Fe3O4/Au binary nanocrystals: Facile synthesis with diverse structure evolution and highly efficient catalytic reduction with cyclability characteristics in 4-nitrophenol

Fe3O4/Au binary nanocrystals have been widely utilized in catalysis, biology, medicine and other fields due to their unique magnetic and optical properties. In the present work, diversely structured Fe3O4/Au core-satellite nanocubes and Fe3O4@Au core-shell nanocrystals are fabricated by a seed deposition and a seed-mediated growth process, respectively. The developed binary nanocrystals equipped with highly efficient and recyclable catalytic reduction characteristics for 4-nitrophenol (4-NP). Extensive x-ray diffraction and transmission electron microscopy studies demonstrate that the amount of Au seeds deposited onto the surfaces of Fe3O4 nanocubes increases with increasing the additive amount of Au seeds. Aiming at structure tailored engineering, Fe3O4@Au core-shell nanocrystals are formed when Fe3O4/Au-50 mL core-satellite nanocubes are chosen as a template for further coating with gold shell by seed-mediated growth. Moreover, the magnetic saturation is gradually weakened with increasing addition quantity of Au seeds. Importantly, 4-NP is employed as a model molecule to investigate the effect of developed Fe3O4/Au binary nanocrystals on the catalytic performance. The rate constant of Fe3O4/Au core-satellite nanocubes is higher than that of Fe3O4@Au core-shell nanocrystals because of distinctly different surface area-to-volume ratio of Au nanocrystals. Fe3O4/Au core-satellite nanocubes show good separation ability and reusability, which could be repeatedly applied for nearly complete reduction of 4-NP for at least six successive cycles. Such cost effective and recyclable catalyst provides a new material paradigm for environmental protection applications.