One-pot preparation of magnetic Fe@Ag bimetallic catalyst for the catalytic reduction of 4-nitrophenol

In this study, a magnetic Fe@Ag bimetallic catalyst was synthesized via a facile one-pot method in the presence of excessive sodium borohydride (NaBH4). The as-synthesized Fe@Ag bimetal was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). The influences of Fe/Ag molar ratio and gum arabic (GA) on the catalytic activity of Fe@Ag bimetal were investigated. It was found that the FeAg3-0.14 wt% bimetal with Fe/Ag molar ratio of 1:3 and GA concentration of 0.14 wt% exhibited the best activity for catalytic reduction of 4-NP, giving a pseudo-first-order rate constant of 48.8 min(-1) g(-1). The saturation magnetization (M-S) of FeAg3-0.14 wt% was 5.6 emu/g, which ensured the catalyst could be easily separated and recycled using a magnet. Moreover, the catalytic activity and phase composition of FeAg3-0.14 wt% showed no obvious changes after five continuous runs, indicating its high stability and reusability. Ag shell coated on the surface of Fe core played a main role in the catalytic reduction of 4-NP and also inhibited the oxidation of Fe core, which can be illustrated by electrochemical potentials and heterogeneous nucleation during the synthetic process. Furthermore, the Langmuir-Hinshelwood (L-H) model was applied to explain the catalytic mechanism of Fe@Ag bimetal.