VOCs Gas Sensitive Properties Of Binary ZnO-based Heterogeneous Composite Semiconductor Materials

Volatile organic compounds（VOCs）pose a serious threat to human life and health.Timely and efficient monitoring of VOCs is an important research work in the field of science.ZnO is a kind of traditional n-type metal oxide semiconductor,which has been extensively studied in terms of gas-sensitive properties due to its adjustable surface and microstructure and good chemical and thermal stability.In this paper,we studied the synthesis of ZnO-based sensitive composite materials using MoS₂,CsPb Br₃,BiOBr and BaTiO₃as carriers by means of microstructure design,surface ligand modification,heterojunction construction,and regulation of defects（oxygen vacancy）,and regulated the electrical properties of the interface carrier migration of the composite.The performance indexes of MoS₂/ZnO,CsPb Br₃-MPA/ZnO,BiOBr/ZnO and BaTiO₃/ZnO composite nanostructure gas sensors are significantly optimized.Different preparation methods were used to construct nano-heterostructures of various kinds of composite materials,and the gas sensitive properties and sensing mechanism of ZnO-based gas sensors to VOCs were investigated.The main research work includes:（1）Based on the different electronic structures,physical properties and sensing advantages of MoS₂and ZnO,we proposed a novel semiconductor heterojunction based on MoS₂/ZnO composites.MoS₂/ZnO micro-bridging composite nanomaterials consisting of MoS₂nanoflowers and ZnO nanosheets were prepared by a two-step hydrothermal method.The application of MoS₂/ZnO sensor in the detection of pollutant triethylamine（TEA）was studied.At the optimum operating temperature of 200℃,the MoS₂/ZnO sensor can respond up to 31.08 to 100 ppm TEA,showing excellent selectivity and stability to TEA.（2）Inorganic halide perovskites（AIHPs）have been widely concerned for their excellent semiconductor properties.Perovskite interface modulation engineering is considered to be a key factor in the preparation of stable and high performance AIHPs devices.In this study,the organic ligand 3-mercaptopropionic acid（MPA）was creatively introduced to regulate the CsPb Br₃nanostructure,and the environmentally stable binary heterojunction of CsPb Br₃nanoparticles（NPs）/ZnO NPs was constructed.The results show that the optimal nano-sized CsPb Br₃NPs has abundant sensitive gas adsorption sites and large specific surface area,which can effectively improve the room temperature sensing of ethanolamine（EA）by CsPb Br₃based composites.In addition,the hydrophilic groups in MPA are conducive to the formation of hydrogen bonds and the formation of MPA network structure,effectively improve the binding affinity of metal oxides on MPA surface,promote the stable anchoring of ZnO to halide perovskite CsPb Br₃and the formation of CsPb Br₃/ZnO heterojunction.The CsPb Br₃-MPA/ZnO sensor shows excellent EA sensing performance.（3）A simple hydrothermal method was used to decorate ZnO nanocrystals（NCs）on BiOBr micron flowers（MFs）surface,and n-n heterojunctions were successfully constructed.The response characteristics of BiOBr/ZnO gas sensors were systematically studied.Compared with pure BiOBr MFs,BiOBr/ZnO composites have a higher response（Ra/Rg,20.57）to 100 ppm TEA at 200℃.The theoretical detection limit is as low as 112 ppb and the response time is only 4 s,showing outstanding selectivity and long-lasting stability.The enhanced gas-sensitive performance of the BiOBr/ZnO sensor is mainly attributed to its unique layered heterogeneous microstructure,and the construction of n-n heterojunction leads to a larger specific surface area and efficient interfacial electron transport,which promotes the reaction and diffusion of target gas molecules on the BiOBr and ZnO surfaces,and improves the TEA gas-sensitive characteristics.（4）BaTiO₃nanospheres/ZnO nanosheets composites were prepared by hydrothermal method.The gas sensitivity test shows that the response of BaTiO₃to 100ppm ethanol is the highest（3.87）at 340℃,while the response of BaTiO₃/ZnO composites to 100 ppm ethanol is 94 at 280℃.The response time of BaTiO₃/ZnO is reduced to 66 s,and the recovery is complete within 162 s.In general,the performance of BaTiO₃/ZnO nanocomposite sensors is better than that of pure BaTiO₃nanospheres and ZnO nanosheets,which may be related to the higher porosity and larger specific surface area of BaTiO₃/ZnO composites.