Rationalized Fabrication of Structure-Tailored Multishelled Hollow Silica Spheres

This work demonstrates a simple approach to rational fabrication of multishelled hollow silica spheres via periodic injections of a given amount of tetramethylammonium hydroxide (TMAH) to catalyze the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in ethanol/water mixtures. Upon TMAH injection each time, the silica networks formed at the early stage of the sol–gel reaction of TEOS was found to possess noticeably lower condensation degree than these formed at the late reaction stage. The former could be readily and completely etched away in boiling water whereas the latter remained intact. The use of TMAH as basic catalyst led to temporally clear-cut separation between the early and late stages during the sol–gel reaction of TEOS and made the volume ratio of the loosely condensed silica gel networks, formed at the early reaction stage, to the densely condensed ones, formed at the late reaction stage well-defined around 3:2, enabling the formation of multishelled hollow spheres with precisely defined shell thickness and spacing between neighboring shells. The present template-free approach will open up new prospects in rational design and fabrication of structure-tailored multishelled silica spheres to accommodate to the demand of improved applications.