Ce / cu-mof crystalline material, preparation method and application

Abstract

The application provides a Ce / Cu-MOF crystalline material, a preparation method and application, and relates to the technical field of materials.The chemical formula of the Ce / Cu-MOF material is: {[Cu6Ce2(MNA)6]·H2O·3DMA} n By coordinating and assembling Ce and Cu bimetallic nodes with thiol-containing pyridine carboxylic acid ligands, a multi-nuclear heterometallic organic framework structure with wide spectrum light response is successfully constructed.The material has simple preparation process, controllable reaction condition, good structural stability, and practical application prospect.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a Ce / Cu-MOF crystalline material, its preparation method, and its applications. Background Technology

[0002] The catalytic conversion of CO2 into high-value chemicals or fuels, especially the reduction of CO2 to methane (CH4) via photocatalysis, can effectively realize the recycling of carbon resources. Methane, as a major component of natural gas, has a high calorific value and is easy to store and transport; therefore, research on photocatalytic CO2 reduction to methane has attracted much attention. However, current photocatalytic systems still face many challenges: traditional photocatalysts (such as TiO2 and ZnO) can only be excited by ultraviolet light, with a solar light utilization rate of less than 5%; at the same time, single-component catalysts have fast photogenerated electron-hole recombination rates, low quantum efficiencies, and limited adsorption and activation capabilities for CO2, resulting in methane selectivity and yield far below the requirements for practical applications.

[0003] Therefore, developing a novel Ce / Cu-MOF photocatalytic material with broad-spectrum photoresponse, high carrier separation efficiency, and high selectivity for CH4 is of great significance for promoting the resource utilization of solar-driven CO2.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a Ce / Cu-MOF crystalline material, its preparation method, and its applications. By coordinating and assembling Ce and Cu bimetallic nodes with mercaptopyridine carboxylic acid ligands, a polynuclear heterometallic organic framework structure with a broad-spectrum photoresponse was successfully constructed. Furthermore, this material exhibits a simple preparation process, controllable reaction conditions, and good structural stability, demonstrating promising practical applications.

[0006] In order to achieve the objective of this invention, the following technical solution is adopted: This invention provides a Ce / Cu-MOF crystalline material, the chemical formula of which is: {[Cu6Ce2(MNA)6]·H2O·3DMA} n .

[0007] This invention also provides a method for preparing the above-mentioned Ce / Cu-MOF crystalline material, comprising the following steps: S1. Mix the cerium source, copper source and 6-mercaptopyridine-3-carboxylic acid; S2. Add organic solvent and deionized water, and finally add regulator to react and adjust the cooling rate. S3. After cooling, the product is collected, activated, and the organic ligands and reaction solvent are removed. The product is then dried to obtain Ce / Cu-MOF material.

[0008] Furthermore, the cerium source is CeCl3·7H2O, and the copper source is CuI.

[0009] Furthermore, the molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is (1-5):(1-5):(1-5).

[0010] Furthermore, the molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is 1:1:1.25.

[0011] Furthermore, the regulator is formic acid.

[0012] Furthermore, in S2, the reaction specifically includes reacting for 3 days at 120℃-150℃.

[0013] Furthermore, in S2, adjusting the cooling rate specifically includes: after the reaction is completed, cooling to 20°C on the third day.

[0014] Furthermore, in step S3, the specific steps for activating and removing the reaction solvent include: using N,N-dimethylacetamide and ethanol to activate and remove the organic ligand and the reaction solvent respectively, replacing N,N-dimethylacetamide and ethanol every 8-10 hours, and repeating this step for 2 days.

[0015] This invention also provides the application of the above-mentioned Ce / Cu-MOF crystalline material in photocatalytic reactions.

[0016] Furthermore, the photocatalytic reaction is the photocatalytic reduction of CO2 to CH4.

[0017] The present invention has the following technical effects: The Ce / Cu-MOF material provided by this invention successfully constructs a polynuclear heterometallic organic framework structure with a broad-spectrum photoresponse by coordinating and assembling Ce and Cu bimetallic nodes with mercaptopyridine carboxylic acid ligands.

[0018] Among them, the material uses Ce 3+ / Ce 4+ Redox couple with Cu + / Cu 2+Electron-trapping sites are synergistically constructed within the same polynuclear heterometallic organic framework; simultaneously, the mercaptosulfur atom and pyridine nitrogen atom in the 6-mercaptopyridine-3-carboxylic acid ligand significantly broaden the material's light absorption range. The synergistic effect of these three elements endows this Ce / Cu-MOF material with excellent structural stability and recyclability. It maintains its crystal phase integrity under different pH conditions and in common organic solvents, and its activity showed no significant decline after multiple catalytic experiments. This successfully solves common problems of existing photocatalysts, such as low light utilization, severe electron-hole recombination, and poor selectivity of CO2 reduction products, with CO being the predominant product. It provides a novel catalytic material for the efficient and highly selective conversion of carbon dioxide to methane, promoting the development of solar-driven carbon resource utilization technology. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 X-ray diffraction (XRD) pattern of Ce / Cu-MOF; Figure 2 Infrared spectrum of Ce / Cu-MOF; Figure 3 : Ball-and-stick model of Ce / Cu-MOF; Figure 4 Thermogravimetric stability test results of Ce / Cu-MOF; Figure 5 pH stability test results of Ce / Cu-MOF; Figure 6 Solvent stability test results for Ce / Cu-MOF; Figure 7 Results of the change in CO2 reduction yield by Ce / Cu-MOF photocatalytic reduction over time; Figure 8 Results of repeated experiments on the yield of CO2 reduction by Ce / Cu-MOF photocatalysis. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] In a first aspect, the present invention provides a Ce / Cu-MOF crystalline material, wherein the chemical formula of the Ce / Cu-MOF material is: {[Cu6Ce2(MNA)6]·H2O·3DMA} n .

[0023] With Ce 3+ / Ce 4+ and Cu + / Cu 2+ As a bimetallic node, it coordinates with 6-mercaptopyridine-3-carboxylic acid to form a polynuclear heterometallic organic framework. The thiol group and pyridine nitrogen atom can extend the light absorption sideband. This overcomes the limitation of traditional photocatalysts that only respond to ultraviolet light, while Ce... 3+ / Ce 4+ Redox pairs provide strong oxidizing holes for Cu + / Cu 2+ As an electron trap to suppress carrier recombination, the prepared Ce / Cu-MOF material has a stable overall structure and photocatalytic potential.

[0024] Secondly, the present invention also provides a method for preparing the above-mentioned Ce / Cu-MOF crystalline material, comprising the following steps: S1. Mix the cerium source, copper source and 6-mercaptopyridine-3-carboxylic acid; S2. Add organic solvent and deionized water, and finally add regulator to react and adjust the cooling rate. S3. After cooling, the product is collected, activated, and the organic ligands and reaction solvent are removed. The product is then dried to obtain Ce / Cu-MOF material.

[0025] By controlling coordination competition and crystal nucleation with a regulator, slow cooling reduces defects, and subsequent activation removes free molecules from the pores. This reaction process is simple and the conditions are controllable; it can also produce MOF crystals with high crystallinity and high phase purity, and the pores are opened after activation, which is beneficial for catalytic reactions.

[0026] In some embodiments, the cerium source is CeCl3·7H2O, and the copper source is CuI.

[0027] In some embodiments, the molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is (1-5):(1-5):(1-5).

[0028] In some embodiments, the molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is 1:1:1.25.

[0029] The ratio of metal to ligand directly affects the coordination mode, framework topology, and intermetallic synergistic effects. This ratio range can optimize Ce / Cu electronic synergy and improve the separation efficiency of photogenerated carriers.

[0030] In some embodiments, the molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is 4:4:5.

[0031] In some embodiments, the regulator is formic acid.

[0032] Formic acid can adjust the pH of the reaction system and, as a competitive ligand, slow down the rapid precipitation of ligands and metals, promoting the growth of ordered crystals. This effectively improves the purity of the crystalline phase and avoids the formation of amorphous byproducts.

[0033] In some embodiments, the reaction in S2 specifically includes reacting for 3 days at 120°C-150°C.

[0034] This temperature range satisfies the reversibility and rearrangement of coordination bonds under solvothermal conditions, ensuring sufficient time for crystal growth. This results in highly crystalline, large-sized crystals. However, if the temperature is too low, the reaction will be incomplete; while if the temperature is too high, the framework will collapse.

[0035] In some embodiments, adjusting the cooling rate in S2 specifically includes: cooling to 20°C on the third day after the reaction is completed.

[0036] Slow cooling helps reduce internal stress and lattice defects, effectively improving the stability of materials and avoiding microcracks or polycrystalline agglomeration caused by rapid cooling.

[0037] In some embodiments, the specific steps of activating and removing the reaction solvent in S3 include: using N,N-dimethylacetamide and ethanol to activate and remove the organic ligand and the reaction solvent, respectively, replacing N,N-dimethylacetamide and ethanol every 8-10 hours, and repeating this step for 2 days.

[0038] DMA and ethanol can exchange unreacted ligands, solvent molecules, and water within the pores. Through repeated replacement, the pores are purified, thereby exposing more active sites, increasing the specific surface area and pore volume, and thus enhancing catalytic performance.

[0039] Thirdly, the present invention also provides the application of the above-mentioned Ce / Cu-MOF crystalline material in photocatalytic reactions.

[0040] In some embodiments, the photocatalytic reaction is the photocatalytic reduction of CO2 to CH4.

[0041] The following is a detailed explanation using specific embodiments: Example 1 0.04 mmol (15 mg) of cerium chloride heptahydrate (CeCl3·7H2O), 0.04 mmol (7.5 mg) of cuprous iodide (CuI), and 0.05 mmol (7.88 mg) of 6-mercaptopyridine-3-carboxylic acid (6-MNA) were added to a 25 mL polytetrafluoroethylene reactor. Then, 1.5 mL of N,N-dimethylacetamide (DMA) and 1 mL of deionized water (H2O) were added sequentially. Finally, 115 μL of formic acid (HCOOH) was added as a regulator. The reactor was placed in a 140 °C oven for 3 days, and the cooling rate was adjusted to bring the temperature down to 20 °C within 3 days, at which point the reaction was complete. The resulting product was a pale blue transparent solution with red crystalline lumps. Pure red blocky crystals were collected by filtration through a copper mesh. The crystals were then activated sequentially with N,N-dimethylacetamide (DMA) and ethanol to remove organic ligands and reaction solvents from the crystal channels, respectively. The DMA was replaced every 8 hours, and the activation process lasted for two days. Finally, the activated crystals were dried in a vacuum oven at 60°C for 12 hours to obtain the red product Ce / Cu-MOF. The final yield of Ce / Cu-MOF was 70%, and the purity was >90%. The raw materials used are shown in Table 1.

[0042] Table 1: Raw Material List Experimental Example 1: Characterization of Ce / Cu-MOF Powder X-ray diffraction (PXRD) patterns were obtained by copper irradiation using a D8 Advance multi-functional X-ray diffractometer (Bruker AXS GmbH, Germany) at 40 kV with a 2θ range of 2–50 °. The experimental results are as follows: Figure 1 As shown, from Figure 1 As can be seen, Ce / Cu-MOF exhibits a crystalline phase and has high phase purity.

[0043] The prepared Ce / Cu-MOF was characterized by infrared spectroscopy. Infrared spectroscopy was performed using a Nicolet i50 Fourier transform infrared spectrometer, and the experimental results are as follows: Figure 2 As shown, from Figure 2 As can be seen from the results, the weakening of the stretching vibrations of the C=O and OH bonds in the prepared catalyst and the reduced SH vibrations in the organic ligand structure indicate that the structure of the prepared Ce / Cu-MOF was successfully formed. Figure 3 The ball-and-stick model of Ce / Cu-MOF clearly shows the structure of Ce / Cu-MOF.

[0044] Experimental Example 2: Stability Test of Ce / Cu-MOF 2.1 Thermal stability test Thermogravimetric (TG) spectra were obtained using a simultaneous thermal analyzer (STA 449 F3) under Ar conditions, with the temperature increased from room temperature to 800℃ at a rate of 5℃ / min. The experimental results are as follows: Figure 4 As shown, from Figure 4 As can be seen, CuCe / Cu-MOF exhibits good stability and can still maintain its intact crystal structure at 350℃.

[0045] 2.2 pH test Solutions with pH values ​​of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13 were prepared using HCl and NaOH, respectively. 10 mg of Ce / Cu-MOF was added to each of the above-prepared solutions at different pH values ​​and immersed in the solution. The solutions were allowed to stand for 10 h and then thoroughly dried at room temperature. The pH stability was determined by powder diffraction.

[0046] Experimental results are as follows Figure 5 As shown, from Figure 5 The results show that the characteristic peaks of Ce / Cu-MOF do not change significantly at different pH values, indicating that Ce / Cu-MOF can maintain structural stability at different pH values.

[0047] 2.3 Solvent stability test Solvent stability test: Take 10 mg of Ce / Cu-MOF and immerse Ce / Cu-MOF in TEA, H2O, C2H5OH, CH3OH, CH3CN and DEF respectively. Let it stand for 10 h and then dry it thoroughly at room temperature. The solvent stability is determined by powder diffraction.

[0048] Experimental results Figure 6 As shown, from Figure 6 As can be seen, the characteristic peaks of Ce / Cu-MOF do not change significantly in different solvents, indicating that Ce / Cu-MOF does not undergo phase transformation or structural damage in the above solvents, further demonstrating the stability of Ce / Cu-MOF.

[0049] Experimental Example 3: Analysis of Photocatalytic CO2 Reduction Performance In a custom-designed reactor, 5 mg of photocatalyst and 20 mg of tris(2,2') chloride were added. The mixture of bipyridine-ruthenium(II) hexahydrate was prepared by adding 4g of triethanolamine and 16mL of deionized water sequentially. The mixture was sonicated for 5 minutes, followed by bubbling with high-purity CO2 for 30 minutes. The pressure of the system was controlled at 0.5 atm using a vacuum pump, and the reactor was sealed. Irradiation was performed at 5°C for 2.5 hours using a 300W xenon lamp as the light source. The product was then quantified by gas chromatography using a flame ionization detector (FID) and a thermal conductivity detector (TCD) to monitor the CO and CH4 content. The experimental results are shown in Table 2. Figures 7-8As shown.

[0050] Table 2: Results of photocatalytic CO2 reduction performance The experimental results above show that Ce / Cu-MOF has photocatalytic CO2 reduction activity, which can reduce CO2 to CH4 and has good selectivity for CH4 reduction.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A Ce / Cu-MOF crystalline material, characterized in that, The chemical formula of the Ce / Cu-MOF material is: {[Cu6Ce2(MNA)6]·H2O·3DMA} n .

2. A method for preparing the Ce / Cu-MOF crystalline material as described in claim 1, characterized in that, Includes the following steps: S1. Mix the cerium source, copper source and 6-mercaptopyridine-3-carboxylic acid; S2. Add organic solvent and deionized water, and finally add regulator to react and adjust the cooling rate. S3. After cooling, the product is collected, activated, and the organic ligands and reaction solvent are removed. After drying, Ce / Cu-MOF material is finally obtained.

3. The method for preparing Ce / Cu-MOF crystalline material according to claim 2, characterized in that, The molar ratio of cerium in the cerium source, copper in the copper source, and 6-mercaptopyridine-3-carboxylic acid is (1-5):(1-5):(1-5).

4. The method for preparing Ce / Cu-MOF crystalline material according to claim 2, characterized in that, The regulator is formic acid.

5. The method for preparing Ce / Cu-MOF crystalline material according to claim 2, characterized in that, In S2, the reaction specifically includes reacting for 3 days at 120℃-150℃.

6. The method for preparing Ce / Cu-MOF crystalline material according to claim 2, characterized in that, In S2, adjusting the cooling rate specifically includes: after the reaction is completed, cooling down to 20°C on the third day.

7. The method for preparing Ce / Cu-MOF crystalline material according to claim 2, characterized in that, In step S3, the specific steps for activating and removing the reaction solvent include: using N,N-dimethylacetamide and ethanol to activate and remove the organic ligand and the reaction solvent respectively, replacing N,N-dimethylacetamide and ethanol every 8-10 hours, and repeating this step for 2 days.

8. The application of the Ce / Cu-MOF crystalline material as described in claim 1 in photocatalytic reactions.

9. The application of the Ce / Cu-MOF crystalline material according to claim 8 in photocatalytic reactions, characterized in that, The photocatalytic reaction is the photocatalytic reduction of CO2 to CH4.

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