Synthesis of plasmonic Ag@SnO₂ core-shell nanoreactors for xylene detection

Ag@SnO₂ core-shell nanoparticles (NPs) were prepared by a microwave-assisted hydrothermal method. The Ag NPs were synthesized by colloidal method and their size (10-24 nm) was controlled by the amount of reducing and stabilizing agents added. The size of Ag NPs was increased and subsequently their surface plasmon (SP) band was red-shifted with increasing reducing agent amount. A SnO₂ NP shell was deposited on Ag NPs by microwave-assisted hydrothermal method. The size of Ag@SnO₂ core-shell NPs was within 50 nm in diameter, which was composed of 15-18 nm Ag NPs and a 10-15 nm SnO₂ shell. The SP band of Ag NPs was red-shifted with SnO₂ shell formation. Ag@SnO₂ core-shell NPs showed higher response to p-xylene as compared to other interfering gases (NO₂, HCHO, CO and H₂). The maximum response of Ag@SnO₂ core-shell NPs to 5 ppm p-xylene was 16.17, whereas the maximum response of bare SnO₂ was 10.79 to 5 ppm H₂. The response of Ag@SnO₂ core-shell NPs to 5 ppm p-xylene was approximately 7 times higher than that of bare SnO₂ NPs. The improved gas sensing performance of Ag@SnO₂ core-shell NPs was attributed to the electronic as well as catalytic activity of Ag NPs. It was proposed that the selective detection of p-xylene was attributed to the effective inwards diffusion of p-xylene through SnO₂ shells and their subsequent dissociation into smaller and more active species by Ag NP catalysts on the inner part of the SnO₂ shell.