| In the face of environmental pollution control,industrial production safety and health of daily life demands,developing gas sensors with high sensitivity,fast response and good stability is urgently necessary.In all kinds of gas sensors,metal oxide gas sensors have attracted considerable attention because of low cost,flexible operation,simple fabrication methods and variety of detected gas etc.In recent years,using biotemplate method to prepare new functional materials with sophisticated fine hierarchical structure is a new research direction.Therefore,choosing simple,abundant and green biotemplate to prepare metal oxide semiconductor gas sensors have displayed important researching value.In the present work,maize straw was used as template to fabricate hierarchical porous Zn O through liquid impregnation process followed by calcination.The phase composition,morphology structure,specific surface area and pore size and gas sensing properties of materials were studied,and the effect of maize straw hierarchical porous structure on the Zn O gas sensing properties were also analyzed.On the basis of the synthesis of maize strawtemplated hierarchical porous Zn O,transition metal ion was doped into Zn O nanostructure to improve Zn O gas sensing properties,which could provide us evidence for the exploration of composition optimization of hierarchical porous materials.The main contents and results are as follows.(1)Maize straw was used as template and maize straw-templated hierarchical porous Zn O material was synthesized through ammonia extraction pretreatment,liquid impregnation process followed by calcination.The samples were characterized,and the results reveal that the as-prepared Zn O retained the original pore morphology of the maize straw material,and the framework was composed of a large amount of nanoparticles with the nearly uniform size about 50 nm.The material has hierarchical macroporous structure and asymmetrical slender mesoporous structure,and the specific BET surface area is 32.84 m2/g,the average pore size is 18.9 nm,and thepore volume is 0.16 m3/g.(2)The gas sensing tests reveal that the responses of maize straw-templated hierarchical porous Zn O gas sensors to acetone were higher than that of normal Zn O gas sensors,but the optimum working temperature was also higher than that of normal Zn O.It may be due to that the surface activity of maize straw-templated hierarchical porous Zn O material is insufficient,and the material could exhibit gas sensing performance under the high working temperature which have large surface reaction activation energy.The responses of maize straw-templated hierarchical porous Zn O gas sensors to 100 ppm acetone operated at 340 ? were 24 and the response and recovery times were about 12 s and 6 s.The special structure in different scales of maize straw-templated hierarchical porous Zn O provided a lot of channels which facilitated the gas transport in the inner of the material,and the material have large specific surface areas both in the micro-scales and the nano-scales,which will provide more active sites for surface reactions to enhance gas sensing properties.(3)We merged the spontaneous hierarchical porous structure of maize straw and the doping with transition metals towards oxidic materials with new structure and composition,better suited for gas sensing application.In this study,nickel was chosen as a dopant for Zn O,and maize straw-templated hierarchical porous Ni doped Zn O material was successfully prepared,and exhibited enhanced gas sensing performance to acetone.The responses of maize straw-templated hierarchical porous Zn O:Ni gas sensors to 100 ppm acetone operated at 340 ? were 68 and the response and recovery times were about 6 s and 2 s.The detection limit was estimated to be 116 ppb.The Zn O:Ni sensors also exhibited good selectivity to acetone and good long-term stability.The improvement of gas sensing properties of Ni doped Zn O material was probably contributed to higher donor defects contents. |
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