Hierarchic Template Approach for Synthesis of Silica Nanocapsules with Tuned Shell Thickness

Nanoporous silica capsules with mesosized diameter (ca. 60 nm) were prepared by using polystyrene (PS) beads and polyethyleneimine (PEI) as the hierarchic core and shell templates, respectively. The coverage of PEI on the PS beads enhanced the positive charge density on the template surface and favored the formation of well-separated hollow spheres with diameters smaller than 100 nm. By tuning the PEI shell template layer on the solid PS bead templates at different pH values, the shell thickness of the hollow silica sphere could also be controlled at the nanometer level in the range 3-12 nm.