Catalytic oxidation and selective sensing of carbon monoxide for sense and shoot device using ZnO–CuO hybrids

Abstract

In the present work, we have demonstrated that ZnO–CuO based hetero-composites exhibit selective CO sensing with T100 is in close proximity to Topt to yield simultaneous CO sensing together with its 100% catalytic oxidation for sense and shoot devices. When these heterocomposites are exposed to CO, reduction of Cu2+ ions in CuO grains leads to a strong metal semiconductor interaction (SMSI) between Cu2+/Cu+/Cu0 species (in CuO grains) and ZnO grains across the ZnO-CuO interface. The SMSI interaction promotes the generation of oxygen vacancies in neighboring ZnO lattice. Eventually activated oxygen (O*ads) and CO (CO*ads) are preferentially chemisorbed on zinc oxide (in its vacant oxygen sites) and CuO (on the surface of Cu2+/Cu+/Cu0 ions) respectively. The activated oxygen reacts immediately with adsorbed CO to yield selective CO sensing together with 100% CO oxidation. For ZnO–CuO (1:1) composites, the measured Topt (∼175 °C) and T100 (∼200 °C) temperatures are significantly lowered as compared to the respective temperatures measured for indium doped ZnO (Topt∼300 °C, T100∼550 °C) and CuO (Topt∼200 °C,T100∼300 °C) catalysts. Fine tuning of the mole fraction of ZnO and CuO are necessary for these hetero-composites to yield T100 of catalytic activity close to Topt for maximum CO sensing.