CO Sensing Properties of Chemiresistive In₂O₃/SnO₂ Composite Nanoparticle Sensors

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.