Magnetically Separable Nanocatalyst with the Fe3O4 Core and Polydopamine-Sandwiched Au Nanocrystal Shell

This work reports a novel Fe3O4@polydopamine/Au/polydopamine core/shell nanocomposite toward a magnetically separable nanocatalyst. Because the polydopamine (PDA) layer-sandwiched Au nanocrystals were prepared by a layer-by-layer method, the content of Au could be controlled by varying the Au shell number (such as burger-like Fe3O4@PDA/Au/PDA/Au/PDA). Fe3O4@PDA/Au/PDA exhibited excellent catalytic activity in reducing p-nitrophenol because the substrate could penetrate the PDA shell. Owing to the protection of the PDA shell, Fe3O4@PDA/Au/PDA presented higher cyclability than Fe3O4@PDA/Au. The activity of Fe3O4@PDA/Au/PDA maintained 95% after 7 cycles, while that of Fe3O4@PDA/Au was only 61%. The detailed cycling catalytic mechanism was investigated, and it was found that the catalytic rate of Fe3O4@PDA/Au/PDA/Au/PDA was faster than that of Fe3O4@PDA/Au/PDA because of the higher Au content. Interestingly, this method could be extended for other magnetic nanocomposites with two different kinds of noble metal nanocrystals integrated within one particle, such as Fe3O4@PDA/Au/PDA/Ag/PDA and Fe3O4@PDA/Au/PDA/Pd/PDA.