WO2023077285A1

WO2023077285A1 - Defect-rich covalent organic framework material, preparation method therefor, and application thereof in photocatalytic hydrogen evolution

Info

Publication number: WO2023077285A1
Application number: PCT/CN2021/128280
Authority: WO
Inventors: 李红喜; 王继贤
Original assignee: 苏州大学
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2023-05-11

Abstract

Disclosed in the present invention are a defect-rich covalent organic framework material, a preparation method therefor, and an application thereof in photocatalytic hydrogen evolution. Specifically, the present invention prepares a series of defect-rich covalent organic framework materials by using unilateral aldehyde as a regulator and adjusting the amount of the unilateral aldehyde. The materials can decompose water under a photocatalytic condition to produce hydrogen, and have the characteristics of high efficiency and environment-friendly and mild reaction conditions. After a conversion reaction is completed, a catalyst is separated from the system and is used in a next round of reaction. After four times of recycling, the stability of the catalyst can still be maintained, and the catalytic activity of the catalyst is not significantly reduced.

Description

A defect-rich covalent organic framework material and its preparation method and application in photocatalytic hydrogen evolution

technical field

The invention belongs to the technical field of catalytic chemistry, and relates to a method for controlling defects in a covalent organic framework and an application of photocatalytic hydrogen evolution.

Background technique

Energy and environmental issues are important problems facing society today. Developing clean energy and reducing the use of fossil fuels can optimize the existing energy structure and is an effective way to solve energy problems. Among them, hydrogen energy is a very green renewable resource. Hydrogen energy combustion provides energy and only water is produced as a by-product. It is an environmentally friendly energy source. However, the generation and storage of hydrogen gas is an important problem currently facing. Among the many hydrogen production methods, the photocatalytic hydrogen evolution reaction is a relatively green and economical way, which uses solar energy as the driving force to minimize energy consumption. Traditional photocatalytic hydrogen evolution mainly relies on inorganic semiconductors, but most of its light absorption depends on the concentration in the ultraviolet region. In order to enhance the utilization of visible light, organic semiconductors are gradually used in the field of photocatalysis, mainly divided into linear polymers, porous polymers compounds, covalent triazine frameworks and covalent organic frameworks. The research on the hydrogen evolution efficiency and stability of covalent organic framework materials is still a problem to be solved at present.

technical problem

In view of the above situation, the object of the present invention is a method for controlling defects in covalent organic framework materials, using a series of covalent organic framework materials with different defect degrees as catalysts and platinum as a cocatalyst to realize photocatalytic hydrogen evolution reaction. The defect-rich covalent organic framework material disclosed by the invention is used as a catalyst, can be recycled more than 4 times, and remains stable after 4 cycles, and its catalytic activity does not decrease significantly, which is an effective and efficient catalyst.

technical solution

In order to achieve the above object, the present invention adopts the following technical scheme: a defect-rich covalent organic framework material, with 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2, It is prepared from 4,6-triformylphloroglucinol and 3,5-dimethylbenzaldehyde as raw materials. Preferably, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-triformylphloroglucinol, 3,5-dimethylbenzaldehyde The molar ratio is 0.04:0.12X%:0.04 (1-X%), 0<X<100; more preferably, 3<X<15, most preferably 5<X<10.

In the present invention, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-triformylphloroglucinol, 3,5-dimethylbenzene Formaldehyde undergoes a solvothermal reaction to obtain defect-rich covalent organic frameworks. Specifically, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-triformylphloroglucinol, 3,5-dimethylbenzaldehyde Dissolved in mesitylene and 1,4-dioxane, a series of defect-rich covalent organic frameworks were obtained through solvothermal reactions. The invention regulates the defects of the covalent organic framework compound through the introduction of the unilateral aldehyde, which can improve the crystallinity of the material and regulate its BET specific surface area.

In the above technical solution, after the solvothermal reaction is completed, centrifugation is performed, and the precipitate is washed with tetrahydrofuran, dimethyl sulfoxide, and ethanol in sequence, and then vacuum-dried to obtain a defect-rich covalent organic framework material.

In the above technical solution, the time for the solvothermal reaction is 24 to 72 hours, preferably 72 hours.

In the technique scheme, the solvothermal reaction uses acetic acid as a catalyst.

In the above technical scheme, the solvothermal reaction is carried out in a nitrogen atmosphere.

The invention discloses the application of the defect-rich covalent organic framework material in the photocatalytic hydrogen evolution reaction; during the photocatalytic hydrogen evolution reaction, platinum is evenly distributed on the covalent organic framework material as a cocatalyst, and the valence of metal platinum is 0 valence, proving that platinum exists in the form of nanoparticles.

In the above technical solution, in the photocatalytic hydrogen evolution reaction, the hydrogen source is water.

In the above technical scheme, the photocatalytic hydrogen evolution reaction is carried out in the presence of triethanolamine in nitrogen; preferably, the ratio of the amount of defect-rich covalent organic framework material, triethanolamine, and water is 20 mg: 5 mL: 45 mL. The catalyst was used in an amount of 3 wt% of the defect-rich covalent organic framework material.

The invention discloses a method for photocatalytic hydrogen evolution, comprising the steps of dispersing the defect-rich covalent organic framework material, an electron sacrificial agent, and a cocatalyst in water, and completing photocatalytic hydrogen evolution in nitrogen and under light conditions.

In the above technical scheme, the electron sacrificial agent is selected from triethanolamine; the cocatalyst is platinum.

In the above technical solution, the temperature of photocatalytic hydrogen evolution is room temperature, preferably 25° C.; the time is 5 hours.

In the above-mentioned technical scheme, the described lighting conditions are equipped with > 420 nm filter.

In the above technical solution, platinum is uniformly distributed as a cocatalyst on the defect-rich covalent organic framework material, wherein the valence of metallic platinum is zero, which proves that platinum exists in the form of nanoparticles.

Beneficial effect

Compared with the prior art, the present invention adopting the above technical solution has the following advantages: (1) The present invention discovers a method for controlling COF defects for the first time, and it can catalyze the hydrogen evolution reaction under light conditions, and the hydrogen evolution efficiency is high.

(2) As described in the present invention; covalent organic framework materials rich in different defect levels, among which 5-10%, especially 7% defects are the best, the crystallinity is the strongest, and the BET specific surface area is the largest.

(3) The reaction described in the present invention has the characteristics of high conversion efficiency and green and mild reaction conditions.

(4) After the conversion reaction, the defect-rich covalent organic framework material and platinum are separated from the reaction system by centrifugation, washed and dried, and the next round of reaction can be carried out. The covalent organic framework material can be recycled at least 4 times , it remained stable after 4 cycles, and its catalytic activity did not decrease significantly. The X-ray powder diffraction (PXRD) characterization after cycle catalysis showed the stability of the covalent organic framework material.

Description of drawings

Fig. 1 is a powder X-ray diffraction pattern of TAPT-COF and TAPT-COF-X of the present invention.

Figure 2 is the _N2 adsorption and desorption curves of TAPT-COF and TAPT-COF-X (X=7%, 15%) of the present invention, comparing the BET surface area of TAPT-COF TAPT-COF-7 and TAPT-COF-15 increase.

Figure 3 is the infrared spectrum of the defect-rich covalent organic framework material of the present invention, from which it can be seen that the Fourier transform infrared (FT-IR) spectrum of TAPT-COF-X contains absorptions at 1572 and 1294 cm ^-1 , respectively Formation of b-ketoenamine functional groups from C=C- and -CN- linkages. A new peak appeared at 2987 cm ^-1 (CH ₃ ) in the Fourier transform infrared spectrum of TAPT-COF-X, indicating that the 3,5-dimethylbenzaldehyde modulator was successfully connected to the TAPT-COF framework.

Fig. 4 is a diagram of the hydrogen production efficiency of the covalent organic framework material of the present invention as a catalyst.

Fig. 5 is the photoelectron spectrum of platinum after the photocatalytic reaction of the covalent organic framework material of the present invention, which shows that the existing form of platinum is zero-valent platinum.

FIG. 6 is a high-resolution transmission electron microscope image of the covalent organic framework material of the present invention after photocatalytic reaction, which shows that platinum exists in the form of platinum nanoparticles.

Fig. 7 is a powder X-ray diffraction pattern of the covalent organic framework material before and after the photocatalytic reaction of the present invention, which shows that the crystallinity does not decrease, and the covalent organic framework material has good stability.

Figure 8 shows the hydrogen production efficiency results for omitting TEOA, platinum particles or light irradiation.

Fig. 9 is a diagram of the hydrogen production efficiency of the covalent organic framework material of the present invention as a catalyst for recycling. It can be seen that the catalyst maintains a high efficiency during the recycling process without significant decline.

Embodiments of the present invention

The preparation method of the defect-rich covalent organic framework material of the present invention can be expressed as follows: under the conditions of liquid nitrogen freezing and pumping, in the presence of 2,4,6-tris(4-aminophenyl)-1,3,5 -Mixed solution of triazine, 3,5-dimethylbenzaldehyde and 2,4,6-triformylphloroglucinol in mesitylene and 1,4-dioxane, add glacial acetic acid as catalyst, thaw at room temperature , and then solvothermal reaction at 120°C for 72h; then cooled to room temperature and then centrifuged to remove the solvent, the obtained precipitate was washed with tetrahydrofuran, dimethyl sulfoxide, and ethanol in sequence, and then vacuum-dried to obtain a defect-rich covalent organic framework material.

The present invention discloses the application of the defect-rich covalent organic framework material in the photocatalytic hydrogen evolution reaction; in the obtained defect-rich covalent organic framework material, platinum is uniformly distributed on the covalent organic framework material as a cocatalyst, The valence of metallic platinum is 0, which proves that platinum exists in the form of nanoparticles.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Unless otherwise stated, the reagents, materials, instruments, etc. used in the following examples can be obtained through commercial means; the test methods involved are conventional methods.

Comparative example TAPT-COF, which was prepared solvothermally from 2,4,6-triformylphloroglucinol (TFP) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine get, as follows:

.

The specific preparation method is: under the condition of liquid nitrogen freezing and pumping, 2,4,6-triformylphloroglucinol (TFP) (84 mg 0.04 mmol) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) (141.2 mg 0.04 mmol) were weighed into a heat-resistant glass tube, and 3 mL 1,4-Dioxane, 3 mL mesitylene, 0.6 1 mL of glacial acetic acid (6M), homogenize the reaction mixture by conventional ultrasonication for 20 minutes, then use the cryopump-thaw cycle to degas three times, seal the heat-resistant glass tube, and react at 120 ° C for 72 h to produce an orange solid, centrifuge Separation, precipitation with dimethyl sulfoxide (3 × 10 mL), THF (3×10 mL), ethanol (3×10 mL) and then vacuum-dried at 80°C for 24 hours to obtain TAPT-COF.

Example TAPT-COF-X (X=3,5,7,10,15):

.

In the comparative example, different molar amounts of 3,5-dimethylbenzaldehyde were added to generate TAPT-COF-X (X=3,5,7,10,15). 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) (0.04 mmol) and 3,5-dimethylbenzaldehyde (3%, 5%, 7%, 10%, 15% respectively relative to three equivalents of TAPT) were added to heat-resistant glass tubes, and 2,4,6-trimethylbenzaldehyde The amount of phloroglucinol (TFP) is 0.04 mmol* (1-X%).

Taking X as an example at 7%, specifically, the preparation method of the defect-rich covalent organic framework material of the present invention is as follows: 2,4,6-triformylphloroglucinol (TFP) (84 mg 0.04 mmol), 0.0084 mmol 3,5-Dimethylbenzaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) (0.0372 mmol) into a heat-resistant glass tube, add 3 mL of 1,4-dioxane, 3 mL of mesitylene, and 0.6 mL of glacial acetic acid (6M), homogenize the reaction mixture for 20 minutes by conventional ultrasound, and then Pump-thaw cycle degassing 3 times, seal the heat-resistant glass tube, react at 120 °C for 72 h, produce an orange solid, centrifuge, precipitate with dimethyl sulfoxide (3×10 mL), tetrahydrofuran (3×10 mL), ethanol (3×10 mL), and then vacuum-dried at 80°C for 24 hours to obtain TAPT-COF-7.

Repeat the above synthesis, but add different molar amounts of 3,5-dimethylbenzaldehyde to generate TAPT-COF-X (X=3,5,10,15), X represents 3,5-dimethylbenzaldehyde relative The molar amount in triequivalent TAPT is X%; the amount in 2,4,6-triformylphloroglucinol (TFP) is 0.04 mmol* (1-X%).

Fig. 1 to Fig. 3 are successively the powder X-ray diffraction pattern, _N2 adsorption-desorption curve, Fourier transform infrared spectrogram of the above-mentioned covalent organic framework material rich in different defect degrees; As can be seen from the powder X-ray diffraction pattern, The crystallinity of covalent organic framework materials can be improved when the proportion of defects is appropriate, and the crystallinity is the best when the proportion of defects is 7%. Compared with TAPT-COF (344.78m ² /g), the BET surface areas of TAPT-COF-7 and TAPT-COF-15 are increased, which are 622.62 m ² /g and 483.23 m ² /g respectively; the Fourier of TAPT-COF-X The leaf-transform infrared (FT-IR) spectrum contained absorptions at 1572 and 1294 cm ⁻¹ , derived from the formation of the C=C- and -CN-bond b-ketoenamine functional group, respectively. A new peak appeared at 2987 cm ^-1 (CH ₃ ) in the Fourier transform infrared spectrum of TAPT-COF-X, indicating that the 3,5-dimethylbenzaldehyde modulator was successfully connected to the TAPT-COF framework.

Application example: The above defect-rich covalent organic framework material is used as a catalyst for photocatalytic hydrogen evolution reaction. Photocatalytic experiments were carried out in quartz flasks sealed under vacuum and kept at 25 °C by water cooling. The light source was a 300 W xenon lamp with a 420 nm cut-off filter. Catalyst (20 mg) and 5 mL of triethanolamine (TEOA) were dispersed in 45 mL of distilled water, 2.0 mg of H ₂ PtCl ₆ (3 wt% of Pt nanoparticles) was added, and the suspension was dispersed by conventional ultrasound for 30 minutes; The air was removed, and then the reaction vessel was connected to a glass-enclosed gas system (Labsolar-6A of Beijing Pofilai Technology Co., Ltd.). The circulating condensing unit is controlled at 25°C. The amount of hydrogen generated in the suspension was determined using an on-line gas chromatograph (Timet GC7900) with a TCD detector. After 5 hours of reaction, the photocatalytic hydrogen production efficiency of TAPT-COF-7 was 33910 μmol·g ^-1 ·h ^-1 , and the photocatalytic hydrogen production efficiency of TAPT-COF was 14980 μmol·g ^-1 ·h ^-1 , which The result is shown in Figure 4. In situ loading of Pt nanoparticles onto the surface of covalent organic frameworks during the photocatalytic reaction.

After the above reaction, the photocatalyst powder (a defect-rich covalent organic framework material loaded with platinum particles) was separated from the reaction system by centrifugation, washed with water, and dried for testing. The X-ray electron spectrum characterization after catalysis shows that most of the Pt metal nanoparticles exist in the form of 0 valence, and the average size of 3.3 Formation of platinum nanoparticles in nm. The lattice distance is about 0.22 nm, corresponding to the (111) crystal plane of Pt(0), and the results are shown in Figure 5 and Figure 6. After photocatalysis, the crystallinity of TAPT-COF-X is basically unchanged, which proves the stability of the prepared defect COF material, as shown in Fig. 7.

Furthermore, on the basis of the above-mentioned photocatalytic hydrogen evolution reaction, if TEOA, platinum particles or light are omitted, the hydrogen production efficiency drops significantly. See Figure 8, using TAPT-COF-7 as the catalyst.

Cycle example: After the above reaction is completed, the photocatalyst powder (defect-rich covalent organic framework material loaded with platinum particles, TAPT-COF-7) is separated from the reaction system by centrifugation, washed and dried, and then added to In the photocatalytic reactor containing 45 mL of H ₂ O solution and TEOA (5 mL, 10 vol%), the catalyst weight was still 20 mg. Then, after ultrasonic dispersion for 30 minutes, pass nitrogen into the obtained suspension for 30 minutes to remove the air. The light reaction is consistent with the above conditions, and the hydrogen production is monitored online; the catalyst is recycled according to the above process, and the cycle is 4 times in five hours. The hydrogen production rate in the interior remains basically unchanged, as shown in Fig. 9.

Claims

A defect-rich covalent organic framework material characterized by the use of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-triformyl m-benzene Triphenol and 3,5-dimethylbenzaldehyde are prepared as raw materials.
The defect-rich covalent organic framework material according to claim 1, characterized in that 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4,6-trimethyl The molar ratio of phloroglucinol to 3,5-dimethylbenzaldehyde is 0.04:0.12X%:0.04 (1-X%), 0<X<100.
The defect-rich covalent organic framework material according to claim 2, characterized in that 3<X<15.
The preparation method of the defect-rich covalent organic framework material according to claim 1, characterized in that 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 2,4, 6-triformylphloroglucinol and 3,5-dimethylbenzaldehyde undergo solvothermal reaction to prepare defect-rich covalent organic frameworks.
According to the preparation method of defect-rich covalent organic framework materials according to claim 4, it is characterized in that, after the solvothermal reaction is completed, the centrifugation is performed, and the precipitate is washed with tetrahydrofuran, dimethyl sulfoxide, and ethanol in sequence, and then vacuum-dried to obtain Defect-rich covalent organic framework materials.
The method for preparing defect-rich covalent organic framework materials according to claim 4, wherein the solvothermal reaction takes 24 to 72 hours; the solvothermal reaction uses acetic acid as a catalyst; and the solvothermal reaction is carried out in a nitrogen atmosphere.
The application of the defect-rich covalent organic framework material in claim 1 in photocatalytic hydrogen evolution reaction.
A method for photocatalytic hydrogen evolution, characterized in that it comprises the steps of dispersing the defect-rich covalent organic framework material, electron sacrificial agent, and cocatalyst in water according to claim 1, in nitrogen, under light conditions, to complete photocatalytic Catalytic hydrogen evolution.
The method for photocatalytic hydrogen evolution according to claim 8, characterized in that the electron sacrificial agent is triethanolamine; the cocatalyst is platinum.
According to the method for photocatalytic hydrogen evolution according to claim 8, it is characterized in that the ratio of the amount of defect-rich covalent organic framework material, triethanolamine, and water is 20 mg: 5 mL: 45 mL, and the amount of cocatalyst is rich in defect 3 wt% of the covalent organic framework material.