Facile synthesis of SnO(2) shell followed by microwave treatment for high environmental stability of Ag nanoparticles

This study describes a new method for passivating Ag nanoparticles (AgNPs) with SnO(2) layer and their further treatment by microwave irradiation. The one-step process of SnO(2) layer formation was carried out by adding sodium stannate to the boiling aqueous AgNPs solution, which resulted in the formation of core@shell Ag@SnO(2) nanoparticles. The coating formation was a tunable process, making it possible to obtain an SnO(2) layer thickness in the range from 2 to 13 nm. The morphology, size, zeta-potential, and optical properties of the Ag@SnO(2)NPs were studied. The microwave irradiation significantly improved the environmental resistance of Ag@SnO(2)NPs, which remained stable in different biological solutions such as NaCl at 150 mM and 0.1 M, Tris-buffered saline buffer at 0.1 M, and phosphate buffer at pH 5.6, 7.0, and 8.0. Ag@SnO(2)NPs after microwave irradiation were also stable at biologically relevant pH values, both highly acidic (1.4) and alkaline (13.2). Moreover, AgNPs covered with a 13 nm-thick SnO(2) layer were resistant to cyanide up to 0.1 wt%. The microwave-treated SnO(2) shell can facilitate the introduction of AgNPs in various solutions and extend their potential application in biological environments by protecting the metal nanostructures from dissolution and aggregation.