Controllable synthesis of Ni/SiO₂ hollow spheres and their excellent catalytic performance in 4-nitrophenol reduction.

The high cost of noble metal nanoparticles used for catalytic reduction of 4-nitrophenol (4-NP) leads to an extensive study of Ni nanoparticles (NPs) for their low cost and magnetic properties. However, the conventional routes for preparing the ferromagnetic Ni NPs usually lead to large particle size and aggregation. In this study, we propose a simple two-step method for the synthesis of hierarchical Ni NP supported silica magnetic hollow microspheres (Ni/SiO2 MHMs). Tiny Ni NPs are well dispersed on the supports with high loading amounts (15 wt%). The size of Ni NPs can be tuned from 10 nm to 21 nm with the size of Ni/SiO2 MHMs increasing from 230 nm to 800 nm. The as-prepared samples exhibit excellent catalytic activity in the reduction of 4-NP. Furthermore, the experimental results prove that the size of Ni NPs plays an important role in the catalytic activity. The catalytic activity of small sized Ni NPs is higher than that of large sized and many other supported Ni NP catalysts as reported. In particular, the magnetic properties of Ni/SiO2 MHMs make them easy to recycle for reuse.