Preparation And Gas Sensitive Properties Of ZIF-8 Derived ZnO Matrix Composites

Metal oxide semiconductor gas sensors are currently an important tool for real-time monitoring and detection of toxic and hazardous gases in the environment.The present research shows that the construction of heterostructures is one of the effective ways to improve the gas-sensitive performance by increasing the utilization of sensitive materials of gas sensors.In this thesis,ZIF-8-derived ZnO-modified spherical LaFeO₃（ZnO/LaFeO₃）p-n heterojunction materials were synthesized by a high-energy ball milling method using the catalytic and electronic properties of p-type carcinogen LaFeO₃.In addition,the in-situ growth method was used to synthesize ZnFe₂O₄/ZnO n-n heterojunction structures with special morphology by growing ZnFe₂O₄on the surface of ZIF-8-derived ZnO as the main material,and the role of ZIF-8-derived ZnO in gas-sensitive performance enhancement was analyzed from different perspectives,and the gas-sensitive enhancement mechanism of the two composites was specifically analyzed.Details are as follows:1.The ZIF-8-derived ZnO and porous LaFeO₃microspheres were synthesized separately by hydrothermal method,and ZnO/LaFeO₃（ZLFO）composites with p-n heterojunction structure were prepared by compounding the ZIF-8-derived ZnO with porous LaFeO₃microspheres by high-energy ball milling.Their gas-sensitive properties to ethanol were investigated.The gas-sensitive test results showed that the composites showed the best enhancement to ethanol（118,10 ppm）when the La/Zn atomic ratio was 1:0.6（ZLFO-6）,and the response value was 3.7 times higher than that of pure LaFeO₃microspheres.The excellent ethanol gas-sensitive performance of ZnO/LaFeO₃sensors was attributed to the high surface adsorbed oxygen content of the composites,the large specific surface area active point of the reaction,and the electron mobility is super high.2.ZnO with rhombic dodecahedral structure was prepared using ZIF-8 as a sacrificial template,and ZnFe₂O₄/ZnO（ZFO）n-n heterojunction composites were prepared by growing ZnFe₂O₄nanoparticles（10～20 nm）in situ on its surface.The heterojunction sensor synthesized by this strategy has a high response value of 225±15 and a fast response time of 6 s.It responds well to acetone at 100 ppm at an optimal operating temperature of 260°C.We deeply investigated the microstructure,surface state and sensing performance of ZnO and ZFO heterojunction materials and found that the structural and morphological features of the tightly bound n-n heterojunction of ZnFe₂O₄/ZnO are the main reasons for the generation of an ultra-high number of free electrons and abundant active sites,which largely improve its sensitivity to acetone,and in addition,the large specific surface area of each sensing region is an important factor in improving the gas-sensitive In addition,the large specific surface area of each sensing region is an auxiliary factor to improve the gas-sensitive performance.