A composite I-COFs / TiO2 photocatalyst and its preparation method

Abstract

This invention discloses a composite I-COFs / TiO2 photocatalyst and its preparation method, belonging to the field of photocatalysis technology. The method involves first constructing a covalent organic framework containing electron-deficient structures and highly dispersed hydroxyl groups using a Schiff base reaction combined with an intermolecular dehydration reaction of boric acid groups. Then, under condensation reaction conditions, titanium dioxide binds water to convert into titanic acid, thereby forming a composite I-COFs / TiO2 photocatalyst with both a conjugated system and electron-deficient structures. The photocatalyst prepared by this invention can be used for photocatalytic water splitting to produce hydrogen, exhibiting excellent hydrogen production rate and stability.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis, and more particularly to a composite I-COFs / TiO2 photocatalyst and its preparation method. Background Technology

[0002] With the rapid development of the global economy, people's demand for energy is increasing. The gradual depletion of traditional fossil fuels inevitably leads to two thorny issues: first, as non-renewable resources, the consumption of traditional fossil fuels will result in an energy crisis; second, the generation of greenhouse gases such as carbon dioxide and sulfur dioxide will inevitably harm the environment. In view of this, hydrogen energy, as a clean and renewable energy source, will solve these problems. Photocatalytic water splitting technology, using a photocatalyst, utilizes a renewable light source to decompose pollution-free water to produce hydrogen, aligning with sustainable development strategies.

[0003] Currently, many inorganic semiconductors, including indium zinc sulfide, titanium dioxide, and cadmium sulfide, have been applied to photocatalytic water splitting for hydrogen production. However, these inorganic photocatalysts still have some limitations, such as difficulty in bandgap tuning, difficulty in structure tuning, and poor visible light response. Currently, porous materials (metal-organic frameworks, covalent organic frameworks, and reduced graphene oxide) are widely studied as photocatalysts. However, simple porous materials also have traditional drawbacks such as poor stability, high photogenerated electron-hole recombination rates, and bandgap mismatch. Therefore, seeking novel photocatalysts with high-speed photogenerated carriers, suppression of charge recombination, and high stability has become a research focus.

[0004] Covalent organic frameworks (COFs) are porous structures formed by organic molecules linked by covalent bonds. Due to their advantages such as tunable and controllable structure, large specific surface area, high stability, and ease of functionalization, COFs have great potential in membrane separation, photoelectrocatalysis, organic synthesis, and drug delivery. Patent CN113512164B describes a post-modification synthesis method to prepare a snowflake-shaped biomimetic covalent organic framework, which was then applied to photocatalytic water splitting for hydrogen production, exhibiting good performance. Patent CN112588323B discloses a method for preparing a bulk porous PdCl / COF material, using K₂PdCl₄ to directly coordinate with COFs, effectively improving the COF material's response to visible light and electron transport capabilities. Patent CN114085388B invented a covalent organic framework material containing oxadiazole linker units. The post-modification strategy not only broadens the absorption range of COFs in the visible light region but also better promotes the separation and transport of photogenerated carriers, thereby improving the performance of photocatalytic water splitting for hydrogen production. However, due to the lack of synergistic effects from a single covalent organic framework, there is still significant room for improvement in valence band and conduction band modulation, and the stability of the monomer needs further improvement. Meanwhile, there is currently limited research on ionic covalent organic frameworks. By synergistically leveraging the ease of electron transfer, easily modulated band gap, and good stability of inorganic semiconductors, and starting from the structure, accelerating the generation of photogenerated carriers and suppressing charge recombination, this approach shows promising application prospects in photocatalytic water splitting for hydrogen production. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing a composite I-COFs / TiO2 photocatalyst to solve the above-mentioned problems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a composite I-COFs / TiO2 photocatalyst, comprising the following steps:

[0007] (1) Boric acid compounds and triamine compounds were added to a binary mixed solvent and a clear solution was formed under ultrasonic conditions. The solution was then heated and reacted under vacuum. After the reaction was completed, the solution was centrifuged in an organic solvent to obtain a yellow powder. After drying, hydroxyl-type covalent organic framework H-COFs were obtained. The hydroxyl structure provides the basis for subsequent polycondensation reactions.

[0008] (2) The hydroxyl-type covalent organic framework H-COFs obtained in step (1) and titanium dioxide are added to a ternary mixed solvent and a clear solution is obtained by ultrasonic vibration;

[0009] (3) Under the protection of an inert gas, a weak acid solution is added dropwise to the clear solution obtained in step (2) to cause a condensation reaction. The hydroxyl-type covalent organic framework H-COFs is converted into the ionic covalent organic framework I-COFs. After the reaction is completed, the solution is poured into water to quench the reaction. The product is extracted with an extractant, the organic phase is separated, a dehydrating agent is added to the organic phase to dehydrate it, centrifuge it, and vacuum dry it to remove the water of crystallization. Then, it is extracted by Soxhlet extraction and dried to obtain the composite catalyst I-COFs / TiO2.

[0010] The above preparation method can yield a novel composite I-COFs / TiO2 photocatalyst. This invention first utilizes a Schiff base reaction combined with intermolecular dehydration of borate groups to construct a novel hydroxyl-type covalent organic framework (H-COFs) containing an electron-deficient borate ring and a highly dispersed hydroxyl structure. The hydroxyl structure provides the basis for subsequent polycondensation reactions. Secondly, under polycondensation reaction conditions, titanium dioxide binds water to form titanic acid, which facilitates the removal of hydrogen halides between molecules in the polycondensation reaction, realizing the transformation from H-COFs to an ionic covalent organic framework (I-COFs) (the branching transformation process is shown in the figure below), thereby forming a composite I-COFs / TiO2 photocatalyst with both a conjugated system and an electron-deficient structure.

[0011] This invention controls the pore size by altering the growth of side chains on the framework of condensation polymerization molecules. Simultaneously, doping I-COFs with TiO2 can directionally change the valence and conduction band positions, thereby controlling the band gap width. The uniform dispersion of Pt is achieved by utilizing the directional anchoring effect of the composite I-COFs / TiO2 photocatalyst. The principle of branch chain change during the conversion from H-COFs to I-COFs is shown in the following equation:

[0012]

[0013] The photocatalyst prepared in this invention, on the one hand, exhibits electron-deficient properties that promote the generation of photoelectrons; on the other hand, its conjugated system prevents charge recombination. Compared with other traditional photocatalysts, this photocatalyst possesses excellent photoelectrophysicochemical properties such as structural stability, tunable pore size, and easily tunable band gap. Furthermore, this catalyst overcomes the instability inherent in traditional doping, generating a new phase interface between I-COFs and TiO2, transitioning from titanic acid to titanium dioxide, thus accelerating the transport and transfer of photogenerated charge carriers. This provides a foundation for the design of novel organic-inorganic composite catalysts and for improving catalytic hydrogen production.

[0014] As a preferred technical solution, in step (1), the boric acid compound is any one of (4-formyl-3-hydroxyphenyl)boronic acid and (4-formyl-3,5-dihydroxyphenyl)boronic acid; the triamine compound is any one of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and pyridine-2,4,6-triamine, and the molar ratio of the boric acid compound to the triamine compound is (1~2):(1~2). This ratio can effectively promote the formation of bond bridges and boric acid rings.

[0015] As a preferred technical solution, in step (1), the binary mixed solvent is any one of 1,4-dioxane / 1,3,5-trimethylbenzene, 1,4-dioxane / N,N-dimethylformamide, and N,N-dimethylformamide / 1,3,5-trimethylbenzene, and the volume ratio of the two solvents in the binary mixed solvent is (1~5):(1~5). This volume ratio can both maximize the dissolution of the reactants and promote mass and heat transfer.

[0016] As a preferred technical solution, in step (1), the heating vacuum reaction conditions are a temperature of 110-130 °C and a time of 24-36 h. This reaction temperature promotes the formation of new bonds to the greatest extent, and the reaction time is obtained through experimental verification.

[0017] As a preferred technical solution, in step (1), the organic solvent is any one or a combination of several of ethanol, 1,4-dioxane and dichloromethane. These solvents are very easy to dissolve the raw materials and have low boiling points, making them easy to dry.

[0018] As a preferred technical solution, in step (2), the molar ratio of the hydroxyl-type covalent organic framework H-COFs to titanium dioxide is (0.5~2):(0.5~2). This ratio has better acidity and fully utilizes the catalytic function of titanium dioxide.

[0019] As a preferred technical solution, in step (2), the ternary mixed solvent is an aromatic halide / ethanol / n-butanol, wherein the aromatic halide is any one of 1,2-dichlorobenzene, 1,2-dibromobenzene, and 1-chloro-2-bromobenzene; the volume ratio of aromatic halide, ethanol and n-butanol is 1:(1~3):(1~5), which can also facilitate the control of morphology under better dissolution conditions.

[0020] As a preferred technical solution, in step (3), the weak acid is any one of phosphoric acid, formic acid, glacial acetic acid, and carbonic acid. These are all weak acids with relatively weak acidity, which can provide suitable acidity for the reaction.

[0021] As a preferred technical solution, in step (3), the condensation reaction temperature is 120~140℃ and the reaction time is 50~72 h; the dehydrating agent is any one of sodium bicarbonate and phosphorus pentoxide; the extractant is any one of petroleum ether, dichloromethane and methanol; the Soxhlet extraction temperature is 50~70℃ and the extraction time is 6~9 h. Using these low-boiling-point solvents for Soxhlet extraction makes it easy to reflux, dissolve small molecules and dry them for post-processing.

[0022] A second objective of this invention is to provide a composite I-COFs / TiO2 photocatalyst prepared by the above method. This catalyst, when used for photocatalytic water splitting to produce hydrogen, exhibits excellent hydrogen production rate and stability.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) In terms of preparation method, the present invention adopts a direct synthesis method combined with a post-modification synthesis method to transform the hydroxyl-type covalent organic framework into an ionic covalent organic framework. In the whole preparation process, titanium dioxide breaks the traditional characteristic of merely acting as a semiconductor framework, but instead acts as a catalyst to promote the formation of polymerization reaction, effectively accelerating the formation of the ionic covalent organic framework I-COFs / TiO2. In the absence of titanium dioxide, the hydroxyl groups on H-COFs cannot be activated, thus affecting the formation of I-COFs.

[0025] (2) In terms of structural composition, the pore size can be directionally controlled during the transformation of H-COFs into I-COFs; at the same time, the inorganic-organic composite catalyst formed by the combination of I-COFs and TiO2: on the one hand, the Schiff base reaction is used to cleverly reserve -OH on the ring to provide a basis for subsequent reactions; on the other hand, the water molecules in the solution are partially converted into titanium dioxide to catalyze the condensation reaction of titanate, and the hydroxyl-type covalent organic framework (H-COFs) is converted into the ionic covalent organic framework (I-COFs), realizing close contact at the phase interface and accelerating charge transfer;

[0026] (3) In terms of catalytic performance, the ionic covalent organic framework I-COFs / TiO2 exhibits a highly efficient synergistic effect: on the one hand, the space is a benzene ring forming a conjugated system, which is conducive to suppressing charge recombination; on the other hand, halogens, as electron-deficient substances, can play the role of absorbing electrons in the photocatalytic hydrogen evolution process, promoting the generation of photogenerated electrons. Therefore, the catalyst has a very high catalytic efficiency and is very stable. Attached Figure Description

[0027] Figure 1 This is the gas phase spectrum of Example 1;

[0028] Figure 2 This is a SEM image of the catalyst from Example 2;

[0029] Figure 3 This is a SEM image of the catalyst in Comparative Example 2. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. Example

[0031] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0032] (1) Weigh 0.498 g of (4-formyl-3-hydroxyphenyl)boric acid and 0.354 g of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and add them to a mixed solvent of 3 mL of 1,4-dioxane and 3 mL of 1,3,5-trimethylbenzene. Under ultrasonic conditions, a clear solution is formed. Under vacuum conditions, the reaction is carried out at 110 °C for 36 h. After the reaction is completed, the solution is washed three times with 1,4-dioxane and three times with ethanol and centrifuged to obtain a yellow powder. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0033] (2) Measure 1 mL of 1,2-dichlorobenzene, 3 mL of ethanol and 4 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution from the beaker and add it into a pressure-resistant tube. Weigh 0.200 g of hydroxyl-type covalent organic framework material and 0.079 g of titanium dioxide obtained in step (1) and add them into the pressure-resistant tube. Obtain a clear solution by ultrasonic vibration.

[0034] (3) Under nitrogen protection, 0.5 mL of 1% phosphoric acid solution was added dropwise to the above clear solution, and the reaction was carried out at 120℃ for 72 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with petroleum ether to separate the organic phase. The organic phase was dehydrated with sodium bicarbonate, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The solution was then extracted by Soxhlet extraction at 50℃ for 9 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0035] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (a TCD thermal conductivity detector, with high-purity argon as the carrier gas), and samples were taken every 30 min.

[0036] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5462 μmol / g·h, and the stability reached 94% after 16h of cycling stability test.

[0037] Comparative Example 1:

[0038] Compared with Example 1 above, this comparative example is the same as Example 1 except that 0.5 mL of phosphoric acid solution is not added to the clear solution during the condensation reaction in step (3).

[0039] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this comparative example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas; ideally, complete chromatographic conditions should be available). Samples were taken every 30 min.

[0040] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 2138 μmol / g·h, and the stability was 63% after 16h cycling. In the comparative example, because phosphoric acid solution was not added during the condensation reaction, the conversion of titanium dioxide to titanate could not be achieved, thus inhibiting the formation of I-COFs. Furthermore, the phase interface was not easily formed, which was detrimental to the formation of photogenerated carriers, thus suppressing the photocatalytic performance. Moreover, the two components were easily separated during the reaction, affecting stability as well. Example

[0041] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0042] (1) Weigh 0.546 g of (4-formyl-3,5-dihydroxyphenyl)boric acid and 0.354 g of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and add them to a mixed solvent of 1 mL of 1,4-dioxane and 5 mL of N,N-dimethylformamide. Under ultrasonic conditions, a clear solution is formed, and the reaction is carried out at 130 °C for 24 h under vacuum. After the reaction is completed, the solution is washed three times with 1,4-dioxane and three times with ethanol, and centrifuged to obtain a yellow powder. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0043] (2) Measure 1 mL of 1,2-dichlorobenzene, 2 mL of ethanol and 3 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution from the beaker and add it into a pressure-resistant tube, weigh 0.205 g of hydroxyl-type covalent organic framework material and 0.158 g of titanium dioxide into the pressure-resistant tube, and obtain a clear solution by ultrasonic vibration;

[0044] (3) Under argon protection, 0.5 mL of 1% formic acid solution was added dropwise to the above clear solution. The reaction was carried out at 120℃ for 72 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with dichloromethane to separate the organic phase. The organic phase was dehydrated with sodium bicarbonate, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The composite catalyst (I-COFs / TiO2) was then extracted by Soxhlet extraction at 50℃ for 6 h and dried at 60℃. The scanning electron microscope image is shown below. Figure 2 As shown.

[0045] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0046] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5633 μmol / g·h, and the stability reached 93% after 16h of cycling stability test.

[0047] Comparative Example 2:

[0048] Compared with Example 2, step (3) of this comparative example is as follows:

[0049] Under argon protection, 0.5 mL of 1% formic acid solution was added dropwise to the above clear solution, and the reaction was carried out at 120℃ for 72 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with dichloromethane, filtered, centrifuged, and dried under vacuum at 60℃. The solution was then extracted by Soxhlet extraction at 50℃ for 6 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0050] That is, after separating the organic phase, no dehydrating agent is used, and the rest is the same as in Example 2.

[0051] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this comparative example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0052] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 3712 μmol / g·h, and the stability after 16h cycling was 58%. Compared with Example 2, because no dehydrating agent was added during the catalyst post-treatment process, only drying was performed, which could not guarantee the conversion of titanic acid back to titanium dioxide. A layer of titanic acid existed at the interface between I-COFs and TiO2, with poor binding force, failing to exert a synergistic effect. Figure 3 As shown, the passage of photogenerated carriers is suppressed, which in turn reduces the photocatalytic performance and affects stability. Example

[0053] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0054] (1) Weigh 0.498 g of (4-formyl-3-hydroxyphenyl)boric acid and 0.124 g of pyridine-2,4,6-triamine and add them to a mixed solvent of 1 mL N,N-dimethylformamide and 5 mL 1,3,5-trimethylbenzene. Under ultrasonic conditions, a clear solution is formed, and the reaction is carried out at 130 °C under vacuum for 30 h. After the reaction is completed, the solution is washed three times with dichloromethane and three times with ethanol, and centrifuged to obtain a yellow powder. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0055] (2) Measure 1 mL of 1,2-dibromobenzene, 3 mL of ethanol and 5 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution from the beaker and add it into a pressure-resistant tube, weigh 0.263 g of hydroxyl-type covalent organic framework material and 0.080 g of titanium dioxide into the pressure-resistant tube, and obtain a clear solution by ultrasonic vibration;

[0056] (3) Under argon protection, 0.5 mL of 1% glacial acetic acid solution was added dropwise to the above clear solution. The reaction was carried out at 140℃ for 60 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with methanol to separate the organic phase. The organic phase was then dehydrated with sodium bicarbonate, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The solution was then extracted by Soxhlet extraction at 70℃ for 8 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0057] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0058] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5633 μmol / g·h, and the stability reached 93% after 16h of cycling stability test.

[0059] Example 4:

[0060] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0061] (1) Weigh 0.546 g of (4-formyl-3,5-dihydroxyphenyl)boric acid and 0.124 g of pyridine-2,4,6-triamine and add them to a mixed solvent of 5 mL of 1,4-dioxane and 1 mL of 1,3,5-trimethylbenzene. Under ultrasonic conditions, a clear solution is formed, and the reaction is carried out at 130 °C for 24 h under vacuum. After the reaction is completed, the solution is washed three times with 1,4-dioxane and three times with ethanol, and centrifuged to obtain a yellow powder. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0062] (2) Measure 1 mL of 1-chloro-2-bromobenzene, 3 mL of ethanol and 3 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution from the beaker and add it into a pressure-resistant tube, weigh 0.173 g of hydroxyl-type covalent organic framework material and 0.040 g of titanium dioxide and add them into the pressure-resistant tube, and obtain a clear solution by ultrasonic vibration;

[0063] (3) Under argon protection, 0.5 mL of 1% (w / w) carbonic acid solution was added dropwise to the above clear solution. The reaction was carried out at 120℃ for 72 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with dichloromethane to separate the organic phase. The organic phase was then dehydrated with sodium bicarbonate, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The solution was then extracted by Soxhlet extraction at 50℃ for 7 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0064] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0065] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5981 μmol / g·h, and the stability reached 91% after 16h of cycling stability test.

[0066] Example 5:

[0067] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0068] (1) Weigh 0.498 g of (4-formyl-3-hydroxyphenyl)boric acid and 0.124 g of pyridine-2,4,6-triamine and add them to a mixed solvent of 3 mL of 1,4-dioxane and 3 mL of N,N-dimethylformamide. Under ultrasonic conditions, a clear solution is formed. The reaction is carried out under vacuum at 120 °C for 24 h. After the reaction is completed, the solution is washed three times with 1,4-dioxane and three times with dichloromethane. After centrifugation, a yellow powder is obtained. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0069] (2) Measure 1 mL of 1,2-dibromobenzene, 3 mL of ethanol and 4 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution into a pressure-resistant tube using a graduated cylinder, weigh 0.263 g of hydroxyl-type covalent organic framework material and 0.316 g of titanium dioxide into the pressure-resistant tube, and obtain a clear solution by ultrasonic vibration;

[0070] (3) Under argon protection, 0.5 mL of 1% phosphoric acid solution was added dropwise to the above clear solution, and the reaction was carried out at 130℃ for 62 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with dichloromethane to separate the organic phase. The organic phase was dehydrated with sodium bicarbonate, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The solution was then extracted by Soxhlet extraction at 70℃ for 6 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0071] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0072] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5548 μmol / g·h, and the stability reached 92% after 16h of cycling stability test.

[0073] Example 6:

[0074] A composite I-COFsTiO2 photocatalyst, the preparation method of which is as follows:

[0075] (1) Weigh 0.546 g of (4-formyl-3,5-dihydroxyphenyl)boric acid and 0.354 g of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and add them to a mixed solvent of 4 mL of 1,4-dioxane and 2 mL of N,N-dimethylformamide. Under ultrasonic conditions, a clear solution is formed. The reaction is carried out under vacuum at 120 °C for 36 h. After the reaction is completed, the solution is washed three times with 1,4-dioxane and three times with dichloromethane. After centrifugation, a yellow powder is obtained. After drying, a hydroxyl-type covalent organic framework (H-COFs) is obtained.

[0076] (2) Measure 1 mL of 1-chloro-2-bromobenzene, 3 mL of ethanol and 2 mL of n-butanol into a beaker using a graduated cylinder, stir with a glass rod to form a homogeneous solution, measure 5 mL of the solution from the beaker and add it into a pressure-resistant tube, weigh 0.410 g of hydroxyl-type covalent organic framework material and 0.158 g of titanium dioxide into the pressure-resistant tube, and obtain a clear solution by ultrasonic vibration;

[0077] (3) Under argon protection, 0.5 mL of 1% glacial acetic acid solution was added dropwise to the above clear solution. The reaction was carried out at 140℃ for 50 h. After the reaction was completed, the solution was poured into water to quench the reaction. The organic phase was extracted three times with methanol to separate the organic phase. The organic phase was then subjected to phosphorus pentoxide to absorb water, filtered, centrifuged, and vacuum dried at 60℃ to remove the water of crystallization. The solution was then extracted by Soxhlet extraction at 60℃ for 8 h and dried at 60℃ to obtain the composite catalyst (I-COFs / TiO2).

[0078] Evaluation conditions: To analyze the photocatalytic water splitting hydrogen production performance of the catalyst, 50 mg of the catalyst prepared in this example was dispersed in 90 mL of water, and 10 mL of triethanolamine and 0.2 mL of H2PtCl6 (3 wt%) were added dropwise. The mixture was sonicated for 30 min under light-protected conditions, and then placed in a reactor. The reactor was then connected to a gas circulation system, and the reaction system was evacuated using a vacuum pump. The system was irradiated under a 300 W xenon lamp with a 420 nm cutoff wavelength filter. The amount of hydrogen produced was monitored online using a gas chromatograph (using a TCD thermal conductivity detector and high-purity argon as the carrier gas), and samples were taken every 30 min.

[0079] The results showed that the hydrogen production rate of the composite I-COFs / TiO2 photocatalyst was 5742 μmol / g·h, and the stability reached 93% after 16h of cycling stability test.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite I-COFs / TiO2 photocatalyst, characterized in that, Includes the following steps: (1) Boric acid compounds and triamine compounds were added to a binary mixed solvent and a clear solution was formed under ultrasonic conditions. The solution was then heated and reacted under vacuum. After the reaction was completed, the solution was centrifuged in an organic solvent to obtain a yellow powder. The powder was then dried to obtain hydroxyl-type covalent organic framework H-COFs. (2) The hydroxyl-type covalent organic framework H-COFs obtained in step (1) and titanium dioxide are added to a ternary mixed solvent and a clear solution is obtained by ultrasonic vibration; (3) Under the protection of an inert gas, a weak acid solution is added dropwise to the clear solution obtained in step (2) to cause a condensation reaction. The hydroxyl-type covalent organic framework H-COFs is converted into the ionic covalent organic framework I-COFs. After the reaction is completed, the solution is poured into water to quench the reaction. The product is extracted with an extractant, the organic phase is separated, a dehydrating agent is added to the organic phase to dehydrate it, centrifuge it, and vacuum dry it to remove the water of crystallization. Then, it is extracted by Soxhlet extraction and dried to obtain the composite catalyst I-COFs / TiO2. In step (1), the boric acid compound is either (4-formyl-3-hydroxyphenyl)boronic acid or (4-formyl-3,5-dihydroxyphenyl)boronic acid; the triamine compound is either 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine or pyridine-2,4,6-triamine.

2. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, The molar ratio of the boric acid compound to the triamine compound is (1~2):(1~2).

3. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (1), the binary mixed solvent is any one of 1,4-dioxane / 1,3,5-trimethylbenzene, 1,4-dioxane / N,N-dimethylformamide, and N,N-dimethylformamide / 1,3,5-trimethylbenzene, and the volume ratio of the two solvents in the binary mixed solvent is (1~5):(1~5).

4. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (1), the heating vacuum reaction conditions are a temperature of 110-130 °C and a time of 24-36 h.

5. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (1), the organic solvent is any one or a combination of several of ethanol, 1,4-dioxane, and dichloromethane.

6. The method for preparing the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (2), the molar ratio of the hydroxyl-type covalent organic framework H-COFs to titanium dioxide is (0.5~2):(0.5~2).

7. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (2), the ternary mixed solvent is an aromatic halide / ethanol / n-butanol, wherein the aromatic halide is any one of 1,2-dichlorobenzene, 1,2-dibromobenzene, and 1-chloro-2-bromobenzene; the volume ratio of aromatic halide, ethanol and n-butanol is 1:(1~3):(1~5).

8. The method for preparing the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (3), the weak acid is any one of phosphoric acid, formic acid, glacial acetic acid, and carbonic acid.

9. The preparation method of the composite I-COFs / TiO2 photocatalyst according to claim 1, characterized in that, In step (3), the condensation reaction temperature is 120~140℃ and the reaction time is 50~72 h; the extractant is any one of petroleum ether, dichloromethane, and methanol; the dehydrating agent is any one of sodium bicarbonate and phosphorus pentoxide; the Soxhlet extraction method has an extraction temperature of 50~70℃ and an extraction time of 6~9 h.

10. The composite I-COFs / TiO2 photocatalyst prepared by the method of any one of claims 1 to 9.

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