Polydopamine as a bridge to decorate monodisperse gold nanoparticles on Fe3O4 nanoclusters for the catalytic reduction of 4-nitrophenol

Herein, gold nanoparticles (Au NPs) were decorated on magnetic Fe3O4 nanoclusters@polydopamine nanocomposites (Fe3O4@PDA NCs) through a direct and green reduction method. The morphology was investigated via transmission electronic microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Results showed that Fe3O4 nanoclusters were successfully coated with a PDA shell layer of 25 nm thickness that could work as a reducing reagent to form Au NPs on the surface of Fe3O4@PDA NCs and prevent the aggregation of Au NPs as well. More interestingly, the concentration of the Au precursor had a great effect on both the size and the dispersion of Au NPs on the surface of Fe3O4@PDA NCs, which directly affected the catalytic activity of Fe3O4@PDA@Au. The catalytic performance of Fe3O4@PDA@Au was determined by reducing 4-nitrophenol to 4-aminophenol in the presence of excessive NaBH4, and the result showed that Fe3O4@PDA@Au prepared from a 130 μM Au precursor exhibited the best catalytic activity with the reaction rate constant of 39.2 s−1 g−1 and a conversion of >99% in ten minutes. After being recycled and reused ten times, the magnetic catalyst still had a conversion of >95%; this suggested that it might have practical applications in the reduction of nitroaromatic compounds.