Preparation And Gas-sensing Properties Of Metal Oxide Semiconductor （TiO₂）-hierarchical Micro / Nanostructures

In recent years,gas sensors play a very important role in the field of production safety,disease detection,energy conservation,environmental protection,road traffic safety management,aerospace,military,chemical and other modern terrorism.Gas sensor based on metal oxide semiconductor has become the research focus in the field of gas sensor because of its low cost and excellent gas sensing properties.For metal oxide semiconductor gas sensors,excellent sensing material is the cornerstone of the fabrication of high performance gas sensors.In order to effectively detect toxic and hazardous or flammable and explosive gases,researchers have explored a variety of novel and unique sensitive materials,and the development of simple,environmentally friendly,low-cost synthesis method has been a huge challenge.In this paper,in order to obtain high performance gas sensor as the goal,the design method is simple,inexpensive,environmentally friendly and efficient synthesis of a variety of oxide semiconductor nano materials with special morphology and good gas sensing properties.The main contents are as follows:1.Anatase hierarchical micro/nanostructured TiO₂ was successfully prepared by a rapid（10 min）one-pot microwave-assisted hydrothermal method.The nanomorphologies（including the exposed crystal facets）of the asprepared TiO₂samples could be facilely tuned in the reaction system.The possible formation mechanism of the hierarchical micro/nanostructured TiO₂ were discussed in detail,it was found that the chelating role of EDTA could control the slow release of Ti-containing species,providing a large space for the controlling of crystallite size and complex nano-morphologies.With the unique structural properties,the hierarchical micro/nanostructured TiO₂ prepared by the present microwave-assisted hydrothermal method might also show potential application in more fields,such as dye-sensitized solar cells,gas sensing and lithium ion batteries.2.Anatase TiO₂ hierarchical microspheres were synthesized by a facile hydrothermal method.Characterization results indicated that the microspheres were consisted of massively aggregative nanothorns with truncated tips,which had exposed{001}and{101}crystal facets,and there were abundant mesoporous structures in the microspheres.A possible growth model of the TiO₂hierarchical microspheres was put forward based on a series of experimental analysis.When used for gas sensing,it was found that the TiO₂ hierarchical microspheres showed a distinct high sensitivity towards acetone,the optimal response to 100 ppm acetone was 14.6,which was much higher than that of other materials reported in previous works.Moreover,the TiO₂hierarchical microspheres exhibited a fast response/recovery speeds（<10 s）,a low detection limit（the response still reaches 6.1 even at a low acetone concentration of10 ppm）and an excellent selectivity.Through systematical analysis,it can be concluded that the enhancement of gas sensing performance of the TiO₂ hierarchical microspheres was ascribed to its unique structural features（perfect hierarchical mesoporous structure as well as specific crystal facets exposing）,which could be described as structurally enhanced gas sensing performance.The present results encourage us to further investigate crystal facets-dependent gas sensing properties of TiO₂ for the designing of conductometric gas sensors with better sensing performance.