ABSTRACT
In2O3/SnO2 composite nanoparticles (NPs) were synthesized by a hydrothermal method. Fringes and spotty patterns were observed in high-resolution TEM images and corresponding selected area electron diffraction pattern, respectively, suggesting the nanoparticles were single crystals. X-ray diffraction results revealed that the In2O3/SnO2 composite NP sensor consisted of three phases: In2O3, SnO2 and In2Sn2O7-x (indium tin oxide: ITO). Energy-dispersive X-ray spectrum of the 9:1 In2O3/SnO2 composite NPs showed the atomic ratio of In2O3 to SnO2 was close to 9:1. The response of the chemiresistive sensor to CO was 9.2, which is within the highest 15% among the response values reported for the past 10 years. The ITO NP-based gas sensor is selective toward CO against other reducing gases such as toluene, acetone and benzene. The enhanced response of the 9:1 In2O3/SnO2 composite NP sensor to CO compared to the pure In2O3 NP sensor can be explained mainly by the stronger resistance modulation at the In2O3/SnO2 junctions.
ABSTRACT
In2O3 nanoparticle (NP)-decorated WO3 nanorods (NRs) were prepared using sol-gel and hydrothermal methods. The In2O3 NRs and WO3 NPs were crystalline. WO3 NP-decorated In2O3 NRs were also prepared using thermal evaporation and hydrothermal methods. The NO2 sensing performance of the In2O3 NP-decorated WO3 NR sensor toward NO2 was compared to that of the WO3 NP-decorated In2O3 NR sensor. The former showed a high response to NO2 due to a significant reduction of the conduction channel width upon exposure to NO2. In contrast, the latter showed a far less pronounced response due to limited reduction of the conduction channel width upon exposure to NO2. When the sensors were exposed to a reducing gas instead of an oxidizing gas (NO2), the situation was reversed, i.e., the WO3 NP-decorated In2O3 NR exhibited a stronger response to the reducing gas than the In2O3 NP-decorated WO3 NR sensor. Thus, a semiconducting metal oxide (SMO) with a smaller work function must be used as the decorating material in decorated heterostructured SMO sensors for detection of oxidizing gases. The In2O3 NP-decorated WO3 NR sensor showed higher selectivity for NO2 compared to other gases, including reducing gases and other oxidizing gases, as well as showed high sensitivity to NO2.
