Influence of the distribution of nanoparticles on the NO2 sensing properties of SnO2 nanorods decorated with CaO and Pt

Abstract

Two types of CaO and Pt nanoparticles (NPs)-decorated SnO2 nanorods (NRs), SnO2 NRs co-decorated with a simple mixture of Pt and CaO NPs (CaO-Pt@SnO2) and SnO2 NRs decorated with Pt-decorated CaO NPs (Pt@CaO@SnO2), were fabricated and their NO2 sensing properties were examined. CaO-Pt@SnO2 was prepared by the decoration of SnO2 NRs with CaO NPs first and then Pt NPs, whereas Pt@CaO@SnO2 was prepared by the decoration of CaO NPs with Pt NPs and then the decoration of SnO2 NRs with the Pt-decorated CaO NPs. Pt@CaO@SnO2 showed significantly better NO2 sensing properties than CaO-Pt@SnO2. This result can be explained through a combination of electronic and chemical sensing in the mechanisms, but the chemical mechanism is dominant. In the Pt@CaO@SnO2 sample, Pt NPs exist only on the surfaces of the CaO NPs. The CaO NPs tend to adsorb H2O molecules environment because of their hygroscopic property and change to Ca(OH)2. The Ca(OH)2 molecules dissociate into CaO at 300 °C. Pt NPs on the CaO NPs catalyze the dissociation of Ca(OH)2 molecules, which enhances the gas sensing properties of the sample. In contrast, the dissociation of Ca(OH)2 molecules is not catalyzed by Pt NPs in the CaO-Pt@SnO2 sample.