Synthesis of catalytically active gold clusters on the surface of Fe3O4@SiO2 nanoparticles

This work proposes a novel method to obtain catalytically active gold clusters by using the water-soluble 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl) porphyrin under mild conditions instead of using strong reducing agents. Uniform gold clusters were obtained with a diameter comprised between 1 and 2 nm and long-term stability. Furthermore, the water-soluble porphyrin was immobilized on the SiO2 shell of a core@shell Fe3O4@SiO2 nanoparticles to directly synthesize gold clusters onto the surface of Fe3O4@SiO2 nanoparticles featuring their magnetic recovery. Fe3O4@SiO2@ Au nanoparticles were found to be catalytically active for the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 and giving very high pseudo-first-order rate constant comprised between 0.7 and 2.7 min(-1). Our results demonstrate that Fe3O4@SiO2@ Au nanoparticles are stable catalysts and do not degrade during the catalytic process under the reaction conditions enabling their magnetic recuperation.