MOCPs-Ag crystal material as well as preparation method and application thereof

Abstract

The invention provides an MOCPs-Ag crystal material and a preparation method and application thereof, the molecular formula of the MOCPs-Ag crystal material is Ag [(PMA) 0.5 (DPE)] 4H2O, PMA is 1, 2, 4, 5-benzene tetracarboxylic acid, DPE is 1, 2-bis (4-pyridyl) ethylene ligand, and the molecular formula of the MOCPs-Ag crystal material is Ag [(PMA) 0.5 (DPE)] 4H2O. The crystal belongs to a P # imgabs0 # space group of a triclinic system, and the cell parameters are as follows: alpha is equal to 66.377 (4) degrees, beta is equal to 86.301 (3) degrees, gamma is equal to 71.838 (3) degrees, a is equal to 10.6957 (4), b is equal to 12.4200 (5), c is equal to 14.3193 (6), the cell volume is 1651.97 3, and Z is equal to 2. The MOCPs-Ag crystal material is synthesized by utilizing a simple room-temperature solvent volatilization method and can be used as a catalyst for electrocatalytic carbon dioxide reduction, and efficient carbon monoxide preparation through carbon dioxide reduction is realized.

Description

Technical Field

[0001] The invention relates to a MOCPs-Ag crystal material and a preparation method and application thereof, belonging to the technical field of catalyst preparation. Background Art

[0002] The use of fossil fuels has forced the concentration of carbon dioxide in the atmosphere to rise sharply. This has not only led to climate anomalies, melting ice and snow, but also had a significant negative impact on people's daily lives. How to effectively reduce the concentration of CO2 in the atmosphere is another major challenge facing the world. Therefore, it is very necessary to use some methods to reduce CO2 emissions from the source and convert it into valuable products. The electrochemical conversion of CO2 has the advantages of mild reaction conditions and adjustable product selectivity. The effective transfer of protons and electrons to the catalyst is crucial for ECR. Compared with composite proton and electron conducting electrocatalysts (PECEs), single-phase PECEs can provide catalytic activity, proton conduction and electron conduction in one material at the same time and uniformly, which is a promising method. Therefore, it is of great significance to construct and design new materials that are easy to regulate proton and electron conduction, so as to achieve the regulation of ECR ​​performance at the molecular level.

[0003] Metal organic coordination polymers (MOCPs) can be transformed into various morphologies and structures and tunable metal centers due to the dynamic nature of coordination bonds, and have broad application prospects in the field of ECR. Compared with traditional metal materials and metal oxides, MOCPs have the following advantages: (1) well-defined structural stability of catalytic sites; (2) high intrinsic electronic conductivity that promotes charge transport; (3) MOCPs combine the beneficial properties of homogeneous and heterogeneous catalysts, acting as host materials to bind guest active catalysts for synergistic catalysis; (4) clear structures have greatly promoted the understanding of the structure-performance mechanism of MOCP-based catalysts in the catalytic process. However, most MOCPs catalysts have insufficient conductivity and stability in the ECR process, and the electron or proton transport ability of MOCPs can be regulated by selecting appropriate ligands and / or metal centers and guest molecules. Therefore, MOCPs are expected to develop into ideal materials for single-phase PECE. Summary of the invention

[0004] The purpose of the present invention is to provide a MOCPs-Ag crystal material and a preparation method and use thereof, so as to solve the above-mentioned problems existing in the prior art.

[0005] The present invention is achieved through the following technical solutions:

[0006] A MOCPs-Ag crystal material, whose molecular formula is Ag[(PMA) 0.5(DPE)]·4H2O, where PMA is 1,2,4,5-benzenetetracarboxylic acid and DPE is 1,2-di(4-pyridyl)ethylene ligand; the crystal belongs to the triclinic system. Space group, unit cell parameters are α = 66.377 (4) °, β = 86.301 (3) °, γ = 71.838 (3) °, The unit cell volume is Z=2.

[0007] As a preferred embodiment, the MOCPs-Ag crystal material has a crystallographic structure in which Ag + It is coordinated with two 1,2-di(4-pyridyl)ethylene ligands in a two-coordinate manner and bridged by Ag-N bonds to form a one-dimensional chain. 1,2,4,5-benzenetetracarboxylic acid forms hydrogen bonds with adjacent water molecules and connects the carboxylic acid ligands through intermolecular hydrogen bond interactions to form a layered hydrogen bond network structure. The overall spatial structure is that the adjacent one-dimensional chains are connected by two π···π force distances between the 1,2-di(4-pyridyl)ethylene pyridine rings. and The π···π stacking interaction further extends into a two-dimensional layered structure. The distance between the H atom on the pyridine ring and the center of mass of the carboxylic acid ligand between adjacent columnar structures is A three-dimensional molecular structure is formed through CH···π interactions.

[0008] A method for preparing the MOCPs-Ag crystal material as described above comprises the following steps:

[0009] The water-soluble silver salt, 1,2,4,5-benzenetetracarboxylic acid and 1,2-di(4-pyridyl)ethylene are dissolved in a mixed solution of ethanol and distilled water, mixed evenly, and then concentrated ammonia is added. The mixture is evaporated slowly at room temperature in the dark to obtain the MOCPs-Ag crystal material.

[0010] As a preferred embodiment, the molar ratio of the water-soluble silver salt, 1,2,4,5-benzenetetracarboxylic acid and 1,2-di(4-pyridyl)ethylene is 1:1:1.

[0011] As a preferred embodiment, the water-soluble silver salt is silver nitrate.

[0012] As a preferred embodiment, the time for the slow volatilization reaction in the dark is 1 week.

[0013] A use of the MOCPs-Ag crystal material as described above in an electrocatalytic reduction working electrode, wherein the electrocatalytic reduction working electrode can reduce CO2 to CO.

[0014] A method for preparing the electrocatalytic reduction working electrode as described above comprises the following steps:

[0015] After the MOCPs-Ag crystal material is dissolved in a mixed solution of ethanol, distilled water and nafion as an electrocatalyst, it is sprayed on the surface of carbon paper to obtain an electrocatalytic reduction working electrode.

[0016] A method for constructing an electrocatalytic CO2 reduction device using the aforementioned electrocatalytic reduction working electrode comprises the following steps:

[0017] A three-electrode system is constructed with an H-type electrolytic cell as the electrolytic cell, a saturated Ag-AgCl electrode as the reference electrode, a platinum mesh electrode as the counter electrode, and the electrocatalytic reduction working electrode. The electrolytic cell solutions used in the cathode chamber and the anode chamber of the electrolytic cell are both 0.5 mol / L KHCO3 solution.

[0018] A method for detecting products of CO2 reduction using the aforementioned electrocatalytic CO2 reduction device comprises the following steps:

[0019] The gas phase product of the reduction reaction is quantitatively detected by gas chromatography, and the liquid phase product of the reduction product is quantitatively detected by nuclear magnetic resonance spectrometer.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention utilizes a simple room temperature solvent volatilization method to synthesize a MOCPs-Ag crystal material, which can be used as a catalyst for electrocatalytic carbon dioxide reduction to achieve efficient carbon dioxide reduction to produce carbon monoxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0023] Figure 1 is a molecular structure diagram of FJU-223-Dpe of Example 1 of the present invention, wherein (a) the simplest asymmetric unit of FJU-223-Dpe, (b) construction method, (c) water network connection method, (d) π···π force and (f) three-dimensional structure analysis;

[0024] Figure 2 is the infrared spectrum analysis spectrum of FJU-223-Dpe of Example 1 of the present invention;

[0025] Figure 3 is a thermogravimetric analysis spectrum of FJU-223-Dpe of Example 1 of the present invention;

[0026] Figure 4 is a schematic diagram of an electrolysis device according to Embodiment 3 of the present invention;

[0027] Figure 5 is the LSV diagram of FJU-223-Dpe of Example 3 of the present invention;

[0028] Figure 6 is a Faradaic efficiency diagram of FJU-223-Dpe at different potentials of Example 4 of the present invention;

[0029] Figure 7 is the XRD spectrum of FJU-223-Dpe in Example 6 of the present invention after being soaked in an electrolyte solution;

[0030] Figure 8 This is the CA diagram of FJU-223-Dpe electrolysis for 1 h in Example 7 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0032] Example 1

[0033] This embodiment provides a method for preparing a MOCPs-silver material, which specifically comprises the following steps:

[0034] Silver nitrate (AgNO3, 1 mmol, 0.17 g), 1,2,4,5-benzenetetracarboxylic acid (PMA, 1 mmol, 0.254 g), 1,2-di(4-pyridyl)ethylene (DPE, 1 mmol, 0.182 g) were dissolved in ethanol (5 mL) and distilled water (5 mL), and 1 ml of NH 3· H2O, ultrasonically treated for 30 min to obtain a transparent mixture. Then, the transparent mixture was placed in a light-proof carton at room temperature 25°C, the bottle cap was unscrewed and slowly evaporated at room temperature for one week to obtain a yellow block crystalline MOCPs-silver material, denoted as FJU-223-Dpe, with a molecular formula of Ag[(PMA) 0.5 (DPE)]·4H2O, with a yield of 80%.

[0035] The diffraction intensity data of MOCPs-silver materials were collected by Agilent Technologies SuperNova single crystal diffractometer. The crystal data and structure refinement parameters of MOCPs-silver materials are listed in Table 1. The single crystal X-ray diffraction analysis results show that MOCPs-silver materials belong to the triclinic system. Space group.

[0036] Table 1 Relevant crystal data of MOCPs-silver material (FJU-223-Dpe)

[0037]

[0038] Detailed analysis of the crystal structure of MOCPs-silver materials, such as Figure 1 As shown in (a), crystallographically, Ag + The two-coordinated ligands are coordinated with two 1,2-di(4-pyridyl)ethylene ligands and bridged by Ag-N bonds to form a one-dimensional chain. Figure 1 (b) 1,2,4,5-benzenetetracarboxylic acid forms hydrogen bonds with adjacent water molecules, connecting the carboxylic acid ligands through intermolecular hydrogen bonding interactions to form a layered hydrogen bond network structure such as Figure 1 (c) The overall spatial structure is that adjacent one-dimensional chains are connected by π···π( and ) The stacking interaction is further extended to a two-dimensional layered structure such as Figure 1 (d), the distance between the H atom on the pyridine ring and the center of mass of the carboxylic acid ligand between adjacent columnar structures is Through this CH···π interaction, a three-dimensional molecular structure is formed. Figure 1 (e) as shown.

[0039] The infrared spectrum of FJU-223-Dpe was tested by Fourier transform infrared spectrometer (FT-IR). The infrared spectrum (FT-IR) was measured by Nicolet 5700 FT-IR Fourier transform infrared spectrometer, KBr pellet, and the measurement range was 4000-400 cm -1 like Figure 2 According to the results obtained, 1554cm -1 The peak near the C=N stretching vibration peak, 3092 cm -1 The peaks on the left and right correspond to the CH characteristic peak of the benzene ring, 1423 cm -1 The peak at the position is the C=C stretching vibration on the benzene ring. About 1612cm -1 and 1355cm -1 The peaks at correspond to the C=O asymmetric stretching vibration and the CO symmetric stretching vibration on the carboxyl group, respectively. Based on the above infrared analysis results, it is shown that FJU-223-Dpe contains relevant functional groups of PMA and DPE.

[0040] Thermogravimetric analysis was used to test the weight loss of the material. Thermogravimetric (TGA) characterization was measured on a METTLER STDA851e thermogravimetric analyzer in a nitrogen atmosphere with a test temperature range of 30-600°C and a heating rate of 10°C / min. According to the results obtained, the material experienced three weight loss stages, such as Figure 3 As shown: the first weight loss occurs at 106℃~231.7℃, which corresponds to the process of the complex losing its crystal water; starting from 231.7℃, the ionic bonds and coordination bonds inside the complex begin to break, and the skeleton also begins to decompose. When the temperature reaches 281℃, the decomposition is basically completed, indicating that FJU-223-Dpe has good thermal stability.

[0041] Comparative Example 1

[0042] The only difference between this comparative example and Example 1 is that the transparent mixture was not subjected to solvent evaporation under light-shielding conditions, resulting in a clear solution without obtaining any product. This is because the silver ions that were not shielded from light underwent a silver mirror reaction and were reduced to silver element, which adhered to the container wall and could not participate in the reaction to obtain crystals.

[0043] Example 2

[0044] This embodiment relates to a method for preparing FJU-223-Dpe as a catalyst working electrode, which specifically includes the following steps: fully grind the above-mentioned crystal material, weigh 10 mg, disperse it in 1 mL of a mixed solution (700 μL of isopropanol, 150 μL of distilled water, 150 μL of 5 wt% Nanion solution), and ultrasonicate for 30 minutes to obtain a uniformly dispersed catalyst ink. Then, 1 mL of the ink solution is evenly sprayed onto a 2×3 cm 2 The catalyst was deposited on carbon paper and dried at room temperature to obtain a catalyst gas diffusion electrode (GDL), i.e., a working electrode.

[0045] Example 3

[0046] This embodiment relates to an electrochemical test method for electrocatalytic carbon dioxide reduction, and the specific operation steps are as follows: In this experiment, carbon dioxide is carried out in an H-type electrolytic cell, and a cation exchange membrane (Nafion117) is used to separate the cathode and the anode. An Ag / AgCl electrode is used as a reference electrode (stored in a saturated potassium chloride solution before use), a platinum mesh electrode is used as a counter electrode, and a carbon paper loaded with a catalyst is used as the working electrode. The working electrode and the reference electrode are placed in the cathode chamber, and the counter electrode (such as Figure 4 Schematic diagram of electrolysis device). The electrolyte solution is 0.5M potassium bicarbonate aqueous solution, and the electrolyte before use is pre-saturated with Ar (pH = 8.2) or CO2 (pH = 7.83). The voltage conversion formula is as follows: V RHE =V Ag / AgCl +V0 Ag / AgClvsNHE +0.059pHAt 25℃, V 0 Ag / AgClvsNHE =0.199V

[0047] Example 4

[0048] This embodiment involves that FJU-223-Dpe can be used as a catalyst for electrocatalytic reduction of carbon dioxide, and specifically includes the following steps: In order to preliminarily explore the CO2 electroreduction performance of the FJU-223-Dpe catalyst, the polarization curves of the catalyst in Ar-saturated and CO2-saturated KHCO3 solutions were tested, such as Figure 5 , as shown in Figure 6: In the Ar-saturated KHCO3 solution, the starting potential of the polarization curve is -1.4V (vsAg / AgCl), indicating that the catalyst has a higher hydrogen evolution (HER) overpotential; in the CO2-saturated KHCO3 solution, the starting potential of the polarization curve is -1.3V (vs Ag / AgCl), which is different from the polarization curve under Ar saturation. When CO2 is saturated, the current increases. It is preliminarily judged that there is a carbon dioxide reduction reaction and the corresponding current is generated.

[0049] Example 5

[0050] The reaction steps COOH, CO and the competitive reaction HER considered in this embodiment for the electrochemical reduction of carbon dioxide are as follows:

[0051]

[0052] Example 6

[0053] This embodiment relates to the determination of the optimal working potential of FJU-223-Dpe as a catalyst, and specifically comprises the following steps: Based on the above-mentioned embodiment 4, the FJU-223-Dpe catalyst is tested at different potentials within the potential range where products may exist, and the products are analyzed accordingly, and the Faradaic efficiency (FE%) of different products at different potentials is calculated, such as Figure 7 As shown in the figure, the carbon dioxide reduction products of the catalyst are basically CO and H2, with only a small amount of formic acid. The FE of FJU-223-Dpe in the wide potential range of -1.4V to -2V (vs Ag / AgCl) CO All of them are maintained above 70%, and at a voltage of -1.8V (vsAg / AgCl), its CO Faradaic efficiency is optimal, which is 77.3%. The selectivity of the product CO can be improved by controlling the electrolysis potential.

[0054] Example 7

[0055] This example involves a stability test of FJU-223-Dpe as a catalyst in an electrolyte solution environment. The specific implementation scheme is as follows: X-ray powder diffraction (XRD) is used to determine the purity of the synthetic material by comparing the position and intensity of the diffraction peaks and to characterize the water stability of the material in the electrolyte solution. Figure 7 As shown in the figure, the powder diffraction patterns of the synthesized crystalline material are basically consistent with the diffraction peak positions simulated by SC-XRD data in the literature. After being immersed in 0.5M KHCO3 electrolyte solution, the material still maintains good crystallinity and the material structure does not collapse significantly. The test results show that the modified FJU-223-Dpe crystalline material has good stability in the electrolyte environment.

[0056] Example 8

[0057] This example involves the stability test of FJU-223-Dpe as a catalyst under electrolysis conditions. The specific implementation plan is as follows: In order to further evaluate the stability of the catalyst, the chronoamperometry (CA) of the catalyst was tested. The test results are as follows: Figure 8 As shown, the material was tested under -1.8V conditions and the chronoamperometry was within 3600s. The test results showed that the catalyst material could maintain a stable current density during the CO2 reduction reaction test, and the detected products showed that FJU-223-Dpe showed that the material had good reaction stability.

[0058] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A MOCPs-Ag crystal material, characterized in that: The molecular formula is Ag [(PMA) 0.5 (DPE)]•4H2O, where PMA is 1,2,4,5-benzenetetracarboxylic acid and DPE is 1,2-di(4-pyridyl)ethylene ligand; the crystal belongs to the triclinic P Space group, unit cell parameters are α=66.377(4)°, β=86.301(3)°, γ=71.838(3)°, a=10.6957(4)Å, b=12.4200(5)Å, c=14.3193(6)Å, unit cell volume is 1651.97 Å 3 , Z=2.

2. The MOCPs-Ag crystal material according to claim 1, characterized in that: Crystallographically, Ag + It coordinates with two 1,2-di(4-pyridyl)ethylene ligands in a two-coordinate manner and forms a one-dimensional chain through Ag-N bond bridging. 1,2,4,5-benzenetetracarboxylic acid forms hydrogen bonds with adjacent water molecules and connects the carboxylic acid ligands through intermolecular hydrogen bond interactions to form a layered hydrogen bond network structure. The overall spatial structure is that the adjacent one-dimensional chains are further extended into a two-dimensional layered structure through the π···π stacking interaction through the two π···π forces between the 1,2-di(4-pyridyl)ethylene pyridine rings, with the distances being 3.706 Å and 3.848 Å respectively. The distances between the H atoms on the pyridine rings and the center of mass of the carboxylic acid ligands between adjacent columnar structures are 2.595 Å, forming a three-dimensional molecular structure through CH···π interactions.

3. A method for preparing the MOCPs-Ag crystal material according to claim 1 or 2, characterized in that: The steps include: The water-soluble silver salt, 1,2,4,5-benzenetetracarboxylic acid and 1,2-di(4-pyridyl)ethylene are dissolved in a mixed solution of ethanol and distilled water, mixed evenly, and then concentrated ammonia water is added. The mixture is evaporated slowly at room temperature in the dark to obtain the MOCPs-Ag crystal material.

4. The method for preparing the MOCPs-Ag crystal material according to claim 3, characterized in that: The molar ratio of the water-soluble silver salt, 1,2,4,5-benzenetetracarboxylic acid and 1,2-di(4-pyridyl)ethylene is 1:1:

1.

5. The method for preparing the MOCPs-Ag crystal material according to claim 4, characterized in that: The water-soluble silver salt is silver nitrate.

6. The method for preparing the MOCPs-Ag crystal material according to claim 3, characterized in that: The time for the slow volatilization reaction in the dark is 1 week.

7. A use of the MOCPs-Ag crystal material as claimed in claim 1 in an electrocatalytic reduction working electrode, wherein the electrocatalytic reduction working electrode can reduce CO2 to CO.

8. A method for preparing an electrocatalytic reduction working electrode as claimed in claim 7, characterized in that: The steps include: After the MOCPs-Ag crystal material is dissolved in a mixed solution of ethanol, distilled water and nafion as an electrocatalyst, it is sprayed on the surface of carbon paper to obtain an electrocatalytic reduction working electrode.

9. A method for constructing an electrocatalytic CO2 reduction device using the electrocatalytic reduction working electrode according to claim 8, characterized in that: The steps include: A three-electrode system is constructed with an H-type electrolytic cell as the electrolytic cell, a saturated Ag-AgCl electrode as the reference electrode, a platinum mesh electrode as the counter electrode, and the electrocatalytic reduction working electrode. The electrolytic cell solutions used in the cathode chamber and the anode chamber of the electrolytic cell are both 0.5 mol / L KHCO3 solution.

10. A method for detecting products of reducing CO2 using the electrocatalytic CO2 reduction device of claim 9, characterized in that: The steps include: The gas phase product of the reduction reaction is quantitatively detected by gas chromatography, and the liquid phase product of the reduction product is quantitatively detected by nuclear magnetic resonance spectrometer.

Images