Gas Sensors Based On Mesoporous Oxide Semiconductors

Gas sensors have been widely used in the fields of environmental protection,resource exploration,safety supervision and medical diagnosis.Among the various gas sensors,the one based on metal oxide semiconductor has been the vital research direction,because of its advantages such as: high sensitivity,tunable selectivity,excellent stability,broad range of measurable objects,all solid state,small size and low power and so on.To enlarge the applicable area of semiconductor gas sensors,it needs to further improve the properties of the sensitivity,selectivity and reliability.The methods such as nanoscale and modification have been the important strategy to enhance the characteristics of such sensors.As indicted in this paper,the mesoporous oxide semiconductor and loaded noble metal were adopt to modify the properties of semiconductor gas sensors.The mesoporous structure of oxide semiconductor sensitive material possesses a large specific surface area,a rich exposed chemical reactive site and an effective gas diffusion pore,which is conducive to improve the gas sensor sensitivity.In addition,the noble metal loaded on the surface of the oxide semiconductor promotes the catalytic effect of the sensitive material.It not only enhances the sensitivity,but also can work at lower temperature,which facilates the decrease of device power.Therefore,precise control of oxide mesoporous structure and noble metal catalytic activity is the key to design high sensitivity,high selectivity,high efficiency and low power gas sensors.The main work of this paper is to prepare the mesoporous metal oxide semiconductor gas sensing material by soft template method and hard template method.Choose one mesoporous material with excellent properties as the base material,and loaded with the noble metal,to investigate the effect of noble metal catalytic activity on the gas sensing properties.Furthermore,the gas sensing mechanism of different sensitive materials was studied carefully.The research contents are as follows:1.Horseshoe-shaped SnO₂ with annulus-like mesoporous was successfully synthesized by soft template method.The horseshoe-shaped samples were assembled by amounts of annulus-like mesoporous with an average diameter about 2 nm and large specific surface area of 398.2 m²/g.Gas sensor based on the as-prepared SnO₂ samples presents excellent gas sening properties,it revealed that the sensitivity towards 100 ppm of ethanol enhanced to 17.3 at the operation temperature of 225 °C for the sensor based on SnO₂ calcined at 400 °C.The horseshoe-shaped nanoparticles with annulus-like mesoporous provide large specific surface area,rich exposed chemical reactive sitea and effective gas diffusion pores for reactions happened on the surface,which is the main reason of the enhanced sensitivity.2.Mesoporous ZnFe₂O₄ with large specific surface area and ordered tunnel has been successfully prepared through hard template.The necessary characterizations such as X-ray diffraction?XRD?,Brunauer-Emmet-Teller?BET?,transmission electron microscopy?TEM?and X-ray photoelectron spectroscopy?XPS?have been carried out to investigate the morphology and chemical state of obtained material.ZnFe₂O₄ with mesoporous structure presents excellent crystallinity and periodic ordered mesostructure.The sensing properties of gas sensor based on ZnFe₂O₄ mesoporous material towards acetone have been investigated.Gas sensor based on the as-prepared samples revealed that the sensitivity towards 100 ppm of acetone was 11.6 under the operation temperature 225 °C.The sensor also presents outstanding selectivity and long time stability.3.Ordered and periodic mesoporous WO₃ has been synthesized by using mesoporous silica KIT-6 as hard template.And noble metal Ag,Au,Pt has been loaded on the mesoporous WO₃ material respectively.The effect of noble metal type,loaded quantity,distributed state on the WO₃ mesostructure and gas sensitive properties have been investigated.It turned out that,during the loading process,the generated noble metal would not disturb the pore structure of mesoporous WO₃.Noble metal Ag and Pt can disperse in the inner pore of the mesoporous,however,noble Au not only dispersed in the inner pore but also aggregated outside the pore structure.Mesoporous WO₃ loaded with noble metal presents excellent gas sensing properties towars NO₂,n-Butanol and NH₃ respectively.The influences of mesoporous structure and noble metal decoration on gas sensing properties were analyzed,and the sensitive mechanism was also given.