CN115646545A - Preparation of bipyridyl group-connected benzotrithienyl covalent organic photocatalytic material and application of bipyridyl group-connected benzotrithienyl covalent organic photocatalytic material in photocatalytic total water decomposition - Google Patents

Abstract

The invention discloses a preparation method of a bipyridyl group-connected benzotrithienyl covalent organic photocatalytic material and application of the material in photocatalytic total water decomposition. The covalent organic framework material has the advantages of mild preparation conditions, convenience in operation, definite void structure, ordered pore structure, large specific surface area, high porosity and low density, and has the semiconductor characteristics of absorbing visible light in a certain waveband and exciting photoelectrons. The structural unit of the covalent organic framework has a rigid pi-shaped framework and a plurality of reaction sites, and NaBH is utilized ₄ The solution loads Pt on a photocatalytic material which generates H by taking water as a reactant through photocatalytic decomposition while utilizing solar energy without adding a sacrificial agent ₂ And O ₂ The method has great potential.

Description

A bipyridyl group-linked benzotrithienyl covalent organic photocatalytic material Preparation and application of photocatalytic total water splitting

technical field

The invention belongs to the field of material preparation and photocatalytic organic synthesis of new energy materials, and is mainly applied to a synthesis scheme of a bipyridyl group-linked benzotrithienyl covalent organic photocatalytic material and its application in photocatalytic total water splitting .

Background technique

Since the beginning of the new century, with the increasing awareness of energy demand and environmental protection, covalent organic framework materials have become a hot research topic in modern scientific circles. The application of covalent organic framework materials in photocatalytic hydrogen production has been widely studied, but there are few studies on photocatalytic water splitting without sacrificial agents. Based on this, this invention studies a new type of bipyridine group link Benzotrithienyl covalent organic frameworks for photocatalytic total water splitting.

The benzotrithienyl covalent organic framework material linked by bipyridyl groups prepared in the present invention is a covalent organic framework linked by imine bonds formed by condensation of aldehyde groups and amine groups, and has good solvent stability and thermal stability , unique photoelectric properties, good light absorption ability, suitable band gap width and energy band structure, satisfying the thermodynamic conditions of photocatalytic water splitting, and can catalytically decompose water into _H2 and _O2 under visible light. Energy is of great significance to solving the energy problem of the earth. It is worthy of continuous deepening by researchers.

Contents of the invention

The present invention utilizes a solvothermal method to prepare a novel benzotrithienyl covalent organic framework material linked by bipyridine groups under relatively mild conditions, and uses _NaBH4 solution to load Pt on the photocatalytic material, The prepared covalent organic photocatalytic material is Pt@BTT-BPY-COF. This method has repeatability, good economic and environmental benefits. Catalytic decomposition of water into H ₂ and O ₂ in the visible light range without using a sacrificial agent.

In order to realize the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

A benzotrithienyl covalent organic photocatalytic material linked by bipyridyl groups, the covalent organic photocatalytic material is Pt@BTT-BPY-COF, and the monomer for synthesizing the covalent organic framework is benzo[1 ,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2'-bipyridyl; Pt after adoption The method of functional modification is to modify the covalent organic framework material BTT-BPY-COF.

A preparation method of benzotrithienyl covalent organic photocatalytic material linked by bipyridyl groups: benzo[1,2-b:3,4-b':5,6-b' ]Trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2'-bipyridine to synthesize bipyridyl group-linked benzotrithienyl covalent organic framework material BTT-BPY-COF ; Pt@BTT-BPY-COF was prepared by modifying metal Pt on the covalent organic framework material BTT-BPY-COF by the post-functional modification method, and the Pt source used in the post-functional modification was chloroplatinic acid hexahydrate.

Further, the preparation method of the covalent organic framework material BTT-BPY-COF specifically includes: adding benzo[1,2-b:3,4-b':5,6-b']tri Thiophene-2,5,8-trialdehyde, 5,5'-diamino-2,2'-bipyridine and acetic acid, the reaction system was quickly frozen and thawed in a liquid nitrogen bath, and vacuumized three times until the internal pressure was 0 mbar and seal it, heat the sealed reaction system from room temperature to 120°C, keep it warm for 3 days, then cool it down to room temperature, and wash and dry it with suction.

Further, benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2' - The mass ratio of bipyridyl is 2:3.

Further, the mixed solvent is mesitylene and dioxane with a volume ratio of 1:1.

Further, the concentration of acetic acid used is 3-6 M.

Further, the method for post-functional modification of Pt specifically includes: mixing the covalent organic framework material BTT-BPY-COF with chloroplatinic acid hexahydrate and methanol for ultrasonication and stirring for 1.5-3 hours, and rotating the stirred solution to obtain Add -18°C low-temperature methanol and NaBH ₄ solution to the powder, continue to stir for 2~6h, and wash to obtain Pt@BTT-BPY-COF.

Application: The bipyridyl group-linked benzotrithienyl covalent organic photocatalytic material Pt@BTT-BPY-COF is used for photocatalytic water splitting driven by visible light.

The beneficial effects of the present invention are:

1) The present invention makes benzo[1,2-b:3,4-b':5,6-b']trithiophene-2 in a mixed solvent of mesitylene and dioxane by solvothermal method , 5,8-trialdehyde and 5,5'-diamino-2,2'-bipyridine were catalyzed to obtain a new type of bipyridine group-linked benzotrithienyl covalent organic framework material, prepared The material has more microporous structure, narrow bandgap width and suitable energy band structure. After the metal Pt is loaded on the covalent organic framework material, the photocatalytic water splitting performance can be studied under visible light.

2) The synthetic method of the present invention has simple process conditions and operations, and strong repeatability; the chemical reagents and equipment used are reasonably priced, easy to obtain, strong in applicability, high in industrial application value, and easy to popularize and utilize.

3) The covalent organic framework prepared by the present invention is a crystalline polymer, a crystalline porous material with a periodic network structure connected by covalent bonds, has a clear void structure, an ordered pore structure, and is relatively large Specific surface area (up to 145.2873m ² /g), uniform pore size distribution (pore size distribution ranges from 1 to 3nm), and semiconductor characteristics that absorb visible light in a certain band and excite optoelectronics. The present invention selects two kinds of monomers with bipyridine group and thiophene group, and the imine bond formed has the ability of hydrolysis, which together with the protonation of bipyridine monomer improves the photocatalytic efficiency, and the covalent organic The structural unit of the framework has a rigid π-type skeleton and multiple reaction sites, and the synergistic interaction of multiple active sites effectively promotes the separation and transfer of photogenerated charges, improves the photocatalytic performance, and uses NaBH ₄ solution to load Pt To the photocatalytic material, this material has great potential in the photocatalytic decomposition of _H2 and _O2 using water as a reactant while utilizing solar energy without adding a sacrificial agent.

Description of drawings

Fig. 1: The structural unit figure of BTT-BPY-COF in the embodiment 1;

Figure 2: X-ray powder diffraction pattern of BTT-BPY-COF in Example 1;

Fig. 3: the Fourier transform infrared spectrogram of BTT-BPY-COF in embodiment 1;

Fig. 4: scanning electron micrograph of BTT-BPY-COF in embodiment 1;

Figure 5: The _N adsorption-desorption isotherm curve of BTT-BPY-COF at 77K in Example 1;

Figure 6: The pore size distribution diagram of BTT-BPY-COF in Example 1;

Figure 7: Scanning electron microscope image of Pt@BTT-BPY-COF in Example 2;

Figure 8: Photocatalytic total water splitting performance diagram of Pt@BTT-BPY-COF in Example 3;

Figure 9: The photocatalytic total water splitting performance cycle diagram of Pt@BTT-BPY-COF in Example 3.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer and easier to understand, the present invention will be further described in detail below in conjunction with the embodiments. It can be understood that the specific implementations described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined as long as there is no conflict with each other.

(1) A method for synthesizing BTT-BPY-COF, a benzotrithienyl covalent organic framework material linked by a bipyridine group, comprising the following steps:

Benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde (BTT) and 5,5'-diamino-2,2 '-Bipyridine (BPY) was added to the mixed solution of mesitylene and dioxane, and acetic acid solution was added as a catalyst. The solution system was sealed with a flame and then placed in an oven at 120°C for 3 days, and filtered After washing and drying, the covalent organic framework material BTT-BPY-COF was obtained.

(2) The synthesis method of Pt@BTT-BPY-COF, including the following steps:

The covalent organic framework material BTT-BPY-COF was mixed with chloroplatinic acid hexahydrate (H ₂ PtCl ₆ 6H ₂ O) and methanol, then ultrasonically stirred and stirred for 1.5~3h, and the stirred solution was rotary evaporated to the obtained Add -18°C methanol and NaBH ₄ solution to the powder, continue to stir for 2~6h, and wash to obtain Pt@BTT-BPY-COF.

(3) Application of Pt@BTT-BPY-COF in photocatalytic total water splitting:

Put the catalyst Pt@BTT-BPY-COF and deionized water into the reactor, put the reaction system in a vacuum state, and stir it. The reaction temperature is controlled at about 20°C. The xenon lamp is used as the light source for photocatalytic water splitting. Gas production was monitored using gas chromatography.

Example 1

A method for synthesizing a benzotrithienyl covalent organic framework material BTT-BPY-COF linked by a bipyridyl group, the specific synthesis steps are:

Benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde (13.22 mg, 0.04 mmol) and 5,5'-diamino -2,2'-bipyridine (11.17 mg, 0.06 mmol) was placed in a Pyrex tube (volume about 5 mL, length 20 cm, diameter 1 cm), add 0.5 mL of mesitylene and 0.5 mL of dioxane Sonicate for 20 min to disperse evenly, then add 0.1 mL of 6 M acetic acid solution. The Pyrex tubes were then snap frozen and thawed in a 77K liquid nitrogen bath, evacuated three times to an internal pressure of 0 mbar and flame sealed. After warming up to room temperature, the Pyrex tube was placed in an oven at 120 °C for 3 days. The precipitate was collected by suction filtration, washed three times with dichloromethane, acetone, and tetrahydrofuran, and dried under vacuum at 60°C overnight to obtain solid powder BTT-BPY-COF. Figures 1 to 6 are the structural unit diagram, X-ray powder diffraction diagram, Fourier transform infrared spectrum diagram, scanning electron microscope diagram, _N2 adsorption-desorption isotherm curve and pore size distribution diagram of BTT-BPY-COF respectively under the condition of 77K .

Example 2

The synthesis method of the above-mentioned Pt@BTT-BPY-COF, the specific synthesis steps are:

Put the mixed solution of covalent organic framework BTT-BPY-COFs (30 mg), 10 mg/mL chloroplatinic acid solution (90 μL), and methanol (3 mL) in a round bottom flask for 20 min, and then place the mixed solution on a magnetic stirrer to stir After 1.5h, the stirred solution was subjected to rotary evaporation to obtain BTT-BPY-COF containing Pt metal ions, and methanol (3mL) at -18°C and 1.5M NaBH ₄ solution (1mL) were added to the obtained powder, and mixed The solution was stirred for 2 hours, washed with a large amount of deionized water, and dried in a vacuum oven at 60°C for 12 hours to obtain Pt@BTT-BPY-COF reduced by NaBH ₄ , and theoretically calculate the Pt in Pt@BTT-BPY-COF The content is 1.0 wt%. Figure 7 is a scanning electron microscope image of Pt@BTT-BPY-COF. It can be seen from the figure that the structure of BTT-BPY-COF is not destroyed after loading Pt, and BTT-BPY-COF is piled up by nanowires before and after loading. Hollow rod-like structure.

Example 3

The covalent organic framework material Pt@BTT-BPY-COF is applied in photocatalytic water splitting, and the specific steps are as follows:

Weigh 20 mg of Pt@BTT-BPY-COF, add 50 mL of deionized water, stir and mix evenly, and sonicate in an ultrasonic machine for 20 minutes, and put it into a quartz glass reactor. After three times of vacuuming, in a vacuum state, a 300W xenon lamp with a 420nm cut-off filter was used as a light source for 4 hours, and the gas composition after the photocatalytic reaction was detected by gas chromatography to test the Pt@BTT-BPY- The performance of COF to completely split water. Figure 8 is the photocatalytic total water splitting performance diagram of Pt@BTT-BPY-COF. It can be seen from the figure that the amount of hydrogen and oxygen produced after four hours is 2.28 μmol and 1.10 μmol, and the molar ratio is about 2: 1. Figure 9 is the photocatalytic water splitting cycle performance diagram of Pt@BTT-BPY-COF. One hour is used as one cycle. It can be seen from the figure that after eight cycles, the amount of hydrogen and oxygen can still reach 0.70 μmol and 0.24 μmol, the catalytic activity of the material can be basically maintained.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (8)

1. A benzotrithienyl covalent organic photocatalytic material linked by a bipyridyl group, characterized in that: the covalent organic photocatalytic material is Pt@BTT-BPY-COF, and a unit of a covalent organic framework is synthesized The body is benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2'- Bipyridine; Pt is modified on the covalent organic framework material BTT-BPY-COF by the method of post-functional modification. 2. the preparation method of the benzotrithienyl covalent organic photocatalytic material that a kind of bipyridine group connects as claimed in claim 1 is characterized in that: adopt solvothermal method to benzo[1,2-b:3 ,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 5,5'-diamino-2,2'-bipyridyl to synthesize benzotris The thienyl covalent organic framework material BTT-BPY-COF; the method of post-functional modification is used to modify metal Pt on the covalent organic framework material BTT-BPY-COF to prepare Pt@BTT-BPY-COF, and the post-functional modification uses Pt The source is chloroplatinic acid hexahydrate. 3. The preparation method according to claim 2, characterized in that: the preparation method of the covalent organic framework material BTT-BPY-COF specifically comprises: adding benzo[1,2-b:3, 4-b':5,6-b']trithiophene-2,5,8-trialdehyde, 5,5'-diamino-2,2'-bipyridine and acetic acid, the reaction system was rapidly Freeze and thaw, evacuate three times until the internal pressure is 0 mbar and seal, heat the sealed reaction system from room temperature to 120 °C, keep it warm for 3 days, then cool down to room temperature, and filter, wash and dry. 4. The preparation method according to claim 2 or 3, characterized in that: benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8- The substance ratio of trialdehyde and 5,5'-diamino-2,2'-bipyridine is 2:3. 5. The preparation method according to claim 3, characterized in that: the mixed solvent is mesitylene and dioxane with a volume ratio of 1:1. 6. The preparation method according to claim 3, characterized in that: the concentration of acetic acid used is 3-6 M. 7. A preparation method as claimed in claim 2, characterized in that: the method for post-functional modification of Pt specifically comprises: mixing the covalent organic framework material BTT-BPY-COF with chloroplatinic acid hexahydrate and methanol and stirring After 1.5~3h, the stirred solution was rotary evaporated, and methanol and NaBH ₄ solution at -18°C were added to the obtained powder, and the stirring was continued for 2~6h, and Pt@BTT-BPY-COF was obtained by washing. 8. The application of the bipyridyl group-linked benzotrithienyl covalent organic photocatalytic material as claimed in claim 1 in the photocatalytic total water splitting without sacrificial agent driven by visible light.

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