N heteroatom-containing vinyl covalent organic framework material as well as preparation method and application thereof

Abstract

The invention discloses a vinyl covalent organic framework material containing N heteroatoms as well as a preparation method and application of the vinyl covalent organic framework material. The structural formula of the material is shown as a formula I, according to the invention, through aldol condensation reaction, 4, 4 '-(pyrazine-2, 5-diyl) dibenzaldehyde or 4, 4'-(pyridazine-3, 6-diyl) dibenzaldehyde and 2, 4, 6-trimethyl-1, 3, 5-triazine are used as raw materials, and TMT-PzDA-COF and TMT-DzDA-COF are prepared. Photocatalysis experiment results show that under visible light irradiation, the two vinyl covalent organic frameworks both show excellent photocatalytic water decomposition hydrogen production performance, the hydrogen production rate of TMT-PzDA-COF reaches 13.2 mmol.g <-1 >. H <-1 > and is remarkably higher than 5.7 mmol.g <-1 >. H <-1 > of TMT-DzDA-COF, and it is indicated that the N atom position in the frameworks has important influence on photocatalytic activity. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a vinyl covalent organic framework material, in particular to a vinyl covalent organic framework material containing N heteroatoms, and a preparation method and application thereof. Background Art

[0002] Fossil fuels, including coal, oil, and natural gas, are resources formed underground by the remains of ancient organisms. Their reserves are limited and non-renewable. As humans continue to exploit and utilize these resources, their reserves are gradually decreasing and may eventually become depleted. Therefore, exploring clean and sustainable energy remains a necessary and realistic option for addressing environmental and energy challenges.

[0003] Photocatalysis is considered one of the most promising technologies for producing clean energy and reducing environmental pollution. Developing new, efficient catalysts and thoroughly understanding their structure-performance relationships are crucial. Covalent organic frameworks (COFs), a class of porous materials with periodic skeletal structures, have garnered widespread attention in applications such as gas separation, catalysis, and energy storage due to their high surface area, tunable pore size, and excellent chemical stability.

[0004] COFs have significant potential for application in photocatalytic water splitting to produce hydrogen due to their customizable light absorption capacity and electronic structure. Currently, most COFs are connected using imine or borate bonds. Although these bonds can impart a certain degree of chemical stability to the material, they are susceptible to hydrolysis in aqueous environments, limiting their long-term and stable application in the field of photocatalytic water splitting to produce hydrogen.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the Invention

[0006] The purpose of the present invention is to provide a vinyl covalent organic framework material containing N heteroatoms, a preparation method and application thereof, which solves the problem that existing COFs materials have poor water stability and are difficult to be applied in the field of photocatalytic hydrolysis and hydrogen production, and can realize photocatalytic hydrolysis and hydrogen production.

[0007] In order to achieve the above object, the present invention provides a vinyl covalent organic framework material containing N heteroatom, the chemical structure of which is shown in Formula I:

[0008] A second object of the present invention is to provide a method for preparing the vinyl covalent organic framework material containing N heteroatoms, the method comprising:

[0009] 2,4,6-trimethyl-1,3,5-triazine is reacted with 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde in the presence of a catalyst and a flux in a vacuum sealed environment at 170-200° C., and the reaction is cooled to room temperature to obtain the vinyl covalent organic framework material containing a N heteroatom.

[0010] Preferably, the reaction is carried out at 180-200° C. in a vacuum sealed environment.

[0011] Preferably, the catalyst and flux are both selected from at least one of phenoxyacetic anhydride, benzoic anhydride and tetrafluorophthalic anhydride; or / and, the reaction time is 120 to 170 hours.

[0012] Preferably, the reaction is carried out in a heat-resistant glass tube. After the reactants are added to the heat-resistant glass tube, the tube is placed in a liquid nitrogen bath and subjected to freezing-vacuuming-thawing-nitrogen filling, and after cyclic degassing, the heat-resistant glass tube is vacuum-sealed with a flame.

[0013] Preferably, the molar ratio of the 2,4,6-trimethyl-1,3,5-triazine to 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde is (2-3):(3-2).

[0014] More preferably, the molar ratio of the 2,4,6-trimethyl-1,3,5-triazine to 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde is 2:3.

[0015] More preferably, the ratio between the molar amount of the 2,4,6-trimethyl-1,3,5-triazine, 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde and the total molar amount of the catalyst and the flux is (2-3):(3-2):12.

[0016] Preferably, the preparation method of the 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde comprises: In an inert atmosphere, 2,5-dibromopyrazine or 3,6-dibromopyridazine and 4-formylphenylboronic acid are subjected to a reflux reaction in the presence of an inorganic base and tetrakistriphenylphosphine palladium using a mixture of 1,4-dioxane and water as a solvent. After the reaction is completed, post-treatment is performed to obtain 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde.

[0017] More preferably, the molar ratio of the 2,5-dibromopyrazine or 3,6-dibromopyridazine to 4-formylphenylboronic acid is 1:2.4~2.5; or / and, the molar ratio of the 2,5-dibromopyrazine to tetrakistriphenylphosphine palladium is 1:0.16~0.18; or / and, the molar ratio of the 2,5-dibromopyrazine to the inorganic base is 1:2.5~16; or / and, the inorganic base is selected from alkali metal carbonates; or / and, the temperature of the reflux reaction is 90~120°C; or / and, the volume ratio of the 1,4-dioxane to water is 4:1.

[0018] Preferably, the preparation method of 2,4,6-trimethyl-1,3,5-triazine comprises: Acetic acid is added dropwise to ethyl acetimidate at room temperature and stirred for reaction. After the reaction is completed, 2,4,6-trimethyl-1,3,5-triazine is obtained by post-treatment.

[0019] More preferably, the molar ratio of acetimide to acetic acid is (3-4):1.

[0020] The third object of the present invention is to provide the use of the vinyl covalent organic framework material containing N heteroatoms in photocatalytic hydrolysis to produce hydrogen.

[0021] Preferably, H2PtCl6 is used as a co-catalyst, and any one or more of ascorbic acid, sodium ascorbate or triethanolamine is used as a sacrificial agent.

[0022] More preferably, the amount of the vinyl covalent organic framework material containing a N heteroatom is 1 to 6 mg; the amount of the co-catalyst is 1 to 7 wt% (the proportion of the mass of the vinyl covalent organic framework material containing a N heteroatom); the sacrificial agent is any one or more of ascorbic acid (AA) with a concentration of 0.05 to 3 mol / L, sodium ascorbate (SA) with a concentration of 0.05 to 3 mol / L, or triethanolamine (TEOA) with a concentration of 8 to 12% v / v, and the concentration is the concentration in the catalytic reaction solution.

[0023] The present invention's vinyl covalent organic framework material containing nitrogen heteroatoms, its preparation method, and its application solve the problem that existing COFs materials have poor water stability and are difficult to apply in the field of photocatalytic hydrolysis hydrogen production, and have the following advantages: (1) The present invention uses in situ synthesis to introduce pyrazine and pyridazine groups into the framework, and finds that vinyl covalent organic framework materials with different atomic arrangements will affect the photocatalytic hydrolysis hydrogen production performance. However, existing research mainly focuses on the electronic structure and conjugated system of COFs, and the effect of the spatial arrangement of the constituent atoms on the photocatalytic hydrogen production activity has not been reported; (2) The present invention uses a triazine structure containing a methyl group and a p-terphenyl type monomer containing an aldehyde group as building monomers, and uses a fusion-assisted synthesis method to prepare a new type of vinyl covalent organic framework material with high crystallinity, high specific surface area and high stability through aldol condensation. It can be used in the fields of photocatalysis, energy storage and adsorption; (3) The photocatalytic experimental results of TMT-PzDA-COF and TMT-DzDA-COF of the present invention show that under visible light irradiation, these two vinyl covalent organic frameworks exhibit excellent photocatalytic water decomposition and hydrogen production performance, among which the hydrogen production rate of TMT-PzDA-COF reaches 13.2 mmol·g -1 ·h -1 , which is significantly higher than that of TMT-DzDA-COF (5.7 mmol·g -1 ·h -1 , indicating that the position of the N atom in its framework has an important influence on the photocatalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the PXRD spectrum of PzDA-TMT-COF of the present invention.

[0025] Figure 2 This is the PXRD spectrum of DzDA-TMT-COF of the present invention.

[0026] Figure 3 The N2 isothermal adsorption-desorption curve and pore size distribution diagram of PzDA-TMT-COF of the present invention are shown.

[0027] Figure 4 The N2 isothermal adsorption-desorption curve and pore size distribution diagram of DzDA-TMT-COF of the present invention are shown.

[0028] Figure 5 FT-IR charts of PzDA-TMT-COF and DzDA-TMT-COF of the present invention.

[0029] Figure 6 1 is the electrochemical impedance spectra of PzDA-TMT-COF and DzDA-TMT-COF of the present invention.

[0030] Figure 7 These are the photocatalytic test results of PzDA-TMT-COF and DzDA-TMT-COF of the present invention. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0032] Note: If specific conditions are not specified in the examples, the experiments were conducted under conventional conditions or those recommended by the manufacturer. Instruments used without manufacturer information are commercially available. Raw materials and reagents used without manufacturer information are commercially available or can be prepared by known methods.

[0033] Throughout this disclosure, all features, such as values, amounts, amounts, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0034] The features described in this disclosure may be combined in any manner, and as long as there are no conflicts between the combinations of these features, all possible combinations should be considered within the scope of this specification. Each feature disclosed in this specification may be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the features disclosed are merely general examples of equivalent or similar features.

[0035] Example 1 A vinyl covalent organic framework material containing a nitrogen heteroatom, having a structural formula as shown in Formula Ia, and a preparation method thereof comprising:

[0036] (1) Preparation of 2,4,6-trimethyl-1,3,5-triazine Acetic acid (30 mmol, 1.8 mL) was added dropwise to ethyl acetimidate (119.4 mmol, 10.4 g) at room temperature and stirred for 24 hours. The reaction was stopped and the low-boiling organic solvent was removed by rotary evaporation. Two volumes of dichloromethane were added to the residue and the insoluble matter was removed by filtration. The solution was washed with saturated aqueous potassium carbonate solution and separated to obtain the organic phase. The organic phase was dried over anhydrous potassium carbonate for 12 hours and the potassium carbonate was removed by filtration. The organic phase was rotary evaporated to dryness to obtain 13.3 g of 2,4,6-trimethyl-1,3,5-triazine as white, transparent crystals with a yield of 76%.

[0037] (2) Preparation of 4,4′-(pyrazine-2,5-diyl)benzaldehyde Cs2CO3 (6.25 mmol, 2.11 g), 2,5-dibromopyrazine (2.5 mmol, 0.6 g), and 4-formylphenylboronic acid (6.25 mmol, 0.94 g) were added to a three-necked flask and degassed three times. Subsequently, 1,4-dioxane and water (4:1, v / v, 25 mL) and tetrakistriphenylphosphine palladium (0.4 mmol, 0.46 g) were slowly added to the flask under a nitrogen atmosphere. The reaction was refluxed at 105 °C under a nitrogen atmosphere for 48 hours. After the reaction was completed, the reactants were poured into distilled water, and a large amount of solid precipitated. The solid was filtered and washed with dichloromethane and ethyl acetate, respectively, to obtain 0.50 g of a yellow solid powder with a yield of 70.0%.

[0038] (3) Preparation of PzDA-TMT-COF A Pyrex tube was charged with 2,4,6-trimethyl-1,3,5-triazine (19.7 mg, 0.16 mmol), 4,4′-(pyrazine-2,5-diyl)benzaldehyde (69.2 mg, 0.24 mmol), and benzoic anhydride (217.6 mg, 0.96 mmol). The tube was rapidly frozen at 77 K, evacuated, and filled with nitrogen three times, and then flame-sealed under vacuum. The reaction was continued at 180°C for 5 days. After completion of the reaction, the reaction mixture was cooled to room temperature. The solid was washed three times with DMF and methanol to obtain the product. Finally, the product was dried under vacuum at 100°C for 24 hours to obtain 79.2 mg of a yellow solid powder, PzDA-TMT-COF, in a 91.0% yield.

[0039] Example 2 A vinyl covalent organic framework material containing a nitrogen heteroatom, having a structural formula as shown in Formula Ib, and a preparation method thereof comprising:

[0040] (1) Preparation of 2,4,6-trimethyl-1,3,5-triazine The preparation is the same as in Example 1; (2) Preparation of 4,4′-(pyridazine-3,6-diyl)benzaldehyde Cs2CO3 (40 mmol, 13.0 g), 3,6-dibromopyridazine (2.5 mmol, 0.6 g), and 4-formylphenylboronic acid (6.0 mmol, 0.9 g) were added to a three-necked flask and degassed three times. Subsequently, 1,4-dioxane and water (4:1, v / v, 25 mL) and tetrakistriphenylphosphine palladium (0.43 mmol, 0.5 g) were slowly added to the flask under a nitrogen atmosphere. The reaction was refluxed at 105 °C under a nitrogen atmosphere for 48 hours. After the reaction was completed, the reactants were poured into distilled water. Then, the product was extracted with dichloromethane and dried over anhydrous sodium sulfate. Subsequently, the organic solvent was removed by vacuum rotary evaporation. Finally, the product was further purified by column chromatography to obtain 0.58 g of a white powdery solid with a yield of 79.6%.

[0041] (3) Preparation of DzDA-TMT-COF A Pyrex tube was charged with 2,4,6-trimethyl-1,3,5-triazine (19.7 mg, 0.16 mmol), 4,4′-(pyridazine-3,6-diyl)benzaldehyde (69.2 mg, 0.24 mmol), and benzoic anhydride (217.6 mg, 0.96 mmol). The tube was rapidly frozen at 77 K, evacuated, and filled with nitrogen three times, and then flame-sealed under vacuum. The reaction was continued at 180°C for 5 days. After completion of the reaction, the tube was cooled to room temperature. The solid was washed three times with DMF and methanol to obtain the product. Finally, the product was dried under vacuum at 100°C for 24 hours to obtain 72.5 mg of a dark brown solid powder with a yield of 83.3%.

[0042] Experimental Example 1 Structural Characterization of PzDA-TMT-COF and DzDA-TMT-COF 1. PXRD Powder X-ray diffraction tests were performed on the PzDA-TMT-COF prepared in Example 1 and the DzDA-TMT-COF prepared in Example 2, and the PXRD spectra were shown in Table 1. Figure 1 and Figure 2 .Depend on Figure 1 The half-peak width of the main peak of PXRD shows that the PzDA-TMT-COF material has good crystallinity. Through Materials Studio simulation calculation, it can be seen that the material is an AA stacking model. Figure 2 The half-peak width of the main peak of PXRD shows that the material has good crystallinity. Through Materials Studio simulation calculation, it can be known that the material is an AA stacking model.

[0043] 2. N2 isothermal adsorption-desorption curve and pore size distribution diagram To further understand the internal pore information of vinyl covalent organic framework materials containing nitrogen heteroatoms, nitrogen adsorption and desorption characterization was carried out. The material was vacuum dried at 100 °C for 24 hours and then its nitrogen adsorption and desorption at 77 K was tested.

[0044] like Figure 3 and Figure 4 As shown in the figure, the N2 isothermal adsorption-desorption curves and pore size distribution diagrams of vinyl covalent organic framework materials PzDA-TMT-COF and DzDA-TMT-COF are respectively. From the figure, we can know that the specific surface areas of PzDA-TMT-COF and DzDA-TMT-COF are 1205 and 727 m 2 / g, and the pore size distribution is also 3.01 nm.

[0045] 3. FT-IR images The FT-IR spectra of vinyl covalent organic framework materials PzDA-TMT-COF and DzDA-TMT-COF containing N heteroatoms were tested by attenuated total reflectance spectroscopy (ATR) method.

[0046] from Figure 5 It can be clearly seen that the two samples have a -1 and 978 cm -1 -C=C- and trans The stretching bond vibration peak of -C=C- indicates that the carbon-carbon double bond is successfully formed.

[0047] Experimental Example 2 Electrochemical Impedance Test The electrochemical impedance spectroscopy of vinyl covalent organic framework materials PzDA-TMT-COF and DzDA-TMT-COF containing N heteroatom was tested under visible light.

[0048] like Figure 6 As shown in the Nyquist plot, the arc radius of PzDA-TMT-COF is slightly smaller than that of DzDA-TMT-COF, indicating that the charge transfer resistance of PzDA-TMT-COF is lower during illumination. Therefore, it can be preliminarily judged that PzDA-TMT-COF has better photocatalytic hydrogen production capacity by water splitting than DzDA-TMT-COF.

[0049] Experimental Example 3 Photocatalytic Test Photocatalytic testing of vinyl covalent organic framework materials PzDA-TMT-COF and DzDA-TMT-COF containing N heteroatoms. The test process is as follows: S1: Weigh a certain amount of COFs material (i.e., PzDA-TMT-COF or DzDA-TMT-COF) and grind the COFs powder thoroughly in a mortar to facilitate dispersion in the aqueous phase; S2: Prepare an aqueous solution of a certain concentration of sacrificial agent, add the ground material into the prepared aqueous solution, and ultrasonicate for 60 minutes to disperse it evenly; S3: Add a certain amount of platinum chlorate aqueous solution and sonicate again for 30 minutes. Transfer the prepared reaction solution to the photocatalytic reactor and evacuate for 30 minutes to eliminate the interference of oxygen in the air. Finally, turn on the xenon lamp light source and the photocatalytic hydrogen production automatic online sampling system to collect data.

[0050] The results are as follows Figure 7 As shown, the photocatalytic hydrolysis hydrogen production rate using PzDA-TMT-COF as catalyst is 13.2 mmol·g –1 ·h –1 , while the hydrogen production rate of DzDA-TMT-COF under the same conditions was 5.7 mmol·g –1 ·h –1 It is speculated that the different numbers of charge recombination centers are generated due to the different atomic arrangement positions in the framework, which in turn affects the rate of hydrogen production by photocatalytic water splitting.

[0051] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A vinyl covalent organic framework material containing N heteroatom, characterized in that: The chemical structure of the material is shown in Formula I: 。 2. The method for preparing a vinyl covalent organic framework material containing N heteroatoms as claimed in claim 1, wherein: The method includes: 2,4,6-trimethyl-1,3,5-triazine is reacted with 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde in the presence of a catalyst and a flux in a vacuum sealed environment at 170-200° C., and the reaction is cooled to room temperature to obtain the vinyl covalent organic framework material containing a N heteroatom.

3. The preparation method according to claim 2, characterized in that The catalyst and flux are both selected from at least one of phenoxyacetic anhydride, benzoic anhydride and tetrafluorophthalic anhydride; Or / and, the reaction time is 120 to 170 hours.

4. The preparation method according to claim 2, characterized in that The reaction is carried out in a heat-resistant glass tube. After the reactants are added to the heat-resistant glass tube, the tube is placed in a liquid nitrogen bath and subjected to freezing-vacuuming-thawing-nitrogen filling, and after cyclic degassing, the heat-resistant glass tube is vacuum-sealed with a flame.

5. The preparation method according to claim 2, characterized in that The molar ratio of the 2,4,6-trimethyl-1,3,5-triazine to 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde is (2-3):(3-2).

6. The preparation method according to claim 5, characterized in that The ratio between the molar amount of the 2,4,6-trimethyl-1,3,5-triazine, 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde and the total molar amount of the catalyst and the flux is (2-3):(3-2):

12.

7. The preparation method according to claim 2, characterized in that The preparation method of the 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde comprises: In an inert atmosphere, 2,5-dibromopyrazine or 3,6-dibromopyridazine and 4-formylphenylboronic acid are subjected to a reflux reaction in the presence of an inorganic base and tetrakistriphenylphosphine palladium using a mixture of 1,4-dioxane and water as a solvent. After the reaction is completed, post-treatment is performed to obtain 4,4′-(pyrazine-2,5-diyl)benzaldehyde or 4,4′-(pyridazine-3,6-diyl)benzaldehyde.

8. The preparation method according to claim 7, characterized in that The molar ratio of the 2,5-dibromopyrazine or 3,6-dibromopyridazine to 4-formylphenylboronic acid is 1:2.4-2.5; Or / and, the molar ratio of 2,5-dibromopyrazine to tetrakistriphenylphosphine palladium is 1:0.16-0.18; Or / and, the molar ratio of 2,5-dibromopyrazine to the inorganic base is 1:2.5-16; or / and, the inorganic base is selected from alkali metal carbonates; or / and, the reflux reaction temperature is 90-120°C; Or / and, the volume ratio of 1,4-dioxane to water is 4:

1.

9. The preparation method according to claim 2, characterized in that The preparation method of 2,4,6-trimethyl-1,3,5-triazine comprises: Acetic acid is added dropwise to ethyl acetimidate at room temperature and stirred for reaction. After the reaction is completed, 2,4,6-trimethyl-1,3,5-triazine is obtained by post-treatment.

10. Use of the vinyl covalent organic framework material containing N heteroatoms as claimed in claim 1 in photocatalytic hydrolysis to produce hydrogen.

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