Synthesis of Au@SnO₂ core-shell nanoparticles with controllable shell thickness and their CO sensing properties

Au@SnO₂ core-shell nanoparticles (NPs) were synthesized by a microwave-assisted hydrothermal method. These NPs were characterized by electron microscopy, UV-visible spectroscopy and X-ray diffraction (XRD). Transmission electron microscope (TEM) images showed the formation Au@SnO₂ core-shell NPs, where 12-15 nm Au NPs were covered with SnO₂ shell layer. SnO₂ shell thickness was controlled from 6 to 20 nm by repeated treatment with sodium stannate (Na₂SnO₃) solution. The surface plasmon resonance (SPR) peak of Au NPs was red-shifted (520-576.5 nm) with increasing shell thickness. XRD results confirmed the formation of the rutile phase of SnO₂ with increasing crystallite size (7-11.6 nm) as shell thickness (6-20 nm) increased. The response of Au@SnO₂ NPs for CO gas was increased with increasing shell thickness, and reached a maximum for 15 nm SnO₂ shell. The response of Au@SnO₂ core-shell NPs was higher than that of bare SnO₂ as well as Au deposited on SnO₂ NPs. Improved performance was attributed to the pronounced electronic sensitization, high thermal stability and low screening effect of Au NPs in Au@SnO₂ core-shell NPs. The sensing mechanism of Au/SnO₂ core-shell NPs for CO gas is also discussed.