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.