Redox Properties on the Surfaces of Silica Networks Encapsulating Clusters of Superparamagnetic Magnetite Nanoparticles

Abstract

Clusters of superparamagnetic magnetite nanoparticles encapsulated by thick silica shells (SiO2/cFe(3)O(4)) have been recognized as useful only in the role of a magnetically separable supporter. In this report, SiO2/cFe(3)O(4) colloids based on a cFe(3)O(4) core (367 nm) and a series of silica shell thicknesses (24, 47, 91, and 134 nm) were prepared and their charge transfer resistances (R-ct) and the redox reactions of Ag+/AgNP on their surfaces were investigated. The R-ct values of the SiO2/cFe(3)O(4) series increased linearly as the silica shell thickness increased. The reductive elaboration of Ag+ to AgNPs by formaldehyde on the surfaces in the SiO2/cFe(3)O(4) series was very poorly manageable in the case of the 24 nm shell but readily controllable as the silica thickness increased. The oxidative dissolution of AgNPs to Ag+ was more resistive as the silica shell thickness decreased. The surface plasmon band (ca. 405 nm) in the AgNP-decorated SiO2/cFe(3)O(4) series was progressively blue-shifted (ca. 10 nm) as the silica thickness decreased, indicating a higher electron density on the AgNPs on the thinner silica shell. Overall results indicate that the cFe(3)O(4) cores exhibit reductive properties through porous silica up to quite a long distance of over ca. 100 nm.