Preparation method and application of a two-dimensional covalent organic framework solid solution

Abstract

The application discloses a preparation method of a two-dimensional covalent organic framework solid solution and application thereof, and the preparation method comprises the following steps: mixing 2,6-dimethylbenzo[1,2-b:5,4-b']dioxazole, trimesic aldehyde, 1,3,5-tri(4-formylphenyl)benzene and benzoic anhydride, and heating and reacting under vacuum condition to obtain a series of ethenyl-linked covalent organic framework solid solutions. The covalent organic framework solid solution material prepared by the method has a full conjugated structure and high crystallinity, and has good photocatalytic water splitting hydrogen production activity after ball milling treatment.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials technology, specifically relating to a method for preparing a two-dimensional covalent organic framework solid solution and its application. Background Technology

[0002] Hydrogen energy is a clean and sustainable green energy source with broad application prospects in energy storage, transportation, and chemical industries. With increasing global focus on low-carbon development, green hydrogen, which produces zero carbon emissions, will play a crucial role in the future energy structure.

[0003] Photocatalytic water splitting for hydrogen production, utilizing Earth's abundant solar and water resources, is currently a major research hotspot. Photocatalysts play a crucial role in this process. Inorganic semiconductor materials, represented by TiO2, ZnO, and SrTiO3, suffer from poor visible light absorption and easy recombination of photogenerated carriers, significantly limiting their practical applications. Forming solid solutions is an effective strategy for improving the light absorption and photocatalytic activity of semiconductor materials. For example, Cd... x Zn 1-x S solid solutions can achieve continuous modulation of the band structure by changing the value of x, thereby maximizing photocatalytic performance.

[0004] Two-dimensional covalent organic frameworks (2D COFs) are crystalline porous materials formed by covalently linked organic building blocks. They possess advantages such as designable structure, regular pores, high specific surface area, and stability, and have been extensively studied in photocatalytic hydrogen production. However, research on introducing solid solution strategies into COFs to systematically regulate their properties and catalytic performance has not yet been reported. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing two-dimensional covalent organic framework solid solutions and their applications. This invention achieves precise control of the band structure of vinyl-linked COF solid solutions by varying the monomer ratio, thereby improving the performance of photocatalytic water splitting for hydrogen production.

[0006] The method for preparing a two-dimensional covalent organic framework solid solution of the present invention includes the following steps:

[0007] Step 1: 4,6-Diaminoresorcinol dihydrochloride, yttrium trifluoromethanesulfonate, triethyl orthoacetate, dimethyl sulfoxide and pyridine were heated and stirred to react. After the reaction was completed, the mixture was cooled to room temperature, water was added and extracted with an organic solvent, and then purified to obtain a methylated monomer for use in the synthesis of COF solid solutions.

[0008] Step 2: Add the purified monomer from Step 1, trimethylbenzene FB, 1,3,5-tris(4-formylphenyl)benzene TFPB and benzoic anhydride to a glass tube. Heat the mixture under vacuum and react it. After the reaction is complete, cool it to room temperature, collect the product, wash it with methanol and tetrahydrofuran, dry it under vacuum, ball mill it, centrifuge it at differential speed, and dry it under vacuum again to obtain the COFs solid solution.

[0009] The synthetic route for the COFs solid solution is shown below:

[0010]

[0011] In step 1, the molar ratio of triethyl orthoacetate to 4,6-diaminoresorcinol dihydrochloride is 3:1 to 10:1, the molar ratio of pyridine to 4,6-diaminoresorcinol dihydrochloride is 2:1 to 2.5:1, and the molar amount of yttrium trifluoromethanesulfonate is 5% to 10% of the molar amount of 4,6-diaminoresorcinol dihydrochloride.

[0012] In step 1, the reaction temperature is 55-80℃ and the reaction time is 1-6 h.

[0013] In step 1, the organic solvent used for extraction is dichloromethane; the subsequent purification includes column chromatography and recrystallization. The eluent for column chromatography consists of ethyl acetate and n-hexane in a volume ratio of 1:2 to 2:1. Recrystallization uses n-heptane at an operating temperature of 90-110℃.

[0014] In step 2, the molar ratio of methyl monomer to aldehyde monomer is 3:2. The molar amount of aldehyde monomer is calculated as the total molar amount of pyromellitic methyl ether and 1,3,5-tris(4-formylphenyl)benzene.

[0015] Furthermore, the molar ratio of pyromellitic methyl ether to 1,3,5-tris(4-formylphenyl)benzene is 2:1 to 1:2, such as 2:1, 1:1 or 1:2.

[0016] 1,3,5-Tris(4-formylphenyl)benzene is also known as 5'-(4-formylphenyl)-[1,1':3',1''-triphenyl]-4,4''-dicarboxaldehyde.

[0017] In step 2, the heating temperature is 180-200℃, and the reaction time is 1-7 days. The COFs solid solution is vacuum dried at 60-120℃.

[0018] The present invention relates to the application of two-dimensional covalent organic framework solid solutions in photocatalytic water splitting for hydrogen production.

[0019] The specific steps are as follows: chloroplatinic acid, water and triethanolamine are added to the vacuum-dried two-dimensional covalent organic framework solid solution, and after being ultrasonically dispersed evenly, it is transferred to a photocatalytic reactor. The reaction is carried out under a nitrogen atmosphere and irradiated with a 300 W xenon lamp. The generated hydrogen is quantified by gas chromatography.

[0020] The beneficial effects of this invention are reflected in:

[0021] 1. This invention prepares vinyl COF solid solutions by melt polymerization without using organic solvents. The synthesis process is simple and green, and the obtained COF solid solutions have high crystallinity and good porosity.

[0022] 2. The COFs solid solution of this invention has a fully conjugated structure. After ball milling, the particle size is reduced, and the dispersibility in water is greatly enhanced, thus exhibiting high activity in photocatalytic water splitting for hydrogen production. The formation of solid solutions greatly enriches the types of COFs and provides new ideas for regulating the photoelectric properties of COFs and improving their catalytic performance. Attached Figure Description

[0023] Figure 1 The hydrogen nuclear magnetic resonance spectrum of the monomer prepared in Example 1 of this invention.

[0024] Figure 2 The X-ray powder diffraction patterns are those of the COFs solid solutions prepared in Examples 2-6 of this invention.

[0025] Figure 3-7 The nitrogen adsorption-desorption curves are for the COFs solid solutions prepared in Examples 2-6 of this invention.

[0026] Figure 8 Fourier transform infrared spectra of the three monomers used in the preparation of COFs solid solutions in this invention.

[0027] Figure 9 The Fourier transform infrared spectra of the COFs solid solutions prepared in Examples 2-6 of this invention are shown.

[0028] Figure 10 This is a comparison of the photocatalytic water splitting rate to hydrogen production of COFs solid solutions prepared in Examples 2-6 of this invention. Detailed Implementation

[0029] Example 1:

[0030] This embodiment provides a method for preparing a benzodioxazole monomer, comprising the following steps:

[0031] 1. Accurately weigh 1.196 g of 4,6-diaminoresorcinol dihydrochloride (5.6 mmol) and 0.184 g of yttrium trifluoromethanesulfonate (0.34 mmol) into a pre-dried 50 ml three-necked flask. Add 10 ml of triethyl orthoacetate (54.6 mmol), 10 ml of dimethyl sulfoxide, and 1.1 ml of pyridine (13.6 mmol). Heat the mixture to 80 °C under a nitrogen atmosphere and stir. Monitor the reaction progress using thin-layer chromatography.

[0032] 2. After the reaction is complete, cool to room temperature, add water, and extract with dichloromethane. Dry the organic phase with anhydrous sodium sulfate, remove the solvent by rotary evaporation, and obtain the crude product.

[0033] 3. The crude product was purified by silica gel column chromatography with an eluent composition of n-hexane / ethyl acetate (1:1, v / v). It was then recrystallized from n-heptane to obtain white crystals, denoted as c-MBO. Its proton NMR spectrum was analyzed, and the results are as follows: Figure 1 . 1 HNMR (400 MHz, CDCl3): δ 2.66 (6H, s), 7.57 (1H, s), 7.87 (1H, s).

[0034] Example 2:

[0035] 34.8 mg c-MBO (0.185 mmol), 20 mg trimesaldehyde (0.123 mmol), and 84 mg benzoic anhydride (0.371 mmol) were weighed into a glass tube. The tube was sonicated briefly to allow the solid powder adhering to the inner wall to fall to the bottom. A vacuum was then applied, and the tube was flame-sealed. The sealed glass tube was placed in an oven at 200°C and reacted for 7 days. After cooling to room temperature, the tube was opened with a glass cutter, the solid was removed, crushed, and transferred to a mortar. Methanol was added and the tube was ground until no obvious particles were felt. The solid was washed three times by centrifugation with methanol and tetrahydrofuran, respectively. After drying, a yellow powder was obtained, designated SS COF-1.

[0036] Example 3:

[0037] 34.8 mg c-MBO, 13.3 mg trimesaldehyde (0.082 mmol), 16 mg 1,3,5-tris(4-formylphenyl)benzene (0.041 mmol), and 84 mg benzoic anhydride were weighed into a glass tube. The tube was sonicated briefly to allow the solid powder adhering to the inner wall to fall to the bottom. A vacuum was then applied, and the tube was flame-sealed. The sealed glass tube was placed in an oven at 200°C and reacted for 7 days. After cooling to room temperature, the tube was opened with a glass cutter, the solid was removed, crushed, and transferred to a mortar. Methanol was added and the tube was ground until no obvious particles were felt. The solid was washed three times by centrifugation with methanol and tetrahydrofuran, respectively. After drying, a yellow powder was obtained, designated SS COF-2.

[0038] Example 4:

[0039] Weigh 34.8 mg c-MBO, 10 mg pyromellitic aldehyde (0.061 mmol), 24 mg 1,3,5-tris(4-formylphenyl)benzene (0.061 mmol), and 84 mg benzoic anhydride into a glass tube. Sonicate briefly to allow the solid powder adhering to the inner wall to fall to the bottom. Then, apply a vacuum and seal the tube with a flame. Place the sealed glass tube in an oven at 200°C and react for 7 days. After cooling to room temperature, open the tube with a glass cutter, remove the solid, crush it, and transfer it to a mortar. Grind with methanol until no obvious particles are felt. Wash three times with methanol and tetrahydrofuran, respectively, by centrifugation. After drying, a yellow powder is obtained, designated SS COF-3.

[0040] Example 5:

[0041] 34.8 mg c-MBO, 6.7 mg trimesaldehyde (0.041 mmol), 32 mg 1,3,5-tris(4-formylphenyl)benzene (0.082 mmol), and 84 mg benzoic anhydride were weighed into a glass tube. The tube was sonicated briefly to allow the solid powder adhering to the inner wall to fall to the bottom. A vacuum was then applied, and the tube was flame-sealed. The sealed glass tube was placed in an oven at 200°C and reacted for 7 days. After cooling to room temperature, the tube was opened with a glass cutter, the solid was removed, crushed, and transferred to a mortar. Methanol was added and the tube was ground until no obvious particles were felt. The solid was washed three times by centrifugation with methanol and tetrahydrofuran, respectively. After drying, a yellow powder was obtained, designated SS COF-4.

[0042] Example 6:

[0043] 34.8 mg c-MBO, 48 mg 1,3,5-tris(4-formylphenyl)benzene (0.123 mmol), and 84 mg benzoic anhydride were weighed into a glass tube. The tube was sonicated briefly to allow the solid powder adhering to the inner wall to fall to the bottom. A vacuum was then applied, and the tube was flame-sealed. The sealed glass tube was placed in an oven at 200°C and reacted for 7 days. After cooling to room temperature, the tube was opened with a glass cutter, the solid was removed, crushed, and transferred to a mortar. Methanol was added and the tube was ground until no obvious particles were felt. The solid was washed three times by centrifugation with methanol and tetrahydrofuran, respectively. After drying, a yellow powder was obtained, designated SS COF-5.

[0044] Example 7:

[0045] This embodiment provides a procedure for ball milling a COF solid solution. Vacuum-dried COF solid solution powder is evenly distributed into two ball mill jars, and the same number of grinding beads and the same volume of ethanol are added. The jars are then fixed in a planetary ball mill. The mixture is ball-milled for 24 hours according to a pre-set program. The jars are then opened, and the slurry is transferred to centrifuge tubes. Differential centrifugation yields smaller-sized materials, which are then vacuum-dried for later use.

[0046] Example 8:

[0047] This embodiment provides the steps for using COF solid solutions for photocatalytic water splitting to produce hydrogen. 5 mg of ball-milled and vacuum-dried COF solid solution was accurately weighed, added to 15 ml of water, 3% (w / w) chloroplatinic acid, and 1.5 ml of triethanolamine. After ultrasonic dispersion, the solution was transferred to a 160 ml quartz glass-topped photocatalytic reactor. Nitrogen gas was purged for 15 min to purge air from the reactor. The reactor was then irradiated with a 300 W xenon lamp equipped with a >380 nm filter for 2 h. The generated hydrogen was quantified using gas chromatography.

[0048] Structural characterization:

[0049] 1. X-ray powder diffraction tests were performed on the COFs solid solutions prepared in Examples 2-6, and the results are as follows: Figure 2 As shown in the figure, all COF solid solutions exhibit high crystallinity. From SS COF-1 to SS COF-5, as the proportion of TFPB monomers increases, the diffraction peak corresponding to the (100) crystal plane shifts to a lower angle, and the 2 Theta value decreases from 3.68° to 2.76°, which is consistent with the continuous increase of the lattice parameters. Meanwhile, SS COF-2 to SS COF-4 all have only a single (100) peak, which is between SS COF-1 and SS COF-5, indicating that the two different sizes of aldehyde monomers, TFB and TFPB, are randomly distributed in the lattice, forming COF solid solutions.

[0050] 2. The COFs solid solutions prepared in Examples 2-6 were subjected to several solvent exchanges with acetone, and then activated under vacuum at 120°C for 12 hours. Subsequently, nitrogen adsorption isotherms were measured, and the results are as follows: Figure 3-7 As shown, the prepared COFs solid solutions all exhibit hysteresis loops, have similar adsorption-desorption curves, and similar BET specific surface areas.

[0051] 3. The Fourier transform infrared spectra of the three monomers used to prepare the COFs solid solution were tested, and the results are as follows: Figure 8 As shown. In the infrared spectrum of c-MBO, 2853 cm⁻¹ -1 and 2870 cm -1These correspond to the symmetric and antisymmetric stretching vibrations of CH in methyl groups, respectively; in the infrared spectrum of TFB, at 1700 cm⁻¹ -1 Corresponding to the stretching vibration of C=O in the aldehyde group; in the infrared spectrum of TFPB, 1687 cm⁻¹ -1 This corresponds to the stretching vibration of C=O in the aldehyde group.

[0052] 4. The COFs solid solutions prepared in Examples 2-6 were mixed and ground with KBr, pressed into tablets, and Fourier transform infrared spectra were measured. Figure 9 As shown. With Figure 8 Compared to the infrared signature of the middle monomer, SS COF-1 to SS COF-5 all have an infrared signature of 1637 cm⁻¹. -1 A new absorption peak appeared nearby, corresponding to the C=C stretching vibration in the COFs solid solution, indicating the successful preparation of a vinyl-linked COFs solid solution. Specifically, SS COF-1 to SS COF-3 showed a peak at 1700 cm⁻¹. -1 The presence of strong absorption peaks indicates that these COF solid solutions contain a large number of terminal aldehyde groups.

[0053] Catalytic performance:

[0054] The photocatalytic hydrogen production activity of COFs solid solution measured in Example 8 is as follows: Figure 10 As shown, the hydrogen generation rate exhibits an approximately volcano-shaped curve with increasing TFPB content in the COF solid solution. Among them, SS COF-4 showed the highest activity, reaching 3630 μmol·g⁻¹. -1 ·h -1 Compared with SS COF-1 and SS COF-5, the activity was increased by 110% and 225%, respectively.

Claims

1. A method for preparing a two-dimensional covalent organic framework solid solution, characterized in that... Includes the following steps: Step 1: 4,6-Diaminoresorcinol dihydrochloride, yttrium trifluoromethanesulfonate, triethyl orthoacetate, dimethyl sulfoxide and pyridine were heated and stirred to react. After the reaction was completed, the mixture was cooled to room temperature, water was added and extracted with an organic solvent, and then purified to obtain a methylated monomer for use in the synthesis of covalent organic framework solid solutions. Step 2: Add the purified monomer from Step 1, trimethylbenzene FB, 1,3,5-tris(4-formylphenyl)benzene TFPB and benzoic anhydride to a glass tube. Heat the mixture under vacuum and react it. After the reaction is complete, cool it to room temperature, collect the product, wash it with methanol and tetrahydrofuran, dry it under vacuum, ball mill it, centrifuge it at differential speed, and dry it under vacuum again to obtain a covalent organic framework solid solution.

2. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of triethyl orthoacetate to 4,6-diaminoresorcinol dihydrochloride is 3:1 to 10:1, the molar ratio of pyridine to 4,6-diaminoresorcinol dihydrochloride is 2:1 to 2.5:1, and the molar amount of yttrium trifluoromethanesulfonate is 5% to 10% of the molar amount of 4,6-diaminoresorcinol dihydrochloride.

3. The preparation method according to claim 1, characterized in that: In step 1, the reaction temperature is 55-80℃ and the reaction time is 1-6 h.

4. The preparation method according to claim 1, characterized in that: In step 1, the organic solvent used for extraction is dichloromethane.

5. The preparation method according to claim 1, characterized in that: In step 1, the subsequent purification includes column chromatography and recrystallization. The eluent for column chromatography consists of ethyl acetate and n-hexane in a volume ratio of 1:2 to 2:

1. Recrystallization uses n-heptane and is performed at an operating temperature of 90-110°C.

6. The preparation method according to claim 1, characterized in that: In step 2, the molar ratio of the monomer purified in step 1 to the aldehyde monomer is 3:2, wherein the molar amount of the aldehyde monomer is calculated as the total molar amount of pyromellitic methyl ether and 1,3,5-tris(4-formylphenyl)benzene.

7. The preparation method according to claim 6, characterized in that: The molar ratio of pyromellitic methyl ether to 1,3,5-tris(4-formylphenyl)benzene is 2:1 to 1:

2.

8. The preparation method according to claim 1, characterized in that: In step 2, the heating temperature is 180-200℃, and the reaction time is 1-7 days.

9. The application of the two-dimensional covalent organic framework solid solution prepared by any one of the preparation methods in claims 1-8 in photocatalytic water splitting for hydrogen production.

10. The application according to claim 9, characterized in that: Chloroplatinic acid, water, and triethanolamine were added to a vacuum-dried two-dimensional covalent organic framework solid solution, and after being ultrasonically dispersed, the mixture was transferred to a photocatalytic reactor and reacted under nitrogen atmosphere and light.

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