Acylhydrazone bond-linked three-component covalent organic framework material and application thereof in photocatalytic full-decomposition of water

Abstract

The invention discloses an acylhydrazone bond-linked three-component covalent organic framework material and application thereof in photocatalytic full-decomposition of water. The three-component COFs expands the designability of the structure and function of the porous organic material by generating ordered anisotropic tiling and ordered pores with abnormal shapes. In addition, COFs connected through acylhydrazone bonds have good thermal stability and chemical stability, and nitrogen atoms on the acylhydrazone bonds can provide a large number of sites for load metal. According to the invention, two electron-deficient and electron-rich nodes are introduced into a COFs framework to form a donor-pi-acceptor structure motif, and Pt metal nanoparticles are loaded onto a three-component covalent organic framework material by using a NaBH4 reduction method. The material has great potential in the aspect of producing H2 and H2O2 through photocatalytic full decomposition of water by taking water as a reactant while solar energy is utilized and a sacrificial agent is not added.

Description

Technical Field

[0001] The invention belongs to the field of material preparation and photocatalysis, and specifically proposes a method for preparing a three-component COF connected by acylhydrazone bonds, and performs photocatalytic full decomposition of water to produce H2 and H2O2. Background Art

[0002] Since the 21st century, people have paid more and more attention to energy shortage and environmental pollution. In order to solve these two problems, people have begun to explore the use of clean and renewable energy such as solar energy to replace fossil energy to achieve green and sustainable development of human society. Photocatalytic decomposition of water to produce H2 and H2O2 is a way to achieve efficient utilization of solar energy. The key lies in finding a suitable photocatalyst. However, the current application of most photocatalysts is limited by problems such as photogenerated carrier recombination, narrow absorption spectrum range, and poor long-term photostability, making it difficult to truly achieve practical application. In the field of photocatalysis, COFs have a large specific surface area that gives them more sites for catalytic reactions, and strong covalent bonds give them good chemical stability and thermal stability. COFs have many of the above advantages in the field of photocatalysis, so exploring the synthesis of COFs and their photocatalytic water decomposition performance is very meaningful for solving environmental pollution and energy shortage problems.

[0003] The present invention found that the three-component COFs greatly enhance the complexity of the skeleton and pores by producing ordered anisotropic tiling and abnormally shaped but ordered pores, realize the diversification of COFs structure, and greatly expand the designability of the structure and function of porous organic materials. In addition, hydrazides and aldehydes can synthesize hydrazone-type COFs connected by acylhydrazone bonds through co-condensation reaction, and COFs connected by acylhydrazone bonds have good thermal stability and chemical stability. The crystallinity of hydrazone-type COFs is comparable to that of boron-containing COFs, but it is not sensitive to water and will not be easily hydrolyzed like boron-containing COFs. Moreover, the presence of nitrogen atoms on the acylhydrazone bonds provides a large number of sites for loading metals, which makes hydrazone-type COFs have great advantages in many applications such as photocatalysis.

[0004] The three-component covalent organic framework material connected by acylhydrazone bonds prepared by the present invention has excellent photoelectric properties, wide spectrum absorption, high charge separation efficiency, high-efficiency catalytic reaction sites and suitable band gap width and band structure, meets the thermodynamic conditions for photocatalytic complete water decomposition, and can catalytically decompose water into H2 and H2O2 under visible light, which has far-reaching significance for achieving high-efficiency utilization of solar energy and thus reducing the use of fossil energy. Summary of the invention

[0005] The present invention uses a solvothermal method to prepare a three-component covalent organic framework material connected by acylhydrazone bonds, and uses a NaBH4 reduction method to load Pt metal nanoparticles onto the covalent organic framework material to prepare Pt@BTD-COF. The method is reproducible and can photocatalytically decompose water to produce H2 and H2O2 in the visible light range without using a sacrificial agent, which has a promoting effect on the research of three-component covalent organic framework materials in photocatalytic decomposition of water.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme: A three-component covalent organic framework material connected by acylhydrazone bonds, wherein the covalent organic framework material is Pt@BTD-COF, and monomers for synthesizing the covalent organic framework are benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide; metal Pt nanoparticles are loaded on the covalent organic framework material BTD-COF by a NaBH4 reduction method.

[0007] A preparation method of a three-component covalent organic framework material connected by acylhydrazone bonds: using a solvothermal method to synthesize a three-component covalent organic framework material BTD-COF connected by acylhydrazone bonds from benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide; using a NaBH4 reduction method to load metal Pt nanoparticles on the covalent organic framework material BTD-COF to prepare Pt@BTD-COF, wherein the metal Pt nanoparticles are sourced from hexahydrate chloroplatinic acid (H2PtCl6 . 6H2O).

[0008] Furthermore, the preparation method of the covalent organic framework material BTD-COF specifically includes: adding benzo[1,2-b:3,4-b′:5,6- b′]trithiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 2,5-diethoxyterephthaloylhydrazide and acetic acid to a mixed solution of an organic solvent; freezing-thawing cycles and degassing three times, and then vacuum sealing the tube, heating the reaction system in a sealed vacuum state from room temperature to 120°C, keeping the temperature for 3 days, and then cooling it to room temperature, filtering, washing and drying to obtain the obtained product.

[0009] Furthermore, the molar ratio of benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide is 1:1:3.

[0010] Furthermore, the organic solvent mixed solution system specifically comprises o-dichlorobenzene and n-butanol, and the volume ratio of the two is 1:1.

[0011] Furthermore, the concentration of acetic acid used was 6 mol / L.

[0012] Furthermore, the method of reducing loaded metal Pt nanoparticles with NaBH4 specifically includes: mixing the three-component covalent organic framework material BTD-COF with chloroplatinic acid hexahydrate and methanol under ultrasonication for 20 minutes, and stirring on a magnetic stirrer for 1.5 hours, then rotary evaporating the stirred solution to remove methanol, and then adding -18°C ice methanol and NaBH4 solution to the obtained powder, continuing stirring for 2 hours, and finally washing to obtain Pt@BTD-COF.

[0013] Application: The three-component covalent organic framework material Pt@BTD-COF connected by acylhydrazone bonds is used for visible light-driven photocatalytic decomposition of water to produce H2 and H2O2 without adding sacrificial agents.

[0014] The significant advantages of the present invention are: 1) The present invention uses benzo[1,2-b:3,4-b′:5,6- b′]trithiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide to obtain a three-component covalent organic framework material connected by acylhydrazone bonds through a solvothermal method. The prepared material has a large specific surface area, a wide spectral absorption and a suitable energy band structure; after metal Pt nanoparticles are loaded on the three-component covalent organic framework material, the photocatalytic decomposition of water to produce H2 and H2O2 can be achieved under visible light without the addition of other sacrificial agents.

[0015] 2) The equipment and chemical reagents used in the synthesis method of the present invention are easy to obtain, the process operation is simple, the process conditions are simple, the applicability is strong, the industrial application value is high, and it is easy to promote and utilize.

[0016] 3) The present invention introduces electron-rich benzotrithiophene and electron-deficient triazine groups into the framework through acylhydrazone bonds to form a donor-π-acceptor structural motif, which is beneficial to the forward dissociation of photogenerated excitons, thereby producing a high carrier separation efficiency. After loading metal Pt nanoparticles, it exhibits excellent activity in the photocatalytic decomposition of water to produce H2 and H2O2. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the synthesis of BTD-COF; Figure 2This is the X-ray powder diffraction pattern of BTD-COF obtained by experiment and fitting; the agreement between the experimental and fitting results indicates the successful synthesis of BTD-COF; Figure 3 This is the Fourier transform infrared spectrum of BTD-COF; the appearance of the C=N characteristic absorption peak indicates the successful synthesis of the material; Figure 4 This is the SEM image of BTD-COF; it can be observed that the morphology of BTD-COF is a rod-like structure stacked by nanowires; Figure 5 The N2 adsorption-desorption isotherm of BTD-COF at 77K; its specific surface area is as high as 1189 m 2 / g; Figure 6 This is the UV-visible absorption spectrum of BTD-COF. The absorption range of BTD-COF covers almost the entire UV-visible spectrum. Figure 7 This is the SEM image of Pt@BTD-COF. It can be seen that the morphology of COF has basically not changed after loading metal Pt nanoparticles. The software calculation shows that the lattice size of the Pt (111) plane is 0.233nm, and the average size is approximately 1.70nm. Figure 8 The photocatalytic water splitting performance of Pt@BTD-COF is shown in the figure. As shown in the figure, the total H2 production after 4 hours of reaction is 721.6 μmol·g −1 The total production of H2O2 was 682.1 μmol·g −1 , the ratio is close to 1:1, which is consistent with the stoichiometric ratio of complete water splitting.

[0018] Fig. 9 This is the photocatalytic water splitting performance cycle diagram of Pt@BTD-COF. It can be seen from the figure that after 3 cycles, the catalyst can still maintain good catalytic activity.

[0019] Fig.10 The following are the photocatalytic test diagrams under different conditions. It can be seen from the figure that in the absence of metallic Pt nanoparticles or light, no generation of H2 and H2O2 was detected, which indicates that Pt co-catalyst and light irradiation are essential for the overall water decomposition on photoactive COFs.

[0020] Fig.11 This is the N1s XPS energy spectrum of COF before and after Pt loading. It can be seen from the figure that after loading metal Pt nanoparticles, the N atom of the acylhydrazone bond shifts to a higher binding energy by 0.1 eV, indicating that coordination occurs between the N atom of the acylhydrazone bond and the Pt atom, and the acylhydrazone bond provides a reaction site for the loading of metal Pt nanoparticles.

[0021] Fig.12 It is H2 of BTD-COF 18 O isotope experiments, 18 O2 was determined by gas chromatography-mass spectrometry, and MnO2 was added to make the generated H2 18 O2 decomposition. As can be seen from the figure, the strong peak m / z = 36 is attributed to 18 O2, weak peak m / z = 38 is attributed to H2 18 O2, indicating that water is the direct source of H2O2 in the photocatalytic process.

[0022] Fig.13 This is the electron paramagnetic resonance image of BTD-COF. It can be seen from the figure that under the condition of changing from dark to light, there is a hydroxyl radical signal captured by the capture agent DMPO, indicating that hydroxyl radicals (·OH) are generated during the reaction, indicating that H2O2 is generated by water oxidation to hydroxyl radicals, and hydroxyl radicals are generated by coupling in pairs (2H2O→2·OH + 2e - + 2H + ). DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the embodiments. It is understood that the specific implementation described herein is only used to explain the present invention and is not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined as long as they do not conflict with each other.

[0024] (1) A method for synthesizing a three-component covalent organic framework material BTD-COF connected by acylhydrazone bonds, comprising the following steps: Benzo[1,2-b:3,4-b′:5,6- b′]trithiophene-2,5,8-trialdehyde (BTT), 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFPT) and 2,5-diethoxyterephthaloylhydrazide (DETH) were added to a mixed solution of o-dichlorobenzene and n-butanol, and acetic acid solution was added as a co-catalyst. After freeze-thaw cycle degassing 3 times, the reaction system was flame-sealed and placed in an oven at 120 ℃ for reaction for 3 days. The covalent organic framework material BTD-COF was obtained after filtration, washing and drying.

[0025] (2) The synthesis method of Pt@BTD-COF comprises the following steps: The three-component covalent organic framework material BTD-COF was mixed with hexahydrate chloroplatinic acid and methanol under ultrasonication for 20 min and stirred on a magnetic stirrer for 1.5 h. The stirred solution was then rotary evaporated to remove methanol. Then, -18 °C ice methanol and NaBH4 solution were added to the obtained powder, and stirring was continued for 2 h. Finally, Pt@BTD-COF was obtained by washing and drying.

[0026] (3) Application of Pt@NTD-COF in photocatalytic water splitting: The catalyst Pt@BTD-COF and deionized water were added to a beaker and placed in an ultrasonic machine for 10 minutes to disperse the catalyst evenly. The ultrasonically treated solution was then transferred to a photocatalytic reactor, the reactor was evacuated to make the reaction system in a vacuum state, and the solution was stirred. A condensation reflux device was used to keep the reactor temperature constant at about 20 °C, and a 300W xenon lamp with a 420nm cutoff filter was used as the light source for photocatalytic water decomposition. The gas yield was detected using a gas chromatograph, and the liquid after the reaction was sampled with a syringe and the liquid yield was detected using a UV-visible spectrophotometer.

[0027] Example 1 A method for synthesizing a three-component covalent organic framework material BTD-COF connected by acylhydrazone bonds, wherein the specific synthesis steps are as follows: Benzo[1,2-b:3,4-b′:5,6- b′]trithiophene-2,5,8-trialdehyde (13.2 mg, 0.04 mmol), 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (15.7 mg, 0.04 mmol), 2,5-diethoxyterephthaloylhydrazide (34.0 mg, 0.12 mmol) and 2 mL of a mixed solution of o-dichlorobenzene / n-butanol (volume ratio 1:1) were placed in a Pyrex tube and ultrasonicated for 15 min to obtain a uniform dispersion, and then acetic acid (0.2 mL, 6 M) was added. The reaction mixture was degassed by freeze-thaw cycles in a 77K liquid nitrogen bath for three times, and the tube was sealed in vacuum and reacted at 120°C for 3 days. The mixture was cooled to room temperature, and the solid was collected by filtration. The solid was washed three times with methanol, N,N-dimethylformamide, dichloromethane and acetone, respectively. The obtained powder was dried in vacuum at 60°C overnight to obtain a bright yellow powder BTD-COF.

[0028] Example 2 The above-mentioned synthesis method of Pt@BTD-COF includes the following specific synthesis steps: 30 mg of BTD-COF was added to a glass tube containing 3 mL of methanol and 90 uL of 10 mg / mL H2PtCl6 was added. .6H2O, add a stirrer, perform ultrasonic treatment for 20 min to disperse the mixed solution evenly, then place it on a magnetic stirrer and stir for 1.5 hours, and then use a rotary evaporator to evaporate the methanol solution. Next, add 3 mL of ice methanol (-18 ℃) and 1 mL of NaHB4 aqueous solution (0.5 M) to the dried sample, place it on a magnetic stirrer and stir for 2 hours, and finally wash it three times with methanol and deionized water, and dry it in a vacuum drying oven at 60 ℃ overnight to obtain Pt@BTD-COF with a theoretical Pt mass fraction of 3wt%.

[0029] Example 3 The three-component covalent organic framework material Pt@BTD-COF is used in photocatalytic water splitting. The specific steps are as follows: Weigh 10 mg Pt@BTD-COF, grind it thoroughly, add 50 mL deionized water, and put it into a quartz glass reactor after ultrasonic treatment for 10 minutes. After the reactor was evacuated, it was irradiated with a 300W xenon lamp with a 420nm cutoff filter at 290~398 K for 4 hours. During the photocatalytic reaction, the gas composition after the photocatalytic reaction was detected by gas chromatography every 1 hour, and the vacuum was re-evacuated. After the photocatalytic reaction was completed, an appropriate reaction liquid was taken and filtered through a 0.22μm nylon filter head, and the liquid composition after the photocatalytic reaction was detected by cerium sulfate calibration method.

[0030] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it is obvious for those skilled in the art to make various modifications and substitutions of the present invention. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A three-component covalent organic framework material connected by acylhydrazone bonds, characterized in that: The covalent organic framework material is Pt@BTD-COF, and the monomers for synthesizing the three-component covalent organic framework are benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide; metal Pt nanoparticles are loaded on BTD-COF by using a NaBH4 reduction method.

2. The method for preparing a three-component covalent organic framework material connected by acylhydrazone bonds as claimed in claim 1, characterized in that: A solvothermal method was used to synthesize a three-component covalent organic framework material BTD-COF connected by acylhydrazone bonds from benzo[1,2-b:3,4-b′:5,6- b′]trithiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide. A NaBH4 reduction method was used to load metal Pt nanoparticles on the covalent organic framework material BTD-COF to prepare Pt@BTD-COF, in which the source of the metal Pt nanoparticles was chloroplatinic acid hexahydrate.

3. The preparation method according to claim 2, characterized in that: The preparation method of the three-component covalent organic framework material BTD-COF specifically includes: adding benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 2,5-diethoxyterephthaloylhydrazide and acetic acid to an organic solvent mixed solution; performing freeze-thaw cycle degassing for 3 times and then vacuum sealing the tube, heating the reaction system in a sealed vacuum state from room temperature to 120° C., keeping the temperature for 3 days and then cooling it to room temperature, and finally washing and drying to obtain the three-component covalent organic framework material.

4. The preparation method according to claim 2 or 3, characterized in that: The molar ratio of benzo[1,2-b:3,4-b′:5,6- b′]terthiophene-2,5,8-trialdehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxyterephthaloylhydrazide is 1:1:

3.

5. The preparation method according to claim 3, characterized in that: The organic solvent mixed solution system specifically comprises o-dichlorobenzene and n-butanol, and the volume ratio of the two is 1:

1.

6. The preparation method according to claim 3, characterized in that: The concentration of acetic acid used was 6 mol / L.

7. The preparation method according to claim 2, characterized in that: The method of reducing loaded metal Pt nanoparticles with NaBH4 specifically includes: mixing the three-component covalent organic framework material BTD-COF with chloroplatinic acid hexahydrate and methanol under ultrasonication for 20 minutes, and stirring on a magnetic stirrer for 1.5 hours, then rotary evaporating the stirred solution to remove methanol, and then adding -18°C ice methanol and NaBH4 solution to the obtained powder, continuing stirring for 2 hours, and finally washing to obtain Pt@BTD-COF.

8. Use of the three-component covalent organic framework material connected by acylhydrazone bonds as claimed in claim 1 for photocatalytic decomposition of water to produce H2 and H2O2 driven by visible light without adding a sacrificial agent.

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