Special Magnetic Catalyst with Lignin-Reduced Au-Pd Nanoalloy

This study describes a new strategy to fabricate a special magnetic catalyst via facile coating Au-Pd nanoalloy catalysts onto a commercial magnetic stirring bar, without the incorporation of iron element. First, the abundant natural "waste" lignin was utilized as the reducing and stabilizing agent to prepare Au-Pd nanoalloys in a green manner. The Au-Pd nanoalloys were assumed to have a core-shell structure with an Au-rich core and a Pd-rich shell. The Au-Pd nanoalloys could be well dispersed in aqueous medium due to the stabilizing effect of lignin and be conveniently coated onto the surface of a commercial stirring bar. The Au_1.0Pd_1.0 nanoalloy catalyst exhibited excellent catalytic activities in the reduction of 4-nitrophenol to 4-amnophenol by NaBH₄, with a rate constant (k) of 0.239 min^-1, which was higher than that of Au_0.5Pd_1.0 and Au_2.0Pd_1.0 nanoalloys and 4 times higher than that of a single-component Au or Pd nanoparticles. Besides, the catalytic ability of Au-Pd nanoalloy catalyst could be maintained even after seven cycles of catalysis. The catalytic rate constant was found to be positively correlated to the stirring speed of the bar. The scanning electron microscopy analysis revealed ravines and pores on the surface of lignin-nanoalloys composites, implying the possible mechanism of the catalytic activities. This study not only proved the feasibility of lignin for green synthesis of Au-Pd nanoalloys but also proposed a facile and innovated strategy for the future production of solid/liquid catalytic platforms where the developed method could be used to coat any surface interfacing the reagents.