2D COFs material constructed based on module units with different lengths and preparation method and application of 2D COFs material

Abstract

The invention provides a 2D (two-dimensional) COFs (covalent organic frameworks) material constructed on the basis of module units with different lengths as well as a preparation method and application of the 2D COFs material. The 2D COFs material is prepared by reacting a BABE monomer with benzenetricarboxaldehyde or benzo [1, 2-b: 3, 4-b ': 5, 6-b'] trithiophene-2, 5, 8-trialdehyde. The preparation method of the 2D COFs material comprises the following steps: adding a BABE monomer, a triangular aldehyde group monomer and an organic solvent into a pyrox tube, and carrying out ultrasonic mixing to obtain a mixture; adding a catalyst into the mixture, carrying out ultrasonic mixing, putting the pyrox tube into a liquid nitrogen bath, freezing, unfreezing, carrying out circulating degassing, and sealing the pyrox tube by using a flame gun; and cooling the temperature of a pyrox tube to room temperature, putting the pyrox tube into a drying oven for heating crystallization, adding a soaking solvent, and carrying out Soxhlet extraction and vacuum drying to obtain the 2D COFs material. According to the 2D COFs material prepared by the method, the photocatalytic performance is enhanced and the photocatalytic efficiency is improved by reducing the length of a molecular chain, shortening the electron transmission distance and inhibiting the compounding of photo-induced electrons and holes.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and particularly relates to a 2D COFs material constructed based on module units of different lengths, and a preparation method and application thereof. Background Art

[0002] The rapid economic development has led to an increasing demand for energy. At the same time, a sustainable development model is imperative. Therefore, the use of clean energy is widely regarded as the key to solving the current energy crisis and environmental problems. Hydrogen (H 2 ) as an ideal pollution-free green energy, water splitting for hydrogen production driven by visible light is a green and sustainable technology for converting solar energy into chemical energy and has been widely developed and utilized. At present, covalent organic framework materials (COFs), as one of the most competitive materials in photocatalysts, can promote the rapid progress of photocatalytic water splitting for hydrogen production due to the designability, adjustability of their composition, structure and porosity, and the characteristics of high crystallinity. However, COFs materials have a high recombination rate of photo-generated carriers, which significantly affects the generation and transport of carriers, and ultimately leads to low photocatalytic performance. In this paper, Schiff base polycondensation reaction is used to prepare 2D COFs by designing and synthesizing different ligand branches, shorten the electron transport distance, reduce the recombination chance of electrons and holes during the transport process, increase the photocatalytic performance, and achieve efficient photocatalytic hydrogen production ability. Summary of the Invention

[0003] In view of this, the present invention proposes a 2D COFs material constructed based on module units of different lengths, and a preparation method and application thereof to solve the above problems.

[0004] The technical solution of the present invention:

[0005] A 2D COFs material constructed based on module units of different lengths, introducing two photocatalytic COFs materials designed with different lengths of module unit branches, and its structure is as follows:

[0006]

[0007] Further, the raw materials for preparing the photocatalytic 2D COFs include BABE monomer, benzene-1,3,5-tricarbaldehyde and benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde, and the molar ratio of BABE monomer to benzene-1,3,5-tricarbaldehyde is 1:0.5 - 3; the molar ratio of BABE monomer to benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde is 1:0.5 - 3.

[0008] The preparation steps of the 2D COFs material constructed by module units of different lengths include:

[0009] S1. Add BABE monomer, triangular aldehyde group monomer and organic solvent into a Pyrex tube, and ultrasonically mix to obtain a mixture.

[0010] S2. Add a catalyst into the mixture and ultrasonically mix. Place the Pyrex tube in a liquid nitrogen bath, freeze, thaw, and perform cyclic degassing, then seal the Pyrex tube with a blowtorch.

[0011] S3. Let the temperature of the Pyrex tube drop to room temperature, place it in an oven for heating crystallization, add a soaking solvent, perform Soxhlet extraction, and then vacuum dry to obtain the 2D COFs material.

[0012] Further, in step S1, the organic solvent is one of the mixed solutions of mesitylene and 1,4 - dioxane with a volume ratio of 1:0.5 - 10, the mixed solution of o - dichlorobenzene and 1 - butanol with a volume ratio of 1:0.5 - 10, the mixed solution of o - dichlorobenzene and benzyl alcohol with a volume ratio of 1:0.5 - 10, and the mixed solution of o - dichlorobenzene and absolute ethanol with a volume ratio of 1:0.5 - 10.

[0013] Further, in step S2, the catalyst is glacial acetic acid, the molar volume concentration range of glacial acetic acid is 0.1 - 10 M / L, and the volume ratio of glacial acetic acid to the volume of the mixture in step S1 is 1:1 - 20.

[0014] Further, in step S3, for the heating crystallization, the heating temperature is 80 - 160 °C and the reaction time is 24 - 120 h.

[0015] Further, in step S3, the soaking solvent is one of anhydrous tetrahydrofuran, absolute ethanol, absolute methanol, and anhydrous acetone.

[0016] Further, in step S3, for the vacuum drying, the drying temperature is 60 - 150 °C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) The 2D COFs material prepared by the method of the present invention significantly shortens the electron transport distance by reducing the molecular chain length, effectively inhibits the recombination of photo - generated carriers, and the hydrogen production amount can reach 8.02 mmol g -1 h -1 .

[0019] (2) The 2D COFs material prepared by the method of the present invention has good stability and regeneration ability. After 4 cycles of photocatalytic water splitting for hydrogen production, its hydrogen production amount can still remain at a high level. Description of the Drawings

[0020] Figure 1:Synthesis route diagram of 2D COFs materials. Mesitylene is 1,3,5-trimethylbenzene and 1,4Dioxane is 1,4-dioxane.

[0021] Figure 2 PXRD patterns of two 2D COFs materials prepared using different modular units; the vertical axis Intensity represents intensity, and the horizontal axis 2θ (two-theta) refers to the angle between the incident X-ray beam and the diffraction detector.

[0022] Figure 3 FT-IR spectra of two 2D COFs materials prepared using different modular units; the vertical axis Transmittance represents transmittance; the horizontal axis Wavenumber represents wave number; in the figure, BABE-BTT COF represents the abbreviation of the synthesized COFs material containing thiophene.

[0023] Figure 4 Photoluminescence spectra of two 2D COFs materials prepared using different modular units; the vertical axis Intensity represents intensity; the horizontal axis Wavelength represents wavelength; BABE-TB COF represents the abbreviation of the COFs material with only one benzene ring in the synthesized intermediate, and BABE-BTT COF represents the abbreviation of the COFs material with thiophene in the synthesized intermediate.

[0024] Figure 5 Photocurrent density spectra of two 2D COFs materials prepared using different modular units; the vertical axis Current Density represents current density; the horizontal axis Time represents time; BABE-TB COF represents the abbreviation of the COFs material with only one benzene ring in the synthesized intermediate, and BABE-BTT COF represents the abbreviation of the COFs material with thiophene in the synthesized intermediate.

[0025] Figure 6 Electrochemical impedance spectra of two 2D COFs materials prepared using different modular units; the vertical axis Z” represents the imaginary part of impedance; the horizontal axis Z’ represents the real part of impedance; BABE-TB COF represents the abbreviation of the COFs material with only one benzene ring in the synthesized intermediate, and BABE-BTT COF represents the abbreviation of the COFs material with thiophene in the synthesized intermediate.

[0026] Figure 7 Photocatalytic hydrogen production of two 2D COFs materials prepared using different modular units 2 Cyclic experiment diagram; the horizontal axis Time represents time; the vertical axis H 2 evolution represents H 2The change amount, BABE-TB COF represents the abbreviation of COF materials with only one benzene ring in the synthesized intermediate, and BABE-BTT COF represents the abbreviation of COF materials with thiophene in the synthesized intermediate. Detailed implementation mode

[0027] To better understand the technical content of the present invention and describe the technical solution clearly and completely, specific embodiments are provided below to further illustrate the present invention. The following are only some embodiments of the present invention.

[0028] The materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial channels without special instructions. The experimental methods used in the embodiments of the present invention are all conventional methods without special instructions. To better understand the technical content of the present invention, specific embodiments, comparative examples and specific tests are provided below to further illustrate the present invention.

[0029] In the embodiment, 1-(4,7-Bis(4-aminophenyl)-1H-benzoimidazole-2-yl)ethan-1-ol (Cryst. Growth Des. 2019, 19, 3543-3550) can be synthesized according to the method reported in the literature "ABenzimidazole-ContainingCovalent Organic Framework-Based QCM Sensor for Exceptional Detection ofCEES" DOI: 10.1021 / acs.cgd.9b00409; Cryst. Growth Des. 2019, 19, 3543-3550. Other raw material compounds such as terephthalaldehyde (TB) and benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-tricarbaldehyde (BTT) are obtained by purchasing from the market without special instructions.

[0030] Table 1 Abbreviation interpretation table

[0031] Abbreviation Chinese Name BABE Benzimidazole monomer TB Trimesic aldehyde BTT Benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde

[0032] Example 1

[0033] (BABE, 20.67 mg, 0.06 mmol) and 1,3,5-benzenetricarboxaldehyde (TB, 6.49 mg, 0.04 mmol) were mixed and added into a 10 mL Pyrex tube. 1 mL of each of the organic solvents mesitylene and 1,4-dioxane were added, and the mixture was sonicated for 30 min. Then, 0.4 mL of 6 M acetic acid was added, and sonication was continued until complete mixing. After that, it was placed in a liquid nitrogen bath and degassed through a freeze-pump-thaw cycle, and then sealed with a blowtorch. After the sealed Pyrex tube cooled to room temperature, it was heated in an oven at 120 °C for 3 days. The post-treatment was carried out by soaking and washing with tetrahydrofuran and Soxhlet extraction, and then drying under vacuum at 100 °C to obtain BABE-TB COF (in claim 1 Figure 1 ).

[0034] Example 2

[0035] (BABE, 20.67 mg, 0.06 mmol) and benzo[1,2-b:3,4-b':5,6-b']terthiophene-2,5,8-tricarbaldehyde (BTT, 13.22 mg, 0.04 mmol) were added into a 10 mL Pyrex tube. 1 mL of o-dichlorobenzene and 1 mL of 1-butanol were added, and the mixture was sonicated for 30 min. Then, 0.2 mL of 6 M acetic acid was added, and sonication was continued for 5 min. After sonication, it was placed in a liquid nitrogen bath and degassed through a freeze-pump-thaw cycle, and then sealed with a vacuum tube. After the sealed Pyrex tube cooled to room temperature, it was heated at 120 °C for 3 days. The post-treatment was carried out by soaking and washing with tetrahydrofuran and Soxhlet extraction, and then drying under vacuum at 120 °C to obtain BABE-BTT COF (in claim 1 Figure 2 ).

[0036] Test Example 1

[0037] Test procedure: 1. Take 10 mg of the synthesized COFs material and place it in an XRD sample holder, and gently press the sample with a glass slide to make it spread evenly and flat. 2. Place the prepared sample into the instrument, set the scanning range from 1° to 30°, the scanning rate at 7° / min, and start the test.

[0038] Powder X-ray diffraction patterns of two photocatalytic materials with different branched-chain length differences were synthesized. By analyzing the X-ray diffraction patterns, highly crystalline organic porous framework materials were obtained, as shown in Figure 2 .

[0039] Test Example 2

[0040] Test procedure: The Fourier transform infrared spectrum of the material was tested by the ATR method, and the test wavelength range was 4000 - 400 cm -1 .

[0041] It can be clearly seen from Figure 3 that the two samples were respectively at 1655 cm -1and 1586 cm -1 There appeared a vibration peak of C=N stretching bond at this position, indicating the successful formation of the imine bond.

[0042] Test Example 3

[0043] Test procedure: 1. Weigh 10 mg of the solid powder sample, put it into the solid sample cell, compact it and then put it into the equipment. 2. Set the excitation wavelength to 380 nm, the starting wavelength to 400 nm, and test the fluorescence intensity in the range of 400 nm to 800 nm.

[0044] From Figure 4 It can be seen that the COFs material with shorter branched chains has a lower fluorescence intensity, indicating a lower recombination rate of photo-generated carriers, which is beneficial to the separation of electron-hole pairs and promotes the photocatalytic reaction performance.

[0045] Test Example 4

[0046] Test procedure: 1. Take 5 mg of the ground COFs material, add it to a 10 mL glass bottle, add 1 mL of absolute ethanol, sonicate, and then continue to add 50 μL of 5% Nafion reagent and sonicate again to make it completely dispersed. 2. Use a hole punch to drill a round hole with a diameter of 6 mm in the transparent tape and stick it to the ITO conductive glass. 3. Use a pipette to take the sonicated solution and drop it onto the ITO conductive glass to complete the sample preparation and wait for it to dry. 4. Electrochemical measurement is carried out in a standard three-electrode system. The platinum foil is used as the counter electrode, Ag / AgCl is used as the reference electrode, and the working electrode is immersed in 0.2 mol / L Na 2 SO 4 solution. The photocurrent density of the two COFs materials is tested at a bias potential of 0.5 V for 310 s, with light irradiation every 20 s. The magnitude of the photocurrent reflects the separation and transport ability of electron-hole pairs.

[0047] From Figure 5 It can be seen that the COFs material with shorter branched chains has a stronger photocurrent, indicating a higher separation efficiency of its electron-hole pairs.

[0048] Test Example 5

[0049] Test procedure: Electrochemical impedance test is carried out using the sample of Test Example 4, with the starting voltage of -0.5 V. Electrochemical impedance can reflect the charge transport ability of the material. The smaller the electrochemical impedance radius, the smaller the electrochemical impedance and the greater the charge transport ability.

[0050] From Figure 6 the electrochemical impedance diagram, it can be seen that the COFs with short branched chains have a lower electrochemical impedance, indicating that it is more prone to photocatalytic hydrolysis to produce hydrogen.

[0051] Test Example 6

[0052] Experimental procedure: 1. Weigh 2 mg of the COF material and grind it. Measure and place it in a 100 mL beaker. Add 1.76 g of ascorbic acid and 5% H 2 PtCl 6 as a cocatalyst, sonicate for 30 minutes, pour the mixed solution into a reaction kettle, and connect it to a photocatalytic reactor. 2. Evacuate the reaction equipment for 30 minutes, set the temperature of the condensed water to 5°C, and start stirring. 3. Turn on the Labsolar-6A automatic on-line gas analysis system, turn on the xenon lamp illumination for 6 h, measure the data. After the reaction is completed, collect the irradiated material and continue to perform the photocatalytic reaction. Four cyclic experiments are carried out. Test the cyclic performance of photocatalytic hydrolysis hydrogen production under the optimal conditions.

[0053] It can be seen from Figure 7 that after four cycles of the two COF materials, their hydrogen production amounts can still remain at a very high level, indicating that the materials have excellent photocatalytic stability.

[0054] The above are only the exemplified embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A 2D COFs material constructed based on modular units of different lengths, characterized in that: The structures of two photocatalytic COFs materials with different designs of module unit branch chain lengths are as follows:

2. The 2D COFs material constructed by modular units of different lengths as claimed in claim 1, characterized in that: The raw materials for preparing photocatalytic 2DCOFs include BABE monomer, trimesic acid and benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde, the molar ratio of BABE monomer to trimesic acid is 1:0.5-3; the molar ratio of BABE monomer to benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde is 1:0.5-3.

3. The 2D COFs material constructed by modular units of different lengths as claimed in claim 1, characterized in that: The preparation steps include: S1, adding BABE monomer, triangular aldehyde monomer and organic solvent into a Pyrex tube, and ultrasonically mixing to obtain a mixture; S2, adding a catalyst to the mixture, ultrasonically mixing, placing the Pyrex tube in a liquid nitrogen bath, freezing, thawing, cyclically degassing, and then sealing the Pyrex tube with a flame gun; S3. The temperature of the Pyrex tube is lowered to room temperature, and the tube is placed in an oven for heating and crystallization. Then, a soaking solvent is added, and the tube is extracted and dried in vacuum to obtain a 2D COFs material.

4. The preparation step of the 2D COFs material constructed by modular units of different lengths as claimed in claim 3, characterized in that: In step S1, the organic solvent is a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:0.5-10, a mixed solution of o-dichlorobenzene and 1-butanol in a volume ratio of 1:0.5-10, a mixed solution of o-dichlorobenzene and benzyl alcohol in a volume ratio of 1:0.5-10, and a mixed solution of o-dichlorobenzene and anhydrous ethanol in a volume ratio of 1:0.5-10.

5. The preparation step of the 2D COFs material constructed by modular units of different lengths as claimed in claim 3, characterized in that: In step S2, the catalyst is glacial acetic acid, the molar volume concentration of the glacial acetic acid is in the range of 0.1-10 M / L, and the ratio of the volume of the glacial acetic acid to the volume of the mixture in step S1 is 1:1-20.

6. The preparation step of the 2D COFs material constructed by modular units of different lengths as claimed in claim 3, characterized in that: Step S3, the heating crystallization, the heating temperature is 80-160° C., and the reaction time is 24-120 hours.

7. The preparation step of the 2D COFs material constructed by modular units of different lengths as claimed in claim 3, characterized in that: In step S3, the soaking solvent is one of anhydrous tetrahydrofuran, anhydrous ethanol, anhydrous methanol and anhydrous acetone.

8. The preparation step of the 2D COFs material constructed by modular units of different lengths as claimed in claim 3, characterized in that: Step S3, vacuum drying, the drying temperature is 60-150°C.

9. Use of the 2D COFs material according to any one of claims 1 to 8 in photocatalytic water splitting to produce hydrogen.

Images