Preparation method and application of amido bond bridging-based covalent organic framework

Abstract

The invention relates to a preparation method of a covalent organic framework based on amido bond bridging, which comprises the following steps: taking melamine and aromatic multi-acyl chloride as raw materials, and carrying out sol-gel reaction, aging, solvent exchange and freeze drying to obtain the covalent organic framework based on amido bond bridging, the aromatic multi-element acyl chloride is trimesoyl chloride or terephthaloyl chloride. The covalent organic framework photocatalyst bridged by crystalline amido bonds and having a layered structure is prepared by taking melamine and aromatic polyacyl chloride as raw materials through sol-gel reaction and other processes, and the covalent organic framework photocatalyst has relatively high photocatalytic activity and can directly decompose water to produce oxygen under the condition of visible light.

Description

Technical Field

[0001] The present invention relates to the technical field of photolysis of water to produce oxygen, and in particular to a preparation method and application of a covalent organic framework based on amide bond bridging. Background Art

[0002] Covalent organic frameworks (COFs) are a class of porous periodically expanded and covalently bonded network structure materials. Their advantages are that they are highly designable in terms of structure and function, and their physical and chemical properties can be precisely adjusted. At present, the performance research of COF photocatalyst materials mainly focuses on photocatalytic reduction reactions such as photocatalytic water splitting to produce hydrogen, photocatalytic carbon dioxide reduction, and photocatalytic synthesis of hydrogen peroxide, but few can achieve the more challenging photocatalytic water splitting to produce oxygen half-reaction. This is because the photocatalytic water splitting to produce oxygen half-reaction is a transfer process of four electrons and four protons, involving the splitting of hydrogen-oxygen bonds and the combination of oxygen-oxygen bonds. It is much more complicated than the hydrolysis reduction process and is the rate-determining step of the overall water splitting reaction. Therefore, the development of a new COF photocatalytic material with excellent photocatalytic water splitting to produce oxygen performance is of great research significance. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a preparation method and application of a covalent organic framework based on amide bond bridging.

[0004] The technical solution adopted by the present invention is:

[0005] On one hand, the present invention provides a method for preparing a covalent organic framework based on amide bond bridging, comprising the following steps: using melamine and aromatic polyacyl chloride as raw materials, undergoing sol-gel reaction, aging, solvent exchange and freeze drying to obtain a covalent organic framework based on amide bond bridging;

[0006] The aromatic polyacid chloride is trimesoyl chloride or terephthaloyl chloride.

[0007] The present invention proposes a method for preparing a covalent organic framework based on amide bond bridging, using melamine and aromatic polyacyl chloride as raw materials, and through a sol-gel reaction and other processes, a layered structure crystalline amide bond-bridged covalent organic framework photocatalyst is prepared, which has high photocatalytic activity and can directly decompose water to produce oxygen under visible light conditions. On the one hand, the photocatalyst has a conjugated structure, which provides the possibility for the generation, migration and separation of photogenerated carriers; on the other hand, the photocatalyst has a rich pore structure, which increases its specific surface area, thereby increasing the contact area between the photocatalyst and the reactants in the photolysis of water reaction, and the photocatalyst surface can produce more active sites, thereby improving its catalytic efficiency in photocatalytic oxygen production. The preparation process of the present invention is simple and easy to promote.

[0008] Preferably, the sol-gel reaction comprises the following steps: dissolving the melamine in a dimethyl sulfoxide solution, adding dropwise thereto a solution of N-methylpyrrolidone dissolved with aromatic polyacyl chloride under stirring at room temperature, continuing stirring at room temperature for a certain period of time, then heating and stirring in an oil bath to obtain a prepolymer wet sol, sealing, and performing hot air heating to obtain a wet gel-like amide-bridged covalent organic framework.

[0009] More preferably, when the aromatic polyacyl chloride is trimesoyl chloride, the usage ratio of the melamine, the dimethyl sulfoxide solution, the aromatic polyacyl chloride, and the N-methylpyrrolidone solution is 0.2-0.3 g:15-20 mL:0.8-1.2 g:1-3 mL;

[0010] When the aromatic polyacyl chloride is terephthaloyl chloride, the usage ratio of the melamine, the dimethyl sulfoxide solution, the aromatic polyacyl chloride and the N-methylpyrrolidone solution is 0.3-0.4 g:15-20 mL:0.9-1.3 g:1-3 mL.

[0011] More preferably, the stirring time at room temperature is 30-60 min;

[0012] The temperature of the oil bath heating and stirring is 60-70°C and the time is 15-45min;

[0013] The hot air heating is performed at a temperature of 70-90° C. for a time of 3-20 hours.

[0014] Preferably, the aging is step-by-step aging, wherein the temperature of the first stage aging is 70-80°C and the time is 24-36h;

[0015] The second stage aging temperature is 60-70℃ and the time is 48-60h.

[0016] Preferably, the solvent used in the solvent exchange is anhydrous ethanol or acetone, the number of exchanges is 3-6 times, and the time for each exchange is 12-24 hours.

[0017] Preferably, the freeze-drying time is 19-24 hours.

[0018] Another aspect of the present invention provides an application of a covalent organic framework based on amide bond bridging prepared by the preparation method described in any of the above technical solutions in photocatalytic decomposition of water to produce oxygen.

[0019] Preferably, the application method comprises the following steps: adding the amide bond-bridging covalent organic framework, sacrificial agent, pH buffer and co-catalyst into water, and reacting under simulated visible light irradiation.

[0020] Preferably, the sacrificial agent is silver nitrate;

[0021] The pH buffer is lanthanum oxide;

[0022] The co-catalyst is cobalt nitrate, and the mass ratio of cobalt ions in the cobalt nitrate to the covalent organic framework based on amide bond bridging is 0.005-0.015:1;

[0023] The wavelength of the visible light is 400-760nm.

[0024] The amide bond-bridging covalent organic framework prepared by the present invention can be used for photolysis of water to produce oxygen, which has innovative significance. At the same time, under the auxiliary catalysis of cobalt ions, its catalytic rate in this regard can be further improved, and it has a high application prospect in the field of photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the carbon NMR spectrum of TMC-MA-COF synthesized in Example 3;

[0026] Figure 2 This is the XPS spectrum of TMC-MA-COF synthesized in Example 3;

[0027] Figure 3 This is a scanning electron microscope image of the TMC-MA-COF synthesized in Example 3;

[0028] Figure 4 This is a transmission electron microscopy image of TMC-MA-COF synthesized in Example 3;

[0029] Figure 5 is a nitrogen adsorption-desorption isotherm diagram of TMC-MA-COF synthesized in Example 3;

[0030] Figure 6 This is the pore size distribution diagram of TMC-MA-COF synthesized in Example 3;

[0031] Figure 7 The rate diagram of the photolysis of water and oxygen production by TMC-MA-COF synthesized in Examples 3-6 and Comparative Example 1 under visible light;

[0032] Figure 8 The rate diagram of photolysis of water and oxygen production by TPC-MA-COF synthesized in Example 2, Examples 7-8 and Comparative Example 2 under full-band and visible light. DETAILED DESCRIPTION

[0033] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0034] Example 1

[0035] A method for preparing a covalent organic framework based on amide bond bridging comprises the following steps:

[0036] S1. Sol-gel reaction: 0.3000 g of melamine was dissolved in 18 mL of dimethyl sulfoxide solution. Under stirring at room temperature, 2 mL of N-methylpyrrolidone solution containing 1.1000 g of trimesoyl chloride was added dropwise thereto. The mixture was stirred at room temperature for 30 min. The mixture was then heated in an oil bath at 60° C. and stirred for 45 min to obtain a prepolymer wet sol. The prepolymer was transferred into a reagent bottle, sealed, and heated in a hot air oven at 80° C. for 10 h to obtain a wet gel-like amide-bridged covalent organic framework (referred to as TMC-MA-COF).

[0037] S2, aging: The wet gel-like TMC-MA-COF is further aged in an oven in steps, wherein the first stage aging temperature is 80° C. for 24 h; the second stage aging temperature is 70° C. for 48 h, to obtain a gel-like TMC-MA-COF.

[0038] S3, solvent exchange: take out the above gel-like TMC-MA-COF, add anhydrous ethanol to carry out solvent exchange, each exchange time is 12 hours, and a total of 6 exchanges are carried out to obtain alcohol-wet gel-like TMC-MA-COF.

[0039] S4. Freeze drying: freeze-dry the alcohol-wet gel-like TMC-MA-COF for 24 hours until it is dry and not damp, to obtain light yellow solid crystalline TMC-MA-COF.

[0040] The method is applied in photocatalytic decomposition of water to produce oxygen, comprising the following steps:

[0041] 50 mg of synthesized TMC-MA-COF was added to 100 mL of water, and then added to the photolysis water reaction system after ultrasound. Then, 0.2 g of lanthanum oxide, 0.17 g of silver nitrate and 2 mL of cobalt nitrate solution (containing 0.5 mg of cobalt ions) were added. The reaction temperature was controlled to 10°C by circulating condensed water, and the air in the reaction system was removed by a vacuum system. A xenon lamp was used to simulate visible light (wavelength of 400-760 nm) for irradiation, and samples were taken at regular intervals. The reaction product gas was analyzed online by gas chromatography.

[0042] Example 2

[0043] A method for preparing a covalent organic framework based on amide bond bridging comprises the following steps:

[0044] S1. Sol-gel reaction: 0.3473 g of melamine was dissolved in 18 mL of dimethyl sulfoxide solution. Under stirring at room temperature, 2 mL of N-methylpyrrolidone solution containing 0.9338 g of terephthaloyl chloride was added dropwise thereto. The mixture was stirred at room temperature for 60 min. The mixture was then heated in an oil bath at 60° C. and stirred for 30 min to obtain a prepolymer wet sol. The prepolymer was transferred into a reagent bottle, sealed, and heated in a hot air oven at 85° C. for 9 h to obtain a wet gel-like amide-bridged covalent organic framework (denoted as TPC-MA-COF).

[0045] S2, aging: The wet gel-like TPC-MA-COF is further aged in an oven in steps, wherein the first stage aging temperature is 75°C for 24 hours; the second stage aging temperature is 60°C for 48 hours, to obtain a gel-like TPC-MA-COF.

[0046] S3, solvent exchange: take out the above gel-like TPC-MA-COF, add anhydrous ethanol to carry out solvent exchange, each exchange time is 12 hours, and a total of 6 exchanges are carried out to obtain alcohol-wet gel-like TPC-MA-COF.

[0047] S4. Freeze drying: freeze-dry the alcohol-wet gel-like TPC-MA-COF for 22 hours until it is dry and not damp, and obtain light yellow solid crystalline TPC-MA-COF.

[0048] The application method of this embodiment is different from that of Embodiment 1 in that "using a xenon lamp to simulate irradiation of visible light (wavelength of 400-760nm)" in Embodiment 1 is replaced by "using a xenon lamp to simulate irradiation of full-band and visible light (wavelength of 400-760nm)". The remaining steps remain unchanged.

[0049] Example 3

[0050] A method for preparing a covalent organic framework based on amide bond bridging comprises the following steps:

[0051] S1. Sol-gel reaction: 0.2840 g of melamine was dissolved in 18 mL of dimethyl sulfoxide solution. Under stirring at room temperature, 2 mL of N-methylpyrrolidone solution containing 1.0000 g of trimesoyl chloride was added dropwise thereto. The mixture was stirred at room temperature for 30 min. The mixture was then heated in an oil bath at 60° C. and stirred for 15 min to obtain a prepolymer wet sol. The prepolymer was transferred into a reagent bottle, sealed, and heated in a hot air oven at 85° C. for 2.5 h to obtain a wet gel-like TMC-MA-COF.

[0052] S2, aging: The wet gel-like TMC-MA-COF is further aged in an oven in steps, wherein the first stage aging temperature is 75° C. for 24 h; the second stage aging temperature is 60° C. for 48 h, to obtain a gel-like TMC-MA-COF.

[0053] S3, solvent exchange: take out the above gel-like TMC-MA-COF, add anhydrous ethanol to carry out solvent exchange, each exchange time is 12 hours, and a total of 6 exchanges are carried out to obtain alcohol-wet gel-like TMC-MA-COF.

[0054] S4. Freeze drying: freeze-dry the alcohol-wet gel-like TMC-MA-COF for 19 hours until it is dry and not damp, to obtain light yellow solid crystalline TMC-MA-COF.

[0055] The application method of this embodiment is the same as that of embodiment 1.

[0056] Example 4

[0057] The difference between this embodiment and embodiment 3 is that the hot air treatment temperature is different, and the "heating in a hot air oven at 85° C. for 2.5 hours" in step S1 of embodiment 3 is replaced by "heating in a hot air oven at 75° C. for 19 hours". The other steps remain unchanged.

[0058] Example 5

[0059] The difference between this embodiment and embodiment 3 is that the number of solvent exchanges is different, and the "exchanges a total of 6 times" in step S3 of embodiment 3 is replaced by "exchanges a total of 3 times". The other steps remain unchanged.

[0060] Example 6

[0061] The difference between this embodiment and embodiment 3 is that the hot air treatment temperature and the number of solvent exchanges are different, and the "placed in an 85°C hot air oven for heating for 2.5 hours" in step S1 of embodiment 3 is replaced by "placed in a 75°C hot air oven for heating for 19 hours"; at the same time, the "exchanged 6 times in total" in step S3 is replaced by "exchanged 3 times in total". The remaining steps remain unchanged.

[0062] Example 7

[0063] The difference between this embodiment and embodiment 2 is that when TPC-MA-COF is applied to photocatalytic decomposition of water to produce oxygen, the mass ratio of cobalt ions to TPC-MA-COF is adjusted to 0.005, that is, 0.25 mg of cobalt ions are contained in 2 mL of the added cobalt nitrate solution. The other steps remain unchanged.

[0064] Example 8

[0065] The difference between this embodiment and embodiment 2 is that when TPC-MA-COF is applied to photocatalytic decomposition of water to produce oxygen, the mass ratio of cobalt ions to TPC-MA-COF is adjusted to 0.015, that is, 0.75 mg of cobalt ions are contained in 2 mL of cobalt nitrate solution added. The other steps remain unchanged.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 3 is that when TMC-MA-COF is applied to photocatalytic decomposition of water to produce oxygen, cobalt nitrate is not added as a co-catalyst. The remaining steps remain unchanged.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 2 is that when TPC-MA-COF is applied to photocatalytic decomposition of water to produce oxygen, cobalt nitrate is not added as a co-catalyst. The remaining steps remain unchanged.

[0070] The present invention uses TMC-MA-COF synthesized in Example 3 as a representative of the covalent organic framework photocatalyst based on amide bond bridging, and characterizes the structural composition. The results are recorded in Figure 1 and Figure 2 .from Figure 1 From the 13C NMR spectrum, we can see that 165.47 and 134.55 correspond to the amide as a bridge in the structural formula and C on the azine ring, indicating the existence of the amide bond as a bridge. Figure 2 From the full XPS spectrum, we can see that C, N, and O elements can be observed on the photocatalyst, which is consistent with Figure 1 The results are consistent with those of the previous work, further confirming the successful synthesis of covalent organic framework photocatalysts bridged by amide bonds.

[0071] The microscopic morphology of the TMC-MA-COF photocatalyst synthesized in Example 3 was further observed, and the results are recorded in Figure 3 and Figure 4As can be seen from the figure, the photocatalyst presents a layered structure. This may be related to the conjugated structure formed by the polymerization of different monomers in the TMC-MA-COF photocatalyst, and the conjugated structure provides the possibility for the generation, migration and separation of photogenerated carriers. At the same time, it also has a rich pore structure, which can increase its specific surface area, thereby providing more active sites for the photocatalytic reaction.

[0072] Figure 5 and Figure 6 They are respectively the nitrogen adsorption-desorption isotherm and pore size distribution diagram of TMC-MA-COF synthesized in Example 3. Figure 5 As shown in the figure, the P / Po value between 0.2-0.5 is the medium pressure zone, and the adsorption amount is slowly increasing. The adsorption amount in the high pressure zone of P / Po value between 0.8-0.99 increases significantly. The hysteresis loop appears in the range of P / Po between 0.5-1.0, which belongs to the IV type nitrogen adsorption and desorption isotherm, indicating that the catalyst has lamellar accumulation. After testing, it is found that its specific surface area is 3.9273m 2 / g. The Barrett-Joyner-Halenda (BJH) method was used to analyze the pore size distribution of the catalyst. Figure 6 As shown, the pore size is mainly concentrated around 2-50 nm, indicating that it is a mesoporous material.

[0073] The test results of applying the TMC-MA-COF synthesized in Examples 3-6 and Comparative Example 1 to photolysis of water to produce oxygen under visible light are recorded in Figure 7 The test results of applying the TPC-MA-COF synthesized in Example 2, Examples 7-8 and Comparative Example 2 to photolysis of water to produce oxygen under full-band and visible light are recorded in Figure 8 .from Figure 7 It can be seen that within the preferred process parameter range of the present invention, the TMC-MA-COF photocatalysts prepared in each embodiment have good catalytic performance for photolysis of water to produce oxygen, and the oxygen production rate under visible light can reach 109.11-128.89 μmol / h. Figure 8 It can be seen that the TPC-MA-COF photocatalyst synthesized in the present invention exhibits a better catalytic effect of photolysis of water to produce oxygen under different cobalt ion concentrations, in the full band and under visible light. When the mass ratio of cobalt ions to photocatalysts is 0.01:1, the photolysis of water to produce oxygen under visible light is the best, and the oxygen production rate reaches 168.2μmol / h; when the mass ratio of cobalt ions to photocatalysts is 0.015:1, the photolysis of water to produce oxygen under the full band is the best, and the oxygen production rate reaches 201.5μmol / h. In addition, Figure 7 and Figure 8The results show that compared with Comparative Examples 1 and 2, when the conjugated organic framework photocatalyst based on amide bond bridging synthesized in Examples 2-8 of the present invention is used to photolyze water to produce oxygen, its photolyzed water oxygen production performance can be significantly improved under the catalytic effect of cobalt ions.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a covalent organic framework based on amide bond bridging, comprising the following steps: Using melamine and aromatic polyacyl chloride as raw materials, a covalent organic framework based on amide bond bridging was obtained through sol-gel reaction, aging, solvent exchange and freeze drying. The aromatic polyacid chloride is trimesoyl chloride or terephthaloyl chloride.

2. The method for preparing a covalent organic framework based on amide bond bridging according to claim 1, characterized in that: The sol-gel reaction comprises the following steps: dissolving the melamine in a dimethyl sulfoxide solution, adding dropwise thereto an N-methylpyrrolidone solution containing an aromatic polyacyl chloride under stirring at room temperature, continuing stirring at room temperature for a certain period of time, then heating and stirring in an oil bath to obtain a prepolymer wet sol, sealing, and performing hot air heating to obtain a wet gel-like amide-bridged covalent organic framework.

3. The method for preparing a covalent organic framework based on amide bond bridging according to claim 2, characterized in that: When the aromatic polyacyl chloride is trimesoyl chloride, the usage ratio of the melamine, the dimethyl sulfoxide solution, the aromatic polyacyl chloride, and the N-methylpyrrolidone solution is 0.2-0.3 g:15-20 mL:0.8-1.2 g:1-3 mL; When the aromatic polyacyl chloride is terephthaloyl chloride, the usage ratio of the melamine, the dimethyl sulfoxide solution, the aromatic polyacyl chloride and the N-methylpyrrolidone solution is 0.3-0.4 g:15-20 mL:0.9-1.3 g:1-3 mL.

4. The method for preparing a covalent organic framework based on amide bond bridging according to claim 2, characterized in that: The stirring time at room temperature is 30-60min; The temperature of the oil bath heating and stirring is 60-70°C and the time is 15-45min; The temperature of the hot air heating is 70-90° C. and the time is 3-20 hours.

5. The method for preparing a covalent organic framework based on amide bond bridging according to claim 1, characterized in that: The aging is step-by-step aging, wherein the temperature of the first stage is 70-80°C and the time is 24-36h; The second stage aging temperature is 60-70℃ and the time is 48-60h.

6. The method for preparing a covalent organic framework based on amide bond bridging according to claim 1, characterized in that: The solvent used in the solvent exchange is anhydrous ethanol or acetone, the number of exchanges is 3-6 times, and the time of each exchange is 12-24 hours.

7. The method for preparing a covalent organic framework based on amide bond bridging according to claim 1, characterized in that: The freeze-drying time is 19-24h.

8. Use of a covalent organic framework based on amide bond bridging prepared by the preparation method according to any one of claims 1 to 7 in photocatalytic decomposition of water to produce oxygen.

9. The use according to claim 8, characterized in that The application method comprises the following steps: adding the covalent organic framework based on amide bond bridging, a sacrificial agent, a pH buffer and a co-catalyst into water, and reacting under simulated visible light irradiation.

10. The use according to claim 9, characterized in that The sacrificial agent is silver nitrate; The pH buffer is lanthanum oxide; The co-catalyst is cobalt nitrate, and the mass ratio of cobalt ions in the cobalt nitrate to the covalent organic framework based on amide bond bridging is 0.005-0.015:1; The wavelength of the visible light is 400-760nm.

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