Study On Graphene-based NO_x Gas Sensor

Nitrogen oxides NOx (such as N2O, NO, NO2, N2O4and N2O5) are thought to bea main cause of air pollution (e.g. haze, acid deposition, eutrophication ofarch-criminal and so on). The real-time, accurate and continuous monitoring to NOx isvery important in our living environment. Currently, market mainly adopts metaloxide semiconductor gas sensor for NOx monitoring. Such sensors with highsensitivity, ease operation and rapid response-recovery characteristics, but they aregeneral poor stability and selectivity, complex sensitivity mechanism, high workingtemperature and short life. Therefore, the development of new and efficientsemiconductor gas sensor is the current and future researchers working hotspot.Graphene is a two-dimensional material with hexagonal lattice structure.Because of the high electron mobility, large speciifc surface area, excellent electricalproperties, good selectivity and a low signal to noise ratio characteristics, thegraphene has been an ideal candidate for NOx gas sensors. However, graphene basedNOx gas sensors always present slow response，poor recovery and low sensitivity.Thereofre，in order to overcome the above problems, the graphene based gas sensor isimproved by the perspective of graphene materials and preparation process in thispaper-Firstly, from the material point of view，we prepared graphene oxide (GO),reduced graphene oxide (RGO)，Ag-RGO composites, high conductivity RGO andAg-S-RGO composites. By characterization, it shows that (1) the GO prepared nopreoxidation is high oxidation degree, good hydrophilicity and can be stable insolution;(2) the RGO prepared by wet reduction is high conductivity;(3) Ag NPs capped in the RGO network plays a important role in improving the electricalproperties of RGO;(4) controlling the oxidation degree of GO can improve the crystalquality of RGO, greatly enhancing the conductivity of RGO;(5) sulfonic acid groupsinbiting the coagulation of RGO can ensure the Ag NPs uniformly dispersed on thesurface of RGO.Secondly, from the sensor process point of view, the flexible Ag-S-RGO gassensor was prepared by a gravure printing method in this paper’ The specific workincludes researching gravure process parameters, designing the sensor structure,sensor performance characterization and researching gas response mechanism. Bycharacterizing, it shows that (1) the viscosity of RGO based ink between60-70mPa sand the substrate etched20s in an oxygen plasma environment ensure the best printeffect;(2) Ag interdigitated electrode can signiifcantly reduce the overall resistance ofAg-S-RGO gas sensor devices, achieving low-power and low-noise ratio detect;(3)the full printed Ag-S-RGO gas sensor for50ppm NO2sensitivity is74.6%, theresponse time of12s, the recovery time20s at room temperature;(4) the good gassensing characteristics of Ag-S-RGO is attributed to the functional modification toRGO.