Ni-Pd-Incorporated Fe₃O₄ Yolk-Shelled Nanospheres as Efficient Magnetically Recyclable Catalysts for Reduction of N-Containing Unsaturated Compounds

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe₃O₄ (Ni-Pd/Fe₃O₄) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe₃O₄ support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe₃O₄ nanoparticles, the as-prepared Ni-Pd/Fe₃O₄ composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe₃O₄ and Pd/Fe₃O₄). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe₃O₄ was superior to many Fe₃O₄-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.