Synthesis,Modification Of Metal Oxide Semiconductors Sensing Materials

As we all know,gas sensors play an important role in our daily life,due to their function of environment monitoring,detecting toxic and pollutant gases.Among the various types of gas sensors,metal oxide semiconductor（MOSs）such as In₂O₃,ZnO,TiO₂,Co₃O₄,SnO₂,and MoO₃ based gas sensors have become one of the most commonly used typed of chemical sensors due to their advantage of effective cost,facile method and easy fabrication.However,pure metal oxide semiconductor gas sensors have some shortcomings such as low selectivity and insufficient sensitivity.So in the past few years,great efforts have been devoted to improve the gas sensor performance.Suitable morphological control can aid address these shortcomings.Use of one-dimensional metal oxide nanostructures such as nanowires,nanofibers,nanorods are known to be helpful.The fabrication of heterojunction,where in one type of MOSs is present over another MOS,is also an efficient method to enhance the sensitivity and selectivity of sensors.Synthesis of metal oxide with well exposure facets is also an important method to enhance gas sensor performance.There are three aspects in this article.Firstly,we have successfully synthesized In₂O₃microcubes and one-dimensional In₂O₃ nanobelts by a facile strategy through a direct hydro-thermal method.The crystal structure and morphology of materials were characterized by XRD,TEM,EDS,HRTEM,and SEM.The gas sensing performance of this two materials were also investigated.The as-prepared In₂O₃ nanobelts gas sensor exhibited a high response and selectivity towards 100 ppm ethanol at optimum temperature of 124^oC with a value of68.74,which is batter than In₂O₃ microcubes of 206 ^oC with a value of 17.17.Moreover,the In₂O₃ nanobelts gas sensor shows fast response/recovery time are 1.5 s/232 s.Secondly,We synthesized MoO₃ nanobelts（NBs）and the Fe₂O₃/MoO₃ heterstructure nanobelts（HNs）using a simple two-step hydrothermal route.The HNs are made by loading Fe₂O₃ on the NBs.The MoO₃ nanobelts have a length of 2-3 um and width of 200-300 nm;The Fe₂O₃ nonospheres on the surface have a size of 15±5 nm.The Fe₂O₃ nanospheres are uniformly distributed on the MoO₃ NBs,and interact chemically with the surface.The HNs have a highest response at optimum temperature of 233 ^oC with a value of 22.48,which is higher than that of MoO₃nanobelts.The response time reduces to 102 secs（HNs）from 187 s（NBs）.Our findings are likely to result in further exploration of simple,one or two step approaches to decorated nanomaterials,that can be used for charge transfer applications（including sensing of other VOCs）.Thirdly,we have successfully synthesized SnO₂ octahedra nanostructures with a large percentage of high energy（221）facets and SnO₂ elongated octahedra by a facile strategy through a direct hydro-thermal method.The crystal structure and morphology of materials were characterized by XRD,TEM,EDS,HRTEM,and SEM.To 100 ppm ethanol,the SnO₂octahedra gas sensor has a response of 37.71,which is higher than SnO₂ elongated octahedra of 8.94.The enhanced gas sensing properties were attribute to the large percentage of high energy（221）facets.