Metallodielectric hollow shells: optical and catalytic properties.

Metallodielectric composites with tunable optical properties were prepared by layer-by-layer assembly of gold nanorods on polystyrene (PS) spheres and subsequent deposition of SiO2 or TiO2 encapsulating shells through a sol-gel process. The optical properties of the core-shells were tailored in the visible and the near-infrared region through the gold nanorod aspect ratio and the gold nanoparticle density. Removal of the PS core by dissolution in an appropriate solvent, such as THF, yielded metallodielectric hollow shells with optical properties identical to those of the original composites. The presence of gold and the porosity of the SiO2 or TiO2 shells, suitable to allow diffusion of reactants and products, make these materials of interest as catalysts, as demonstrated by the reduction of potassium hexacyanoferrate(III) with NaBH4.