Anomalous effect of the aging degree on the ionic permeability of silica shells

We present a systematic study on the ionic permeability and protective ability of silica shells with different aging degrees by using the acid etching of silica-coated iron oxide nanoparticles as the model reaction. Contradictory to common impressions, we found that the ionic permeability of silica shells increased rather than decreased with the increasing aging degree. This trend may be explained by the chemical nature of the sol–gel silica shell that affects the wettability and, thereby, the transportation of water molecules and hydrated ions. Our study provides novel insights into the protective ability of sol–gel derived silica, which enables us to design thin but low-permeability shells for the stability of inner nanoparticles under harsh conditions without scarifying the performance of core–shell nanostructures.