[4+3+2] type covalent organic framework material, preparation method and application thereof

Abstract

The present application relates to catalytic material technical field, specifically [4+3+2] type covalent organic framework material and its preparation method and application. The present application is with 4, 4', 4'', 4'''-(pyrene-1, 3, 6, 8-tetrayl) tetraphenylamine, 4, 4', 4''-(1, 3, 5-triazine ring-2, 4, 6-triyl) triphenylaldehyde and 4, 4'-diamino triphenyl as raw material, solvent thermal reaction is carried out in oxygen-free environment, and [4+3+2] type covalent organic framework material is obtained. The present application introduces 4, 4'-diamino triphenyl, realizes the regulation of the polarity, electron delocalization degree and crystallinity of covalent organic framework material at molecular level, thereby effectively improves the charge separation efficiency, improves the photocatalytic hydrogen production performance of [4+3+2] type covalent organic framework material, and solves the technical defects existing in the prior art of introducing triazine and pyrene structure into covalent organic framework material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic materials, in particular to a [4+3+2] type covalent organic framework material and a preparation method and application thereof. BACKGROUND

[0002] At present, developing green, efficient and sustainable energy conversion technology has become a research hotspot. Photocatalytic hydrogen production technology is considered an important direction for the development of future hydrogen energy industry because it can utilize solar energy to decompose water into hydrogen with zero carbon emission and abundant raw materials. However, traditional inorganic photocatalytic materials such as TiO2, CdS and ZnO generally have the problems of narrow light absorption wavelength range, low quantum efficiency, easy corrosion and lack of design flexibility of catalytic center, which greatly limits their practical application.

[0003] Covalent organic framework material is a kind of high crystallinity porous material self-assembled by organic units through covalent bond, which has highly ordered and designed framework structure, large specific surface area and excellent photoelectric performance, and has become a research frontier of new generation photocatalytic materials. In particular, covalent organic framework materials based on donor-acceptor structure design have broad application prospects because they can effectively promote the separation and transmission of photo-generated electrons and holes. However, the main problems of existing covalent organic framework materials are as follows: 1. Limited selection of structure and function units: most of the photocatalytic covalent organic framework materials currently use conventional aromatic units as connecting structures, and there is a lack of effective coordination between functional units, making it difficult to accurately control the light absorption range and electron transport path; 2. Severe recombination of photo-generated carriers: the recombination rate of photo-generated electrons and holes in existing covalent organic framework materials is high, resulting in low photocatalytic efficiency; 3. Insufficient stability of covalent organic framework materials: many covalent organic framework materials are easily degraded under light, heat or acid-base conditions, with short photocatalytic life, which restricts their promotion and application in practical systems.

[0004] Triazine, as a typical electron acceptor unit, is applied to covalent organic framework materials due to its rich nitrogen atoms and strong electron attraction ability, which can regulate the energy band structure of covalent organic framework materials and enhance the electron transport behavior; however, its excessive use can easily lead to low efficiency of skeleton electron separation, which needs to be optimized in cooperation with other structures. Pyrene is a typical large-conjugated rigid planar aromatic structure with good light absorption capacity and stability, which is widely used in the skeleton construction of covalent organic framework materials as an electron donor unit; however, the steric hindrance of pyrene is large, and its excessive introduction can easily cause framework stacking obstacles, affecting the crystallinity and pore connectivity of covalent organic framework materials.

[0005] Therefore, the key to the research breakthrough is to introduce triazine and pyrene structures into the covalent organic framework material to realize efficient matching of structure, function and photocatalytic performance, but there are still the following problems in introducing triazine and pyrene structures into the covalent organic framework material:

[0006] 1. Precise regulation of triazine and pyrene structures in the covalent organic framework material: it is difficult to effectively control the distribution and configuration of triazine and pyrene conjugated units in the skeleton of the covalent organic framework material, which limits the regulation space of the light absorption capacity and carrier migration efficiency of the covalent organic framework material.

[0007] 2. Insufficient separation efficiency of photo-generated electron-hole pairs: the carrier recombination rate is high, and the electron-hole separation is insufficient, which limits the photocatalytic efficiency and activity of the covalent organic framework material.

[0008] 3. Long-term stability problem: the existing covalent organic framework material has the problems of unstable structure and catalytic activity attenuation in continuous photocatalytic reaction, which is difficult to meet the long-term use demand.

[0009] 4. Lack of effective regulation mechanism between molecular structure and electronic behavior: there is a lack of method for targeted regulation of photo-generated carrier behavior at the electronic structure level through molecular design, which limits the improvement of photocatalytic performance of the covalent organic framework material. SUMMARY

[0010] In view of the above technical problems existing in the prior art, the present application provides a [4+3+2] type covalent organic framework material and a preparation method and application thereof. The present application introduces adjustable linear two-position connecting units 4,4'-diaminotriphenyl instead of part of four-position connecting units, and systematically regulates the number of benzene rings in the two-position connecting units, so as to regulate the polarity, electronic delocalization degree and crystallinity of the covalent organic framework material at the molecular level, thereby effectively improving the charge separation efficiency and the photocatalytic hydrogen production performance of the [4+3+2] type covalent organic framework material, providing a new design strategy, and solving the technical defects existing in the prior art of introducing triazine and pyrene structures into the covalent organic framework material.

[0011] In order to achieve the above technical purpose, the present application adopts the following technical scheme:

[0012] The present application protects a preparation method of a [4+3+2] type covalent organic framework material, comprising the following steps:

[0013] 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylaldehyde and 4,4'-diaminotriphenyl are used as raw materials, dispersed in a solvent, and subjected to a solvothermal reaction in an oxygen-free environment to obtain a [4+3+2] type covalent organic framework material.

[0014] Preferably, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylmethanol and 4,4'-diaminotriphenyl is 76:76:62~66. If 4,4'-diaminotriphenyl is too much, excessive crosslinking, the increase of side reactions, the decrease of product purity, the impairment of crystallinity, the increase of defects, the destruction of ordered assembly, the residual of unreacted monomers in the channels, the blockage of channels or the adsorption on the surface, and the decrease of specific surface area; If 4,4'-diaminotriphenyl is too little, the weak electronic delocalization and the poor crystallinity, in terms of weak electronic delocalization, the insufficient conjugation degree, the decrease of photo-induced electron migration efficiency, and the decrease of photocatalytic rate; in terms of poor crystallinity, the weak skeleton rigidity, the formation of disordered structure or low crystallinity structure of [4+3+2] type covalent organic framework material, and the influence of catalytic activity.

[0015] Preferably, the solvent is heated at 115℃~125℃ for 72h.

[0016] Preferably, the solvent is composed of 1,4-dioxane, mesitylene and aqueous acetic acid, and the solvent composition is obtained by hydrogen production experiment screening.

[0017] The application also protects a [4+3+2] type covalent organic framework material prepared by the above preparation method.

[0018] Preferably, in the [4+3+2] type covalent organic framework material, 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine is a four-position connecting unit, 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylmethanol is a three-position connecting unit, and a linear two-position connecting unit 4,4'-diaminotriphenyl is introduced to replace part of the four-position connecting unit to obtain the [4+3+2] type covalent organic framework material.

[0019] The application also protects the application of the [4+3+2] type covalent organic framework material in preparing a visible light water splitting hydrogen production catalyst, and the visible light water splitting hydrogen production catalyst is prepared according to the following steps:

[0020] After the [4+3+2] type covalent organic framework material is dispersed in the ascorbic acid solution, the chloroplatinic acid solution is added, and the visible light water splitting hydrogen production catalyst is obtained by light treatment. The visible light water splitting hydrogen production catalyst is a [4+3+2] type covalent organic framework material loaded with Pt on the surface.

[0021] Preferably, in the [4+3+2] type covalent organic framework material loaded with Pt on the surface, the mass percentage of Pt is 3wt%~5wt%.

[0022] Compared with the prior art, the present application has the beneficial effects that:

[0023] 1、The present application takes 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylaldehyde and two-site connection unit 4,4'-diaminotriphenyl as raw materials, and carries out solvent thermal reaction under an oxygen-free environment. During the solvent thermal reaction process, the amino group of 4,4'-diaminotriphenyl reacts reversibly with the aldehyde group of 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylaldehyde, water molecules are released at the same time, and an imine bond is formed. The imine bond can be reversibly broken / recombined under acidic or heated conditions, promoting defect repair and crystal ordered growth. 4,4'-diaminotriphenyl serves as a linear connection unit, and reacts with the amino groups at two ends with two 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylaldehyde molecules respectively, so as to extend the triazine node into a two-dimensional network structure. At the same time, the 120° bond angle between the benzene rings of 4,4'-diaminotriphenyl helps to lock the square lattice topology and avoid the formation of disordered crosslinking. 4,4'-diaminotriphenyl connects 4,4',4''-(1,3,5-triazin-2,4,6-triyl)triphenylaldehyde to form a basic grid, and 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine serves as a four-node unit to further expand into a three-dimensional interpenetrating or multi-layer structure, so as to obtain a [4+3+2] type covalent organic framework material.

[0024] 2、The preparation of the [4+3+2] type covalent organic framework material of the present application adopts the following innovative strategies: (1) adopting a substoichiometric strategy + structure regulation method, by introducing a linear two-site connection unit 4,4'-diaminotriphenyl with three benzene rings, the structure polarity is adjusted; (2) regulating the electronic structure behavior at the molecular level: by controlling the number of aromatic rings of the linear two-site connection unit 4,4'-diaminotriphenyl, the molecular dipole moment adjustment, built-in electric field enhancement, electron delocalization expansion and exciton binding energy reduction are realized, thereby significantly improving the photocatalytic hydrogen production efficiency.

[0025] 3、The present application realizes the introduction of a linear two-site connection unit, i.e. 4,4'-diaminotriphenyl, which further improves the photocatalytic performance. By introducing linear aniline connection units with different numbers of benzene rings, the molecular polarity, electron delocalization and crystallinity of the [4+3+2] type covalent organic framework material are optimized. This structure regulation method effectively enhances the separation efficiency of photo-generated carriers, reduces the recombination of electrons and holes, and improves the stability of the [4+3+2] type covalent organic framework material.

[0026] The present application carries out substoichiometric strategy and structure regulation: the present application further optimizes the photoelectric performance and catalytic efficiency of the [4+3+2] type covalent organic framework material by regulating the number of benzene rings in the linear aniline connecting unit. The present application particularly protects the application of the linear aniline connecting unit in the synthesis of the [4+3+2] type covalent organic framework material, and regulates the electronic structure, molecular polarity and crystallinity of the [4+3+2] type covalent organic framework material by adjusting the number of benzene rings, so as to improve the photocatalytic hydrogen production performance.

[0027] 4, The present application also protects the specific application of the [4+3+2] type covalent organic framework material in photocatalytic hydrogen production, especially the high hydrogen production efficiency and long-term stability under visible light irradiation, and through optimizing the separation and transmission of photo-generated carriers, the [4+3+2] type covalent organic framework material exhibits excellent performance in photocatalytic reaction.

[0028] 5, The linear aniline connecting unit introduced in the present application precisely regulates the substoichiometry of the triazine monomer and the pyrene monomer, and through this series of innovative means, the photocatalytic hydrogen production performance of the [4+3+2] type covalent organic framework material is improved, and its light absorption capacity, electron separation efficiency and stability are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] In the drawings of the present application, P represents a pyrene monomer, specifically 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraniline; T represents a triazine monomer, specifically 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritolylaldehyde; COF represents a covalent organic framework material, PA represents p-phenylenediamine, BPA represents 4,4'-diaminobiphenyl, and TPA represents 4,4'-diaminotriphenyl.

[0030] Figure 1 It is a chemical reaction equation diagram of PT COF of Comparative Example 1.

[0031] Figure 2 It is a chemical reaction equation diagram of PT-TPA COF of Example 1.

[0032] Figure 3 It is an infrared spectrum diagram, wherein a) is an infrared spectrum diagram of raw materials P, T, PA, BPA and TPA; b) is an infrared spectrum diagram of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1; c) is an infrared spectrum diagram of PT COF of Comparative Example 1.

[0033] Figure 4are X-ray diffraction patterns, wherein a) is the X-ray diffraction pattern of PT COF of Comparative Example 1; b) is the X-ray diffraction pattern of PT-PA COF of Comparative Example 2; c) is the X-ray diffraction pattern of PT-BPA COF of Comparative Example 3; d) is the X-ray diffraction experimental data pattern and X-ray diffraction refinement pattern of PT-TPA COF of Example 1, and the inset in d) is a schematic diagram of the stacking model of PT-TPA COF.

[0034] Figure 5 are plots of exciton binding energy and dipole moment, wherein a) is the plot of exciton binding energy of PT-PA COF of Comparative Example 2, d) is the plot of dipole moment of PT-PA COF of Comparative Example 2, b) is the plot of exciton binding energy of PT-BPA COF of Comparative Example 3, e) is the plot of dipole moment of PT-BPA COF of Comparative Example 3, c) is the plot of exciton binding energy of PT-TPA COF of Example 1, f) is the plot of dipole moment of PT-TPA COF of Example 1; the insets in a), b) and c) are plots of wavelength versus fluorescence emission intensity.

[0035] Figure 6 are plots of electrochemical performance and transient fluorescence spectrum, wherein a) is the plot of electrochemical performance of PT-PA COF of Comparative Example 2, b) is the plot of electrochemical performance of PT-BPA COF of Comparative Example 3, c) is the plot of electrochemical performance of PT-TPA COF of Example 1, d) is the plot of transient fluorescence spectrum of PT-PA COF of Comparative Example 2, e) is the plot of transient fluorescence spectrum of PT-BPA COF of Comparative Example 3, and f) is the plot of transient fluorescence spectrum of PT-TPA COF of Example 1.

[0036] are plots of photocurrent response spectrum and electrochemical impedance, wherein a) is the plot of photocurrent response spectrum of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1; b) is the plot of electrochemical impedance of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1.

[0037] Figure 7 are plots of hydrogen production performance and cycle test, wherein a) is the plot of hydrogen production reaction time course of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, PT-TPA COF of Example 1 and PT COF of Comparative Example 1; b) is the columnar plot of hydrogen production performance of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, PT-TPA COF of Example 1 and PT COF of Comparative Example 1; c) is the cycle test plot of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1.

[0038] Figure 8 are schematic diagrams of band structure of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1.

[0039] Figure 9 Differential pulse voltammograms of the PT-PA COF of Comparative Example 2, the PT-BPA COF of Comparative Example 3, and the PT-TPA COF of Example 1. DETAILED DESCRIPTION

[0040] In order for those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments and drawings, but the embodiments are not limiting of the present application. The following test methods and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0041] In view of the defects in the prior art of introducing triazine and pyrene structures into covalent organic framework materials, the present application overcomes the technical defects, specifically:

[0042] In view of the difficulty in structural regulation in the prior art, the difficulty in precise control of the structure and distribution of triazine and pyrene units, and the problem that the carrier migration rate cannot reach the optimal state, the present application uses 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzenamine as a four-position connecting unit and triazine monomer as a three-position connecting unit, and by introducing a linear two-position connecting unit TPA to replace part of the four-position connecting units, the effective regulation of the structure and unit distribution is achieved, and the purpose of precise regulation of the structure is achieved.

[0043] In view of the problem of severe carrier recombination, insufficient separation efficiency of photo-generated electrons and holes, and more carrier recombination, which limits the improvement of photocatalytic activity in the prior art, the present application introduces a linear two-position connecting unit 4,4'-diamino triphenyl to replace part of the four-position connecting units, regulates the number of benzene rings, enhances the molecular polarity and built-in electric field, promotes the separation of photo-generated carriers, reduces the electron-hole recombination rate, and improves the photocatalytic efficiency.

[0044] In view of the problem of insufficient durability and limited structural stability in the photocatalytic process due to the insufficient stability of the covalent organic framework material in the prior art, which makes it difficult to ensure the performance stability in long-term use, the present application enhances the conjugated electron delocalization and crystallinity of the [4+3+2] type covalent organic framework material by expanding the benzene ring, thereby improving the long-term photocatalytic activity of the framework.

[0045] In view of the problem of insufficient space for improvement in the photocatalytic hydrogen production efficiency of the covalent organic framework material in the prior art, especially the insufficient optimization in terms of molecular polarity, charge transport, and crystallinity, the present application realizes the regular improvement of the photocatalytic hydrogen production performance through molecular structure design and connection mode optimization, thereby providing new strategies and ideas for molecular-level regulation of the photo-generated carrier behavior of the covalent organic framework material.

[0046] The synthetic PT-TPA COF has wide tunability and excellent photocatalytic hydrogen production performance. The electronic structure of the covalent organic framework material is regulated through a molecular design strategy, providing a generalizable structural design framework and synthesis idea for the development of new efficient photocatalytic materials in the future.

[0047] In summary, the present application has significant innovation in structural design, synergistic regulation of functional units, and improvement of photocatalytic performance. By proposing a brand-new molecular construction strategy, the key problems of low electron-hole separation efficiency and poor structural stability of the traditional covalent organic framework material with synergistic introduction of triazine and pyrene structure in photocatalysis are solved, which has a broad practical application prospect.

[0048] The technical solutions of the present application are further studied by using examples and comparative examples, and the specific research methods and results are as follows:

[0049] Example 1

[0050] A preparation method of a [4+3+2] type covalent organic framework material, comprising the following steps:

[0051] 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) benzaldehyde, 17 mg, 0.064 mmol of 4,4'-diaminotriphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL of 6 mol / L aqueous acetic acid, were added into a 15 mL ampoule, and three freeze-pumping-thaw cycles were performed for degassing, then sealed and heated at 120℃ under vacuum for 72h. After the reaction was completed, it was cooled to room temperature to obtain a crude product.

[0052] The crude product was first filtered, then washed with ethanol and N,N-dimethylformamide three times, then extracted with acetone and tetrahydrofuran for 12h, and finally washed with ethanol and deionized water three times, and then placed in a freeze dryer and freeze-dried at-70℃ for 12h to obtain a [4+3+2] type covalent organic framework material, denoted as PT-TPA COF, and the chemical reaction equation is as shown in Figure 2

[0053] Example 2

[0054] A preparation method of a [4+3+2] type covalent organic framework material, comprising the following steps:

[0055] ​Take 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzenamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazin-2,4,6-triyl) benzaldehyde, 17.5 mg, 0.066 mmol of 4,4'-diaminotriphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL of 6 mol / L aqueous acetic acid, together into a 15 mL ampoule, three freeze-pumping-thaw cycles are carried out for degassing, then sealed and heated at 125℃ under vacuum for 72h, after the reaction is completed, it is cooled to room temperature to obtain a crude product.

[0056] The crude product is first suction filtered, then washed with ethanol and N,N-dimethylformamide three times, then Soxhlet extracted with acetone and tetrahydrofuran for 12h, and finally washed with ethanol and deionized water by suction filtration three times, placed in a freeze dryer, and freeze-dried at -70℃ for 12h to obtain a [4+3+2] type covalent organic framework material.

[0057] Example 3

[0058] A method for preparing a [4+3+2] type covalent organic framework material, comprising the following steps:

[0059] Take 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzenamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazin-2,4,6-triyl) benzaldehyde, 16.5 mg, 0.062 mmol of 4,4'-diaminotriphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL of 6 mol / L aqueous acetic acid, together into a 15 mL ampoule, three freeze-pumping-thaw cycles are carried out for degassing, then sealed and heated at 115℃ under vacuum for 72h, after the reaction is completed, it is cooled to room temperature to obtain a crude product.

[0060] The crude product is first suction filtered, then washed with ethanol and N,N-dimethylformamide three times, then Soxhlet extracted with acetone and tetrahydrofuran for 12h, and finally washed with ethanol and deionized water by suction filtration three times, placed in a freeze dryer, and freeze-dried at -70℃ for 12h to obtain a [4+3+2] type covalent organic framework material.

[0061] Comparative Example 1

[0062] A method for preparing a covalent organic framework material, which is the same as the preparation steps of Example 1, except that 4,4'-diaminotriphenyl is not used as a raw material, comprising the following steps:

[0063] Take 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzenamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazin-2,4,6-triyl) benzaldehyde, 7 mg, 0.064 mmol of p-phenylenediamine, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL of 6 mol / L aqueous acetic acid, together into a 15 mL ampoule, three freeze-pump-thaw cycles were carried out for degassing, then sealed and heated at 120°C under vacuum for 72 h. After the reaction was completed, it was cooled to room temperature to obtain a crude product.

[0064] The crude product was first filtered, then washed with ethanol and N,N-dimethylformamide three times, then Soxhlet extracted with acetone and tetrahydrofuran for 12 h, and finally filtered and washed with ethanol and deionized water three times, placed in a freeze dryer, and freeze-dried at -70°C for 12 h to obtain a covalent organic framework material, denoted as PT-PA COF. Figure 1

[0065] Comparative Example 2

[0066] A method for preparing a covalent organic framework material, the preparation steps are the same as those of Example 1, the only difference is that 4,4'-diaminobenzene is replaced by equimolar amount of p-phenylenediamine, including the following steps:

[0067] Take 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrabenzenamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazin-2,4,6-triyl) benzaldehyde, 7 mg, 0.064 mmol of p-phenylenediamine, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL of 6 mol / L aqueous acetic acid, together into a 15 mL ampoule, three freeze-pump-thaw cycles were carried out for degassing, then sealed and heated at 120°C under vacuum for 72 h. After the reaction was completed, it was cooled to room temperature to obtain a crude product.

[0068] The crude product was first filtered, then washed with ethanol and N,N-dimethylformamide three times, then Soxhlet extracted with acetone and tetrahydrofuran for 12 h, and finally filtered and washed with ethanol and deionized water three times, placed in a freeze dryer, and freeze-dried at -70°C for 12 h to obtain a [4+3+2] type covalent organic framework material, denoted as PT-PA COF.

[0069] Comparative Example 3

[0070] ​A preparation method of a covalent organic framework material, the same as the preparation steps of example 1, the only difference is that 4,4'-diaminobenzene is replaced by 4,4'-diaminobiphenyl of equal molar quantity, comprising the following steps:

[0071] 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) benzaldehyde, 12 mg, 0.064 mmol of 4,4'-diaminobiphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, 1 mL, 6 mol / L aqueous acetic acid, are added into a 15 mL ampoule, three freeze-pump-thaw cycles are carried out for degassing, then sealed and heated at 120℃ under vacuum for 72h, after the reaction is completed, it is cooled to room temperature to obtain a crude product.

[0072] The crude product is first suction filtered, then washed with ethanol and N,N-dimethylformamide three times, then Soxhlet extracted with acetone and tetrahydrofuran for 12h, and finally washed with ethanol and deionized water three times by suction filtration, and then placed in a freeze dryer and freeze-dried at-70℃ for 12h to obtain a [4+3+2] type covalent organic framework material, denoted as PT-BPA COF.

[0073] The [4+3+2] type covalent organic framework material with excellent hydrogen production catalytic performance for electrolytic water is prepared in example 1~example 3 of the present application, and the following takes PT-PA COF of comparative example 2, PT-BPA COF of comparative example 3, PT-TPA COF of example 1 and PT COF of comparative example 1 as examples for research, and the specific research methods and results are shown as follows:

[0074] As shown in Figure 3 , it is a Fourier transform infrared spectrum, and the results show that the aldehyde group HC=O stretching vibration characteristic peak of the triazine monomer at 1699cm -1 disappears, and in the COF, a C=N stretching vibration peak appears at 1613cm -1 , indicating that the aldehyde group and the amine group have undergone condensation reaction to form an imine bond. At the same time, as shown in Figure 3 b) and c) figures, the N-H stretching vibration peak is detected in the 3430cm -1 ~3190cm -1 region of PT COF, while in PT-TPA COF, PT-BPA COF and PT-PA COF, the characteristic peak is not observed, which indicates that there is basically no free amine group in the [4+3+2] type COF structure, further verifying the formation of the framework. In addition, the synthesized COF structures are all in the 810cm-1 The PT-TPA COF shows a triazine in-plane stretching vibration peak, indicating that the triazine structural unit is retained, further confirming the stability and integrity of the framework.

[0075] Figure 4 The powder X-ray diffraction test results of the PT-TPA COF show that the PT-TPA COF is highly consistent with the orthorhombic stacking model; in view of the consistent synthesis method of all the COFs, it is presumed that the PT-BPA COF and the PT-PA COF also adopt the orthorhombic stacking mode. The PT COF has four diffraction peaks at 2θ = 4.6°, 10.6°, 14.8° and 22.2°, wherein the broad diffraction peak at 2θ = 22.2° indicates that it is a two-dimensional COF rather than a three-dimensional structure. Compared with the PT COF, the PT-TPA COF, the PT-BPA COF and the PT-PA COF all show 8-9 significant diffraction peaks at different 2θ angles; for the PT-PA COF, the diffraction peaks include 1.9°, 3.8°, 4.4°, 5.6°, 7.6°, 9.8°, 11.3°, 24.2°; for the PT-BPA COF, the diffraction peaks include 1.7°, 3.8°, 4.3°, 5.4°, 7.4°, 9.4°, 11.0°, 25.2°; for the PT-TPA COF, the diffraction peaks include 1.8°, 3.7°, 4.2°, 5.2°, 6.2°, 7.4°, 10.1°, 11.5°, 23.7°; indicating that compared with the PT COF, the PT-TPA COF, the PT-BPA COF and the PT-PA COF have higher crystallinity, which is consistent with the design expectation. In the COF system, since the pyrene has two possible connection modes, only when the amine group along the diagonal direction of the pyrene is condensed, a periodic and ordered COF structure can be formed. However, when the pyrene exists as a connection unit, free amine groups remain in the system, thereby causing disordered reactions in the synthesis process, resulting in structural defects and reducing the crystallinity.

[0076] The present application realizes effective regulation of intramolecular polarity by constructing PT-TPA COF, PT-BPA COF and PT-PA COF with different linear benzene ring connection units, thereby significantly improving the electron-hole separation efficiency and carrier migration performance. Figure 5 The research results show that with the increase of the number of benzene rings in the connection unit, the exciton binding energy is significantly reduced, and the dipole moment is significantly increased, which helps to inhibit the recombination of carriers and improve the effective utilization rate of photo-generated electrons.

[0077] The photocatalytic hydrogen production performance of the COFs was investigated. The specific method involved loading 3 wt% Pt onto the surfaces of PT COF, PT-TPA COF, PT-BPA COF, and PT-PA COF, respectively, and producing hydrogen via photocatalytic reduction. Specifically, 5 mg of PT COF, PT-TPA COF, PT-BPA COF, or PT-PA COF was dispersed in 100 mL of a 0.2 mol / L ascorbic acid solution. The ascorbic acid solution served as a sacrificial agent, consuming the photogenerated holes in the COFs and retaining the photogenerated electrons. Subsequently, 203 L of a 2 g / L chloroplatinic acid solution was added to obtain a reaction system. The reaction system was evacuated and exposed to light for 0.5 h, then evacuated again. Samples were taken every 0.5 h, and hydrogen production was measured using a gas chromatograph to evaluate the photocatalytic hydrogen production performance of the different COFs. Illumination was performed using a 300 W xenon lamp with a wavelength of λ > 420 nm.

[0078] Compared with PT-BPA COF and PT-PA COF, PT-TPA COF exhibits a more negative conduction band position and stronger visible light absorption ability. Its photocatalytic hydrogen production performance is significantly better than the other two materials, and it shows the highest hydrogen production rate under visible light irradiation, which is 10.44 mmol g -1 h -1 , and has the longest carrier lifetime, the strongest photocurrent response and the lowest charge transfer impedance, such as Figure 6 As shown, it fully demonstrates the excellent photoelectric conversion performance.

[0079] The present invention further improves the photocatalytic efficiency by selecting sacrificial agents, optimizing Pt loading and controlling reaction conditions. Figure 7 As shown, the PT-TPA COF exhibits good structural stability and reaction durability during multiple cycles, showing promising industrial application prospects. Compared with the prior art, the PT-TPA COF of the present invention combines high efficiency, stability, and safety, and can be widely used in the field of solar-driven photocatalytic hydrogen production.

[0080] Combine Figures 5 to 7 , and draw the following conclusions:

[0081] PT-PA COF exhibits a certain degree of visible light absorption, with an absorption band edge of approximately 550 nm, a conduction band position of -0.79 V vs. NHE, and an exciton binding energy of 82.9 meV. The photocatalytic hydrogen production rate is 5.20 mmol g -1 h -1 Although electron-hole recombination is more significant, the PT-PA COF has good stability and its performance has basically not decayed after eight cycles, proving that its structure is stable and has practical potential.

[0082] PT-BPA COF has two benzene ring connecting units, and the intramolecular polarity is enhanced compared with PT-PA COF. Its dipole moment is 2.10D, the exciton binding energy is reduced to 63.3meV, and the conduction band position is further negatively shifted to-0.88V vs. NHE, which is conducive to promoting the proton reduction reaction. The photocatalytic hydrogen production rate is increased to 5.64mmol g -1 h -1 , which shows better charge separation and migration ability. The transient fluorescence spectrum shows that the photo-generated carrier lifetime is prolonged, and the electrochemical impedance spectrum shows that the charge transfer resistance is reduced, and the comprehensive performance is better than PT-PA COF.

[0083] PT-TPA COF has the highest intramolecular polarity, and its dipole moment is 2.25D. Its electron-hole separation is the most significant, and the exciton binding energy is further reduced to 53.2meV, and the conduction band potential is-0.97V vs. NHE, which is much higher than the thermodynamic 0V requirement of hydrogen generation. The photocatalytic hydrogen production rate is as high as 10.44mmol g -1 h -1 , which is the highest among the three structures. At the same time, the photo-generated carrier lifetime is the longest, the photocurrent response is the strongest, the charge transfer resistance is the lowest, and the fluorescence emission intensity is the lowest, indicating that its photo-generated carrier recombination rate is the lowest. Surface photovoltage test and transient photovoltage lifetime results further prove its excellent photoelectric performance. PT-TPA COF still maintains stable structure and performance in 8 cycles of test, showing high application prospect.

[0084] The application systematically enhances the intramolecular polarity and photoelectric activity of COF by regulating the structure of linear aromatic amine unit from PA to BPA to TPA, thereby significantly improving the photocatalytic hydrogen production capacity. Among them, PT-TPA COF has the optimal structure, excellent photoelectric performance and strong stability, and is suitable for popularization and application.

[0085] Figure 8 The results show that the conduction band potential of PT-TPA COF is the most negative, which is-0.97V vs. NHE, the conduction band potential of PT-BPA COF is-0.88V vs. NHE, and the conduction band potential of PT-PA COF is-0.79V vs. NHE. The conduction band potential of PT-TPA COF is significantly higher than that of PT-BPA COF and PT-PA COF. Since the conduction band energy levels of all COFs are higher than the reduction potential of 2H + / H2, i.e. 0V vs. NHE, it shows that they can all achieve proton reduction to produce hydrogen in thermodynamics. Among them, PT-TPA COF has the most negative conduction band potential and the optimal light absorption performance, and shows the highest photocatalytic hydrogen production potential.

[0086] Figure 9The differential pulse voltammetry results further confirm that PT-TPA COF has the most negative reduction potential, i.e. -0.958 V vs. NHE, which is significantly higher than -0.880 V vs. NHE of PT-BPA COF and -0.810 V vs. NHE of PT-PA COF. This result is in perfect agreement with the conduction band position in the band structure shown in FIG. 8, further confirming that PT-TPA COF has a stronger thermodynamic reduction driving force, which is directly related to its optimal photocatalytic hydrogen evolution performance. Figure 8

[0087] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.​

Claims

1. A method for preparing a [4+3+2] type covalent organic framework material, characterized in that: The steps include: 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde and 4,4'-diaminoterphenyl are used as raw materials, dispersed together in a solvent, and subjected to solvothermal reaction in an oxygen-free environment to obtain a [4+3+2] type covalent organic framework material; The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde and 4,4'-diaminoterphenyl is 76:76:62~66.

2. The method for preparing a [4+3+2] type covalent organic framework material according to claim 1, characterized in that: The conditions of the solvent thermal reaction are: heating at 115°C~125°C for 72h.

3. The method for preparing a [4+3+2] type covalent organic framework material according to claim 1, characterized in that: The solvent consists of 1,4-dioxane, mesitylene and aqueous acetic acid solution.

4. A [4+3+2] type covalent organic framework material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 3, wherein in the [4+3+2] type covalent organic framework material, 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine is a four-position connecting unit, 4,4',4''-(1,3,5-triazine ring-2,4,6-triyl)tribenzaldehyde is a three-position connecting unit, and a linear two-position connecting unit 4,4'-diaminoterphenyl is introduced to replace part of the four-position connecting units to obtain the [4+3+2] type covalent organic framework material.

5. Use of the [4+3+2] type covalent organic framework material according to claim 4 in the preparation of a visible light photolysis water hydrogen production catalyst, characterized in that: The visible light photolysis water hydrogen production catalyst was prepared according to the following steps: After dispersing the [4+3+2] type covalent organic framework material in an ascorbic acid solution, adding a chloroplatinic acid solution and performing light treatment, a visible light photolysis water hydrogen production catalyst is obtained. The visible light photolysis water hydrogen production catalyst is a [4+3+2] type covalent organic framework material with Pt loaded on the surface.

6. The use according to claim 5, characterized in that In the [4+3+2] type covalent organic framework material with Pt loaded on the surface, the mass percentage of Pt is 3wt%~5wt%.

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