Tailoring the nickel nanoparticles anchored on the surface of Fe₃O₄@SiO₂ spheres for nanocatalysis

Herein, we report an efficient and universal strategy for synthesizing a unique triple-shell structured Fe₃O₄@SiO₂@C-Ni hybrid composite. Firstly, the Fe₃O₄ cores were synthesized by hydrothermal reaction, and sequentially coated with SiO₂ and a thin layer of nickel-ion-doped resin-formaldehyde (RF-Ni²⁺) using an extended Stöber method. This was followed by carbonization to produce the Fe₃O₄@SiO₂@C-Ni nanocomposites with metallic nickel nanoparticles embedded in an RF-derived thin graphic carbon layer. Interestingly, the thin SiO₂ spacer layer between RF-Ni²⁺ and Fe₃O₄ plays a critical role on adjusting the size and density of the nickel nanoparticles on the surface of Fe₃O₄@SiO₂ nanospheres. The detailed tailoring mechanism is explicitly discussed, and it is shown that the iron oxide core can react with the nickel nanoparticles without the SiO₂ spacer layer, and the size and density of the nickel nanoparticles can be effectively controlled when the SiO₂ layer exits. The multifunctional composites exhibit a significantly enhanced catalytic performance in the reduction of 4-nitrophenol (4-NP).