observed that the surface of the nanopetal-like stacked structure of this sample exhibits obvious fine nanoparticles, and the overall structure of the MOF(Cu,Fe) compound is not significantly affected during this process. This indicates that CdS particles are dispersed on the surface of MOF(Cu,Fe) during the synthesis step, and CdS is successfully loaded onto the surface of MOF(Cu,Fe) without significantly altering its original crystal structure. Furthermore, Figure 3TEM images in (c,d) reveal the presence of a (100) crystal plane of CdS in the outer layer of the composite material, with a lattice spacing of d = 0.37 nm and CdS nanoparticles ranging in size from 8 to 16 nm. Furthermore, mapping images of the MOF(Cu,Fe)-CdS catalyst ( Figure 3 (e to j) clearly show that elements such as Fe, Cu, Cd and S are uniformly distributed in MOF(Cu,Fe)-CdS, which further confirms that CdS has been successfully loaded onto the surface of MOF(Cu,Fe) to form MOF(Cu,Fe)-CdS composite material.

[0049] Crystal structure analysis of MOF(Cu,Fe)-CdS catalyst.

[0050] The microstructure and crystal phase structure of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS samples were analyzed by X-ray diffraction. Figure 4 As shown, for the MOF(Cu,Fe) sample, its XRD pattern exhibits typical diffraction peaks at 2θ values ​​of 24.2°, 33.2°, 35.5°, 49.8°, 54.2°, 65.6°, 80.8°, and 90.4°, which is consistent with the results reported in previous literature, indicating that the target framework structure was successfully constructed. Furthermore, the diffraction peaks observed at 2θ values ​​of 26.6°, 37.8°, 51.8°, 61.8°, and 65.7° are attributed to tetragonal rutile SnO2 (PDF#46-1088) on the FTO conductive glass substrate and are unrelated to the bulk material structure. After introducing CdS nanoparticles, no significant new diffraction peaks appeared in the XRD pattern of the MOF(Cu,Fe)-CdS composite material. This phenomenon can be attributed to two factors: first, the low percentage content of CdS in the composite material results in weaker intensity of its characteristic diffraction peaks; second, the small size and uniform distribution of CdS particles further weaken its diffraction signal, affecting the crystallinity of CdS and the observability of diffraction peaks. These factors combined make the characteristic CdS peaks in the XRD pattern of the MOF(Cu,Fe)-CdS sample indistinct.

[0051] To further investigate the elemental composition and valence state of the prepared MOF(Cu,Fe)-CdS, X-ray photoelectron spectroscopy (XPS) analysis was performed. Figure 5 (a) The elemental survey spectrum reveals the presence of Cu, Fe, Cd, S, O, and C as the major components of MOFs. (C1s XPS spectrum) Figure 5 (b) Three characteristic peaks were observed at 284.80, 285.62, and 288.50 eV, attributable to C / C=C, CO, and C=O bonds, respectively. This was observed in the finely scanned O1s spectrum. Figure 5In (c), peaks at 529.81, 531.00, 532.03 and 533.36 eV were observed, which were attributed to lattice oxygen (Fe-O, Cu-O), C=O species, surface adsorbed oxygen species and surface hydroxyl (-OH), respectively. Figure 5 (d) shows the XPS spectrum of Cu2p, revealing three characteristic peaks centered at ~932.30 eV, 952.07 eV, and 953.87 eV. These peaks can be attributed to Cu(Ⅰ)2p, respectively. 3 / 2 Cu(Ⅰ)2p 1 / 2 and Cu(Ⅱ)2p 1 / 2 The formation of Cu(Ⅰ) orbitals may be attributed to the partial reduction of Cu(Ⅱ) during the hydrothermal reaction at high temperatures. Figure 5 (e) shows the XPS spectrum of Fe2p. The peaks at 710.08 and 723.95 eV are characteristic of Fe(II), while the peak at 711.67 eV corresponds to Fe(III), indicating that Fe(II) and Fe(III) oxidation states coexist. The other two peaks at 719.04 and 732.89 eV are satellite peaks of Fe(III). The formation of Fe(II) may be attributed to the departure of anionic ligands caused by the synthesis conditions and the reduction of Fe(III) caused by DMF. The coexistence of Fe(III) / Fe(II) and Cu(II) / Cu(I) binary redox pairs can promote electron transfer. Figure 5 (f) shows the XPS spectrum of Cd3d, revealing two characteristic peaks centered at ~411.91 eV and 405.10 eV, which can be attributed to Cd3d. 3 / 2 and Cd3d 5 / 2 orbital. XPS spectrum of S2p Figure 3-3 (g) Peaks are observed at 161.33 and 162.45 eV, which are attributed to S2p, respectively. 3 / 2 S2p 1 / 2 Its characteristics.

[0052] Analysis of the light absorption characteristics of MOF(Cu,Fe)-CdS catalyst.

[0053] To investigate the optical properties of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS samples, ultraviolet-visible absorption spectroscopy was performed on them. Figure 6The MOF(Cu,Fe) exhibits significant light absorption in the ultraviolet region, with the absorption peak edge located at approximately 330 nm. Compared to MOF(Cu,Fe), MOF(Cu,Fe)-CdS shows significantly enhanced absorption intensity in both the ultraviolet and visible light regions. CdS, a well-known visible-light-induced photocatalyst (with a band gap of 2.4 eV), possesses highly efficient visible light absorption capabilities, enabling it to capture photons over a wider spectral range. Simultaneously, CdS also exhibits excellent carrier transport capabilities, effectively promoting the separation and migration of photogenerated electrons and holes, thereby improving light energy utilization efficiency. These characteristics collectively contribute to the significant improvement in the absorption performance of MOF(Cu,Fe)-CdS in the ultraviolet and visible light regions. The calculated band gaps of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS are 4.13 eV and 3.88 eV, respectively, indicating that the introduction of CdS can narrow the band gap of the MOF(Cu,Fe) composite, which is beneficial for enhancing the visible light capture capability.

[0054] Analysis of the textural properties of MOF(Cu,Fe)-CdS catalysts.

[0055] The pore size distribution and specific surface area of ​​the synthesized samples were studied using the BET method. The low-temperature N2 adsorption-desorption isotherms and pore size distributions of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS are shown below. Figure 7 As shown. From Figure 7 (a) It can be seen that different types of MOF catalysts exhibit a distinct H3-type hysteresis loop at p / p0>0.5, which is a typical type IV isothermal adsorption curve. The pore size distribution of the samples was analyzed using the Barrett-Joyner-Halenda (BJH) method, and the results are as follows: Figure 7 As shown in (b), the pore size distribution of the MOF(Cu,Fe) catalyst exhibits a bimodal characteristic, mainly concentrated in the range of 1.7–2 nm (micropores) and 10–12 nm (mesopores). The micropores originate from the inherent crystalline channel structure of the MOF framework, while the mesopores are primarily formed by the packing voids between nanoscale MOF(Cu,Fe) and CdS particles. This hierarchical porous structure not only facilitates electrolyte wetting and ion diffusion but also provides efficient transport channels for reactant molecules, effectively promoting contact between reactants and active sites, thereby improving the efficiency of the catalytic reaction. Table 1 summarizes the specific surface area (S) of the prepared MOF(Cu,Fe) and MOF(Cu,Fe)-CdS samples. BET ), pore volume (V pore ) and aperture (D pore The corresponding data for MOF(Cu,Fe) is as follows: The specific surface area is 11.03 m². 2Compared to MOF(Cu,Fe), the surface area of ​​MOF(Cu,Fe)-CdS increased by 78.69% to 19.71 m² / g. 2 / g, this increase in surface area is beneficial for the catalyst to adsorb more methane molecules, while exposing more active sites, which is conducive to the effective contact between methane molecules and H2O2 and the active sites on the surface of MOF catalyst material.

[0056] Table 1. Specific surface area and pore structure distribution of different MOF catalysts Evaluation of photocatalytic activity and stability of MOF(Cu,Fe)-CdS catalyst.

[0057] The photocatalytic oxidation activity of methane was tested in a gas-liquid-solid mobile phase system under ambient temperature and pressure. The experiment mainly focused on the analysis and statistical analysis of gaseous and liquid products. The results showed that the liquid product of methane photocatalytic oxidation was mainly methanol, with trace amounts of formaldehyde and formic acid (negligible), while the gaseous product was mainly carbon dioxide. Important indicators for evaluating the performance of low-concentration methane photocatalytic conversion to methanol are methane conversion rate, the amount of methanol produced, and its selectivity. Due to the low solubility of methane in water, the methane conversion rate can be indirectly obtained by measuring the change in methane concentration in the upper gas phase space of the reactor. Products such as methanol and CO2 were determined by gas chromatography equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD). The methane conversion rate and the selectivity of the target product methanol were calculated using the following formulas: Methane conversion rate = (Number of moles of methane converted / Initial number of moles of methane) × 100% Methanol selectivity = (moles of methanol / moles of methane converted) × 100% Experimental results on the photocatalytic conversion of methane to methanol clearly reveal the differences in catalytic performance between MOF(Cu,Fe) and MOF(Cu,Fe)-CdS. For example... Figure 8 As shown in (a), the methanol yield of nano-MOF(Cu,Fe) was 13.56 μmol·g in 0.5 hours. -1 The average formation rate was 27.12 μmol·g. -1 ·h -1 However, after 2.5 hours of reaction, the methanol yield showed a decreasing trend, possibly due to the excessive oxidation of some methanol into byproducts. In contrast, the methanol yield of the MOF(Cu,Fe)-CdS composite material significantly increased to 31.86 μmol·g after the introduction of CdS nanoparticles. -1 The generation rate reached 63.72 μmol·g -1 ·h -1The efficiency improvement is twice that of pure MOF(Cu,Fe). This significant improvement indicates that the introduction of CdS not only optimizes the catalyst performance but may also effectively suppress the over-oxidation of methane, thereby improving the selectivity and yield of methanol. This performance improvement may stem from the synergistic effect between CdS and MOF, where the introduction of CdS promotes the efficient separation and migration of photogenerated carriers while reducing electron-hole recombination, thus significantly improving catalytic efficiency. Therefore, MOF(Cu,Fe)-CdS composite materials exhibit superior performance in the photocatalytic methane-to-methanol reaction.

[0058] Further analysis of methane conversion rate ( Figure 8 (b) and methanol selectivity ( Figure 8 (c) It was found that the methane conversion rate continuously increased with the progress of the reaction, indicating that the photocatalytic reaction proceeded stably under light conditions. However, analysis of the curve slope revealed that the rate of increase in methane conversion gradually slowed down, especially reaching a minimum at 3.0 hours, indicating a decrease in catalyst activity in the later stages of the reaction. Simultaneously, the amount of carbon dioxide generated continuously increased throughout the reaction, further confirming the persistence of the photocatalytic reaction. Notably, the amount of carbon dioxide generated peaked at 3.0 hours, and its generation rate significantly accelerated. This phenomenon may be related to the over-oxidation of methanol, i.e., some methanol was further oxidized to carbon dioxide in the later stages of the reaction, leading to a significant increase in its generation. In summary, the MOF(Cu,Fe)-CdS composite material exhibits higher catalytic activity and selectivity in the photocatalytic methane-to-methanol reaction, providing a new approach for the efficient conversion of methane.

[0059] For the catalytic oxidation of methane, besides catalytic efficiency, catalyst stability is also crucial for practical production applications. Therefore, this paper collects the Jt curves of methane photoelectrochemical oxidation over 1 hour (3600 s) to characterize catalyst stability. Figure 9 As shown, the photocurrent tends to stabilize after about 60 seconds of simulated sunlight supply, and no decay was observed in the following hour, indicating that MOF(Cu,Fe)-CdS exhibits excellent stability.

[0060] Study on the photocatalytic mechanism of MOF(Cu,Fe)-CdS.

[0061] To investigate the activity of MOF catalysts and the oxidation reaction process on the catalyst surface, linear voltammetric scan (LSV) curves of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS catalysts were measured under illumination using a three-electrode PEC system (electrolyte: 0.35 mol L⁻¹). -1 Na2SO3 and 0.25 mol L-1 An aqueous solution of Na₂S with a light density of 100 mW / cm² -2 ).like Figure 10 As shown in (a), the photocurrent densities of the two catalysts as photoanodes under illumination conditions differ. After the MOF(Cu,Fe) catalyst was modified with nano-CdS particles, its photocurrent density was significantly improved, from the original 14.47 mA cm⁻¹. -2 It jumped to 22.92 mA cm⁻¹ -2 (Measured at a potential of 1.5 V relative to the reversible hydrogen electrode), this significant increase is likely primarily attributed to the effective broadening of the light absorption range and enhanced light-harvesting capability resulting from the introduction of nano-CdS particles. Photocurrent response testing, as a reliable method, is used to evaluate the photogenerated charge separation efficiency and transport kinetics of the catalyst, such as... Figure 10 As shown in (b), in the Ampere Jt curve measured at a potential of 1 V relative to the reversible hydrogen electrode (RHE), the MOF(Cu,Fe)-CdS catalyst exhibits a higher photocurrent density than the MOF(Cu,Fe) catalyst, specifically reaching 1.05 mA cm⁻¹. -2 This result further confirms that MOF(Cu,Fe)-CdS not only has a stronger photoresponse intensity, but also possesses superior photogenerated carrier separation efficiency.

[0062] Electrochemical impedance spectroscopy (EIS) is a valuable tool for elucidating the migration process of photogenerated charges at the interface between solid catalysts and electrolytes. The radius of the semicircle in the Nyquist plot indicates the charge transfer resistance, such as... Figure 10 As shown in (c), MOF(Cu,Fe)-CdS has a significantly smaller semi-circular radius compared to MOF(Cu,Fe), indicating that MOF(Cu,Fe)-CdS has the lowest charge transfer resistance at the electrode-electrolyte interface when used as a photoanode. This further demonstrates that the modification of MOF(Cu,Fe) and CdS can effectively promote the migration of photogenerated carriers between the MOF(Cu,Fe) surface and the electrolyte.

[0063] The inherent activity and the number of active sites of an electrocatalyst are crucial to its overall electrochemical activity. Electrochemically active surface area (ECSA) refers to the active surface area on the electrode surface that can participate in electrochemical reactions; it is an important characterization parameter of the catalyst, directly reflecting the number of active sites. The non-Radial double-layer capacitance (C0) corresponding to the cyclic voltammetry curves at different scan rates was measured. dl ) current ( Figure 11 (a)-(b)), half of each difference between the positive and negative current densities in the central part of the scan potential range is related to the voltage scan rate, and the fitted straight line ( Figure 11The slope of (c) represents the electrochemical double-layer capacitance. We also calculated the roughness factor (R) of each electrode. f ): R f =C dl / 40.

[0064] Finally, the C of each electrode dl and R f As shown in Table 2, compared to MOF(Cu,Fe), MOF(Cu,Fe)-CdS exhibits a larger electrochemically active surface area and a higher roughness factor. This improvement may be attributed to the fact that the embedding of CdS nanoparticles increases the specific surface area of ​​the MOF framework, providing more active sites for electrochemical reactions. Furthermore, the interfacial interaction between CdS and MOF(Cu,Fe) may promote charge transfer and transport, further enhancing the electrochemical activity of the composite material.

[0065] Table 2. C content of MOF(Cu,Fe) and MOF(Cu,Fe)-CdS electrodes dl and R f This study focuses on the bimetallic synergistic mechanism and heterojunction interface engineering of the MOF(Cu,Fe)-CdS system, revealing its physicochemical essence for efficient photocatalytic methane-to-methanol production through systematic characterization and mechanistic analysis. Specifically, Fe(II) and Cu(I) in MOF(Cu,Fe)-CdS play a crucial role as key active sites. The catalytic cycle begins with the reaction of these active sites with hydrogen peroxide (H2O2) to generate Fe(III) and Cu(II). Notably, this process not only establishes the basis of the redox cycle but also provides the necessary intermediate states for subsequent catalytic steps. During methane oxidation, Fe(III) and Cu(II) can accept electrons, thus restoring to their initial Fe(II) and Cu(I) states, ensuring the continuous progress of the catalytic cycle. In this process, the Cu species acts as an electron bridge. Its lower redox potential (Cu(II) / Cu(I), E°=0.17V vs. NHE) is more favorable than that of Fe(III) / Fe(II) (E°=0.77V vs. NHE), accelerating the transfer of electrons from Cu(II) to Fe(II) and promoting the rapid regeneration of Fe(II). Therefore, Fe(III) / Fe(II) and Cu(II) / Cu(I) form a stable catalytic cycle in the photocatalytic reaction, ensuring the rapid regeneration of Fe(II) and the efficient generation of ·OH, thus realizing the recyclable use of the copper-iron bimetallic compound.

[0066] The efficient generation of hydroxyl radicals (·OH) is crucial for the activation of the CH bond in methane using the MOF(Cu,Fe)-CdS system. This study delves into the significant enhancing effect of the copper-iron bimetallic active sites in the MOF(Cu,Fe)-CdS system on the generation efficiency of hydroxyl radicals (·OH), aiming to achieve efficient methane activation. In this process, the synergistic effect of holes (h+) and electrons (e-) plays a vital role, jointly driving an innovative dual-pathway radical generation mechanism that greatly accelerates the ·OH generation rate. The Fe(II) and Cu(I) sites in the MOF(Cu,Fe)-CdS framework serve as core active centers, reacting with hydrogen peroxide to generate hydroxyl radicals, providing necessary reactive oxygen species for subsequent methane oxidation steps. Furthermore, hydrogen peroxide interacts with photogenerated electrons, further promoting hydroxyl radical generation. To directly monitor the generation and dynamic changes of ·OH, this study employed electron paramagnetic resonance (ESR) spectroscopy, with DMPO acting as a radical spin trapping agent to capture and stabilize the radical signal. Experimental results show (see appendix)... Figure 12 (a) No free radical signal peak was detected under dark conditions; however, a strong quartet signal with an intensity ratio of 1:2:2:1 was observed under visible light irradiation, clearly indicating the generation of hydroxyl radicals. The intensity of this signal significantly increased with prolonged illumination time, indicating a positive correlation between the amount of ·OH generated and illumination time. Furthermore, the interaction between the generated hydroxyl radical (·OH) and the methane molecule (CH4) led to the breaking of the CH bond, thereby forming a methyl radical (·CH3). This conclusion was strongly verified by electron paramagnetic resonance (ESR) spectroscopy (see Appendix). Figure 12 (b) Specifically, no signal peak of methyl radicals was detected under unilluminated conditions; however, after illumination, a typical six-line signal of the ·CH3 radical adduct was observed, and its signal intensity gradually increased over time, indicating that photoinduction promoted the formation of methyl radicals. Notably, the trends of methyl radicals (·CH3) and hydroxyl radicals (·OH) showed consistency, further confirming the argument that the Fe(II) and Cu(I) bimetallic active sites in the MOF(Cu,Fe)-CdS system significantly enhanced the generation efficiency of hydroxyl radicals (·OH), thereby activating methane.

[0067] The MOF(Cu,Fe)-CdS catalyst design combines the advantages of metal-organic frameworks and semiconductor cadmium sulfide, achieving a significant improvement in catalytic performance by constructing a heterojunction electric field between MOF(Cu,Fe) and CdS. Under visible light irradiation, the MOF(Cu,Fe)-CdS catalyst is excited, with photogenerated electrons transitioning from the valence band (VB) to the conduction band (CB), generating electron-hole pairs. Due to the potential difference between MOF(Cu,Fe) and CdS, photogenerated electrons tend to migrate from the conduction band of MOF(Cu,Fe) to the conduction band of CdS, thus forming a heterojunction electric field at the interface. This heterojunction electric field significantly suppresses the recombination of photogenerated electron-hole pairs, prolongs carrier lifetime, and accelerates the interfacial charge transfer process (verified by the reduction of the EIS semicircle radius). This mechanism not only facilitates the rapid regeneration of the Fe(III) / Fe(II) redox pair (verified by XPS characterization), but also achieves efficient separation and migration of photogenerated carriers in the bimetallic MOF(Cu,Fe)-CdS heterojunction (transient photocurrent response improved by 1.1 times), thus significantly enhancing photocatalytic activity. Furthermore, CdS, as a photosensitizer, plays a crucial role in promoting the transfer of photogenerated electrons and the activation of methane molecules. Its unique optical properties enable CdS to absorb visible light and generate photogenerated electrons, which are subsequently transferred to the MOF(Cu,Fe) moiety to participate in the redox cycle. This process not only provides the necessary energy for the catalytic cycle but also promotes the generation of active species, thereby driving the entire catalytic reaction.

[0068] Ultimately, the hydroxyl radicals derived from hydrogen peroxide interacted with the previously formed methyl radicals, successfully promoting methanol synthesis and demonstrating a highly efficient catalytic conversion process. This discovery not only reveals the specific pathway of methane CH bond activation but also provides new ideas and methods for the efficient conversion and utilization of methane.

[0069] This invention successfully developed a novel strategy for the efficient photocatalytic oxidation of methane to methanol under mild conditions. The MOF(Cu,Fe)-CdS catalyst synthesized using a hydrothermal and photochemical deposition method exhibited superior catalytic performance, significantly increasing methanol yield to 31.86 μmol·g. -1 Compared to a single MOF(Cu,Fe) catalyst, the yield was increased by 2 times. The significant advantages of this catalytic system are mainly reflected in the synergistic effect of the bimetallic combination and the heterojunction interface engineering. The copper-iron bimetallic center achieves dynamic regeneration of Fe(III) / Fe(II) through an efficient redox cycle system combined with an optimized electron transport pathway. Fe(II) and Cu(I) serve as key active sites, significantly enhancing the generation efficiency of hydroxyl radicals (·OH) (confirmed by ESR testing), thereby efficiently activating the methane CH bond. The introduction of CdS significantly narrowed the band gap of MOF(Cu,Fe) (from 4.13 eV to 3.88 eV), broadened the photoresponse range, and improved the light capture efficiency by 58.4%. Furthermore, the construction of the MOF(Cu,Fe)-CdS heterojunction electric field increased the transient photocurrent response by 1.1 times (to 1.05 mA cm⁻¹). -2 EIS testing showed a significant reduction in the semi-circle radius, indicating an accelerated charge transfer rate and effective suppression of electron-hole recombination, thereby significantly enhancing photocatalytic activity. This invention not only provides new ideas and methods for the photocatalytic conversion of methane, but also offers important theoretical basis and practical guidance for the design and synthesis of highly efficient catalysts.

[0070] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a MOF(Cu,Fe)-CdS catalyst, characterized in that, The method includes the following steps: S1 is used to prepare MOF(Cu) catalyst powder; S2 Preparation of MOF(Cu,Fe) catalyst powder: MOF(Cu,Fe) catalyst powder is prepared using the MOF(Cu) catalyst powder as raw material; Preparation of MOF(Cu,Fe)-CdS catalyst powder by S3: MOF(Cu,Fe)-CdS was synthesized by photodeposition. The MOF(Cu,Fe) catalyst powder was uniformly dispersed in anhydrous ethanol to form a suspension. S8 and CdCl2·5H2O were added to the suspension, and nitrogen gas was introduced in the dark. The suspension was irradiated with a xenon arc lamp. After the reaction was completed, the powder was recovered by centrifugation, and the recovered powder was dried in an oven to obtain the MOF(Cu,Fe)-CdS catalyst.

2. The method according to claim 1, characterized in that, The mass-to-volume ratio of the MOF (Cu,Fe) catalyst powder to anhydrous ethanol in step S3 is 40:

1.

3. The method according to claim 2, characterized in that, In step S3, the amount of S8 added is 1 / 42 to 1 / 38 of the mass of the MOF (Cu,Fe) catalyst powder, and the amount of CdCl2·5H2O added is 7 to 8 times the amount of S8 added.

4. The method according to claim 3, characterized in that, The nitrogen gas is introduced in step S3 for 30 minutes.

5. The method according to claim 4, characterized in that, The xenon arc lamp mentioned in step S3 has a power of 300W, the incident light wavelength is ≥420nm, and the irradiation time is 4h.

6. The method according to claim 1, characterized in that, Step S1, the preparation of MOF(Cu) catalyst powder, includes: preparing MOF(Cu) catalyst powder using a hydrothermal method; mixing DMF, ethanol, and distilled water to obtain a mixture; simultaneously adding BTA and BTC while sonicating the mixture; then adding CuCl2·2H2O; and then magnetically stirring and sonicating the mixture to obtain a uniform colloidal suspension; transferring the colloidal suspension to a polytetrafluoroethylene container and reacting it in a sealed environment for 10 hours to obtain a reaction mixture; after cooling the reaction mixture, recovering the powder by filtration; and drying the recovered powder in an oven to obtain MOF(Cu) catalyst powder.

7. The method according to claim 1, characterized in that, Step S2, the preparation of MOF(Cu,Fe) catalyst powder, includes: dissolving FeCl3·6H2O in DMF, then dispersing MOF(Cu) in the solution and sonicating it to obtain a mixture suspension; sealing the mixture suspension in a high-pressure reactor containing polytetrafluoroethylene and reacting it for 10 hours to obtain a reaction mixture; cooling the reaction mixture and recovering the powder by filtration; and drying the recovered powder in an oven to obtain MOF(Cu,Fe) catalyst powder.

8. A MOF(Cu,Fe)-CdS catalyst, wherein the MOF(Cu,Fe)-CdS catalyst is prepared by the method described in any one of claims 1-7.

9. The MOF(Cu,Fe)-CdS catalyst according to claim 8, characterized in that, The outer layer of the MOF(Cu,Fe)-CdS catalyst has a (100) crystal plane of CdS, with a lattice spacing of d = 0.37 nm. Fe, Cu, Cd, and S elements are uniformly distributed in the MOF(Cu,Fe)-CdS. The specific surface area of ​​the MOF(Cu,Fe)-CdS catalyst is 19.71 m². 2 / g.

10. An application of the MOF(Cu,Fe)-CdS catalyst as described in any one of claims 8 and 9, wherein the MOF(Cu,Fe)-CdS catalyst is used for photocatalytic conversion of methane to methanol.

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