H2N-Cu-MOF / TpPa-1-COF Photocatalyst and Its Preparation Method and Application

Abstract

The present invention relates to an H2N-Cu-MOF / TpPa-1-COF photocatalyst, its preparation method and application. First, H2N-Cu-MOF crystals are prepared by a solvothermal method, and then H2N-Cu-MOF is added to the synthesis process of TpPa-1-COF. Through the Schiff base reaction, H2N-Cu-MOF is tightly combined with TpPa-1-COF to obtain a highly stable and highly active photocatalyst H2N-Cu-MOF / TpPa-1-COF. The catalyst is ultrasonically dispersed in an aqueous solution of ascorbic acid, nitrogen is introduced into the solution to remove oxygen, the reaction system is maintained at 5 °C, and a catalytic reaction is carried out under visible light (λ≥420 nm), so as to achieve efficient catalytic water splitting for hydrogen production under visible light.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic hydrogen production, and particularly relates to an H2N-Cu-MOF / TpPa-1-COF photocatalyst and its application in photocatalytic water splitting for hydrogen production. Background Art

[0002] With the increasing attention of people to energy crisis and environmental pollution problems, finding sustainable clean energy has become one of the most significant challenges faced by human society. Photocatalytic water splitting for hydrogen production is very active in the field of energy research, and it is the most promising strategy to obtain alternative energy. Therefore, people are committed to developing efficient light-induced water splitting and hydrogen evolution systems. Covalent organic framework materials (COFs) and metal-organic framework materials (MOFs) are crystalline porous materials assembled from pure organic molecules or metal ions (metal clusters) and organic ligands. They have the characteristics of high stability, large specific surface area, good crystallinity, and long-range ordered structure, so they are widely used in many fields including photocatalysis. In recent years, the photocatalytic water splitting performance of porous semiconductor materials has been systematically studied. Research shows that most COFs, especially Schiff-base COFs, exhibit strong visible light response ability due to the characteristics of groups and large conjugated systems. However, the serious recombination of photo-generated carriers makes it difficult to further improve their photocatalytic activity. In addition, although most MOF materials have the advantages of structural modification and regulation, their wide band gaps and narrow light absorption ranges further limit their application in photocatalytic hydrogen production. How to improve the carrier separation efficiency to obtain catalytic materials with high activity and good stability is the current research focus, and MOF and COF materials modified by different methods are widely used in the research of the catalytic field. Summary of the Invention

[0003] The purpose of the present invention is to compound H2N-Cu-MOF with TpPa-1-COF by a solvothermal method to obtain a new material H2N-Cu-MOF / TpPa-1-COF. This material has good application prospects in catalytic water splitting for hydrogen production.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: an H2N-Cu-MOF / TpPa-1-COF photocatalyst, by mass ratio, H2N-Cu-MOF:TpPa-1-COF = 1:5.

[0005] Preparation method of H2N-Cu-MOF / TpPa-1-COF photocatalyst, comprising the following steps: fully mixing and grinding phloroglucinol trialdehyde (Tp) and p-phenylenediamine (Pa), adding the obtained mixture and H2N-Cu-MOF crystals into DMF, then adding acetic acid, after ultrasonic homogenization, carrying out solvothermal reaction, centrifuging the obtained reactant, washing successively with tetrahydrofuran and acetone, and drying in vacuum to obtain the target product.

[0006] Preferably, the preparation method of the H2N-Cu-MOF crystals comprises the following steps: adding appropriate amount of Cu(NO3)2·3H2O (copper nitrate trihydrate) and H2N-BDC (2-aminoterephthalic acid) into DMF, ultrasonic homogenization, carrying out solvothermal reaction at 110 °C for 24 h to obtain H2N-Cu-MOF crystals.

[0007] Preferably, the grinding time is 10 min.

[0008] Preferably, the concentration of the acetic acid is 3 M.

[0009] Preferably, the ultrasonic time is 20 min.

[0010] Preferably, the solvothermal reaction is carried out at 120 °C for 72 h.

[0011] Application of the H2N-Cu-MOF / TpPa-1-COF photocatalyst provided by the present invention as a catalyst in photocatalytic water splitting for hydrogen production.

[0012] Preferably, the method is as follows: ultrasonically dispersing the H2N-Cu-MOF / TpPa-1-COF photocatalyst in an aqueous solution dissolved with a sacrificial agent, purging nitrogen into the solution to remove oxygen, keeping the reaction system at 5 °C through a low-temperature constant temperature bath, and carrying out catalytic reaction under visible light.

[0013] Preferably, the sacrificial agent is ascorbic acid.

[0014] The beneficial effects of the present invention are: the present invention uses a simple solvothermal method to obtain H2N-Cu-MOF crystals, fully grinds phloroglucinol trialdehyde (Tp) and p-phenylenediamine (Pa) and then adds them together with H2N-Cu-MOF crystals into DMF, then adds acetic acid and ultrasonic homogenization, and prepares a catalyst H2N-Cu-MOF / TpPa-1-COF with high photocatalytic performance through the solvothermal method. This catalyst can realize efficient photocatalytic water splitting for hydrogen production under visible light. Description of the Drawings

[0015] Figure 1It is the solid ultraviolet-visible diffuse reflection spectrum diagrams of TpPa-1-COF, H2N-Cu-MOF crystals and H2N-Cu-MOF / TpPa-1-COF photocatalysts.

[0016] Figure 2 It is the scanning electron microscope image of H2N-Cu-MOF (a) and the transmission electron microscope images of TpPa-1-COF (b) and H2N-Cu-MOF / TpPa-1-COF (c).

[0017] Figure 3 It is the schematic diagram of water splitting for hydrogen production catalyzed by H2N-Cu-MOF / TpPa-1-COF photocatalyst under visible light (λ≥420nm).

[0018] Figure 4 It is the comparison diagram of hydrogen production from water splitting catalyzed by TpPa-1-COF, H2N-Cu-MOF and H2N-Cu-MOF / TpPa-1-COF under visible light (λ≥420nm). Detailed implementation methods

[0019] Example 1

[0020] (I) Preparation of H2N-Cu-MOF crystals:

[0021] Add 0.15 g of Cu(NO3)2·3H2O into a beaker containing 15 mL of DMF, and ultrasonicate for 30 min. Then, add 10 mL of DMF solution containing 0.2 g of H2N-BDC under stirring, transfer the mixture to a 50 mL three-necked flask, and react at 110 °C for 24 h. The product is separated by centrifugation, washed three times with DMF and anhydrous ethanol respectively, and finally dried in vacuum at 60 °C for 12 h to obtain H2N-Cu-MOF crystals.

[0022] (II) Preparation of TpPa-1-COF:

[0023] Fully mix and grind 0.021 g of phloroglucinol trialdehyde (Tp) and 0.017 g of p-phenylenediamine (Pa) for 10 min, then load them into a 10 mL tubular solvent storage bottle. Then add 3 mL of DMF and 0.5 mL of acetic acid solution with a concentration of 3 M, ultrasonicate for 20 min, and after freezing with liquid nitrogen and evacuating, carry out solvothermal reaction at 120 °C for 72 h. Collect the product solid by centrifugation, then wash it three times with tetrahydrofuran and acetone respectively, and dry it in vacuum to obtain TpPa-1-COF.

[0024] (III) Preparation of H2N-Cu-MOF / TpPa-1-COF:

[0025] After thoroughly mixing 0.021 g of tri-formylphloroglucinol (Tp) and 0.017 g of p-phenylenediamine (Pa) by grinding for 10 min, 0.008 g of the H2N-Cu-MOF crystals prepared in step (1) was added, and the mixture was uniformly mixed and then loaded into a 10 mL tubular solvent storage bottle. Then, 3 mL of DMF and 0.5 mL of acetic acid solution with a concentration of 3 M were added successively, and the mixture was sonicated for 20 min. After freezing with liquid nitrogen and evacuating, a solvothermal reaction was carried out at 120 °C for 72 h. The product solid was collected by centrifugation, then washed three times with tetrahydrofuran and acetone respectively, and dried in vacuo at 60 °C for 12 h to obtain H2N-Cu-MOF / TpPa-1-COF.

[0026] (IV) Test Results

[0027] Figure 1 It is the solid ultraviolet-visible diffuse reflectance spectra of TpPa-1-COF, H2N-Cu-MOF crystals and H2N-Cu-MOF / TpPa-1-COF composites. As can be seen from Figure 1 it, the light absorption range of H2N-Cu-MOF is relatively small, while H2N-Cu-MOF / TpPa-1-COF exhibits strong visible light response ability, indicating that after the combination of H2N-Cu-MOF and TpPa-1-COF, the visible light absorption range becomes significantly larger.

[0028] Figure 2 It is the scanning electron microscope image of H2N-Cu-MOF (a), and the transmission electron microscope images of TpPa-1-COF and H2N-Cu-MOF / TpPa-1-COF (b-c). As can be seen from Figure 2 (a) therein, the H2N-Cu-MOF crystals are a square polyhedron structure; as Figure 2 (b) therein shows, TpPa-1-COF presents a nanorod structure; as Figure 2 (c) therein shows, H2N-Cu-MOF and TpPa-1-COF are tightly combined together.

[0029] Example 2 Preparation of hydrogen by water splitting catalyzed by H2N-Cu-MOF / TpPa-1-COF photocatalyst

[0030] The method is as follows: The reaction is carried out in a quartz glass reactor, and a 300W xenon lamp is used as a light source to simulate sunlight. 10 mg of H2N-Cu-MOF / TpPa-1-COF photocatalyst is ultrasonically dispersed in 100 mL of an aqueous solution of ascorbic acid with a concentration of 5.7 mM. High-purity nitrogen is introduced into the reaction system for 30 minutes to remove oxygen. The reaction system is maintained at 5 °C by a low-temperature constant temperature bath, and then the reaction is carried out for 5 h under visible light (λ≥420 nm) irradiation. During the reaction, the amount of hydrogen generated is detected by gas chromatography every 30 minutes. In the reference experiment, H2N-Cu-MOF and TpPa-1-COF are used as catalysts instead of H2N-Cu-MOF / TpPa-1-COF respectively.

[0031] Figure 3 It is a schematic diagram of the photocatalytic water splitting for hydrogen production by H2N-Cu-MOF / TpPa-1-COF photocatalyst under visible light. The experimental results are as Figure 4 , when H2N-Cu-MOF is used as the catalyst, due to its relatively wide band gap and narrow light absorption range, the hydrogen production amount after 5 h of reaction is relatively low, about 0.48 mmol / g. When TpPa-1-COF is used as the catalyst, due to the serious recombination of photogenerated carriers during the photocatalytic process, the hydrogen production amount after 5 h is only 0.96 mmol / g; while when H2N-Cu-MOF / TpPa-1-COF is used as the catalyst, the catalytic performance is significantly enhanced, and the hydrogen production amount increases linearly with the increase of reaction time. No activity decay is observed after 5 h of reaction, and the total hydrogen production amount after 5 h is as high as 20.9 mmol / g. It can be seen that when H2N-Cu-MOF and TpPa-1-COF are combined to form a heterojunction, due to the improved separation efficiency of electron-hole pairs and the accelerated migration rate of photogenerated carriers, the catalytic activity of TpPa-1-COF for water splitting to produce hydrogen is increased by about 21.8 times. Therefore, the H2N-Cu-MOF / TpPa-1-COF photocatalyst has high catalytic activity and stability, and the preparation method is simple, and it has good application prospects in the field of photocatalytic water splitting for hydrogen production.

Claims

1. Application of the H2N-Cu-MOF / TpPa-1-COF photocatalyst as a catalyst in photocatalytic water splitting for hydrogen production, characterized in that, The H2N-Cu-MOF / TpPa-1-COF photocatalyst has a mass ratio of H2N-Cu-MOF:TpPa-1-COF = 1:5; The preparation method of the H2N-Cu-MOF / TpPa-1-COF photocatalyst includes the following steps: fully mix and grind phloroglucinol trialdehyde and p-phenylenediamine, add the obtained mixture and H2N-Cu-MOF crystals to DMF, then add acetic acid, after ultrasonic homogenization, carry out solvothermal reaction, after centrifuging the obtained reactant, wash it successively with tetrahydrofuran and acetone, and dry it under vacuum to obtain the target product.

2. The application according to claim 1, characterized in that, The preparation method of the H2N-Cu-MOF crystals includes the following steps: add appropriate amounts of Cu(NO3)2·3H2O and H2N-BDC to DMF, ultrasonic homogenize, carry out solvothermal reaction at 110 °C for 24 h to obtain H2N-Cu-MOF crystals.

3. The application according to claim 1, characterized in that, The grinding time is 10 min.

4. The application according to claim 1, characterized in that, The concentration of the acetic acid is 3 M.

5. The application according to claim 1, characterized in that, The ultrasonic time is 20 min.

6. The application according to claim 1, characterized in that, The solvothermal reaction is carried out at 120 °C for 72 h.

7. The application according to claim 1, characterized in that, The method is as follows: ultrasonically disperse the H2N-Cu-MOF / TpPa-1-COF photocatalyst in an aqueous solution containing a sacrificial agent, pass nitrogen into the solution to remove oxygen, keep the reaction system at 5 °C through a low-temperature constant temperature bath, and carry out the catalytic reaction under visible light.

8. The application according to claim 7, characterized in that, The sacrificial agent is ascorbic acid.

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