Preparation Of In₂O₃-based Composite Nanofibers And Their Low-temperature NO₂ Gas Sensing Properties

NO2,an important atmospheric pollutant,endangers the ecological environment and threatens the health of people.Therefore,it is particularly important to effectively detect and monitor NO2 gas.Gas sensors can monitor the toxic and harmful gases in the environment.Among them,resistance-based metal oxide gas sensors have been widely used to monitor NO2 due to their fast response speed,high sensitivity,light weight and low cost.At present,researchers are dedicated to studying the response properties of various metal oxide materials to NO2.Among various sensing materials,In2O3 has wide band gap,low resistivity,and high chemical stability,showing promising sensing properties.Although considerable researches concerning In2O3 sensing materials have been studied and a great progress has been achieved,the NO2 sensing properties of pure In2O3 nanostructures still require to be further improved.The surface modifications based on metals or metal oxides can improve sensing performances of In2O3 by increasing the surface activity and promoting the adsorption and desorption of target gas on the surface of In2O3.In this work,porous In2O3-based nanofibers were fabricated by an electrospinning technique,and surface modification of these pre-fabricated nanofibers with noble metal Ag was used to promote the sensing performances to low-concentration NO2 at room temperature.Although noble metal surface modifications can effectively improve the NO2 sensing responses of In2O3,the high prices of noble metals restrict the large-scale fabrication and application of noble metal-In2O3 sensing materials.Hence,we also attempted to select low-cost metal-In2O3 sensing materials to explore sensing response to NO2.The main research contents of this work were as follows:Porous rGO-In2I3 nanofibers were synthesized by a simple electrospinning approach firstly,and Ag-rGO-In2O3 composite nanofibers with different Ag molar ratios(0.5%,1%and 3%)were then prepared by a photodeposition method.The specific surface area and surface O2 species absorbing capability of the Ag-rGO-In2O3 composite nanofibers can be reasonably tuned through the surface modulation of Ag.The sensing performances of Ag-rGO-In2O3 composite nanofibers to NO2 were investigated at room temperature(25?).In comparison with rGO-In2O3 nanofibers,the Ag-rGO-In2O3 composite nanofibers exhibited improved NO2 sensing response.Particularly,1%Ag-rGO-In2O3 composite nanofibers were demonstrated with the highest sensing performance as compared with other composite nanofibers.The response of the 1%Ag-rGO-In2O3 composite nanofibers was 83.53-1000 ppb NO2,which was 16.6 times as high as that of rGO-In2O3 nanofibers.Furthermore,the Ag-rGO-In2O3 composite nanofibers also exhibited good NO2 selectivity,stability and low detection limit.The enhanced NO2 performances can mainly be attributed to the Schottky barrier between Ag nanoparticles and rGO-In2O3 nanofibers.Meanwhile,increased specific surface areas and high surface O2-species absorbing capability of the Ag-rGO-In2O3 composite nanofibers enhanced the resistance modulation capability,which further improved the gas sensing performance of the sensor.Porous In2O3 nanofibers were fabrication by an electrospinning technique,and then Zn nanoparticles decorated In2O3 nanofibers were constructed via a simple chemical vapor deposition approach.The decrease in sensor resistance and the improvement of surface O2-species absorbing capability were observed due to the surface modification of In2O3 nanofibers with Zn nanoparticles.In comparison with pure In2O3 nanofibers;Zn-In2O3 composite nanofibers exhibited much higher NO2 response.The optimum operation temperature is 50? for both sensors.At the optimal temperature,the response of Zn-In2O3 composite nanofibers was up to 130.00 to 5 ppm NO2,which is 13.7 times higher than that of pure In2O3.Additionally,good selectivity,lower detection limit and relatively high response under high RH to NO2 were also demonstrated for the Zn-In2O3 composite nanofibers.From our perspective,the enhancement sensing mechanism of Zn-In2O3 composite nanofibers were mainly attributed to the enhanced resistance modulation owing to the formation of ohmic contacts between Zn nanoparticles and In2O3 nanoparticles.Replacing traditional noble metal with non-noble metal Zn can reduce production costs,which was in favor of the large-scale fabrication and application of In2O3 sensing materials.