A metal-organic framework-based single-site photocatalyst, a preparation method thereof and application of the photocatalyst to photocatalytic reduction of carbon dioxide into methanol

Abstract

This invention discloses a metal-organic framework-based single-point photocatalyst, its preparation method, and its application in the photocatalytic reduction of carbon dioxide to methanol; belonging to the interdisciplinary field of chemistry, materials science, and catalysis. The method is as follows: MOF materials are synthesized via a solvothermal method; then, defective DMOFs are formed through ligand exchange; the DMOF, nitrogen source, and metal salt are dissolved in a solvent, stirred at room temperature, heated to evaporate the solvent, washed, and dried; finally, the photocatalyst material is synthesized through doping pyrolysis. This invention employs a ligand exchange strategy to prepare a metal-organic framework material with a mesoporous structure. The synthesized material has large-size nanopores with tunable pore size and uniform distribution. Using this material as a carrier, a novel metal-organic framework-based single-point copper photocatalyst is prepared through doping pyrolysis. Its closely contacted heterostructure promotes the separation and transport of photogenerated electrons, exhibiting high catalytic activity and long-term stability in the photocatalytic reduction of carbon dioxide to methanol, a high-value-added product.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of chemistry, materials science and catalysis science. Specifically, it relates to a metal-organic framework-based single-point photocatalyst and its preparation method; as well as its application in the photocatalytic production of methanol from carbon dioxide. Background Technology

[0002] The overuse of fossil fuels has led to a sharp increase in atmospheric carbon dioxide concentration and a gradual rise in global temperatures. Carbon dioxide reduction can convert CO2 into valuable chemical products, thus helping to address the ongoing global warming crisis. The reduction of CO2 to methanol is highly attractive because methanol is a basic industrial feedstock that can be used to synthesize a range of commercial chemicals, such as low-carbon olefins and gasoline.

[0003] Solar energy is a clean and sustainable energy source in nature. In recent years, researchers have focused on using photocatalysis to reduce CO2 to CH3OH. Currently reported catalysts produce CH3OH at concentrations ranging from tens to hundreds of micromoles per gram per hour, which is one to two orders of magnitude lower than actual production requirements. Therefore, developing efficient photocatalysts for CH3OH production is of great significance.

[0004] Most of the MOF / PCN materials reported in the current literature are pre-synthesized MOF and PCN that are post-processed to form a bulk composite material. However, this results in problems such as poor contact between MOF and PCN interfaces and easy aggregation of PCN, which reduces the efficiency and selectivity of the material in photocatalytic reduction of CO2 to CH3OH. Summary of the Invention

[0005] Metal-organic frameworks (MOFs) are porous crystalline materials constructed from organic linkers and metal nodes. Their porous structure exhibits high affinity and adsorption for CO2 molecules. Polymer carbon nitride (PCN) is widely used in photocatalysis due to its ease of synthesis, low cost, and high stability, including CO2 reduction, catalytic hydrogen production, pollutant degradation, and organic matter conversion. The conjugated interaction between the aromatic rings of the organic ligands in MOFs and the aromatic rings of PCNs enables them to achieve close contact in the heterojunction structure, resulting in effective charge splitting and transfer, thus creating a synergistic effect.

[0006] The purpose of this invention is to provide a method for preparing a metal-organic framework-based single-point photocatalyst and its application in the reduction of carbon dioxide to methanol. Firstly, a defective metal-organic framework material is prepared through ligand exchange. This material exhibits characteristics such as uniform mesopore size distribution and good material stability. Using this material as a support, the metal-organic framework-based single-point catalyst prepared by doping pyrolysis displays excellent light absorption characteristics in the visible light absorption range, high charge separation efficiency, excellent stability, and high catalytic activity, achieving a high yield in the photocatalytic reduction of carbon dioxide to methanol.

[0007] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0008] The present invention aims to provide a metal-organic framework-based single-point photocatalyst, wherein the single-point photocatalyst is described as Metal@PCN@MOF, wherein the Metal is selected from one or two of Fe, Co, Ni, Cu, Zn, Pt, Pd, and Ag; and the MOF is selected from one of UiO-66, UiO-66-NH2, UiO-67, MIL-125, MIL-125-NH2, MOF-808, MIL-53, and HKUST-1. The preparation method of the metal-organic framework-based single-point photocatalyst includes the following steps:

[0009] Step 1: Synthesize MOF materials via a solvothermal method;

[0010] Step 2: Then, defective DMOFs are formed through ligand exchange;

[0011] Step 3: Dissolve DMOF, nitrogen source and metal salt in solvent, stir at room temperature, heat to evaporate solvent, wash and dry;

[0012] Step 4: Then, through doping and pyrolysis, a metal-organic framework-based single-point photocatalyst is obtained.

[0013] Further specifying, in step 1, the solvothermal reaction is carried out at 30℃~220℃ for 12h~72h.

[0014] Further specifying, in step 2, the reaction is carried out at 60℃~100℃ for 6h~20h.

[0015] Further specifying, in step 2, the ligand is selected from one of sodium acetate, potassium acetate, sodium propionate, and sodium benzoate.

[0016] Further specifying, in step 3, the nitrogen source is selected from one of dicyandiamide, melamine, urea, guanidine hydrochloride, aminoguanidine hydrochloride, 3-amino-1,2,4-triazole, and 5-amino-1H-tetrazole.

[0017] Further specifying, in step 3, the metal salt is selected from one or a combination of two in any ratio from ferric chloride, ferric acetylacetone, ferric nitrate, cobalt sulfate, cobalt acetate, cobalt chloride, cobalt nitrate, nickel acetylacetone, nickel acetate, copper sulfate, copper acetate, copper chloride, copper bromide, copper nitrate, zinc nitrate, zinc chloride, zinc acetate, zinc sulfate, platinum acetylacetone, palladium acetate, and silver nitrate.

[0018] Further specifying, in step 4, the pyrolysis is carried out at 200℃~600℃ for 0.5h~4h.

[0019] The above-mentioned single-point photocatalyst or any of the single-point photocatalysts prepared by the above methods are used for visible light photocatalytic reduction of carbon dioxide to methanol.

[0020] Further specifying, water, acetonitrile, and triethylamine are mixed in a volume ratio of (1-2):(1-10):(0.5-3), and then 1 mg / mL to 10 mg / mL of a metal-organic framework-based single-point catalyst is added. The mixture is then magnetically stirred under visible light irradiation for 0.5-8 hours to obtain the product methanol.

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

[0022] This invention employs a ligand exchange strategy to synthesize hierarchically porous metal-organic framework materials. The operation is simple, the conditions are controllable, and the synthesized materials have uniform pore size (e.g., ...). Figure 2 (As shown), the aperture is adjustable.

[0023] This invention uses a hierarchical porous metal-organic framework as a carrier to prepare heterogeneous single-point photocatalysts via pyrolysis.

[0024] The single-point catalyst obtained by this invention has a through-pore structure, visible light absorption properties, high charge separation efficiency, and excellent chemical and catalytic stability.

[0025] The metal-organic framework-based single-point catalyst obtained in this invention achieves a high yield of methanol from photocatalytic carbon dioxide reduction, which is comparable to that of commercially available thermal catalysts.

[0026] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0027] Figure 1 This is the powder X-ray (PXRD) spectrum of the metal-organic framework-based single-point material prepared by the method in Example 1;

[0028] Figure 2This is a transmission image of the metal-organic framework-based single-point material prepared by the method in Example 1;

[0029] Figure 3 This is the solid-state ultraviolet absorption spectrum of the metal-organic framework-based single-point material prepared by the method in Example 1;

[0030] Figure 4 This is a photocurrent test image of the metal-organic framework-based single-point material prepared by the method in Example 1;

[0031] Figure 5 This is a photocatalytic yield diagram of the metal-organic framework-based single-point material prepared by the method in Example 1. Detailed Implementation

[0032] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] Example 1: The preparation method of the metal-organic framework-based single-point photocatalyst CuSAs@PCN@UiO-66 in this example is carried out according to the following steps:

[0034] Step 1: Synthesis of MOF material: 35 mg ZrCl4, 27 mg 2-aminoterephthalic acid (NH2-BDC), 10 mL N,N'-dimethylformamide (DMF) and 0.7 mL acetic acid were added to a sealed reactor. The reactor was then placed at 120 °C and reacted for 24 h. After that, the mixture was centrifuged at 7000 rpm for 2 min. The lower solid was washed three times with DMF and twice with anhydrous ethanol. The resulting solid was then dried at 70 °C for 8 h to obtain dried UiO-66-NH2 crystal material.

[0035] Step 2, ligand exchange to form defective DMOF: 100 mg of UiO-66-NH2 crystal material prepared in Step 1, 820 mg of sodium acetate, and 150 mg of polyvinylpyrrolidone were added sequentially to 50 mL of deionized water. After stirring at 100 °C for 6 h, the mixture was centrifuged at 7000 rpm for 2 min. The lower solid was washed three times with deionized water, three times with DMF, and twice with ethanol. The resulting solid was dried at 70 °C for 8 h to obtain mesoporous D-UiO-66 material.

[0036] Step 3: Add 150 mg of mesoporous D-UiO-66 material, 800 mg of 3-amino-1,2,4-triazole, and 30 mL of CuCl2 aqueous solution with a concentration of 2 g / L to a beaker. Stir at room temperature for 1 h, then heat at 70 °C to evaporate the solvent. Wash the resulting solid three times with DMF and twice with ethanol, and then dry the solid at 70 °C for 8 h.

[0037] Step 4: Then, take 200 mg and place it in a tube furnace, calcine it at 200℃ for 4 hours under a nitrogen atmosphere to obtain the metal-organic framework-based CuSAs@PCN@UiO-66 catalyst.

[0038] The powder X-ray diffraction (PXRD) pattern of the metal-organic framework-based single-point material prepared by the method in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that the D-UiO-66 and CuSAs@PCN@UiO-66 materials retain the main characteristic peaks of UiO-66, indicating that the catalyst was successfully prepared.

[0039] The transmission spectrum of the metal-organic framework-based single-point material prepared by the method in this embodiment is shown in the figure below. Figure 2 As shown, by Figure 2 It can be seen that the CuSAs@PCN@UiO-66 catalyst has a uniform pore structure.

[0040] The solid-state UV absorption spectrum of the metal-organic framework-based single-point material prepared by the method in this embodiment is shown below. Figure 3 As shown, by Figure 3 It can be seen that the CuSAs@PCN@UiO-66 catalyst has a wide visible light absorption range.

[0041] The photocurrent measurement diagram of the metal-organic framework-based single-point material prepared by the method in this embodiment is shown below. Figure 4 As shown, by Figure 4 It can be seen that the CuSAs@PCN@UiO-66 catalyst has high photogenerated charge separation efficiency.

[0042] The prepared metal-organic framework-based single-point material is used for photocatalytic carbon dioxide reduction. The specific steps are as follows: 2 ml of water, 6 ml of acetonitrile, and 2 ml of triethylamine are added to a glass vial, followed by the addition of 10 mg of the metal-organic framework-based single-point catalyst. The mixture is magnetically stirred under visible light irradiation for 4 hours to obtain the methanol product. Finally, the product is filtered, and the reaction yield is determined by GC-MS. The photocatalytic yield of the metal-organic framework-based single-point material prepared by this embodiment is shown in the figure below. Figure 5 As shown, by Figure 5 It can be seen that CuSAs@PCN@UiO-66 has good catalytic activity, and the methanol yield can reach 17 mmol / g.

[0043] Example 2: The preparation method of the metal-organic framework-based single-point photocatalyst PdSAs@PCN@UiO-67 in this example is carried out according to the following steps:

[0044] Step 1: Synthesis of MOF material: 60 mg ZrCl4, 50 mg biphenyl dicarboxylic acid (H2BPDC), 10 mL N,N'-dimethylformamide (DMF) and 1 mL acetic acid were added to a sealed reactor. The reactor was then placed at 100 °C and reacted for 48 h. After that, the mixture was centrifuged at 9000 rpm for 1 min. The lower solid was washed three times with DMF and twice with ethanol. The resulting solid was then dried at 50 °C for 12 h to obtain dried UiO-67 crystal material.

[0045] Step 2, ligand exchange to form defective DMOF: 200 mg of UiO-67 crystal material prepared in Step 1, 960 mg of sodium propionate and 300 mg of polyvinylpyrrolidone were added sequentially to 100 mL of deionized water. After stirring at 60 °C for 20 h, the mixture was centrifuged at 9000 rpm for 1 min. The lower solid was washed three times with deionized water and DMF and twice with ethanol. The resulting solid was dried at 50 °C for 12 h to obtain mesoporous D-UiO-67 material.

[0046] Step 3: Add 50 mg of mesoporous D-UiO-67 material, 200 mg of urea, and 5 mL of 3 g / L palladium acetate aqueous solution to a beaker. Stir at room temperature for 2 h, then heat at 90 °C to evaporate the solvent. Wash the resulting solid three times with DMF and twice with ethanol, and then dry the solid at 50 °C for 12 h.

[0047] Step 4: Then, take 100 mg and place it in a tube furnace, calcine it at 600℃ under a nitrogen atmosphere for 0.5 h to obtain the metal-organic framework-based PdSAs@PCN@UiO-67 catalyst.

[0048] Example 3: The preparation method of the metal-organic framework-based single-point photocatalyst AgSAs@PCN@HKUST-1 in this example is carried out according to the following steps:

[0049] Step 1: Synthesis of MOF material: 438 mg Cu(NO3)2·H2O, 210 mg mesitylene benzoic acid (H2BTC), 6 mL ethanol and 6 mL water were added to a sealed reactor. The reactor was then placed at 100 °C and reacted for 24 h. After that, the mixture was centrifuged at 5000 rpm for 4 min. The lower solid was washed three times with DMF and twice with ethanol. The resulting solid was then dried at 50 °C for 12 h to obtain the dried HKUST-1 crystal material.

[0050] Step 2, ligand exchange to form defective DMOF: 200 mg of HKUST-1 prepared in Step 1, 1960 mg of potassium acetate, and 200 mg of polyvinylpyrrolidone were added sequentially to 200 mL of deionized water. After stirring at 80 °C for 12 h, the mixture was centrifuged at 5000 rpm for 4 min. The lower solid was washed three times with deionized water and DMF, and twice with ethanol. The resulting solid was dried at 50 °C for 12 h to obtain the mesoporous D-HKUST-1 material.

[0051] Step 3: Add 10 mg of mesoporous D-HKUST-1 material, 50 mg of dicyandiamide, and 10 mL of 3 g / L AgNO3 aqueous solution to a beaker. Stir at room temperature for 12 h, then heat at 80 °C to evaporate the solvent. Wash the resulting solid three times with DMF and twice with ethanol, and then dry the solid at 50 °C for 12 h.

[0052] Step 4: Then, take 100 mg and place it in a tube furnace, and calcine it for 2 hours under an oxygen atmosphere and a temperature of 400℃ to obtain the metal-organic framework AgSAs@PCN@HKUST-1 catalyst.

[0053] Example 4: The preparation method of the metal-organic framework-based single-point photocatalyst FeSAs@PCN@MOF-808 in this example is carried out according to the following steps:

[0054] Step 1: Synthesis of MOF material: 40 mg ZrOCl2·8H2O, 27 mg mesitylene benzoic acid (H3BTC), 5 mL N,N'-dimethylformamide (DMF) and 5 mL formic acid were added to a sealed reactor. The reactor was then placed at 130 °C and reacted for 48 h. After that, the mixture was centrifuged at 7000 rpm for 2 min. The lower solid was washed three times with DMF and twice with ethanol. The resulting solid was then dried at 70 °C for 8 h to obtain the dried MOF-808 crystal material.

[0055] Step 2, ligand exchange to form defective DMOF: 300 mg of MOF-808 crystal material prepared in Step 1, 1000 mg of sodium benzoate, and 400 mg of polyvinylpyrrolidone were added sequentially to 100 mL of deionized water. After stirring at 100 °C for 15 h, the mixture was centrifuged at 7000 rpm for 2 min. The lower solid was washed three times with deionized water and DMF, and twice with ethanol. The resulting solid was dried at 70 °C for 8 h to obtain mesoporous D-MOF-808 material.

[0056] Step 3: Add 200 mg of mesoporous D-MOF-808 material, 800 mg of guanidine hydrochloride, and 25 mL of FeCl3 aqueous solution with a concentration of 4 g / L to a beaker. Stir at room temperature for 6 h, then heat at 70 °C to evaporate the solvent. Wash the resulting solid three times with DMF and twice with ethanol, and then dry the solid at 70 °C for 8 h.

[0057] Step 4: Then, take 150 mg and place it in a tube furnace, and calcine it for 1 h in an oxygen atmosphere at a temperature of 500℃ to obtain the metal-organic framework FeSAs@PCN@MOF-808 catalyst.

[0058] Example 5: The preparation method of the metal-organic framework-based single-point photocatalyst Zn-Co@PCN@MIL-125 in this example is carried out according to the following steps:

[0059] Step 1: Synthesis of MOF material: 0.32 mL of titanium tetraisopropionate, 600 mg of terephthalic acid (H2BDC), 9 mL of N,N'-dimethylformamide (DMF) and 1.2 mL of methanol were added to a sealed reactor. The reactor was then placed at 150 °C and reacted for 24 h. After centrifugation at 5000 rpm for 4 min, the lower solid was washed three times with DMF and twice with ethanol. The resulting solid was then dried at 50 °C for 12 h to obtain dried MIL-125 crystal material.

[0060] Step 2, ligand exchange to form defective DMOF: 100 mg of MIL-125 prepared in Step 1, 1960 mg of potassium acetate, and 150 mg of polyvinylpyrrolidone were added sequentially to 100 mL of deionized water. After stirring at 60 °C for 20 h, the mixture was centrifuged at 5000 rpm for 4 min. The lower solid was washed three times with deionized water and DMF, and twice with ethanol. The resulting solid was dried at 50 °C for 12 h to obtain mesoporous D-MIL material.

[0061] Step 3: Add 10 mg of D-MIL-125 material, 50 mg of melamine, and 15 mL of ZnCl2 and CoCl2 aqueous solution to a beaker. Stir at room temperature for 12 h, then heat at 60 °C to evaporate the solvent. Wash the resulting solid three times with DMF and twice with ethanol, and then dry the solid at 50 °C for 12 h.

[0062] In step 3, the concentrations of ZnCl2 and CoCl2 in the aqueous solutions are 2 g / L and 2 g / L, respectively.

[0063] Step 4: Then, take 100 mg and place it in a tube furnace, calcine it at 370℃ under a nitrogen atmosphere for 3 hours to obtain the metal-organic framework-based Zn-Co@PCN@MIL-125 catalyst.

[0064] Example 6: The preparation method of the metal-organic framework-based single-point photocatalyst Pt-Ni@PCN@MOF-808 in this example is carried out according to the following steps:

[0065] Step 1: Synthesis of MOF material: 1300 mg Al(NO3)3·9H2O, 288 mg terephthalic acid (H2BDC) and 5 mL water were added to a sealed reactor. The reactor was then placed at 220 °C and reacted for 72 h. After centrifugation at 7000 rpm for 2 min, the lower solid was washed three times with DMF and twice with ethanol. The resulting solid was then dried at 70 °C for 8 h to obtain dried MIL-53 crystal material.

[0066] Step 2, ligand exchange to form defective DMOF: 100 mg of the MIL-53 crystal material prepared in Step 1, 1000 mg of sodium acetate and 400 mg of polyvinylpyrrolidone were added sequentially to 100 mL of deionized water. After stirring at 100 °C for 5 h, the mixture was centrifuged at 7000 rpm for 2 min. The lower solid was washed three times with deionized water and DMF and twice with ethanol. The resulting solid was dried at 70 °C for 8 h to obtain the mesoporous D-MIL material.

[0067] Step 3: Add 100 mg of mesoporous D-MIL material, 400 mg of aminoguanidine hydrochloride, 25 mL of platinum acetylacetonate and nickel acetate aqueous solution to a beaker, stir at room temperature for 10 h, then heat at 80 °C to evaporate the solvent, wash the obtained solid three times with DMF and twice with ethanol, and then dry the obtained solid at 70 °C for 8 h.

[0068] In step 3, the concentrations of platinum acetylacetonate and nickel acetate in the aqueous solutions are 4 g / L and 2 g / L, respectively.

[0069] Step 4: Then, take 150 mg and place it in a tube furnace, and calcine it at 350℃ under an oxygen atmosphere for 2 hours to obtain the metal-organic framework-based Pt-Ni@PCN@MOF-808 catalyst.

[0070] The prepared metal-organic framework-based single-point material is used for photocatalytic carbon dioxide reduction. Water, acetonitrile, and triethylamine are added to a glass vial in a volume ratio of 1–2:1–10:0.5–3, followed by 1–10 mg of the metal-organic framework-based single-point catalyst. The mixture is magnetically stirred under visible light irradiation for 0.5–8 h to obtain methanol product. Finally, the product is filtered, and the reaction yield is determined by GC-MS.

[0071] As can be seen from the above embodiments, this invention provides a highly efficient photocatalyst for the conversion of carbon dioxide to methanol. The preparation strategy provided by this invention has the advantages of low cost, strong universality, and wide applicability. The photocatalyst prepared by pyrolysis exhibits full visible light absorption and highly efficient photogenerated charge properties. Experimental results show that at room temperature, the conversion frequency of carbon dioxide to methanol by visible light photocatalysis can reach 4-8 mmol·g. -1 ·h -1 .

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A metal-organic framework-based single-point photocatalyst, characterized in that, The single-point photocatalyst is described as Metal@PCN@MOF. The Metal is selected from one or two of Fe, Co, Ni, Cu, Zn, Pt, Pd, and Ag; The MOF is selected from one of UiO-66, UiO-66-NH2, UiO-67, MIL-125, MIL-125-NH2, MOF-808, MIL-53, and HKUST-1; The PCN is polymeric carbon nitride; The single-point photocatalyst is prepared by the following steps: Step 1, synthesizing MOF material by solvothermal method; Step 2: Then, defective MOFs, i.e., DMOFs, are formed through ligand exchange; Step 3: Dissolve DMOF, nitrogen source and metal salt in solvent, stir at room temperature, heat to evaporate solvent, wash and dry; Step 4: Then, through doping and pyrolysis, a metal-organic framework-based single-point photocatalyst is obtained. In step 2, the reaction is carried out at 60℃~100℃ for 6h~20h; In step 2, the ligand is selected from one of sodium acetate, potassium acetate, sodium propionate, and sodium benzoate.

2. The method for preparing the single-point photocatalyst as described in claim 1, characterized in that, The preparation method includes the following steps: Step 1: Synthesize MOF materials via a solvothermal method; Step 2: Then, defective MOFs, i.e., DMOFs, are formed through ligand exchange; Step 3: Dissolve DMOF, nitrogen source and metal salt in solvent, stir at room temperature, heat to evaporate solvent, wash and dry; Step 4: Then, through doping and pyrolysis, a metal-organic framework-based single-point photocatalyst is obtained.

3. The preparation method according to claim 2, characterized in that, In step 1, the reaction is carried out at 30℃~220℃ for 12h~72h.

4. The preparation method according to claim 2, characterized in that, In step 3, the nitrogen source is selected from one of dicyandiamide, melamine, urea, guanidine hydrochloride, aminoguanidine hydrochloride, 3-amino-1,2,4-triazole, and 5-amino-1H-tetrazole.

5. The preparation method according to claim 2, characterized in that, In step 3, the metal salt is selected from one or any combination of two of the following: ferric chloride, ferric acetylacetone, ferric nitrate, cobalt sulfate, cobalt acetate, cobalt chloride, cobalt nitrate, nickel acetylacetone, nickel acetate, copper sulfate, copper acetate, copper chloride, copper bromide, copper nitrate, zinc nitrate, zinc chloride, zinc acetate, zinc sulfate, platinum acetylacetone, palladium acetate, and silver nitrate.

6. The preparation method according to claim 2, characterized in that, In step 4, pyrolysis is performed at 200℃~600℃ for 0.5h~4h.

7. The application of the single-point photocatalyst as described in claim 1 or the single-point photocatalyst prepared by any one of claims 2-6, characterized in that, Used for visible light photocatalytic reduction of carbon dioxide to methanol.

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