Microstructure and CO gas sensing property of Au/SnO ₂ core-shell structure nanoparticles synthesized by precipitation method and microwave-assisted hydrothermal synthesis method

Au/SnO ₂ core-shell structure NPs were prepared by a precipitation method and a microwave hydrothermal synthesis method, and their CO responses were measured by a high resistance meter. It was found that the CO response of the sample prepared by the precipitation method was extremely low, 0.18, with comparison to the one by the hydrothermal synthesis method, 0.965. Microstructures achieved by two-dimensional TEM characterization showed that both samples maintained the similar core-shell structures with their sizes ranging between 30 and 50 nm, as the core consists of Au NP and the shell consists of SnO ₂ NPs. The average grain sizes of SnO ₂ NPs of precipitation method and hydrothermal synthesis method were measured as 5.2 nm and 8.3 nm, respectively. The thickness and the porosity variation of SnO ₂-shell layers were characterized further by three-dimensional electron tomography, and correlated with the sensing properties. It was found that the porosity within SnO ₂-shell layers prepared by the precipitation method was lower than the one prepared by the hydrothermal synthesis method. Since Au NP could act as the catalyst for CO oxidation reaction, high porosity within SnO ₂-shell layers would have lead the accessibilities of Au NP to the CO gas molecules and resulted high CO responses.