Preparation Of Dual ZIFs Core-shell Nanomaterial And Study On Gas Sensing Properties Of Derivative

With the continuous improvement of the level of industrialization and urbanization,air pollution and toxic and harmful gas leakage continue to threaten people's health and property safety.As the key equipment of gas information acquisition,gas sensor can monitor the target gas dynamically in real time and is widely used.Gas sensor based on metal oxide semiconductor(MOSs)has the advantages of simple structure,low cost and adjustable performance,and the research on sensitive materials as the core components of sensors can significantly improve the performance of the sensors,which has important research value and market prospect.In recent years,MOSs sensitive materials prepared based on metal-organic framework structure(MOFs)retain their structural advantages such as large specific surface area,high surface activity and adjustable pore structure,and become an ideal micro-nano structure for high-performance sensitive materials.However,single phase MOSs derived from single MOFs has not solved the disadvantages of poor selectivity and difficult sensitivity modulation of traditional gas sensitive materials.On this basis,the compound derivative strategy further developed is an excellent solution to achieve uniform compounding of heterogeneous MOSs and improve gas sensitive performance.This scheme not only allows the partition design of each component in microstructure,but also adjusts the proportion of each component to achieve the purpose of modulating the electronic structure and improving the gas sensitive characteristics.However,the reported composite MOFs still have many synthesis steps,complicated process and high cost.In this paper,we constructed Zn O@Co₃O₄ hollow cubes based on the isomorphic structure of ZIF-8 and ZIF-67,revealed the formation process and assembly mechanism of hollow cubes structure,and established the structure-activity relationship between micro/nano structure and gas sensitive performance.The main research contents and conclusions are as follows:(1)ZIF-8@ZIF-67 solid core-shell nanocubes structure was prepared by chemical precipitation method.The core-shell cubes has a smooth surface and good monodispersion,with the length of side about 400 nm.The ZIF-67 phase is uniformly coated on the outer surface of ZIF-8,and the coating thickness is about 40nm.Meanwhile,the effects of CTAB and the ratio of ligand to metal salt on the morphology and structure of Zn/Co-ZIF were investigated,and the formation mechanism of ZIF-8@ZIF-67 homogeneous heterogeneous core-shell structure was explained.(2)Based on ZIF-8@ZIF-67 solid core-shell cubes prepared above,Zn O@Co₃O₄ hollow cubes(HCs)with edge length of about 200 nm and shell thickness of about 20 nm was synthesized by annealing.The shell of the cube is a hierarchical micro/nano structure composed of Zn O and Co₃O₄ nanoparticles with a size of 5-10 nm as the primary structural units,with a specific surface area of 51.9m~2 g^-1 and a good micromesoporous structure.The formation of hollow structure is the thermal decomposition of ZIF-8@ZIF-67 solid core-shell cubes controlled by a heterogeneous contraction mechanism.(3)The Zn O@Co₃O₄ hollow cubes based gas sensor has a response/recovery time of 11.2/12.5 s for the 100 ppm C₇H₈ at an optimal operating temperature of290°C.The sensitivity of Zn O@Co₃O₄ hollow cubes to C₇H₈ has an excellent linear relationship with concentration in the range of 10-100 ppm.The sensitivity of Zn O@Co₃O₄ hollow cubes to 100 ppm C₇H₈ was 26.4,which is 8 times and 2.3times that of Co₃O₄ and Zn O hollow cubes.Compared with Co₃O₄ and Zn O hollow cubes,the main reasons for the improvement of gas sensitive properties of Zn O@Co₃O₄ hollow cubes can be concluded as follows:higher specific surface area provides more surface active sites;the interfacial diffusion between Zn O and Co₃O₄resulted in a large number of p-n heterojunctions and the gas sensitive catalytic activity of Co₃O₄.In summary,in this paper,a simple two-step method was used to prepare Zn O@Co₃O₄ heterogeneous hollow cubic porous material,which was used for the first time in the detection of toluene gas,with excellent sensitivity.