Preparation Of ZnO Nanomaterials Heterojuncyion Materials And Study On NO₂ Gas Sensitivity And Mechanism

With the development of industry and technology,air pollution comes into public view.In particular,NO2 is a toxic gas that directly causes deterioration of human health when exposed to ppm levels of NO2.In addition,NO2 is also one of the causes of acid rain,with various environmental impacts,such as reduced atmospheric visibility and acidification of surface water.Therefore,it is necessary to develop highly sensitive,low-cost,and maintenance-free NO2 monitoring technology.Metal oxide semiconductors(MOS)have been widely studied and developed for gas sensor applications due to their easy fabrication,low cost,and excellent stability.ZnO is an ideal and widely studied gas sensing material due to its wide band gap,high electron mobility,and non-toxicity,but single ZnO-based sensors exhibit low sensing performance.This paper focuses on the rGO-NiO/ZnO and ZnWO4/ZnO-rGO studies to investigate the gas-sensitive properties of NO2 and its sensing mechanism.1.In this paper,rGO-NiO/ZnO composite were synthesized by hydrothermal and hydrazine reduction methods for the detection of N02 Under the operating temperature of 140 0C and relative humidity of 33.7%,the response of rGO(0.5wt%)-NiO/32ZnO based sensor to 2 ppm NO2 reaches 80.1,which is 4.55 times and 1.38 times of pure ZnO and NiO/32ZnO composite materials,respectively.At the same time,it shows a faster response time(39 s)and a lower detection limit(46 ppb)..The enhanced gas sensing performance results from the formation of p-n heterojunctions that facilitate the formation of additional depletion layers at the contacts,while the modification of rGO increases the surface active sites and accelerates the electron transfer.This work will contribute to the improvement of metal oxide semiconductor-based gas sensors.2.In this paper,6ZnO/ZnWO4-rGO(0.6 wt%)composites were successfully synthesized by precursor calcination and hydrazine reduction.The composition,morphology and structure analysis showed that 6ZnO/ZnWO4 was successfully fixed on the rGO sheets.The effective p-n junction between ZnWO4 and ZnO nanoparticles was formed by the modification of rGO sheets.The immobilization of ZnWO4 and ZnO nanorods on rGO not only provides more p-n junction,but also significantly improves the gas-sensitive response to NO2.At 110?,the sensing performance of 6ZnO/ZnWO4-rGO(0.6wt%)composite is 1.53 times and 2.32 times that of 6ZnO/ZnWO4 composite and pure ZnO sample for 2 ppm NO2(45.38),while exhibiting faster response time(35 s)and lower detection limit(0.096 ppm).In addition,the optimal operating temperature of 6ZnO/ZnWO4-rGO(0.6 wt%)composites for 2 ppm NO2 is 110?,which is lower than that of pure ZnO(130?).At the same time,bimetallic oxide ZnWO4 is used to modify ZnO in this project,and the application of ZnWO4 in gas sensing field is also expanded.The presence of a sufficient number of effective p-n junctions between ZnWO4-ZnO in rGO sheets stabilizes the 6ZnO/ZnWO4-rGO(0.6 wt%)sensor with excellent sensitivity to NO2.This result provides a facile and effective method for the preparation of graphene-decorated metal oxides based gas sensors.