Synthesis and mesoporous-structures of indium oxide nanowires for high sensitivity formaldehyde gas sensor

Mesoporous indium oxide nanowires (In2O3 NWs) were synthesized using ordered mesoporous SBA-15 silica as hard templates with nanocasting method, and then the bundled In2O3 nanowires (In2O3 BNWs) were separated from the dispersed In2O3 nanowires (In2O3 DNWs) by centrifugation technique. From the characterization with XRD, SEM, TEM, UV–vis spectra and nitrogen adsorption-desorption isotherm, both samples present the same mesoporous-structures, diameter and the similar defects due to the same synthesis conditions. The specific surface area (57.37 m2/g) of In2O3 BNWs are higher than that of In2O3 DNWs for the better mesoporous-structures. In2O3 BNWs with the smaller grain size and higher surface area absorb more oxygen in air and increase the thickness of electron depletion layer, leading to the larger change of resistance in air. Therefore, In2O3 BNWs sensor presents the better sensitivity (26.16) to formaldehyde than In2O3 DNWs sensor at optimized operating temperature owing to the high surface area and small grain size.