Preparation And Application Of Indium Oxide Based VOCs Gas Sensitive Materials

With the increasing attention to environmental quality,the advanced techniques for detecting harmful gases in air have attracted widespread concerns.The chemiresistor-type gas sensors based on semiconductor metal oxides have gradually played an important role in monitoring the flammable,explosive and toxic gases in air.As one of the most important gas detection candidates,In2O3 has the advantages of wider band gap,lower resistivity and higher catalytic activity.However,inherent defects still exist in its pure oxide form.Therefore,it is of great significance to to overcome the shortcomings of pure In2O3 and build high-performance sensors for practical applications.In this paper,the micro-nanostructures In2O3 with different morphologies were prepared by simple hydrothermal method or constant temperature oil bath method.Then the pure In2O3 with different morphologies was used as the main material,and the strategies of element doping,surface functional modification and multiple metal oxide compounding were adopted to enhence gas-sensing properties of In2O3 gas sensor.First,a transition metal cation substitution method was used to synthesize Co-doped In2O3 spongy-like microstructures via a simple hydrothermal method combined with an annealing process.The microstructure,crystal structure and elemental composition of materials were systematically studied by various material characterization methods.The results show that the Co-doped In2O3 sensor has high sensitivity toward ethanol.The 3 mol%Co-doped In2O3 presents the highest response to acetone at 240?,which is about 3.25 times higher than that of pure In2O3.The sensor also exhibits rapid response-recovery time(1.143 s/37.5 s),low detection limit(2.76 at 5 ppm)and good stability,making it a promising material for acetone detection.To reduce the working temperature of In2O3 sensor,the surface functionalization was performed by noble metal nanoparticles on the basis of cation substitution doping.The Ni-doped In2O3 nanorods were fabricated via simple oil bath and annealing processes,and different concentrations of Ag were modified by subsequent chemical reduction.The experimental results reveal that these composites exhibit excellent formaldehyde-sensing property as compared with the pure In2O3 nanorods.In particular,6%-Ag/Ni5.0In presents significantly enhanced gas-sensing properties toward 100 ppm formaldehyde gas at a low working temperature(160 0C)with high sensitivity(123.97),fast response speed(1.45 s/58.2 s),good selectivity and strong stability,providing an effective strategy to achieve excellent gas sensing performance for formaldehyde gas sensors.?-Fe2O3 is another traditional sensing material.In this paper,In2O3/?-Fe2O3 heterojunction nanocomposite was synthesized by a simple hydrothermal method and chemical precipitation process.A series of characterization and gas sensitivity tests were carried out for the composite materials.The results indicate that the diameter of In2O3/?-Fe2O3 nanospheres is about 250-350 nm,the specific surface area was 57.89 m2 g-1,and the pore size is mainly distributed around 13.64 nm.Moreover,the In2O3/?-Fe2O3 sensor has a higher response to ethanol gas at 200?(about 65.31),and a shorter response and recovery time(1.66 s/18.91 s)compared to pure In2O3 and pure ?-Fe2O3 sensors.