Morphology control and temporal growth of a continuous silver shell on core-shell spheres

We report the synthesis of Fe@TiO2@Ag core-shell-structured spheres with an extremely continuous and complete Ag shell (at least 50 nm in thickness). In particular, we investigated the Ag shell growth on the Fe@TiO2 spheres using an electroless deposition technique based on electrostatic attraction. In order to induce a well-defined Ag shell surface, we controlled various synthesis variables and found that the concentration of trisodium citrate, the molar ratio of NaOH/AgNO3, and the aging time of ammoniacal Ag solution all played a critical role in the formation and growth of the Ag shell. We investigated, for the first time, the temporal growth of the Ag shell at the early stage of the Ag growth reaction to examine how Ag islands grow and coalesce when trisodium citrate is used. In addition, we also investigated the reflectance of the resultant particles to evaluate the degree of continuity of the Ag shell.