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

From the inside out: Silica colloids can be spontaneously transformed from solid spheres to hollow structures in aqueous solutions of NaBH4 (see picture). The high pH value and gradual decomposition of NaBH4 facilitate the formation of hollow structures first by partial dissolution of silica cores and then by regrowth of the silicate species on the colloid surfaces to form shells.