Facile preparation of tiny gold nanoparticle loaded magnetic yolk–shell carbon nanoreactors for confined catalytic reactions

Abstract

Yolk–shell magnetic nanoreactors consisting of a mesoporous carbon shell and Fe₃O₄ core coated by tiny gold nanoparticle loaded SiO₂ were fabricated through a facile method. Fe₃O₄@SiO₂@RF nanospheres were firstly prepared by a one-pot process that combined the sol–gel process of tetraethyl orthosilicate and condensation polymerization of resorcinol and formaldehyde in the mixed solvent of water and ethanol with the help of ammonia, based on the similar mechanism of these two processes. Au nanoparticles were in situ immobilized after the Fe₃O₄@SiO₂@RF nanospheres were annealed under an inert atmosphere and the silica shell was partially etched. The Fe₃O₄ core not only provides sites for the immobilization of Au nanoparticles but also allows the nanoreactor to be easily recovered from liquid media by an external magnetic field. The outer mesoporous carbon shell protects the Au nanoparticles from aggregation and harsh external conditions. Furthermore, the reactants and products easily diffuse in and out of the cavities between the core and the shell because of their numerous channels. The obtained materials exhibit excellent catalytic activity for the reduction of p-nitrophenol to p-aminophenol in the presence of NaBH₄ due to their special yolk–shell structure. No dramatic decrease in catalytic activity was noted, even after the synthesized catalyst was used 10 times. This work indicates that magnetic porous carbon yolk–shell spheres could provide the ideal support for noble metal nanospheres in the development of highly efficient catalysts.