A general and feasible method for the fabrication of functional nanoparticles in mesoporous silica hollow composite spheres

This paper presents a general and feasible method for the fabrication of uniform hollow mesoporous nanocomposite silica spheres (HMNSs) loaded with functional nanoparticles (Au, Pt, Fe3O4, etc.) on their inner walls. In this approach, carboxylic-capped polystyrene (PS) spheres were first synthesized by a soap-free emulsion polymerization and then deposited on a layer of poly(diallyldimethylammonium chloride) (PDDA). Next, the functional nanoparticles were self-assembled onto the surfaces of the PS spheres through electrostatic interactions between the negatively-charged citrate groups and the positively-charged PDDA layer. After encapsulation of the hybrid shell derived from the sol-gel process of tetraethoxysilane (TEOS) and n-octadecyltrimethoxysilane (C18TMS), followed by calcination, various HMNSs loaded with functional nanoparticles such as Au@SiO2, Pt@SiO2, Fe3O4@SiO2, etc. could be fabricated. This approach allows the control of the numbers of functional nanoparticles loaded into the hollow spheres very easily and prevents nanoparticle aggregation effectively. As a prototype, the as-obtained Au@SiO2 HMNSs displayed very good catalytic reusability.