Massage ball-like, hollow porous Au/SiO2 microspheres templated by a Pickering emulsion derived from polymer–metal hybrid emulsifier micelles

Abstract

In this study, we reported a novel, facile, Pickering emulsion-templating method to prepare massage ball-like, hollow-structured Au/SiO₂ microspheres. Firstly, oil-in-water Pickering emulsions stabilized by Au@poly(ethylene oxide)-b-poly(4-vinylpyridine) (Au@PEO-b-P4VP) hybrid emulsifier micelles, which were formed by a P4VP/Au complex induced self-assembly process, were generated. Then hollow Au/SiO₂ hybrid microspheres with nano-/submicro-sized protrusions on their shells, termed as massage ball-like microspheres, were successfully synthesized using the generated Pickering emulsion as template, in which the P4VP catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS) in the TEOS/n-decanol mixed oil phase occurred at the oil/water interface. As a result, a continuous SiO₂ shell was formed. The uneven adsorption of polydisperse hybrid micelles at the oil/water interface as well as the volume shrinkage of the oil phase during the early hydrolysis and condensation of TEOS facilitated the formation of protrusions on the shell surface. After further removal of the polymer components embedded in the shell by calcination, hollow Au/SiO₂ hybrid microspheres with micropore/mesopore bimodal porous shells were produced. The as-prepared Au/SiO₂ hybrid microspheres were applied as catalysts for the reduction of p-nitrophenol with NaBH₄, showing a high catalytic activity with a good recyclability owing to the large specific areas, the easily accessible Au active centres, and the enhanced mass transportation.