Activation of the Solid Silica Layer of Aerosol-Based C/SiO₂ Particles for Preparation of Various Functional Multishelled Hollow Microspheres

Abstract

Double-shelled C/SiO₂ hollow microspheres with an outer nanosheet-like silica shell and an inner carbon shell were reported. C/SiO₂ aerosol particles were synthesized first by a one-step rapid aerosol process. Then the solid silica layer of the aerosol particles was dissolved and regrown on the carbon surface to obtain novel C/SiO₂ double-shelled hollow microspheres. The new microspheres prepared by the facile approach possess high surface area and pore volume (226.3 m² g^–1, 0.51 cm³ g^–1) compared with the original aerosol particles (64.3 m² g^–1, 0.176 cm³ g^–1), providing its enhanced enzyme loading capacity. The nanosheet-like silica shell of the hollow microspheres favors the fixation of Au NPs (C/SiO₂/Au) and prevents them from growing and migrating at 500 °C. Novel C/C and C/Au/C (C/Pt/C) hollow microspheres were also prepared based on the hollow nanostructure. C/C microspheres (482.0 m² g^–1, 0.92 cm³ g^–1) were ideal electrode materials. In particular, the Au NPs embedded into the two carbon layers (C/Au/C, 431.2 m² g^–1, 0.774 cm³ g^–1) show a high catalytic activity and extremely chemical stability even at 850 °C. Moreover, C/SiO₂/Au, C/Au/C microspheres can be easily recycled and reused by an external magnetic field because of the presence of Fe₃O₄ species in the inner carbon shell. The synthetic route reported here is expected to simplify the fabrication process of double-shelled or yolk–shell microspheres, which usually entails multiple steps and a previously synthesized hard template. Such a capability can facilitate the preparation of various functional hollow microspheres by interfacial design