Formation of Hollow Silica Colloids through a Spontaneous Dissolution–Regrowth Process

tence of a large number of silicate species and their rich chemical interactions makes the dissolution and growth of silica challenging to study. However, this complexity also provides enormous opportunities for the development of materials with new structures and functionalities. For example, systematic investigation of the dissolution and formation of silica nanoparticles has made it possible to control the nucleation and growth, and subsequently the crystal size and shape, of zeolite materials. [4–6] Herein, we report that amorphous silica colloids, when dispersed in an aqueous solution of NaBH4, undergo a spontaneous morphology change from solid to hollow spheres. Concurrent but separate coredissolution and shell-growth processes appear to be responsible to the formation of the hollow structures. Besides the interesting fundamental aspects of this spontaneous process, this work also provides an effective self-templated route for the preparation of hollow silica nanostructures, which may find immediate applications in fields such as catalysis and drug delivery. [7–12] Since silica can coat many nanostructures through simple sol–gel processes, our discovery also allows convenient transformation of core–shell particles into yolk– shell structures, which are promising for use as nanoscale reactors and controlled-release vehicles. Compared to widely adopted methods using polymer beads and micelle and