Preparation method and application of covalent organic framework material containing imine bonds and benzoxazole rings in different proportions

Abstract

The invention discloses a preparation method and application of a covalent organic framework material containing imine bonds and benzoxazole rings in different proportions. The preparation method comprises the following steps: by taking amido and aldehyde group as construction units, adjusting the feeding proportion of a third monomer, quickly freezing in a liquid nitrogen bath, carrying out freezing-unfreezing circulating degassing, reacting in a water-free and oxygen-free environment, and after the reaction, filtering and cleaning, Soxhlet extraction, washing and freeze-drying to obtain the covalent organic framework material. Wherein different molecular construction units are beneficial to regulating and controlling the adsorption strength of an oxygen intermediate in an electrochemical process, so that an energy barrier in an electro-catalysis OER process is changed, and the catalytic activity of an electro-catalyst is improved. The preparation method is simple and has potential application prospects in the field of electrochemical catalysis.

Description

Technical Field

[0001] The invention relates to the field of catalyst preparation and electrocatalysis, and in particular to a preparation method and application of a covalent organic framework material containing imine bonds and benzoxazole rings in different proportions. Background Art

[0002] The low crustal abundance and high price of precious metal Ru / Ir-based materials have hindered the development of precious metal catalysts in commercial applications. Therefore, it is urgent to develop efficient non-precious metal catalysts and metal-free carbon-based electrocatalysts as alternatives to precious metal electrocatalysts. Metal-free carbon-based materials mainly include carbon nanotubes, graphene, carbon nitrogen compounds, biomass or polymer-derived carbon materials, etc. According to current research progress, the preparation and performance optimization of metal-free carbon-based materials used in the field of electrochemistry lies in the introduction of defects and heteroatom doping regulation. However, some metal-free carbon-based materials have unclear active sites, low stability and conductivity, which will limit the large-scale application of carbon-based metal-free catalysts to a certain extent.

[0003] As a covalent organic framework of metal-free carbon-based materials, it is a polymer network structure formed by coplanar self-assembly of various types of organic molecular building units through covalent bonds. Due to its strong structural controllability, designability, high stability and large specific surface area, it shows great development potential in energy catalysis, optoelectronic materials, gas separation and storage, sensing and biomedicine. Summary of the invention

[0004] The functional modification scheme of the bottom-up design and synthesis of functional covalent organic frameworks is to adopt a hybridization strategy of building modules, target the selection of molecular building units with different affinity molecules, and adjust the adsorption strength of the structure to oxygen intermediates during the electrochemical process while introducing heteroatoms, thereby affecting the difference in reaction energy barriers during the OER reaction and improving the electrocatalytic activity of the electrocatalyst. In addition, the introduction of the third monomer also helps to change the pore structure and porosity of the structure, increase the specific surface area of ​​the material, facilitate mass transfer and electron transport during the electrocatalytic reaction, and further optimize the electrocatalytic performance of the electrocatalyst.

[0005] The object of the present invention is to provide a method for preparing a covalent organic framework material containing imine bonds and benzoxazole rings in different proportions.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a covalent organic framework material containing imine bonds and benzoxazole rings in different proportions comprises the following steps:

[0008] The amino monomer, the aldehyde monomer and the third monomer are added with a dehydrogenating agent / catalyst and a solvent, mixed and ultrasonicated, and then rapidly frozen in a liquid nitrogen bath, degassed by freeze-thaw cycles, reacted in an anhydrous and oxygen-free environment, filtered and cleaned after the reaction, extracted with Soxhlet, washed and freeze-dried to obtain a covalent organic framework material;

[0009] The aldehyde monomers include trimesic acid aldehyde, terephthalic acid aldehyde, 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,4,6-trimethylbenzene-1,3,5-tricarbaldehyde;

[0010] The amino monomers include 2,5-diamino-1,4-dihydroxybenzene dihydrochloride, p-phenylenediamine, 2,5-dihydroxy p-phenylenediamine (hydrochloride) and tetrakis(4-aminophenyl)ethylene.

[0011] Preferably, the third monomer is one of the aldehyde monomer or the amine monomer.

[0012] Preferably, the solvent and the solvent of the Soxhlet extraction include one or more of dimethyl sulfoxide, N,N-dimethylformamide, o-dichlorobenzene, N-methylpyrrolidone, mesitylene, tetrahydrofuran, and isopropyl acetate.

[0013] Preferably, the dehydrogenating agent / catalyst includes benzimidazole, benzoxazole, isoquinoline, acetic acid or acetic acid aqueous solution, imidazole and 2,3-dichloro-5,6-dicyanobenzoquinone.

[0014] Preferably, the reaction time is 3 to 7 days and the temperature is 120°C to 200°C.

[0015] Preferably, the freeze-drying time is 24 to 48 hours.

[0016] Preferably, the molar masses of the amino monomer, the aldehyde monomer and the third monomer are respectively 0.1 to 0.5 mmol.

[0017] Preferably, when the dehydrogenator / catalyst is a solid powder, the molar mass of the dehydrogenator / catalyst is 3.0 to 5.0 times the total molar mass of the amino monomer and the third monomer; when the dehydrogenator / catalyst is a liquid, the amount of the dehydrogenator / catalyst is 0.1 to 2.0 mL.

[0018] Preferably, when the third monomer is an amino monomer, the feeding ratio of the amino monomer to the amino monomer of the third monomer is 0:1, 1:2, 1:1, 2:1, 1:0; when the third monomer is an aldehyde monomer, the feeding ratio of the aldehyde monomer to the aldehyde monomer of the third monomer is 0:1, 1:2, 1:1, 2:1, 1:0.

[0019] A covalent organic framework material containing different ratios of imine bonds and benzoxazole rings can be used in the field of electrochemical catalysis.

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

[0021] (1) The present invention selects suitable molecular building blocks and adjusts the feed ratio of the third monomer to effectively regulate the adsorption intensity of oxygen intermediates in the electrochemical process, thereby changing the energy barrier in the electrocatalytic OER process and improving the catalytic activity of the electrocatalyst;

[0022] (2) The morphology of the catalyst prepared by the present invention presents different states as the feeding ratio of the third monomer changes, and the size and thickness of the nanoparticles change accordingly, which can effectively improve the specific surface area activity of the electrocatalyst;

[0023] (3) Catalyst MEC-L prepared by the present invention x P y , compared with the covalent organic framework without the incorporation of the third monomer, the changes in the pore structure and pore size are helpful to improve the mass transfer and electron transport in the electrocatalytic process;

[0024] (4) The catalyst prepared by the present invention is a metal-free carbon-based material, which avoids a series of problems such as metal agglomeration and deactivation caused by the introduction of metals, and has good physical and chemical stability, thereby ensuring the excellent electrochemical stability of the catalyst during the electrocatalytic process.

[0025] (5) Electrocatalyst MEC-L prepared by the present invention x P y In a classic three-electrode system with 1.0 M KOH as the alkaline electrolyte, at a current density of 10 mA cm -2 When the overpotential of the catalyst on the glassy carbon electrode is in the range of 300-370 mV, the performance improvement range is 10-20 mV compared with the electrocatalyst without the third monomer doping.

[0026] (6) MEC-L1P1 has excellent stability during electrochemical testing. -2 The potential of the sample was only attenuated by 2.3% after 250 hours of continuous testing at a current density of 100 mA·cm -2 The potential fluctuation is ±1.7mV after 50 hours of continuous testing at a current density of

[0027] (7) The metal-free carbon-based material prepared by the present invention has high potential application value in the field of energy catalysis and can be applied to various organic catalytic reactions such as electrocatalytic reactions such as OER. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 MEC-L x P y X-ray powder diffraction patterns of a series of covalent organic framework materials.

[0029] Figure 2 MEC-L x P y Scanning electron micrographs of a series of covalent organic framework materials.

[0030] Figure 3 MEC-L x P y Transmission electron micrographs of a series of covalent organic framework materials.

[0031] Figure 4 MEC-L x P y Nitrogen adsorption curves and pore size distribution diagrams of a series of covalent organic framework materials.

[0032] Figure 5 MEC-L x P y OER linear sweep voltammetry curves of a series of covalent organic framework materials on glassy carbon.

[0033] Figure 6 MEC-L x P y Tafel plots of a series of covalent organic framework materials.

[0034] Figure 7 The MEC-L1P1 of the present invention is 10mA·cm -2 Diagram of constant current electrolysis under current density.

[0035] Figure 8 MEC-L x P y CV graphs of a series of covalent organic framework materials tested at different scan rates and C dl picture.

[0036] Fig. 9 MEC-L x P y Electrochemical impedance spectroscopy of a series of covalent organic framework materials. DETAILED DESCRIPTION

[0037] Example 1 MEC-L x P y Preparation

[0038] The reaction monomers trimesaldehyde (0.0543 g, 0.335 mmol), 2,5-diamino-1,4-dihydroxybenzene dihydrochloride, p-phenylenediamine (the total molar mass of the two reaction monomers is 0.50 mmol) and benzimidazole (0.177 g, 1.50 mmol) were weighed and added to the inner quartz tube of the high-intensity magnetic stirring parallel synthesizer reactor, and solvents N-methylpyrrolidone and mesitylene (V / V=1 / 1, 2.25 mL:2.25 mL) were added thereto. The above mixture was ultrasonically dispersed uniformly, quickly frozen in a liquid nitrogen bath at 77 K, and vacuumed to remove oxygen and other gas impurities in the reaction system, providing an oxygen-free reaction condition for the reaction system. In this experiment, the feed ratio (molar mass ratio) of the reaction monomer 2,5-diamino-1,4-dihydroxybenzene dihydrochloride and p-phenylenediamine in the reaction system was adjusted to control the ratio of imine bonds to benzoxazole rings in the skeleton. We set the feed ratio of 2,5-diamino-1,4-dihydroxybenzene dihydrochloride to p-phenylenediamine to be 1:0 (specifically 0.500mmol:0mmol) (MEC-L), 2:1 (specifically 0.334mmol:0.165mmol) (MEC-L2P1), 1:1 (specifically 0.250mmol:0.250mmol) (MEC-L1P1), 1:2 (specifically 0.165mmol:0.334mmol) (MEC-L1P2), 0:1 (specifically 0mmol:0.500mmol) (MEC-P). When the temperature in the reaction system rises to room temperature, the reaction is set at 185°C for 5 days (the temperature remains unchanged during the reaction). After the reaction is completed, the system is cooled to room temperature, and the solid matter is separated by centrifugation, washed with acetone (3×5mL) and tetrahydrofuran (3×5mL) solution, and dried at room temperature. Next, N,N-dimethylformamide was used as solvent and Soxhlet extraction was performed in a Soxhlet extractor for 2 days to remove the retained guest molecules, oligomers and unreacted monomers. Then, the obtained powder was washed with ethanol and freeze-dried for 24 hours. The product was MEC-L with different ratios of imine bonds and benzoxazole rings in the structure. x P y For metal-free pure organic materials, this method mainly adjusts the ratio of strong oxygen affinity to weak oxygen affinity reaction monomers to step-by-step regulate the adsorption energy barrier of reaction intermediates in the electrocatalytic process, thereby affecting the electrocatalyst MEC-L x P y The catalytic activity of the product is shown in Figure 1 ; Scanning electron microscopy images are shown in Figure 2 Transmission electron microscopy images are shown in Figure 3 ; Nitrogen adsorption curve and pore size distribution diagram are shown in Figure 4 .

[0039] Example 2MEC-L x P y Electrocatalytic OER performance test

[0040] MEC-L obtained in Example 1 x P y The electrocatalytic OER performance test of the series of covalent organic framework materials was carried out on a CHI760E electrochemical workstation through a classic three-electrode system. The electrochemical test temperature was controlled at 25°C room temperature, and the electrolyte was an alkaline 1.0M KOH solution. Hg / HgO and Pt sheets were used as the reference electrode and counter electrode of the reaction system. The working electrode of the electrochemical catalyst was prepared, that is, the catalyst MEC-L was weighed. x P y 3 mg of a series of covalent organic framework materials were mixed with a certain ratio of isopropanol / ultrapure water (V / V, 1 / 2, with a total volume of 600 μL) and 50 μL of Nafion to prepare a catalyst slurry. After the mixed solution was ultrasonically homogenized, 10 μL was evenly coated on a 5 mm glassy carbon electrode and allowed to stand and dry at room temperature for 6 hours to form a uniform film. Figure 5 The linear sweep voltammetry curve shown was obtained at a scan rate of 5 mV / s. From the legend, it can be seen that at a current density of 10 mA cm -2 When the catalyst MEC-L x P y The overpotential range of the series of covalent organic framework materials is 300-370mV. Figure 6 The Tafel curve shown is from Figure 5 Obtained by calculation. Figure 7 Shown is the electrochemical stability of MEC-L1P1 during 250 h of electrolysis.

[0041] Example 3MEC-L x P y Electrochemical surface area test

[0042] To determine the electrochemical surface area (ECSA), the double layer capacitance method (C dl ) The ECSA of the catalysts was evaluated. CV scans were performed in the non-Faraday range (0.9–1.0 V vs RHE) at scan rates of 20, 40, 60, 80, 100, and 120 mV s -1 By plotting the double layer capacitance current against the scan rate, the slope of the curve is C dl Electrochemical specific surface area diagram Figure 8 .

[0043] Example 4 MEC-L x P y Electrochemical Impedance Spectroscopy Test

[0044] Electrochemical impedance spectroscopy (EIS) measurements were performed at an AC voltage with an amplitude of 5 mV in the frequency range of 0.01 Hz to 100 kHz. Fig. 9 .

Claims

1. A method for preparing a covalent organic framework material containing different proportions of imine bonds and benzoxazole rings, characterized in that: The following steps are involved: The amino monomer, the aldehyde monomer and the third monomer are added with a dehydrogenating agent / catalyst and a solvent, mixed and ultrasonicated, and then rapidly frozen in a liquid nitrogen bath, degassed by freeze-thaw cycles, reacted in an anhydrous and oxygen-free environment, filtered and cleaned after the reaction, extracted with Soxhlet, washed and freeze-dried to obtain a covalent organic framework material; The aldehyde monomers include trimesic acid, terephthalaldehyde, 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,4,6-trimethylbenzene-1,3,5-tricarbaldehyde; The amino monomers include 2,5-diamino-1,4-dihydroxybenzene dihydrochloride, p-phenylenediamine, 2,5-dihydroxy p-phenylenediamine (hydrochloride) and tetrakis(4-aminophenyl)ethylene.

2. The method according to claim 1, characterized in that The third monomer is one of the aldehyde monomer and the amine monomer.

3. The method according to claim 1, characterized in that The solvent and the solvent of the Soxhlet extraction include dimethyl sulfoxide, N, N -Dimethylformamide, o-dichlorobenzene, N - one or more of methyl pyrrolidone, mesitylene, tetrahydrofuran, isopropyl acetate.

4. The method according to claim 1, characterized in that: The dehydrogenation agent / catalyst includes benzimidazole, benzoxazole, isoquinoline, acetic acid or acetic acid aqueous solution, imidazole and 2,3-dichloro-5,6-dicyano-p-benzoquinone.

5. The method according to claim 1, characterized in that The reaction time is 3 to 7 days, and the temperature is 120 o C~200 o C.

6. The method according to claim 1, characterized in that The freeze-drying time is 24 to 48 hours.

7. The method according to claim 1, characterized in that The molar masses of the amino monomer, the aldehyde monomer and the third monomer are respectively 0.1-0.5 mmol.

8. The method according to claim 1, characterized in that When the dehydrogenating agent / catalyst is a solid powder, the molar mass of the dehydrogenating agent / catalyst is 3.0 to 5.0 times the total molar mass of the amino monomer and the third monomer; when the dehydrogenating agent / catalyst is a liquid, the amount of the dehydrogenating agent / catalyst is 0.1 to 2.0 mL.

9. The method according to claim 2, characterized in that: When the third monomer is an amino monomer, the feeding ratio of the amino monomer to the amino monomer of the third monomer is 0:1, 1:2, 1:1, 2:1, 1:0; when the third monomer is an aldehyde monomer, the feeding ratio of the aldehyde monomer to the aldehyde monomer of the third monomer is 0:1, 1:2, 1:1, 2:1, 1:

0.

10. Use of the covalent organic framework material prepared by the method according to claims 1 to 9, characterized in that: Covalent organic frameworks can be used in the field of electrochemical catalysis.

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