An acylhydrazone-linked three-component covalent organic framework material and application thereof to photocatalytic overall splitting of water

Abstract

The application discloses a kind of acylhydrazone bond connected three-component covalent organic framework material and its application of photocatalytic overall decomposition water.The three-component COFs expand the designability of structure and function of porous organic material by generating ordered anisotropic tile and shape anomaly but ordered pore.In addition,COFs connected by acylhydrazone bond have good thermal stability and chemical stability, and the nitrogen atom on acylhydrazone bond can also provide a large number of sites for metal loading. The application introduces two electron-deficient and electron-rich nodes into the COFs framework to form donor-π-acceptor structure motif, and uses NaBH4 reduction method to load Pt metal nanoparticles on the three-component covalent organic framework material. The material has great potential in photocatalytic overall decomposition water to produce H2 and H2O2 using solar energy without sacrificial agent.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of material preparation and photocatalysis, and specifically proposes a method for preparing three-component COFs connected by acylhydrazone bonds and an application of the three-component COFs in photocatalytic overall water splitting to produce H2 and H2O2. BACKGROUND

[0002] After entering the 21st century, energy shortage and environmental pollution have attracted more and more attention. In order to solve these two problems, people began to explore the use of clean and renewable energy such as solar energy to replace fossil energy to realize the green and sustainable development of human society. Photocatalytic splitting of water to produce H2 and H2O2 is a way to achieve efficient use of solar energy, and the key is to find a suitable photocatalyst. However, the application of most current photocatalysts is limited by problems such as recombination of photo-generated carriers, narrow absorption spectrum range, and poor long-term light stability, making it difficult to truly realize practical application. Corresponding to the field of photocatalysis, COFs have a large specific surface area, which provides more sites for catalytic reactions, and strong covalent bonds, which provide good chemical stability and thermal stability. COFs have many advantages in the field of photocatalysis, so it is very meaningful to explore the synthesis of COFs and their photocatalytic overall water splitting performance to solve the problems of environmental pollution and energy shortage.

[0003] The present application has found that three-component COFs can greatly enhance the complexity of the skeleton and the pore by generating an ordered anisotropic tiling and an ordered but abnormal shaped pore, realize the diversification of COF structure, and greatly expand the designability of the structure and function of porous organic materials. In addition, hydrazide and aldehyde can be synthesized into 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 can be comparable to that of boron-containing COFs, but it is not sensitive to water and will not hydrolyze as easily as boron-containing COFs, and the presence of nitrogen atoms on the acylhydrazone bond provides a large number of sites for loading metals, which makes hydrazone-type COFs have great advantages in many aspects such as photocatalysis.

[0004] The three-component covalent organic framework material connected by acylhydrazone bonds prepared by the present application has excellent photoelectric properties, wide spectrum absorption, high charge separation efficiency, high efficient catalytic reaction sites, and suitable band gap width and energy band structure, meets the thermodynamic conditions of photocatalytic overall water splitting, and can catalytically split water into H2 and H2O2 under visible light, which has profound significance for realizing efficient use of solar energy and reducing the use of fossil energy. SUMMARY

[0005] The application utilizes 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 on the covalent organic framework material to prepare Pt@BTD-COF. The method has repeatable operation, can produce H2 and H2O2 by photocatalytic overall decomposition of water in the visible light range without using a sacrificial agent, and promotes the research on three-component covalent organic framework materials in photocatalytic overall decomposition of water.

[0006] To achieve the above-mentioned application purposes, the application adopts the following technical solutions:

[0007] A three-component covalent organic framework material connected by acylhydrazone bonds, wherein the covalent organic framework material is Pt@BTD-COF, the monomers for synthesizing the covalent organic framework are 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-diethoxylterephthalic hydrazide, and the metal Pt nanoparticles are loaded on the covalent organic framework material BTD-COF by using a NaBH4 reduction method.

[0008] A preparation method of a three-component covalent organic framework material connected by acylhydrazone bonds, comprising the following steps: using a solvothermal method to synthesize the three-component covalent organic framework material BTD-COF 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-diethoxylterephthalic hydrazide; and 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 derived from hexahydrated chloroplatinic acid (H2PtCl6 . 6H2O).

[0009] Further, the preparation method of the covalent organic framework material BTD-COF specifically comprises the following steps: 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-diethoxylterephthalic hydrazide and acetic acid into an organic solvent mixed solution; degassing for 3 times after freeze-thaw cycle, vacuum sealing, increasing the temperature of the reaction system in a sealed vacuum state from room temperature to 120 ℃, keeping the temperature for 3 days, then decreasing the temperature to room temperature, and preparing the covalent organic framework material through filtration, washing and drying.

[0010] Further, the molar ratio of 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-diethoxylterephthalic hydrazide is 1:1:3.

[0011] Further, the organic solvent mixed solution system is specifically o-dichlorobenzene and n-butanol, and the volume ratio of the two is 1:1.

[0012] Further, the concentration of acetic acid used is 6 mol / L.

[0013] Further, the method for reducing metal Pt nanoparticles by NaBH4 specifically comprises the following steps: ultrasonic mixing of three-component covalent organic framework material BTD-COF, chloroplatinic acid hexahydrate and methanol for 20 min, stirring on a magnetic stirrer for 1.5 h, removing methanol from the stirred solution by rotary evaporation, adding ice methanol at-18 ℃ and NaBH4 solution to the obtained powder, continuing to stir for 2 h, and finally washing to obtain Pt@BTD-COF.

[0014] Application: The acylhydrazone bond connected three-component covalent organic framework material Pt@BTD-COF is used for visible light driven photocatalytic overall water splitting to produce H2 and H2O2 without adding a sacrificial agent.

[0015] The significant advantages of the present application are:

[0016] 1) The present application obtains an acylhydrazone bond connected three-component covalent organic framework material by using 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-diethoxylterephthalic dihydrazide through a solvothermal method. The prepared material has a large specific surface area, a wide spectral absorption and a suitable energy band structure; after loading metal Pt nanoparticles on the three-component covalent organic framework material, the material can realize photocatalytic overall water splitting to produce H2 and H2O2 without adding other sacrificial agents under visible light.

[0017] 2) The equipment and chemical reagents used in the synthesis method of the present application 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 the method is easy to popularize and utilize.

[0018] 3) The present application introduces electron-rich benzo-trithiophene and electron-deficient triazine groups into the framework through acylhydrazone bonds to form a donor-π-acceptor structure motif, which is beneficial to the positive dissociation of photo-generated excitons, thereby producing high carrier separation efficiency, and after loading metal Pt nanoparticles, the material exhibits excellent activity in photocatalytic overall water splitting to produce H2 and H2O2. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a synthesis schematic diagram for preparing BTD-COF;

[0020] Figure 2is the X-ray powder diffraction pattern of BTD-COF obtained by experiment and fitting; the coincidence of the experimental and fitting results indicates the successful synthesis of BTD-COF;

[0021] Figure 3 is the Fourier transform infrared spectrogram of BTD-COF; the appearance of the C=N characteristic absorption peak indicates the successful synthesis of the material;

[0022] Figure 4 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;

[0023] Figure 5 is the N2 adsorption-desorption isotherm curve of BTD-COF at 77 K; the specific surface area of BTD-COF is as high as 1189 m 2 / g;

[0024] Figure 6 is the UV-Vis absorption spectrum of BTD-COF; the light absorption range of BTD-COF almost covers the entire UV-Vis spectrum region;

[0025] Figure 7 is the SEM image of Pt@BTD-COF; it can be seen that after loading metal Pt nanoparticles, the morphology of COF has not changed basically; through software calculation, the lattice size of Pt (111) plane is 0.233 nm, and the average size is about 1.70 nm;

[0026] Figure 8 is the photocatalytic overall water splitting performance of Pt@BTD-COF; as shown in the figure, the total yield of H2 is 721.6 μmol·g −1 , and the total yield of H2O2 is 682.1 μmol·g −1 , and the ratio is close to 1:1, which is consistent with the stoichiometric number ratio of overall water splitting.

[0027] Figure 9 is the photocatalytic overall water splitting performance cycle of Pt@BTD-COF; as shown in the figure, after 3 cycles, the catalyst can still maintain good catalytic activity.

[0028] Figure 10 is the photocatalytic test under different conditions; as shown in the figure, no H2 and H2O2 are detected in the absence of metal Pt nanoparticles or light, which indicates that Pt cocatalyst and light irradiation are essential for the overall water splitting on the photoactive COFs.

[0029] Figure 11The N1s XPS energy spectrum of COF before and after loading Pt is shown in the figure, and it can be seen from the figure that after loading metal Pt nanoparticles, the N atom of the acylhydrazone bond is displaced by 0.1 eV to a high binding energy position, 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.

[0030] Figure 12 H2 of BTD-COF 18 O isotope experiment, 18 O2 is measured by gas chromatography-mass spectrometry, and MnO2 is added to make the generated H2 18 O2 decompose. As shown in the figure, the strong peak m / z = 36 belongs to 18 O2, and the weak peak m / z = 38 belongs to H2 18 O2, which shows that water is the direct source of H2O2 in the photocatalytic process.

[0031] Figure 13 The electron paramagnetic resonance diagram of BTD-COF is shown in the figure, and it can be seen from the figure that under the condition of from darkness to light, the hydroxyl radical signal is captured by the capture agent DMPO, indicating that the hydroxyl radical (·OH) is generated in the reaction process, and it is indicated that H2O2 is generated by water oxidation to generate hydroxyl radicals, and the hydroxyl radicals are coupled to generate (2H2O→2·OH + 2e - + 2H + ). DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer, more obvious and easier to understand, the present application will be further described in detail in combination with the embodiments. It can be understood that the specific implementation described herein is only used to explain the present application, and is not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined as long as they do not conflict with each other.

[0033] (1) A synthesis method of an acylhydrazone bond connected three-component covalent organic framework material BTD-COF, comprising the following steps:

[0034] Benzene[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-diethoxyterephthaldehyde hydrazine (DETH) are added to a mixed solution of o-dichlorobenzene and n-butanol, and acetic acid solution is added as a cocatalyst, the reaction system is degassed for 3 times after freeze-thaw cycle, and then sealed by flame, and placed in a 120 ℃ oven for reaction for 3 days. After filtration, washing and drying, the covalent organic framework material BTD-COF is obtained.

[0035] (2) The synthesis method of Pt@BTD-COF, comprising the following steps:

[0036] The three-component covalent organic framework material BTD-COF is mixed with chloroplatinic acid hexahydrate and methanol under ultrasonic for 20 min, and is stirred on a magnetic stirrer for 1.5 h. The methanol in the stirred solution is removed by rotary evaporation. Then, ice methanol at-18 ℃ and a NaBH4 solution are added to the obtained powder, and the stirring is continued for 2 h. Finally, the Pt@BTD-COF is obtained by washing and drying.

[0037] (3) Application of Pt@NTD-COF in photocatalytic overall water splitting:

[0038] The catalyst Pt@BTD-COF and deionized water are added into a beaker, and the catalyst is uniformly dispersed by ultrasonic for 10 min. The ultrasonic treated solution is transferred into a photocatalytic reactor, the reactor is vacuumized, the solution is stirred, and the temperature of the reactor is kept at about 20 ℃ by using a condensation reflux device. The photocatalytic overall water splitting is carried out by using a 300W xenon lamp with a 420 nm cut-off filter as a light source. The gas production is detected by using a gas chromatograph, and the liquid production after reaction is sampled by using a syringe and detected by using a UV-Vis spectrophotometer.

[0039] Example 1

[0040] A synthesis method of a three-component covalent organic framework material BTD-COF connected by an acylhydrazone bond, and the specific synthesis steps are as follows:

[0041] Benzene[1,2-b:3,4-b′:5,6-b′]trithiophene-2,5,8-tricarboxaldehyde (13.2 mg, 0.04 mmol), 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (15.7 mg, 0.04 mmol), 2,5-diethoxylterephthalic hydrazide (34.0 mg, 0.12 mmol) and 2 mL of a mixed solution of o-dichlorobenzene / n-butanol (volume ratio 1:1) are placed in a Pyrex tube, and a uniform dispersion is obtained by ultrasonic for 15 min. Acetic acid (0.2 mL, 6M) is added. The degassing is carried out by freeze-thaw cycles in a liquid nitrogen bath for 3 times. After vacuum sealing, the reaction is carried out at 120 ℃ for 3 days. After cooling to room temperature, the solid is collected by suction filtration, and is washed with methanol, N,N-dimethylformamide, dichloromethane and acetone for three times, respectively. The obtained powder is dried at 60 ℃ under vacuum overnight to obtain a bright yellow powder BTD-COF.

[0042] Example 2

[0043] The synthesis method of the above Pt@BTD-COF, and the specific synthesis steps are as follows:

[0044] 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, a stirrer was added, the mixed solution was dispersed uniformly by ultrasonic treatment for 20 min, and then placed on a magnetic stirrer for stirring for 1.5 hours. Then the methanol solution was evaporated to dryness by a rotary evaporator. Next, 3 mL of ice methanol (-18 ℃) and 1 mL of NaHB4 aqueous solution (0.5 M) were added to the above dried sample, which was placed on a magnetic stirrer for stirring for 2 hours. Finally, it was washed with methanol and deionized water for three times, and dried in a vacuum drying oven at 60 ℃ overnight to obtain Pt@BTD-COF with a theoretical Pt mass fraction of 3wt%.

[0045] Example 3

[0046] The specific steps of the application of the three-component covalent organic framework material Pt@BTD-COF in photocatalytic overall water splitting are as follows:

[0047] 10 mg of Pt@BTD-COF was weighed and ground thoroughly, and then added to 50 mL of deionized water. After ultrasonic treatment for 10 min, it was put into a quartz glass reactor. After the reactor was vacuumed, it was irradiated with a 300W xenon lamp with a 420nm cutoff filter as the light source at 290~398 K for 4 hours. During the photocatalytic reaction, the gas composition after photocatalytic reaction was detected by gas chromatography every 1 hour, and the reactor was re-vacuumed. After the photocatalytic reaction was completed, the appropriate reaction liquid was taken and filtered through a 0.22μm nylon filter, and the liquid composition after photocatalytic reaction was detected by cerium sulfate calibration method.

[0048] Although the content of the application has been described in detail by the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the application. After reading the above content, various modifications and alternatives of the application are obvious to those skilled in the art. Therefore, the protection scope of the application should be defined by the appended claims.

Claims

1. An acylhydrazone bond linked three-component covalent organic framework material, characterized in that: The covalent organic framework material is Pt@BTD-COF, the monomers of the synthesized three-component covalent organic framework are benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarboxaldehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxylterephthalic hydrazide, and the metal Pt nanoparticles are loaded on the BTD-COF by NaBH4 reduction method.

2. The method for preparing a three-component covalent organic framework material linked by acylhydrazone bonds as described in claim 1, characterized in that: The solvent thermal method is used to synthesize the acylhydrazone bond connected three-component covalent organic framework material BTD-COF from benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarboxaldehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxylterephthalic hydrazide, and the metal Pt nanoparticles are loaded on the covalent organic framework material BTD-COF by NaBH4 reduction method to prepare Pt@BTD-COF, wherein the metal Pt nanoparticles are derived from chloroplatinic acid hexahydrate.

3. The production method according to claim 2, characterized by: The preparation method of the three-component covalent organic framework material BTD-COF specifically comprises the following steps: adding benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarboxaldehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 2,5-diethoxylterephthalic hydrazide and acetic acid into an organic solvent mixed solution; after three times of freeze-thaw cycle degassing, vacuum sealing tube, the reaction system in the sealed vacuum state is heated from room temperature to 120 DEG C, and then cooled to room temperature after 3 days of heat preservation, and finally washed and dried to obtain the three-component covalent organic framework material.

4. The production method according to claim 2 or 3, characterized by: The molar ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarboxaldehyde, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 2,5-diethoxylterephthalic hydrazide is 1:1:

3.

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

1.

6. The production method according to claim 3, characterized by: The concentration of the used acetic acid is 6 mol / L.

7. The production method according to claim 2, wherein: The method for loading the metal Pt nanoparticles by NaBH4 reduction specifically comprises the following steps: mixing the three-component covalent organic framework material BTD-COF, chloroplatinic acid hexahydrate and methanol for ultrasonic for 20 min, stirring on a magnetic stirrer for 1.5 h, removing the methanol from the stirred solution by rotary evaporation, then adding ice methanol at-18 DEG C and NaBH4 solution into the obtained powder, continuing to stir for 2 h, and finally washing to obtain Pt@BTD-COF.

8. The use of the acylhydrazone bond connected three-component covalent organic framework material in visible light driven photocatalytic overall water splitting to produce H2 and H2O2 without sacrificial agent.

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