Highly selective and sensitive xylene sensors using Cr2O3-ZnCr2O4 hetero-nanostructures prepared by galvanic replacement

Cr2O3/ZnCr2O4 nanocomposite powders and phase-pure ZnCr2O4 powders were prepared by the galvanic replacement of Zn in ZnO hollow spheres by Cr and subsequent heat treatment. The Cr2O3/ZnCr2O4 nanocomposite powders prepared by galvanic replacement consisted of nanocrystalline Cr2O3 and ZnCr2O4 particles, which showed a high response (resistance ratio) of 69.2 to 5 ppm xylene at 275 °C and excellent xylene selectivity. In contrast, both Cr2O3 and ZnO powders showed selectivity to ethanol, and no significant selectivity to a specific gas was found for the ZnCr2O4 powders. The Cr2O3/ZnCr2O4 composite powders consisting of coarse particles prepared by solid-state reaction showed relatively low response and selectivity to xylene. The high selectivity and response to xylene of the Cr2O3/ZnCr2O4 nanocomposite powders were attributed to the synergistic promotion of the methylbenzene-sensing reaction by two sensing materials with different catalytic activities and the high chemiresistive variation of the small particles, respectively, both of which result from the intimate and uniform mixing of nanocrystalline Cr2O3 and ZnCr2O4 particles.