Research On Gas Sensors Based On Co₃O₄ Nano-heterojunctions

With the development of industrialization and urbanization,people's living standard has been increased,but the rapid economic development has also brought great damage to the natural environment.In particular,air pollution has become a hot issue of environment in today's society.The metal oxide semiconductor-based gas sensors have characteristics including simple structure,high sensitivity,convenient operation and real-time detection,so they have been widely used in environmental monitoring,home safety,public medical security,industrial production and other fields.The gas sensors based on p-type metal oxide semiconductor have a low humidity dependence,fast response and unique catalytic activity for volatile organic compounds(VOCs),making them ideal for the design of high-performance gas sensors.However,their inherent conductive mode leads to a poor sensitivity to most gases,so it is of important research significance to through appropriate modification methods to optimize the performance of the p-type oxide semiconductor sensor.The heterojunctions(such as p-n heterojunctions and p-p heterojunctions)among different metal semiconductor oxides can significantly improve the selectivity and sensitivity of a sensor to the target gases by promoting the reaction of the target gas(chemical sensitization)or modulating the resistance(electronic sensitization).Based on the above reasons,the typical p-type oxide semiconductor Co3O4(AB2O4 cubic spinel structure)is used as a matrix sensing material,and realizes the improvement of sensing performance by constructing oxide-Co3O4 nano-heterostructure in this work.The research content is as follows:First of all,we prepared nanoparticles self-assembled into CoWO4-Co3O4 nano-heterojunction spherical structure through hydrothermal method,combined with the excellent catalytic properties of Co3O4 and the regulation of the heterojunction on the carrier realize the improvement of the sensing performance.The results indicate that the response of the CoWO4-Co3O4 based(W/Co=30 at%)sensor was 51.6 towards 100 ppm xylene.In addition,the sensor also showed a low cross-response to interfering gases such as ethanol(Sxylene/Sethanol=6.6)and the ppb detection limit(300 ppb).The sensor based on CoWO4-Co3O4 nanocomposite materials also showed a long-term stability and anti-humidity properties.To further improve the selectivity of the sensor to xylene and reduce the detection limit,the nano-structured SnO2-Co3O4 composite sensing material was synthesized by a simple one-step hydrothermal method,and the prepared sensing materials were characterized and the sensing properties were studied.The gas sensitivity test results show that the gas sensor based on SnO2-Co3O4(Sn/Co=15 at%)nano-heterostructure exhibited good selectivity(Sxylene/Sethanol=12.4,Sxyiene/Sacetone=9.7)and stability for xylene.Its response to 100 ppm xylene at 175? is 101.9,which was about 16.4 times higher than that of pure Co3O4,and its detection limit for xylene was also as low as 50 ppb.Compared with pure Co3O4 gas sensors,the performance of Sno2-Co3O4 and CoWO4-Co3O4 nanocomposite gas sensors has been significantly improved,which was mainly attributed to the regulation of carriers completed by the presence of heterojunctions.In addition,combined with the characterization results of transmission electron microscopy(TEM),specific surface area test(BET)and X-ray photoelectron spectroscopy(XPS),it can be seen that the structural parameters of composite oxide sensing materials have been significantly optimized.A larger specific surface area and a larger amount of adsorbed oxygen on the surface also play a non-negligible effect on the improvement of sensing performance.