Study On Gas-Sensing Properties Of ZnO-based Heterostructures

Gas sensors can effectively detect the composition and concentration of polluting gases,and have been widely used in industrial production,environmental testing and other fields.The selection of sensitive materials is the most important factor in determining the performance of gas sensors.In this paper,a series of heterostructures with special morphology and uniform size are constructed by changing the synthesis conditions of typical n-type ZnO semiconductor.Compared with pure ZnO gas sensors,the gas sensors based on these heterostructures not only have significantly improved the sensitivity and selectivity for specific target gases,but also have obviously shortened the response/recovery time.In addition,the baseline resistance and operating temperature of the gas sensor are effectively reduced by laser assisted irradiation,thus realizing the room temperature detection of testing gas.The research results have provided new ideas for the development of ZnO-based gas sensors for detecting special gases and low energy consumption.The main studies in this paper can be seen as follows:ZnO/NiO p-n heterostructures with a porous 3D microflower-like structure were designed and fabricated.The gas sensing performance of ZnO/NiO heterostructures was studied systematically,and the results showed that with the increasing content of NiO nanoparticles,the response value of heterostructures followed the trend of increasing first and then decreasing.Among them,at the optimal operating temperature of 240°C,the response value of ZnO/NiO heterostructure with 5%Ni²⁺to 100 ppm TEA gas was 20.74,which was nearly 5 times higher than that of pure ZnO-based gas sensor.At the same time,its response and recovery time were 2 s and11 s,respectively,and good selectivity for TEA.The formation of p-n heterojunction was the key factor for the improvement of gas sensing performances of composites.The theoretical calculation results show that new chemical bonds are formed at the interface of the heterojunction,the charge density is higher,and the density of states near the Fermi level of the heterostructure is mainly provided by Ni,indicating that NiO can effectively control the electrical properties of the heterostructure,thereby improving its gas-sensing performance.Columnar ZnO nanorods were synthesized,and then Fe₂O₃nanoparticles with different contents were modified on the surface to form ZnO/Fe₂O₃n-N heterostructures.In the gas sensing tests,the response value of the 1 wt%Fe₂O₃/ZnO-based sensor to 100 ppm TEA gas was 14.5 at 260℃,which was nearly 3times higher than the pure ZnO-based sensor,its response and recovery time were 1 s and 14 s,respectively.The sensor also has good selectivity and long-term stability.The enhanced gas sensing performance was attributed to the formed n-N heterojunctions.The DFT simulation results confirmed that the Fe₂O₃/ZnO heterostructure had the lowest adsorption energy for TEA molecules,and there is an obvious charge transfer phenomenon between the adsorption model and the adsorbed molecule.ZnO/In₂O₃n-N heterostructures composed of ZnO nanosheets and In₂O₃nanoparticles were successfully synthesized.Under the 405 nm blue-violet laser irradiation,the baseline resistance of the ZnO/In₂O₃-based gas sensor was effectively reduced,and a large number of n-N heterojunction barriers can effectively control the carriers and realize the resonant tunneling transport of carriers.Gas sensing studies shown that at room temperature,for NO₂gas with a concentration of 10 ppm,the response value of the sensor was 29.1,the response and recovery time were 61 s and39 s,respectively,and the detection limit concentration was 800 ppb.At the same time,the sensor also had good selectivity and long-term stability.The heterojunction barriers can effectively control the resonant tunneling transport of carriers,which is the key factor of the ZnO/In₂O₃heterostructure to detect NO₂gas at room temperature.