Triazine-based covalent organic framework material for efficient visible light-driven water splitting and preparation method thereof

Abstract

The present application relates to a kind of triazine-based covalent organic framework material for high-efficiency visible light decomposition water hydrogen production and its preparation method, belong to triazine-based covalent organic framework material and photocatalytic water decomposition hydrogen production technical field. By 2-bromine p-benzenedimethanal and 4,4',4"-(1,3,5-triazine-2,4,6-triazyl) triphenylamine under vacuum condition and catalysis solvent hot polymerization reaction, bromine atom monosubstituted monomer is introduced into triazine-based covalent organic framework skeleton, can improve its crystallinity and optical property, improve the activity of photocatalytic water decomposition hydrogen production;And the preparation method of the triazine-based covalent organic framework material is simple, easy to operate, raw material is easy to obtain and low in cost, the crystallinity of the synthesized bromine atom monosubstituted triazine-based covalent organic framework material is high, optical property is excellent and photocatalytic performance is excellent, with good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a triazine-based covalent organic framework material for efficient visible light decomposition of water to produce hydrogen and a preparation method thereof, and belongs to the technical field of triazine-based covalent organic framework materials and photocatalytic water decomposition to produce hydrogen. BACKGROUND

[0002] Covalent organic framework (COF) materials are a new type of crystalline porous organic polymers with permanent porosity and high ordered structure. Unlike other polymers, one of the remarkable features of COF materials is that they are structurally predictable, synthetically controllable and functionally designed. At the same time, COF materials also have the unique advantages of on-demand chemical functionalization, adjustable pore size, large surface area, high crystallinity and light weight. COF materials are widely used in photocatalytic water decomposition to produce hydrogen, carbon dioxide conversion, pollutant degradation and organic synthesis, etc. due to their excellent visible light absorption, fast electron-hole separation and transfer, and rich available catalytic sites.

[0003] Triazine-containing COFs are usually referred to as CTFs, which have great photocatalytic potential due to their high nitrogen element-induced visible light response, good tunability and good chemical stability. However, most of the reported CTFs are of low crystallinity or amorphous, which greatly affects the photoexcitation and separation of charge carriers, limiting their photocatalytic activity. In addition, there are many ways to connect the monomer building blocks of COF materials, such as borate ester linkages, imine linkages, beta-ketoenamine linkages, hydrazine linkages, imide group linkages and other connection methods. Triazine COFs with imine linkages are affected by the poor light trapping ability, limited crystallinity and structural distortion in the process of photocatalytic water decomposition to produce hydrogen, which hinders the effective separation of photo-carriers and thus exhibits low photocatalytic activity for water decomposition to produce hydrogen. SUMMARY

[0004] In view of the problem of poor photocatalytic decomposition of water activity of triazine-based covalent organic framework materials at present, the present application provides a triazine-based covalent organic framework material for efficient visible light decomposition of water to produce hydrogen and a preparation method thereof. By introducing a monosubstituted monomer of bromine atom into the triazine-based covalent organic framework skeleton, the crystallinity and light absorption of the material can be improved, and the activity of photocatalytic water decomposition to produce hydrogen can be improved. In addition, the preparation method of the COF material is simple, easy to operate, and the raw materials are easy to obtain, and the preparation cost is low. Moreover, the prepared monosubstituted COF material of bromine atom has excellent photoelectric properties and has great application prospect.

[0005] The purpose of the present application is achieved by the following technical solutions.

[0006] A triazine-based covalent organic framework material for efficient visible light decomposition of water to produce hydrogen, the triazine-based covalent organic framework material is a monosubstituted triazine-based covalent organic framework material of bromine atoms, and the structural formula is as follows:

[0007]

[0008] A preparation method of a triazine-based covalent organic framework material for efficient visible light decomposition of water to produce hydrogen, the triazine-based covalent organic framework material (abbreviated as Br-COF material) is formed by solvent thermal polymerization reaction of 2-bromoterephthaldehyde (abbreviated as Br-TA) and 4,4',4''-(1,3,5-triazine-2,4,6-triazyl) triphenylamine (abbreviated as TTA) under the catalysis of vacuum conditions.

[0009] Preferably, a mixed solvent of 1,2-dichlorobenzene and n-butanol is selected as the reaction solvent, and acetic acid is selected as the catalyst.

[0010] Preferably, the volume ratio of 1,2-dichlorobenzene and n-butanol in the reaction solvent is (0.9-1.1):1.

[0011] Preferably, the concentration of acetic acid in the reaction solvent is 0.5-0.7 mol / L.

[0012] Preferably, Br-TA and TTA are mixed according to the stoichiometric ratio, that is, the molar ratio of Br-TA to TTA is 3:2; and the concentration of Br-TA in the reaction solvent is more preferably 0.08-0.1 mol / L.

[0013] Preferably, the temperature of the solvent thermal polymerization reaction is 100-120 DEG C, and the time is 72-120 h.

[0014] Advantages:

[0015] (1) The present application introduces a monosubstituted monomer containing bromine atoms into the triazine-based covalent organic framework skeleton, which significantly improves and adjusts the structure and optical physical properties, promotes more efficient charge transfer, and thus improves the crystallinity and light absorption, and improves the activity of photocatalytic water decomposition to produce hydrogen.

[0016] (2) It is found through experiments that the introduction of different halogens has different effects on the photoelectric properties of the triazine-based covalent organic framework material, and the present application selects a monosubstituted monomer containing bromine atoms to introduce into the triazine-based covalent organic framework skeleton, which can ensure high crystallinity, excellent light absorption and high catalytic activity for photocatalytic water decomposition to produce hydrogen.

[0017] (3) The triazine-based covalent organic framework material is prepared by a solvothermal polymerization reaction, raw materials are widely sourced and low in price, the process is simple and easy to operate, and no complex post-modification of the triazine-based covalent organic framework material is needed.

[0018] (4) The composition of the reaction solvent affects the crystallinity of the triazine-based covalent organic framework material. The mixed solvent composed of 1,2-dichlorobenzene and n-butanol in a certain ratio is selected as the reaction solvent, so that the high crystallinity of the product can be ensured.

[0019] In summary, the triazine-based covalent organic framework material has high crystallinity, excellent light absorption, and excellent photocatalytic performance, and the preparation process is simple, low in cost, and has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A comparison chart of powder X-ray diffraction (PXRD) spectra of the Br-COF material prepared in Example 1 and the H-COF material prepared in Comparative Example 1.

[0021] Figure 2 A comparison chart of Fourier transform infrared spectra of the Br-COF material prepared in Example 1 and the H-COF material prepared in Comparative Example 1.

[0022] Figure 3 A comparison chart of ultraviolet-visible light absorption spectra of the Br-COF material prepared in Example 1 and the H-COF material prepared in Comparative Example 1.

[0023] Figure 4 A comparison chart of photocatalytic hydrogen production performance of the Br-COF material prepared in Example 1, the H-COF material prepared in Comparative Example 1, and the Cl-COF material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0024] The application will be further described below in conjunction with specific embodiments, wherein the methods are all conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0025] In the following examples, the main instruments involved are as follows: Japan Science X-ray polycrystalline diffractometer, Ultima IV, 40 kV, 40 mA, Cu Kα target ((λ = 0.154056 nm)); Bruker ALPHA spectrometer for Fourier transform infrared (FTIR) spectrum (at 400-4000 cm -1UV-Vis absorption spectra were measured by a UV-Vis spectrometer (Shimadzu UV-3600) in the range of 200-800 nm; the photocatalytic water splitting test reaction device (Q0350 (28# ball mill) from Beijing Portifilm Technology Co., Ltd.) was connected to a closed micro-gas analysis system (Labsolar-6A from Beijing Portifilm Technology Co., Ltd.) for testing the photocatalytic water splitting performance, and the specific test steps were as follows: before testing, 10 mg of catalyst sample (the corresponding material prepared in the examples and comparative examples as the catalyst) was dispersed in 50 mL of water, and 3 wt% Pt was added as a co-catalyst (H2PtCl6 was used as the precursor of Pt) and 0.88 g of ascorbic acid was added as a sacrificial agent to form a mixed solution, which was uniformly dispersed by ultrasonic for 30 min. The mixed solution was vacuumed and degassed before light irradiation. Then, a xenon lamp (CEL-HXF300, Au-Light, China) was used as the light source at the top of the reaction device, and a 400 nm cut-off filter was used as the light source. The produced gas products were analyzed by a gas chromatograph (Shimadzu GC-2014C, TCD, carrier gas argon 99.999%) and the reaction temperature was controlled at about 6°C by using cooling water during the reaction.

[0026] Example 1

[0027] (1) 0.059 mmol of TTA and 0.089 mmol of Br-TA were placed in a 10 mL heat-resistant tube;

[0028] (2) 0.5 mL of 1,2-dichlorobenzene and 0.5 mL of n-butanol were first added to the heat-resistant tube of step (1), and then 0.1 mL of 6M acetic acid solution was added after ultrasonic mixing;

[0029] (3) The heat-resistant tube of step (2) was frozen to 77 K by liquid N2, and degassed by three cycles of freeze-pump-thaw, and then sealed under vacuum;

[0030] (4) The heat-resistant tube of step (3) was transferred to an oven, and the temperature was set to 120°C, and the solvothermal polymerization reaction was carried out at 120°C for 72 h, at which time a precipitate was formed in the heat-resistant tube;

[0031] (5) The precipitate in step (4) was collected by centrifugation, and then washed with N,N-dimethylformamide, tetrahydrofuran, and n-hexane, respectively, and then vacuum dried at 80°C for 12 h to obtain a bromine atom monosubstituted triazine-based covalent organic framework material, which is abbreviated as Br-COF material.

[0032] The crystal and chemical structure of the Br-COF material prepared in Example 1 and the H-COF material prepared in Comparative Example 1 were characterized by PXRD spectra, respectively. From the PXRD spectra of the Br-COF material and the H-COF material, it can be seen that the Br-COF material and the H-COF material have the same crystal structure, and the Br-COF material is a single phase material. Figure 1It can be seen that the 2θ peak of the H-COF material at a small angle (2.7°) corresponds to the reflection crystal surface (100), and the 2θ peak at a large angle (25.1°) corresponds to the (001) crystal surface; compared with the H-COF material, the intensity of the Br-COF material at 2.7° is significantly increased, indicating that the crystallinity of the Br-COF material is better.

[0033] The Br-COF material prepared in Example 1 and the H-COF material prepared in Comparative Example 1 were respectively subjected to Fourier transform infrared spectroscopy and ultraviolet-visible light absorption spectrum test, and the test results are shown in Figures 2-3 From Figure 2 it can be seen that the H-COF material and the Br-COF material both have a peak at 1624 cm -1 , which corresponds to the characteristic peak of the imine bond, indicating that the Schiff base polymerization reaction of TTA with TA and Br-TA generates an imine bond. From Figure 3 it can be seen that the ultraviolet-visible absorption range of the Br-COF material is extended to 650 nm, and the absorption range is larger than that of the H-COF material, indicating that the light absorption performance of the Br-COF material is better than that of the H-COF material.

[0034] The Br-COF material prepared in Example 1, the H-COF material prepared in Comparative Example 1, and the Cl-COF material prepared in Comparative Example 2 were respectively used as catalysts for photocatalytic water splitting to prepare hydrogen, and the test results are shown in Figure 4 . Figure 4 The test results show that when the Br-COF material, the H-COF material and the Cl-COF material are used for photocatalytic water splitting to prepare hydrogen, they respectively show hydrogen production rates of 46.1 umol·g -1 ·h -1 , 14.0 umol·g -1 ·h -1 and 19.1 umol·g -1 ·h -1 , the hydrogen production performance of the Br-COF material is improved by 2.3 times compared with the H-COF material, and the hydrogen production performance of the Br-COF material is improved by more than 1.4 times compared with the Cl-COF material.

[0035] Comparative Example 1

[0036] On the basis of Example 1, only Br-TA in step (1) was replaced by TA (terephthalaldehyde), and other steps and conditions were the same as those of Example 1, and a triazine-based covalent organic framework material without halogen atom substitution was obtained, which was simply denoted as H-COF material.

[0037] Comparative Example 2

[0038] On the basis of example 1, only Br-TA in step (1) is replaced by Cl-TA (2-chloro-p-xylyleneglycol), and other steps and conditions are the same as example 1, and the corresponding single-substituted triazine-based covalent organic framework material of chlorine atom is obtained, which is abbreviated as Cl-COF material.

[0039] According to the PXRD characterization results, the peak intensity of the Cl-COF material at about 2.7° of 2θ is weaker than that of the H-COF material prepared in Comparative Example 1, indicating that the crystallinity of the Cl-COF material is lower than that of the H-COF material.

[0040] Comparative Example 3

[0041] On the basis of example 1, only 0.5 mL of 1,2-dichlorobenzene and 0.5 mL of n-butanol in step (2) are modified to 0.25 mL of 1,2-dichlorobenzene and 0.75 mL of n-butanol, and other steps and conditions are the same as example 1, and the corresponding single-substituted triazine-based covalent organic framework material of bromine atom is obtained, which is abbreviated as Br-COF-1 material.

[0042] According to the PXRD characterization results, the peak intensity of the Br-COF-1 material at about 2.7° of 2θ is significantly weaker than that of the Br-COF material prepared in example 1, indicating that the crystallinity of the Br-COF-1 material is significantly lower than that of the Br-COF material prepared in example 1. The low crystallinity or amorphous state of the material greatly affects the photoexcitation and separation of carriers, thereby limiting its photocatalytic activity.

[0043] Comparative Example 4

[0044] On the basis of example 1, only 0.5 mL of 1,2-dichlorobenzene and 0.5 mL of n-butanol in step (2) are modified to 0.75 mL of 1,2-dichlorobenzene and 0.25 mL of n-butanol, and other steps and conditions are the same as example 1, and the corresponding single-substituted triazine-based covalent organic framework material of bromine atom is obtained, which is abbreviated as Br-COF-2 material.

[0045] According to the PXRD characterization results, the peak intensity of the Br-COF-2 material at about 2.7° of 2θ is significantly weaker than that of the Br-COF material prepared in example 1, indicating that the crystallinity of the Br-COF-2 material is significantly lower than that of the Br-COF material prepared in example 1.

[0046] In summary, the above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A triazine-based covalent organic framework material for efficient visible light driven water splitting for hydrogen production, characterized in that: The structural formula of the triazine-based covalent organic framework material is as follows: The triazine-based covalent organic framework material is formed by solvothermal polymerization of 2-bromoparadimaldehyde and 4,4',4"-(1,3,5-triazine-2,4,6-triyl) triphenylamine under the catalysis and vacuum condition; The mixed solvent of 1,2-dichlorobenzene and n-butanol is selected as the reaction solvent, and acetic acid is selected as the catalyst. In the reaction solvent, the volume ratio of 1,2-dichlorobenzene to n-butanol is (0.9-1.1):

1.

2. The triazine-based covalent organic framework material for efficient visible light driven water splitting to produce hydrogen according to claim 1, characterized in that: The concentration of acetic acid in the reaction solvent is 0.5-0.7 mol / L.

3. The triazine-based covalent organic framework material for efficient visible light driven water splitting to produce hydrogen according to claim 2, characterized in that: 2-bromoparadimaldehyde and 4,4',4"-(1,3,5-triazine-2,4,6-triyl) triphenylamine are mixed according to the stoichiometric ratio, and the concentration of 2-bromoparadimaldehyde in the reaction solvent is 0.08-0.1 mol / L. 4.The triazine-based covalent organic framework material for efficient visible light driven water splitting to produce hydrogen according to claim 1, characterized in that: The temperature of the solvothermal polymerization reaction is 100-120 DEG C, and the time is 72-120 h.

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