Synthesis of single crystalline In2O3 octahedra for the selective detection of NO2 and H2 at trace levels

Abstract

Single crystalline indium oxide (In₂O₃) octahedra have been synthesized by means of a vapor phase transport method at high temperature. The resulting material has been characterized by FE-SEM, HR-TEM, XRD, XPS and PL. The gas sensing properties of this material against oxidizing and reducing gases have been examined and the conditions for selectively detecting such gases have been established. A high response towards NO₂ has been obtained at a relatively low optimal operating temperature (i.e., 130 °C) and even at room temperature. The fact that the response of the nanomaterial is more than two orders of magnitude higher for NO₂ than for H₂, even in the presence of ambient moisture, makes it very promising for the selective detection of oxidizing species (at ppb levels) under real ambient conditions. The addition of noble metal nanoparticles (Pt and Pd) combined with an increase in the operating temperature (i.e., 250 °C) significantly increases H₂ sensitivity and dramatically decreases the response to NO₂. However, in this case, the presence of humidity negatively affects the response to H₂. The sensing mechanisms are introduced and discussed.