Hydrothermal Synthesis And Gas Sensing Properties Of Zinc Oxide Matrix Composites

Gas sensors are widely used in coal chemical production process control,atmospheric gas monitoring,Internet of things,clinical diagnosis,environmental protection and disaster relief and other fields.Gas sensor is consisted of two parts,sensitive materials and conversion device.Sensitive materials are the key to determine the gas sensing properties of sensors,including carbon materials（r GO,SCNTs,etc.）,metal oxide ceramic materials（ZnO,In₂O₃,Sn O₂,WO₃,Ni O,etc.）,two-dimensional materials（Mo S₂,g-C₃N₄,etc）.Among them,metal oxide ceramic material is one of the earliest materials studied,which has the characteristics of good stability,long response and recovery time,high operating temperature and high sensitivity.Here,the main work of this paper is to improve the characteristics of metal oxide ceramic materials.In this paper,we take ZnO ceramic materials as the research object,and improve the sensitivity of ZnO gas sensor and reduce its optimal operating temperature by designing hierarchical structure and constructing heterojunction structure.1.Design of CeO₂/ZnO coral spheres with hierarchical structure.Firstly,ZnO and CeO₂/ZnO coral spheres with hierarchical structure are synthesized by thermostatic hydrothermal synthesis;Then,the structure and surface element composition of ZnO and CeO₂/ZnO coral spheres are studied by X-ray diffraction spectroscopy,scanning electron microscopy,elemental analysis,X-ray photoelectron spectroscopy and ICP technology;then,at 20%relative humidity,we tested the gas-sensing performance of ZnO and CeO₂/ZnO coral spheres to100 ppm acetone on the gas measurement system.The results show that the optimum working temperature of ZnO coral spheres is 300^oC and the sensitivity is 18,while the optimum working temperature of CeO₂/ZnO coral spheres is245^oC,and the sensitivity is much higher than that of ZnO coral spheres,among which the sensitivity of CeO₂/ZnO-2 is 143.Compared with ZnO coral spheres,the sensitivity of CeO₂/ZnO-2 coral spheres are increased by 8 times,and the optimum working temperature is reduced by 55^oC.The enhanced sensing performance of CeO₂/ZnO coral spheres is due to the formation of heterojunction structure between CeO₂ and ZnO.In addition,CeO₂/ZnO coral spheres have better performance than other acetone sensors based CeO₂/ZnO material under the same humidity condition,which indicates that the coral spheres with multistage structure features designed by us are conducive to improving the gas sensitivity of the material.2.Design of CeO₂/ZnO-hf hierarchical thin films.First of all,ZnO-hf-3 and CeO₂/ZnO-hf-3 hierarchical films are synthesized by hydrothermal method with FTO conductive glass as the base;then,the structure and surface elelment composition of ZnO-hf-3 and CeO₂/ZnO-hf-3 hierarchical thin films are studied by XPS,SEM and XRD;finally,the gas-sensing properties of ZnO-hf-3 and CeO₂/ZnO-hf-3 hierarchical thin films are studied with 100 ppm n-butanol gas as target gas at relative humidity of 20%,40%and 60%.The results show that ZnO-hf-3 and CeO₂/ZnO-hf-3 hierarchical films can effectively detect n-butanol gas at different ambient humidity.When the relative humidity is 20%,the highest sensitivity of CeO₂/ZnO-hf-3 to 100 ppm n-butanol is 378.