Study On Sysnthesis And Properties Of Nanostructured In₂O₃ Gas Sensing Materials

Semiconductor metal oxide for gas sensor which have high sensitivity, good stablility, and rapid response-recovery time are low cost, and easy to be fabricated. Therefore, they have been widely used in environmental protection, food safety, indoor environment, disease diagnosis and safety alarm. Semiconductor In₂O₃ is a novel functional gas sensing materials which has been widely used to detect all kinds of toxic and explosive gases, such as CO, H2, NOx, H2 S and so on. The gas sensing performance of semiconductor metal oxide is mainly dependent on the composition of chemical elements, microstructure and surface modification of dopant. In this thesis, In₂O₃ nanospheres and Ni-doped In₂O₃ nanoparticles have been successfully synthesized via different reaction system and its sensitive performance were studied in detail. These gas sensing materials show high sensitivity, good stability and short response-recovery time. This thesis contains the following two results:In₂O₃ nanospheres with excellent sensing ability to explosive nitro-compounds have been successfully synthesized via a two-step method including a mild solvothermal process and calcination at elevated temperature in air. The as-synthesized In₂O₃ nanospheres are of 200-300 nm in diameter and are composed of small nanoparticles with a size of around 5 nm. The structure, morphology and thermal stability are investigated by XRD, SEM, TEM, HRTEM, TG and XPS. At 140 °C, the responses of this sensor towards 100 ppm nitromethane, nitroethane and nitropropane are 163, 220 and 375, respectively. And what’s more, the sensor also exhibits short response time of less than 1 s, good long-term stability（50 times）, and low detection limits（100 ppb）. The good sensing performance should be attributed to the strong electron-withdrawing effect of nitro group and low working temperature.Aromatic hydrocarbons, generic terms of benzene and its derivatives, are important organic solvents and widely used in daily life and production. But monitoring lowconcentration aromatic hydrocarbons vapors is still a challenging task because their structure and chemical properties largely confine the interaction with the surface of sensing materials. Hereby, we use a simple solvothermal synthesis of pure In₂O₃ and Nidoped In₂O₃ nanoparticles. The Ni-doped In₂O₃ nanoparticles are amorphous at a calcining heat of 450 °C. All of the XRD characteristic diffraction peaks can be indexed to the cubic phase In₂O₃ with the increasing of sintering temperature. The grain size of Ni-doped In₂O₃ nanoparticles is about 20-30 nm and the motion of crystallites is restricted from TEM. The adsorbed oxygen content of Ni-doped In₂O₃ nanoparticles is much higher than that of In₂O₃ from XPS. The gas sensor performance of the Ni-doped In₂O₃ nanoparticles for benzene, toluene and xylene exhibit fast response time（1 s）, relatively low work temperature（200 °C）, low detection limits（100 ppb） and high response（50, 18 and 34）. The as-prepared Ni-doped In₂O₃ nanoparticles based sensor shows potential applications in detecting aromatic hydrocarbons.