Preparation method and application of covalent organic framework photocatalytic material rich in Se element

Abstract

The invention discloses a preparation method and application of a covalent organic framework photocatalytic material rich in Se element. The method comprises the following steps: (1) preparing an amine monomer (PB) and an aldehyde monomer (BS) through a coupling reaction; and (2) carrying out ultrasonic dispersion and freeze thawing degassing on PB and BS in a mixed solvent, and synthesizing BS-PB-COF through solvothermal reaction. According to the material, based on the synergistic effect of a conjugated skeleton and selenium active sites, the visible light absorption capacity and the photon-generated carrier separation efficiency are remarkably improved. The method adopts a mild solvothermal reaction system, avoids high-temperature and high-pressure conditions, has the characteristics of simple and convenient process, low energy consumption and environmental protection, and is suitable for large-scale production. The obtained BS-PB-COF material shows excellent activity in production of hydrogen peroxide (H2O2) through seawater photocatalysis, the performance of the BS-PB-COF material is remarkably superior to that of a similar COF photocatalyst, and an efficient solution is provided for green chemical synthesis and seawater resource utilization.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor photocatalytic materials, and particularly relates to a preparation method and application of a covalent organic framework photocatalytic material rich in Se element. Background Art

[0002] Hydrogen peroxide (H2O2), as a key oxidant, is widely used in the chemical industry, environmental governance, and medical fields. Traditional preparation methods rely on industrial synthesis under high temperature and high pressure, which have problems such as high energy consumption, environmental pollution, and harsh reaction conditions, and there is an urgent need to develop new preparation methods that are efficient, green, and low-cost.

[0003] Photocatalytic production of H2O2 has attracted much attention due to its green characteristics. This process uses light energy to excite semiconductor materials to generate electron-hole pairs, driving the water decomposition reaction to produce H2O2. Covalent organic framework materials (COF) have become a research hotspot for new photocatalysts due to their excellent structural regulation and photocatalytic activity. COF materials have a highly ordered pore structure and a large specific surface area, which are suitable for gas adsorption and catalytic reactions, and have great potential in photocatalytic production of H2O2.

[0004] However, existing COF materials have many problems: the synthesis process is complex and costly, restricting large-scale production; poor stability and slow reaction rate limit practical applications; and the selectivity and product distribution in photocatalytic reactions are affected by various factors such as light source intensity and reaction environment, and controlling these factors to improve efficiency still faces challenges.

[0005] In summary, developing an efficient, green, and low-cost method for preparing hydrogen peroxide, especially optimizing the preparation process and performance of covalent organic framework materials, has important practical significance and broad application prospects. Summary of the Invention

[0006] Aiming at the problems of low yield, long process, relatively serious pollution, or high cost existing in the prior art, the present invention provides a preparation method and application of a covalent organic framework photocatalytic material rich in Se element.

[0007] The technical solution adopted by the present invention is as follows: A preparation method of a covalent organic framework photocatalytic material rich in Se element, comprising the following steps: S1. Preparation of amine monomer (PB): 1,4-dibromobenzene and 4-aminophenylboronic acid pinacol ester are refluxed in a mixed solvent of 1,4-dioxane and water under an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, potassium carbonate is added; after the reaction is completed, it is extracted, dried, and purified by column chromatography to obtain 4,4'-diaminobiphenyl, denoted as PB; S2. Preparation of aldehyde monomer (BS): Dissolve 4,7-dibromo-2,1,3-benzoselenadiazole and 3,5-diformylphenylboronic acid pinacol ester in a mixed solvent of 1,4-dioxane and water, use tetrakis(triphenylphosphine)palladium as the catalyst and potassium carbonate as the base, and carry out a coupling reaction under a nitrogen atmosphere; Wash and dry the reaction product to obtain 5,5'-(benzo[c][1,2,5]selenadiazole-4,7-diyl)diisophthalaldehyde, denoted as BS; S3. Synthesis of BS-PB-COF: Mix PB obtained in step S1 and BS obtained in step S2 at a molar ratio of 1-3:1, add a mixed solvent, after ultrasonic dispersion and freeze-thaw degassing, react at 110-130 °C for 50-80 hours in a sealed environment; After washing and drying the obtained precipitate, yellow powdery BS-PB-COF is obtained.

[0008] Furthermore, in step S1, the molar ratio of 1,4-dibromobenzene to 4-aminophenylboronic acid pinacol ester is 1:1.5-4, preferably 1:2-3, and the dosage of tetrakis(triphenylphosphine)palladium is 0.5%-1% of the total molar amount of the reactants.

[0009] Furthermore, in step S1, the reflux reaction time is 10-30 hours, preferably 12-24 hours.

[0010] Furthermore, in step S2, the coupling reaction temperature is 80-120 °C and the time is 18-30 hours.

[0011] Furthermore, in step S2, the washing is carried out successively with water, methanol, toluene and chloroform for 2-5 times, preferably 3-4 times.

[0012] Furthermore, in step S3, the mixed solvent is a mixed solvent composed of n-butanol, o-dichlorobenzene and aqueous acetic acid solution, and the volume ratio of n-butanol, o-dichlorobenzene to aqueous acetic acid solution is 7-10:1:1.

[0013] Furthermore, the concentration of the aqueous acetic acid solution is 3-9 mol / L.

[0014] Furthermore, in step S3, the ultrasonic dispersion time is 1-5 minutes, preferably 2-3 minutes.

[0015] Furthermore, in step S3, the freeze-thaw degassing includes at least 2 freeze-pump-thaw cycles in a liquid nitrogen bath, preferably 2-5 times.

[0016] Furthermore, in step S3, the washing is carried out successively with tetrahydrofuran and acetone.

[0017] The above-mentioned covalent organic framework photocatalytic material rich in Se elements is used for photocatalytic production of hydrogen peroxide in seawater and exhibits excellent photocatalytic activity.

[0018] The beneficial effects of the present invention are as follows: (1) The present invention uses a solvothermal reaction to prepare a covalent organic framework material (COF), avoiding the complex conditions of high temperature and high pressure in traditional methods. The process operation is simple and the post-treatment steps are streamlined. By means of a mild reaction system (such as a mixed solvent of n-butanol / o-dichlorobenzene) combined with a low-temperature degassing and sealing technology, the energy consumption and equipment requirements are significantly reduced, realizing a green and environmentally friendly synthesis process, which is suitable for large-scale production.

[0019] (2) The Se element-rich BS-PB-COF material prepared by the present invention, due to the synergistic effect of the unique conjugated system and Se active sites, exhibits excellent visible light absorption ability and high separation efficiency of photo-generated carriers, and the rate of generating H2O2 in a seawater environment is as high as 3057.17 μmol·g -1 ·h -1 , which is significantly better than most of the similar COF photocatalysts.

[0020] (3) The introduction of selenium element and the conjugated framework design in the materials of the present invention not only enhance the photocatalytic activity, but also endow it with chemical stability and controllability. This characteristic makes it show broad application prospects in the fields of photocatalytic production of H2O2, seawater resource utilization, etc. At the same time, the raw materials are easily available and the synthesis cost is low, further improving the technical economy. Brief Description of the Drawings

[0021] Figure 1 XRD patterns of BS-PB-COF and BS-MB-COF obtained in Example 1, which prove the successful synthesis of COF.

[0022] Figure 2 Scanning electron microscope (SEM) image of BS-PB-COF obtained in Example 1, showing that the prepared BS-PB-COF is strip-columnar.

[0023] Figure 3 Fourier transform infrared spectra of BS-PB-COF and BS-MB-COF obtained in Example 1, showing the disappearance of the absorption peak of aldehyde group and the formation of imine bond.

[0024] Figure 4 Photocatalytic H2O2 production rate diagrams of BS-PB-COF and BS-MB-COF obtained in Example 1 under visible light irradiation, and BS-PB-COF shows excellent photocatalytic activity.

[0025] Figure 5 Photocurrent response test diagrams of BS-PB-COF and BS-MB-COF obtained in Example 1, showing the strong ability of BS-PB-COF in light absorption. Detailed Embodiments

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0027] Example 1 Step 1, synthesis of amine monomer: Dissolve 1,4-dibromobenzene (0.55 g, 2.33 mmol) and 4-aminophenylboronic acid pinacol ester (1.29 g, 5.89 mmol) in 1,4-dioxane (8 mL), add potassium carbonate (0.85 g, 6.16 mmol), distilled water (8 mL) and tetrakis(triphenylphosphine)palladium (0.03 g, 0.03 mmol), and reflux the reaction mixture for 18 hours under an argon atmosphere. Subsequently, remove 1,4-dioxane and evaporate under vacuum. The resulting residue is treated with water, extracted with dichloromethane, and dried over anhydrous sodium sulfate. Evaporate the separated organic layer, and the obtained compound is purified by column chromatography using ethyl acetate and petroleum ether as eluents to finally obtain 4,4-diaminobiphenyl (PB).

[0028] Step 2, synthesis of aldehyde monomer: Bubble a mixture of a degassed mixture of 4,7-dibromo-2,1,3-benzoselenadiazole (0.10 g, 0.29 mmol), 3,5-diformylphenylboronic acid pinacol ester (0.21 g, 0.81 mmol), potassium carbonate (0.28 g, 2.04 mmol), 1,4-dioxane (6.0 mL) and H2O (6.0 mL) for 30 minutes, and then add tetrakis(triphenylphosphine)palladium (0.03 g, 0.03 mmol). Heat the resulting mixture to 100 °C under a nitrogen atmosphere and stir for 24 hours. Cool the reactant to room temperature and pour it into 100.0 mL of water. Wash the residue several times with excess water, methanol, toluene and chloroform. Dry at 60 °C to obtain 5,5'-(benzo[c][1,2,5]selenadiazole-4,7-diyl)diisophthalaldehyde (BS).

[0029] Step 3, synthesis of BS-PB-COF: Charge BS (15 mg, 0.04 mmol), PB (19 mg, 0.08 mmol), n-butanol (1.8 mL), o-dichlorobenzene (0.2 mL), and aqueous acetic acid solution (6 M, 0.2 mL) into a Pyrex tube. Ultrasonically treat the Pyrex tube for 3 minutes, and then perform rapid freezing and degassing with three freeze-pump-thaw cycles at 77 K using a liquid nitrogen bath. Seal the Pyrex tube under vacuum and place it in an oven at 120 °C for 3 days. A yellow precipitate is formed, which is separated by filtration and washed with tetrahydrofuran and acetone respectively. Dry the sample in a vacuum drying oven for 12 hours to obtain BS-PB-COF.

[0030] Example 2 Step 1, Synthesis of amine monomer: Dissolve 1,4-dibromobenzene (0.55 g, 2.33 mmol) and 4-aminophenylboronic acid pinacol ester (1.29 g, 5.89 mmol) in 1,4-dioxane (16 mL), add potassium carbonate (0.85 g, 6.16 mmol), distilled water (8 mL), and tetrakis(triphenylphosphine)palladium (0.03 g, 0.03 mmol), and reflux the reaction for 10 hours under an argon atmosphere. Follow the subsequent treatment as in Example 1 to obtain PB.

[0031] Step 2, Synthesis of aldehyde monomer: Control the reaction at 80 °C for 18 hours, wash it with water, methanol, toluene, and chloroform twice each in sequence, and follow the remaining steps as in Example 1 to obtain BS.

[0032] Step 3, Synthesis of BS-PB-COF: The volume ratio of n-butanol, o-dichlorobenzene, and 3 mol / L aqueous acetic acid solution in the mixed solvent is 7:1:1. Ultrasonically disperse for 2 minutes and perform 2 cycles of freeze-thaw degassing. Follow the remaining conditions as in Example 1 to obtain BS-PB-COF.

[0033] Example 3 Step 1, Synthesis of amine monomer: The reaction conditions are the same as in Example 1, but the reflux time is adjusted to 20 hours.

[0034] Step 2, Synthesis of aldehyde monomer: The coupling reaction is carried out at 90 °C for 24 hours, and wash it with water, methanol, toluene, and chloroform three times each.

[0035] Step 3, Synthesis of BS-PB-COF: The volume ratio of n-butanol, o-dichlorobenzene and 6 mol / L acetic acid aqueous solution in the mixed solvent is 8.5:1:1. Ultrasonic dispersion is carried out for 2 minutes, and freeze-thaw degassing is carried out for 3 cycles. The remaining steps are the same as those in Example 1 to obtain BS-PB-COF.

[0036] Example 4 Step 1, synthesis of amine monomer: The reaction conditions are the same as those in Example 1, but the reflux time is extended to 30 hours.

[0037] Step 2, synthesis of aldehyde monomer: The coupling reaction is carried out at 110 °C for 30 hours. When washing, water, methanol, toluene and chloroform are used 4 times in sequence.

[0038] Step 3, synthesis of BS-PB-COF: The volume ratio of n-butanol, o-dichlorobenzene and 9 mol / L acetic acid aqueous solution in the mixed solvent is 10:1:1. Ultrasonic dispersion is carried out for 5 minutes, and freeze-thaw degassing is carried out for 4 cycles. The remaining conditions are the same as those in Example 1 to obtain BS-PB-COF.

[0039] The materials obtained in the above examples were characterized and tested. Taking Example 1 as a typical representative, the experimental results are described as follows: The XRD patterns of BS-PB-COF and BS-MB-COF are as Figure 1 shown. It can be seen from Figure 1 that there is a very sharp absorption peak between 2 - 10°, proving the successful synthesis of COF.

[0040] The scanning electron microscope (SEM) image of BS-PB-COF is as Figure 2 shown. It can be seen from Figure 2 that the prepared BS-PB-COF is strip-columnar.

[0041] The Fourier transform infrared spectra of BS-PB-COF and BS-MB-COF are as Figure 3 shown. It can be seen from Figure 2 that the absorption peak of aldehyde group (1700 cm -1 ) disappears and the formation of imine bond (1627 cm -1 ) occurs.

[0042] The photocatalytic H2O2 production rates of BS-PB-COF and BS-MB-COF under visible light irradiation are as Figure 4 shown. It can be seen from Figure 4 that BS-PB-COF reaches an amazing 3057.17 μmol g -1 h -1, exceeding most of the currently reported COF photocatalysts, exhibits excellent photocatalytic activity.

[0043] The photocurrent response test diagrams of BS-PB-COF and BS-MB-COF are as Figure 5 shown. From Figure 5 it can be seen that BS-PB-COF has a very high response value, indirectly proving its strong ability in light absorption.

[0044] Comparative Example 1 Preparation of Selenium-Free COF The rest is the same as in Example 1, except that: 4,7-dibromo-2,1,3-benzoselenadiazole is replaced by 4,7-dibromo-2,1,3-benzothiadiazole, and other conditions remain unchanged.

[0045] The experimental results show that the H2O2 production rate of the obtained BS-PB-COF (selenium-free) in seawater is 820 µmol·g -1 ·h -1 , significantly lower than 3057 µmol·g -1 ·h -1 of Example 1, proving the decisive role of selenium element.

[0046] Comparative Example 2 High Temperature and High Pressure Synthesis The rest is the same as in Example 1, except that: in S3, the reaction temperature is increased to 200 °C and the pressure is 2 MPa, and other conditions remain unchanged.

[0047] The experimental results show that the H2O2 production rate is 3130 μmol·g -1 ·h -1 , which is similar to that of Example 1, but the energy consumption increases significantly and the equipment requirements are complex, not meeting the principles of green chemistry.

Claims

1. A preparation method of a covalent organic framework photocatalytic material rich in Se element, characterized in that, It includes the following steps: S1. Preparation of amine monomer: 1,4-dibromobenzene and 4-aminophenylboronic acid pinacol ester are refluxed in an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, potassium carbonate added, and in a mixed solvent of 1,4-dioxane and water; after the reaction, it is extracted, dried, and purified by column chromatography to obtain 4,4'-diaminoterphenyl, denoted as PB. S2. Preparation of aldehyde monomer: 4,7-dibromo-2,1,3-benzoselenadiazole and 3,5-diformylphenylboronic acid pinacol ester are dissolved in a mixed solvent of 1,4-dioxane and water, and coupled with tetrakis(triphenylphosphine)palladium as a catalyst and potassium carbonate as a base under a nitrogen atmosphere; the reaction product is washed and dried to obtain 5,5'-(benzo[c][1,2,5]selenadiazole-4,7-diyl)diisophthalaldehyde, denoted as BS. S3. Synthesis of BS-PB-COF: PB obtained in step S1 and BS obtained in step S2 are mixed at a molar ratio of 1 - 3:1, a mixed solvent is added, after ultrasonic dispersion and freeze-thaw degassing, it is reacted at 110 - 130 °C for 50 - 80 hours in a sealed environment; the obtained precipitate is washed and dried to obtain yellow powdery BS-PB-COF.

2. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S1, the molar ratio of 1,4-dibromobenzene to 4-aminophenylboronic acid pinacol ester is 1:1.5 - 4, and the dosage of tetrakis(triphenylphosphine)palladium is 0.5% - 1% of the total molar amount of the reactants.

3. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S1, the reflux reaction time is 15 - 30 hours.

4. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S2, the coupling reaction temperature is 80 - 120 °C and the time is 18 - 30 hours.

5. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S2, the washing is carried out successively with water, methanol, toluene, and chloroform for 2 - 5 times.

6. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S3, the mixed solvent is a mixed solvent composed of n-butanol, o-dichlorobenzene, and acetic acid aqueous solution, and the volume ratio of n-butanol, o-dichlorobenzene to acetic acid aqueous solution is 7 - 10:1:

1.

7. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 6, characterized in that, The concentration of the acetic acid aqueous solution is 3 - 12 mol / L.

8. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S3, the ultrasonic dispersion time is 2 - 5 minutes.

9. The preparation method of the covalent organic framework photocatalytic material rich in Se element according to claim 1, characterized in that, In step S3, the freeze-thaw degassing includes at least 2 freeze-pump-thaw cycles in a liquid nitrogen bath; the washing is carried out successively with tetrahydrofuran and acetone.

10. Application of the covalent organic framework photocatalytic material rich in Se element obtained by the preparation method according to any one of claims 1 to 9 in photocatalytic production of hydrogen peroxide in seawater.

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