Preparation, characterization and catalytic activity of core–satellite Au/Pdop/SiO2/Fe3O4 magnetic nanocomposites

Abstract

In this study, we report a facile method to synthesize core–satellite structured Au/Pdop/SiO₂/Fe₃O₄ composite nanoparticles (NPs). Firstly, polydopamine-coated silica/magnetite nanoparticles (Pdop/SiO₂/Fe₃O₄ composites) were synthesized by the combination of a sol–gel process and an in situ polymerization method, in which tetraethyl orthosilica (TEOS) as well as dopamine acted as the precursor for silica and polydopamine (Pdop), respectively. The Pdop/SiO₂/Fe₃O₄ composites revealed a multilayer core–shell structure, where Pdop is the outer shell of the composite. Then, numerous ‘‘satellites’’ of gold nanoparticles were assembled on the surface of Pdop/SiO₂/Fe₃O₄via the reduction of Au³⁺ by the Pdop/SiO₂/Fe₃O₄ composite itself. In addition, the size and density of the gold nanoparticles can be easily adjusted by controlling the concentration of the HAuCl₄ solution. The morphology, structure, and composition of the nanocomposites are characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometry (XPS), and vibrating sample magnetometry (VSM). The resulting Au/Pdop/SiO₂/Fe₃O₄ composite NPs show not only a strong magnetic response to an externally applied magnetic field, but also a high catalytic performance on catalyzing the reduction of methylene blue (MB), at ambient temperature.