Study On Gas Sensitive Properties Of Ordered Mesoporous Nickel Oxide Doped With Indium

At present,with the problem of air pollution becoming more and more serious,especially the vigorous development of automobile industry and the fast rising of car sales,the problem of nitrogen dioxide pollution caused by automobile exhaust has become the focus of environment protection.Nitrogen dioxide is the main component of air pollutants,and is the important source of acid rain and acid mist.In the field of medical diagnosis,nitrogen dioxide is also featured as a momentous index of disease diagnosis.So it has become a hot spot to design and manufacture a novel nitrogen dioxide gas sensor with low detection limit and high sensitivity.Among many types of gas-sensitive materials,metal oxide semiconductors are known for their wide use of various gas detectors because of their low cost,high adaptability and high stability.Nickel oxide as a p-type metal oxide semiconductor,due to the strong surface adsorption between nitrogen dioxide molecules and nickel oxide,is more sensitive to nitrogen dioxide.However,considering the sensitivity to nitrogen dioxide is not high,there is a need for pure nickel oxide to improve sensing performance by composite technology.In this paper,the response of nickel oxide is improved by adjusting the morphology of nickel oxide and doping base metal,and the mechanism of increased gas sensing performance is analyzed.In this paper,ordered mesoporous nickel oxide was prepared by wet etching using KIT-6 molecular sieve as a template.Then,indium was doped onto the surface of ordered mesoporous nickel oxide by impregnation and precipitation.The results showed that the sensing responses of ordered mesoporous In-NiO composites to nitrogen dioxide were significantly improved compared with pure NiO.This paper investigated the optimum ratio of indium doping was 5.0 at%of nickel oxide.It was obtained that the highest response about 3 towards 15 ppm NO₂ sensing at room temperature and 55 toward 5 ppm NO₂ sensing at 250°C for 5.0 at%In₂O₃-decorated NiO compared to other decorated and pure samples.Moreover,the sensor displayed excellent selectivity and stability towards NO₂ in the presence of other interfering gases.The reasons for enhanced gas sensing were analyzed as follow:firstly the improved NO₂ sensing properties through indium doping were firstly ascribed to increase of the surface activity of nickel oxide which resulted in a larger specific surface area and more reactive sites;secondly,due to the energy level match between nickel oxide and indium oxide,p-n junction was formed at the contact interface,regulating carrier concentration on the surface of the nickel oxide which made the material more sensitive to the same concentration of the target gas.