Controllable Preparation of Monodisperse Mesoporous Silica from Microspheres to Microcapsules and Catalytic Loading of Au Nanoparticles.

A unique structural transition from pomegranate-like monodisperse mesoporous silica microspheres (M-MSMs) with tunable mesopores to mesoporous silica microcapsules has been reported. The unique evolution occurred together with varying the cross-linking degrees (CLDs) of templates. Herein, using monodisperse sulfonated cross-linked polystyrene (S-CLPS) as templates, S-CLPS/SiO composite microspheres were synthesized by the sol-gel method. Subsequently, the templates were removed by calcination to obtain the M-MSMs or microcapsules. The pore sizes of M-MSMs could be tailored from 3.2 to 7.4 nm by facilely varying the CLDs from 0.5 to 20%. Interestingly, mesoporous silica microcapsules were gradually formed when the CLDs were beyond 20%. Meanwhile, the specific surface area also could be adjusted by this strategy without hardly affecting the monodispersity, and the specific surface area increased to 391.9 m/g. Significantly, Au@M-MSM was prepared by supporting Au nanoparticles (NPs) on M-MSM and used as nanocatalysts to reduce 4-nitrophenol (4-NP). The ultrathin shell and interconnected three-dimensional (3D) porous structure of M-MSMs can increase the mass transfer and protect the Au NPs from leakage, which reveals high recyclability and high conversion (>95%) after 10 regeneration-catalysis cycles. This approach provides a nanotechnology platform for the preparation of mesoporous silica materials with different microstructures, which will have enormous potential in practical applications involving different molecular sizes.