Preparation method and application of heterojunction catalyst based on two-dimensional zinc porphyrin metal organic framework

Abstract

The invention discloses a preparation method and application of a heterojunction catalyst based on a two-dimensional zinc porphyrin metal organic framework, and belongs to the field of photochemical energy conversion and photocatalytic degradation. The invention aims to solve the technical problems of high-quality preparation of the artificial photosynthetic photocatalytic composite material and how to effectively improve the photochemical energy conversion efficiency. The method comprises the following steps: 1, dissolving bismuth nitrate pentahydrate, sodium tungstate dihydrate and sodium dodecyl dimethyl benzene sulfonate in deionized water, fully stirring, and transferring the solution to a reaction kettle for hydrothermal reaction; cooling to room temperature, washing and drying to obtain bismuth tungstate solid powder; 2, adding bismuth tungstate and meso-tetra (4-carboxyl phenyl) porphin into a mixed solution of N, N-dimethylformamide and ethanol, carrying out ultrasonic treatment, and fully stirring to obtain a solution A; dissolving zinc nitrate hexahydrate, pyrazine and polyvinylpyrrolidone in a mixed solution of N, N-dimethylformamide and ethanol, and fully stirring to obtain a solution B; after the solution is fully dissolved, dropwise adding the solution B into the solution A under ultrasonic and stirring conditions, and then putting the beaker into an oil bath pan for heating; and cooling to room temperature, washing, and storing in an ethanol solution to obtain the Zn-MOF / Bi2WO6 heterojunction composite material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photochemical energy conversion and photocatalytic degradation. BACKGROUND

[0002] With the deepening of global industrialization, energy crisis and environmental pollution problems are becoming increasingly serious, and developing efficient and clean new technologies and functional materials has become the front focus of current scientific research. Under this background, artificial photosynthetic photocatalytic system has attracted widespread attention. This system is inspired by the mechanism of natural photosynthesis, and builds a photocatalytic composite material system based on semiconductor materials. The separation and migration behavior of photo-generated carriers can be explained by the S-scheme heterojunction model. Using in-situ growth method, two semiconductor materials are constructed into S-scheme heterojunction structure. Due to the advantages of simple process, no need for noble metal or additional electron mediator, tight interface combination, clear electron transfer path and consistent with energy band matching theory, this method has become a research hotspot in the field of photocatalytic material design.

[0003] In the research of constructing efficient artificial photosynthetic system, the design of heterojunction structure is particularly important. Among them, two-dimensional material heterojunction exhibits excellent photo-induced charge separation efficiency and carrier migration ability due to its unique interface effect and significant quantum confinement effect, providing a new way for the improvement of photocatalytic performance. The ultrathin layered structure of two-dimensional material is beneficial to the full exposure of active sites, realizing efficient spatial separation of photo-generated electron-hole pairs, thereby effectively inhibiting recombination and enhancing light response activity. In addition, metal-organic framework material, as a kind of porous crystalline material formed by self-assembly of metal nodes and organic ligands, has the outstanding advantages of high specific surface area, adjustable pore structure and flexible surface chemical properties. Especially two-dimensional metal-organic framework material, while inheriting the advantages of three-dimensional metal-organic framework, further takes advantage of its ultrathin characteristics and rich edge active sites, significantly improving the electron transfer efficiency and photocatalytic reaction kinetics. The combination of two-dimensional metal-organic framework and nanoflower-like inorganic semiconductor material can fully exert the interface synergistic effect of two-dimensional heterojunction and the structural and functional characteristics of metal-organic framework, realizing efficient separation of photo-generated carriers, and providing a new idea for constructing efficient and stable S-scheme photocatalytic system.

[0004] In summary, the application provides a preparation method and application of a two-dimensional zinc porphyrin metal organic framework heterojunction catalyst. The preparation method uses a simple, mild and rapid oil bath method to grow a two-dimensional zinc porphyrin metal organic framework (Zn-MOF) in situ on the surface of a pre-synthesized bismuth tungstate nanoflower, and successfully constructs a high-efficiency photocatalytic composite material with an S-scheme heterojunction structure. The composite material can synergistically optimize the processes of sunlight absorption, photogenerated charge separation and surface catalytic reaction, and significantly improve the photocatalytic performance. Compared with the traditional strategy of constructing a heterojunction by a two-step hydrothermal method, the method described in the application can complete the compounding in less than 3 hours under normal pressure and at a temperature lower than 100 DEG C, and the process conditions are more mild and efficient. The prepared composite material has a tightly combined heterojunction interface, a stable structure and a uniform and complete morphology. In addition, the preparation method has the advantages of simple process, low energy consumption, green environmental protection and economy, and meets the requirements of sustainable development of low carbon and energy saving. SUMMARY

[0005] The application relates to solving the problems of efficient preparation of an organic-inorganic hybrid artificial photosynthetic heterojunction photocatalyst based on a metal organic framework and improvement and optimization of catalyst performance, and provides a simple and efficient new strategy for synthesizing a hybrid heterojunction composite material.

[0006] Step one: bismuth nitrate pentahydrate, sodium tungstate dihydrate and sodium dodecyl dimethyl benzene sulfonate are dissolved in deionized water, and then the solution is transferred to a reaction kettle for hydrothermal reaction. After cooling to room temperature, the bismuth tungstate solid powder is obtained by washing and drying.

[0007] Step two: the bismuth tungstate prepared in step one and meso-tetra (4-carboxyphenyl) porphyrin are added to an N,N-dimethylformamide and ethanol mixed solution, and then ultrasonic and fully stirred, which is called A liquid. Then, zinc nitrate hexahydrate, pyrazine and polyvinylpyrrolidone are dissolved in an N,N-dimethylformamide and ethanol mixed solution, and then fully stirred, which is called B liquid. After fully dissolving, the B liquid is added dropwise into the A liquid under ultrasonic and stirring, and then the beaker is placed in an oil bath for heating. After cooling to room temperature, the Zn-MOF / Bi2WO6 heterojunction composite material is obtained by washing, and is stored in an ethanol solution.

[0008] Further limited, in step one, 1900-2000 mg of bismuth nitrate pentahydrate, 900-1000 mg of sodium tungstate dihydrate and 100-200 mg of sodium dodecyl dimethyl benzene sulfonate are dissolved in 50-80 mL of deionized water.

[0009] Further limited, in step one, the stirring and dissolving time is 30 min.

[0010] Further limit, the hydrothermal reaction in step one uses 100mL reaction kettle, filling degree 50%~80%, reaction temperature 160~200℃, reaction time 20~25h.

[0011] Further limit, in step one, dry in 60℃ vacuum drying box for 12h.

[0012] Further limit, in step two, 700~800mg of bismuth tungstate, 20~25mg of meso-tetra(4-carboxyphenyl)porphyrin are added to mixed solution A consisting of 10~12mL of N,N-dimethylformamide and 4~5mL of anhydrous ethanol. 25~30mg of zinc nitrate hexahydrate, 4~5mg of pyrazine and 180~120mg of polyvinylpyrrolidone are dissolved in mixed solution B consisting of 30~35mL of N,N-dimethylformamide and 10~11mL of anhydrous ethanol.

[0013] Further limit, in step two, the ultrasonic and stirring time of A liquid is 10min, and the stirring time of B liquid is 10min.

[0014] Further limit, in step two, the heating temperature is 80~100℃, and the holding time is 2~3h.

[0015] The heterojunction catalyst based on two-dimensional zinc porphyrin metal organic framework prepared by the method specifically is that Zn-MOF nanosheet is in-situ grown on the surface of Bi2WO6 nanoflower ball to form Zn-MOF / Bi2WO6 organic-inorganic hybrid heterojunction composite material. The application provides a preparation technology of a novel 2D / 2D artificial photosynthetic heterojunction composite material realized under simple, low-temperature, rapid and normal pressure conditions, so that a closely combined heterojunction interface is achieved, efficient spatial separation of photo-generated electrons is realized, and the effective improvement of photocatalytic performance is finally realized. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the XRD pattern of BWO, ZM and 24BZM; Figure 2 is the XPS spectrum of BWO, ZM and 24BZM; Figure 3 is the scanning electron microscope photos of BWO, ZM and 24BZM and the transmission electron microscope photo and energy spectrum analysis diagram of 24BZM; Figure 4 is the ultraviolet-visible absorption spectrum of BWO, ZM and 24BZM; Figure 5 is the band gap diagram of BWO, ZM and 24BZM; Figure 6 is the Mott-Schottky electrochemical test spectrum line of BWO, ZM and 24BZM; Figure 7 is the electrochemical impedance test spectrum line of BWO, ZM and 24BZM;Figure 8 is the photocatalytic reduction degradation curve of each sample over time against 100 mL of 40 mg / L potassium dichromate indicator; Figure 9 is the photocatalytic reduction degradation chemical reaction kinetics fitting of each sample against 100 mL of 40 mg / L potassium dichromate indicator; Figure 10 is the degradation rate conversion comparison of each sample against 100 mL of 40 mg / L potassium dichromate indicator. DETAILED DESCRIPTION

[0017] Example 1: In this example, the preparation of bismuth tungstate nanoflower balls is carried out according to the following steps: 1940 mg of bismuth nitrate pentahydrate, 989.61 mg of sodium tungstate dihydrate and 139.2 mg of sodium dodecyl dimethyl benzene sulfonate are dissolved in 60 mL of deionized water and stirred for 30 min, and then the solution is transferred to a 100 mL reaction kettle for hydrothermal reaction at 180°C for 24 h. The product is washed with deionized water and ethanol for 3 times, and then dried in a vacuum drying oven at 60°C for 12 h to obtain bismuth tungstate powder.

[0018] In this embodiment, a preparation method of a heterojunction catalyst based on a two-dimensional zinc porphyrin metal organic framework is completed by the following steps:

[0019] Step one, 1940 mg of bismuth nitrate pentahydrate, 989.61 mg of sodium tungstate dihydrate and 139.2 mg of sodium dodecyl dimethyl benzene sulfonate are added to 60 mL of deionized water and stirred for 30 min, and then the solution is transferred to a 100 mL reaction kettle for hydrothermal reaction at 180°C for 24 h. The product is washed with deionized water and ethanol for 3 times, and then dried in a vacuum drying oven at 60°C for 12 h to obtain bismuth tungstate powder.

[0020] Step two, 480, 600, 720 and 840 mg of the prepared bismuth tungstate are respectively dispersed in four mixed solutions of 11 mL of N,N-dimethylformamide and 4 mL of ethanol containing 24 mg of meso-tetra(4-carboxyphenyl) porphine, and then ultrasonic and stirred for 10 min, which is called A liquid. Then, 4 portions of 27 mg of zinc nitrate hexahydrate, 4 mg of pyrazine and 100 mg of polyvinylpyrrolidone are respectively prepared, and each is dissolved in a mixed solution of 34 mL of N,N-dimethylformamide and 11 mL of ethanol, and then stirred for 10 min, which is called B liquid. After being fully dissolved, the B liquid is added dropwise into the A liquid under ultrasonic and stirring, and then the beaker is placed in an oil bath pot for reaction at 90°C for 2 h. The product is washed with ethanol for 3 times, and then stored in an ethanol solution. According to the mass ratio of the bismuth tungstate input to the zinc porphyrin metal organic framework, the product is respectively named as 16BZM, 20BZM, 24BZM and 28BZM.

[0021] The photocatalytic reduction degradation of Cr(VI) solution reaction was simulated by a 300 W xenon lamp. 10 mg of the catalyst to be tested and 100 mL of Cr(VI) solution with a concentration of 40 mg / L were placed in a beaker. The beaker was fixed in front of the light source at a distance of 5 cm, and the magnetic stirring was kept uniform during the degradation reaction. The absorbance of the reaction solution was detected at the same time interval, and the concentration of the reaction solution was calculated to draw the degradation rate-time curve, and the photocatalytic activity of the samples was analyzed and compared. Figure 8

[0022] As can be seen from Figure 9 , the performance of the four composite materials 16BZM-24BZM in the photocatalytic reaction is higher than that of the reference ZM and BWO catalysts. Among them, the degradation rate of the 24BZM sample is the fastest, and the degradation rate reaches 33.6 μmol·min -1 ·g -1 cat The performance shows that the unique photo-induced electron migration path of the BZM artificial photosynthetic catalyst creates favorable conditions for the separation of space charge, not only prolongs the lifetime of photo-induced electrons, but also effectively increases the reaction thermodynamic potential energy of photo-induced electrons, which macroscopically shows a significant improvement in the photocatalytic performance of the material.​

Claims

1. A method for the preparation and use of a two-dimensional zinc porphyrin metal-organic framework based heterojunction catalyst characterized in that The preparation method is completed by the following steps: step one, dissolving bismuth nitrate pentahydrate, sodium tungstate dihydrate and sodium dodecyl dimethyl benzene sulfonate in deionized water and stirring thoroughly, transferring the solution to a reaction kettle for hydrothermal reaction. After cooling to room temperature, washing and drying, a bismuth tungstate solid powder is obtained. Step two, adding bismuth tungstate and meso-tetra(4-carboxyphenyl) porphyrin into a mixed solution of N,N-dimethylformamide and ethanol, ultrasonicating and stirring thoroughly, which is referred to as A liquid. Then dissolving zinc nitrate hexahydrate, pyrazine and polyvinylpyrrolidone in a mixed solution of N,N-dimethylformamide and ethanol and stirring thoroughly, which is referred to as B liquid. After complete dissolution, under ultrasonicating and stirring, B liquid is added dropwise into A liquid, and then the beaker is placed in an oil bath for heating. After cooling to room temperature, washing and storing in an ethanol solution, a Zn-MOF / Bi2WO6 composite material is obtained.

2. The method of claim 1, wherein In step one, 1900-2000 mg of bismuth nitrate pentahydrate, 900-1000 mg of sodium tungstate dihydrate and 100-200 mg of sodium dodecyl dimethyl benzene sulfonate are dissolved in 50-80 mL of deionized water.

3. The method of claim 1, wherein In step one, the stirring and dissolving time is 30 min.

4. The method of claim 1, wherein In step one, a 100 mL reaction kettle is used for the hydrothermal reaction, the filling degree is 50-80%, the reaction temperature is 160-200°C, and the reaction time is 20-25 h.

5. The method of claim 1 wherein In step one, the drying is performed in a 60°C vacuum drying box for 12 h.

6. The method of claim 1, wherein In step two, 450-850 mg of bismuth tungstate, 20-25 mg of meso-tetra(4-carboxyphenyl) porphyrin are added to a mixed solution A liquid composed of 10-12 mL of N,N-dimethylformamide and 4-5 mL of anhydrous ethanol. 25-30 mg of zinc nitrate hexahydrate, 4-5 mg of pyrazine and 180-120 mg of polyvinylpyrrolidone are dissolved in a mixed solution B liquid composed of 30-35 mL of N,N-dimethylformamide and 10-11 mL of ethanol.

7. The method of claim 1 wherein In step two, the ultrasonicating and stirring time of A liquid is 10 min, and the stirring time of B liquid is 10 min.

8. The method of claim 1, wherein In step two, the heating temperature is 80-100°C, and the holding time is 2-3 h.

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