The Preparation And Photoelectrochemical Properties Of Zn-Co Bimetallic ZIF-based Semiconductor Materials

With the advantages of low energy consumption,no secondary pollution and high economic efficiency,semiconductor photocatalytic technology is expected to deal with water pollution.However,the problems of low light energy utilization rate and high recombination of photogenerated carriers seriously hinder the development of this technology.Therefore,it is very important to promote the modification of traditional photocatalysts and to investigate new semiconductor materials.MOFs materials have remarkable performances such as high specific surface areas,high porosities and diverse structures.Particularly,bimetallic MOFs materials can optimize the energy conversion mechanism of the system by virtue of the synergistic effect between the two metal elements,and it shows broad research potential in the modification of traditional semiconductor photocatalysts.In this paper,Zn-Co bimetallic MOF material ZIF8@ZIF67 is used as the precursor to improve the photocatalytic activity by constructing heterojunction and the internal mechanism is discussed.The main research contents are as follows:?1?Zn-Co bimetallic MOF material with core-shell double layer diamond-shaped dodecahedron structure was prepared by two-step solvothermal method,and the optimal synthesis route was determined by adjusting the reaction parameters.The particle diameter of ZIF8@ZIF67 was about 600?750 nm,and the shell thickness of ZIF67 was about 150?200 nm.The composite material shows high thermal stability,high specific surface area and high crystallinity.?2?Zn O/Co₃O₄ composite material with p-n heterojunction was prepared by adjusting the calcination conditions with the sacrificial template of ZIF8@ZIF67.The results showed that the carrier concentration of ZnO/Co₃O₄ composite material was 4.82×10²⁴ /cm³,the photocurrent response was 8 ?A/cm³,and the rate constant of methyl orange decomposition was 0.2397 /h under UV-light illumination,they were significantly improved compared with pure ZnO.This was attributed to the regular morphology of MOF template and the successful construction of p-n junction,which significantly improved the separation efficiency of photogenerated carriers.?3?g-C₃N₄/ZIF8@ZIF67 heterogeneous composite material was prepared by in-situ reduction method of that deposited ZIF8@ZIF67 on g-C₃N₄ nanosheet,and the optimal deposition amount of ZIF8@ZIF67 nanocrystalline was determined to be 25 mass%.The results showed that,compared with pure g-C₃N₄,the specific surface area of the heterogeneous composite had increased significantly,the photocurrent response was increased by 6 times under simulated solar illumination,the photodegradation rate of methyl orange was increased by 3.6 times,and the degradation rate was 93.7% under 1 h of light.According to the test of free radicals capture,the main active substance in the process of degradation was ·O₂^-.On the one hand,the improvement of performance was attributed to the fact that the construction of heterojunction improves the separation efficiency of photogenerated carriers and light energy utilization rate;on the other hand,the high specific surface area of the composite material provides more active sites for photocatalytic reaction.