Research On Reduced Graphene Oxide-In2O₃ Composites Based NO₂ Gas Sensors

Industrial waste gas,automobile exhaust and agricultural incineration produced a large amount of air pollutants.As the main atmospheric pollutant,nitrogen dioxide forms particles of PM 2.5 in the atmosphere reaction field,which is one of the main causes of haze.Nitrogen dioxide can generate photochemical smog and acid rain after reacted,and can destroy the ecosystem.Nitrogen dioxide will also stimulate the respiratory system and endanger health.Therefore,gas sensors with simple structure,cheap price and high response to NO2 are important for physical health and environmental testing.Because of its high sensitivity,fast response and recovery speed and other advantages,metal oxide semiconductor based sensor has been widely used.As a n-type semiconductor,the NO2 sensitivity of indium oxide(In2O3)has been widely accepted,but it also requires additional heating to work,costs high energy consumption.Graphene has been highly studied since its discovery.It has excellent electrical properties and large specific surface area.It is also a good material for the preparation of gas sensors at room temperature.But there are interactions between graphene layers,which are easy to assemble and stack,and the gas sensing properties need to be improved.Graphene and semiconductor oxide based composite materials have been potential applied in gas sensing.In this paper,we prepared composite materials of hierarchical In2O3 with graphene,and graphene aerogels with In2O3 nanoparticles.Through their synergistic effect,we prepared nitrogen dioxide sensors with high performance and low energy consumption.The contents of the experiment are as follows:1.In this work,we described the materials composed of hierarchical flower-like In2O3 and reduced graphene oxide(r GO),which were fabricated by a facile one-step hydrothermal method.The information such as morphology and composition of obtained materials are measured by analytical techniques of XRD,SEM,TEM,XPS and so on.The r GO-In2O3 composites exhibited enhanced sensing performance towards NO2 through comparison with the pure In2O3 sample.The operating temperature can be tuned by the percentage of r GO in the composites.The sensor based on 5 wt% r GO-In2O3 could work at room temperature(the response to 1 ppm NO2 is 1101).3 wt% r GO-In2O3 composite was adopted for the ultra-sensitivity gas sensor at 74℃ with a high response value(1337)to 1 ppm NO2.Its limit of detection was extremely low(10 ppb),and its response to NO2 was rapid.The sensor also exhibited excellent selectivity and stability.The flower-like In2O3 has a good sensitivity to NO2.The existence of r GO provides more active sites for NO2 and it plays a chemical sensitization effect.At the same time,p-n heterogeneous contact formed by r GO and In2O3 plays an electronic sensitization effect.The ultra-sensitivity of composites should be related to synergistic effect of the hierarchical structure of In2O3 and the presence of r GO.2.By changing the reagents and the reaction conditions,the composites of r GO and flower-like In2O3 built of sticks were prepared by one-step hydrothermal method.The information such as morphology and composition of the material was analyzed by means,such as XRD,SEM,TEM and XPS.To explore the effect of mass ratio to gas sensing properties of different composite materials,the results show that the response of pure In2O3 to 500 ppb NO2 at 66℃ is 291.But the optimum working temperature of the composites was room temperature(25℃),and the gas sensing properties to NO2 were better than that of pure In2O3 materials.Especially 1 wt% r GO-In2O3 to 500 ppb NO2 shows the highest sensitivity(591)with good selectivity and stability.In addition,its response and recovery were very fast.3.A series of cubic In2O3 modified graphene aerogels were prepared,and the maximum value of In2O3 modified for aerogels was explored.When the weight percentage of In2O3 in composites was less than 33%,graphene aerogels could be formed.The gas sensing properties of the obtained graphene aerogels were tested.The experimental results show that the sensitivity of the composites to 5 ppm NO2 was great.The detection limit of 4.8 wt% In2O3-r GO was 500 ppb.The humidity had an effect on the gas sensing properties.However,the sensitivity was stable in the range of 70%~100% R.H.,showing the application prospect in high humidity environment.