Preparation And Gas-sensing Performances Of Hierarchical Arrays Composite Nanooxides Based On ZnO Nanostructures

With the improvement of living standards and quality,people pay more attention to the problems of atmospheric environment detection,food safety,industrial pollution and so on.Therefore,the demand for high sensitivity,good selectivity and stability of gas sensors is increasing year by year.Compared to other types of gas sensors,metal oxide semiconductors have occupied the significant positions due to their advantages of high sensitivity low-cost,and good stability and selectivity,making semiconductor gas sensors to be a focus and hot spot in the field of gas sensors.It is well known that excellent sensor materials are the basis for building high-performance gas sensor.In recent years,the development of nanotechnology has provided new power to the research of sensitive materials and the design of material microstructures.Zinc oxide,one of the most important functional semiconductor material,has attracted intensive research and versatile applications in chemical sensors.The gas sensing performance is closely related to the morphology and component of sensing material.In this paper,we firstly synthesized ZnO nanorods by an ultrasonic spray pyrolysis?USP?method on FTO substrate.ZnO nanorods modified with second component,such as NiO and CuO,which can improve the sensing performance through a simple chemical bath method.The main study contents are as following:We presented a simple USP method for the synthesis of well-aligned ZnO nanorod arrays.The ZnO nanorods have smooth surface,and the diameter at the bottom of the nanorods is larger the diameter of the top,the average diameter is in 300nm.These rod-like nanostructures with the lengths of about 5?m were grown on the seed layer substrates.The nonpolar planes of ZnO crystal structure parallel to the{1010}?c-axis?,which has lower surface energy and higher stability so that the ZnO grew preferentially along the?0001?direction and the nanorods generated.In order to improve the sensing performance,ZnO/Ni O heterojuction was designed to detect ethanol gas,where NiO nanosheets were implanted onto the surface of ZnO nanorods by CBD.The hierarchicaland porous morphologiesof ZnO/NiO core-shell nanoherterojunctions could be controlled by changing the growth time of NiO sheets.The“oriented attachment”and“self-assembly”crystal growth mechanisms were proposed to explain the formation of the ZnO/NiO nanostructures.The sensors based on ZnO/NiO hetero-junction nanostructure were fabricated and investigated the ethanol-sensing properties.The result indicated that response was about 80%toward 100 ppm ethanol at the operating temperature of 200°C.Nanotubular arrays composed of ZnO and CuO were prepared by USP and CBD,consisting of internal hexagonal ZnO and external monoclinic CuO shell.Inside-out Ostwald ripening is proposed to explain the formation mechanism of the ZnO/CuO nanotubular arrays.The sensors based on ZnO/CuO nanostructure were fabricated and investigated the H₂S-sensing properties.The results indicated that the sensor fabricated by ZnO/CuO nanotubes showed enhanced gas sensing properties compared to sensors based on pure ZnO nanorods and ZnO/CuO nanorods.The response of ZnO/CuO sensor was 42%towards to20ppm H₂S at 50°C,the relative lower working temperature is benefit for the response.The response of the sensor changed immediately when H₂S was injected and then reached a steady state quickly,the response time based on ZnO/CuO nanotubes sensor lies in within37s.After circulating the sensor was transferred into air to recover and the time consumed by recovery was about 94s.While response time based on ZnO/CuO nanorods sensor is longer than ZnO/CuO nanotubes sensor?¹22?and cannot return to its original state in time.These tube-like architectures could facilitate the diffusion and adsorption of the gas molecules,which could provide plenty of active sites between H₂S gases and adsorbed oxygen.Therefore,an enhanced gas response,the relatively lower working temperature and shorter response time process could be achieved using ZnO/CuO tube-like architecture.