Regulation Of Oxygen Vacancies On SnO₂ Surface And Influence On Gas Sensing Properties

With the improvement of safety and environment,monitor and control of atmospheric pollutants have attracted researchers' attention.Development of high-performance and low-power-consumption gas sensors has become an urgent task.Gas sensors based on metal-oxide semiconductors which are highsensitive,low-cost and easy to integrate have become one of the effective methods to detect various harmful,explosive and toxic gases.The sensing mechanism of metal-oxide sensors is based on gas-gas,gas-solid reactions which happen on surface of semiconductors.Among these process,adsorption and desorption of oxygen ions and their reactions with target gases play an important role.The surface defects affect physical and chemical properties greatly,such as adsorption,catalytic reactivity and thermal dynamics.Among defects,oxygen vacancies?non-stoichiometry?are the most common and studied anion defects which can effectively adjust the band gap and electron distribution due to its low formation energy.Systematic researches on the regulation,existence and influence of oxygen vacancies are still needed which plays an important role in further enhancing the gas sensing properties and mechanism of reactions between metal oxides and gases.In this work,highperformance SnO₂ nanostructrues are selected and various methods are designed to regulate oxygen vacancies.The influence of surface oxygen vacancies on gas sensing properties is studied based on the structure-property relationship.The specific research results are as follows:Firstly,SnO₂ nanomaterials with different morphologies are synthesized by one-step hydrothermal method.As the ethanol content of precursor increases,SnO₂ transforms from separated particles into spheres.SnO₂ nanospheres prepared with ethanol: water?volume ratio?= 10:1 exhibit excellent response to ethanol gas.At the optimal operating temperature?180??,the response to 100 ppm ethanol is about 15.1,the response/recovery time is 13s/9s.However,due to its high gas sensing activity,SnO₂ nanospheres exhibit responses to other gases,and its selectivity needs improved.The gas sensing properties of SnO₂ nanomaterials depends on the surface morphology.Secondly,Ni-doped SnO₂ nanospheres are prepared via an impregnation process.Via regulating concentration of the dipping solution,we find that an appropriate concentration of 0.5mol · L-1 reduces the aggregation of Ni on SnO₂ surface and helps Ni2+ ions to access the lattice structure of SnO₂.At a low operating temperature of 180?,response to 100 ppm ethanol is about 51.3,which is 3.62 times of pure SnO₂,and responses to other gases are less than a third of ethanol.the gas sensing properties are enhanced due to the high content of oxygen vacancies and surface-adsorbed oxygen introduced by Ni doping.Thirdly,the self-doped SnO₂ nanoparticles are further obtained by dipping in hydrogen peroxide solution,which retained the dominant morphology of nanospheres.The results reveal that the content of oxygen vacancy relates to the dipping time of hydrogen peroxide.SnO₂ nanospheres dipped for 1h with the most Sn2+ and surface oxygen vacancies show a response of 26.3 to 100 ppm ethanol,which is 1.87 times higher than that of pure SnO₂.At the same time,self-doped SnO₂ exhibit high responses to different alcohols.