This work reports a novel FeO@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 FeO@PDA/Au/PDA/Au/PDA). FeO@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, FeO@PDA/Au/PDA presented higher cyclability than FeO@PDA/Au. The activity of FeO@PDA/Au/PDA maintained 95% after 7 cycles, while that of FeO@PDA/Au was only 61%. The detailed cycling catalytic mechanism was investigated, and it was found that the catalytic rate of FeO@PDA/Au/PDA/Au/PDA was faster than that of FeO@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 FeO@PDA/Au/PDA/Ag/PDA and FeO@PDA/Au/PDA/Pd/PDA.

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A one-step strategy combining in situ redox-oxidation polymerization and a ZIF-8 sacrifice template is reported for constructing Au/PDA cubic microcapsules.