Uniform Ni/SiO2@Au magnetic hollow microspheres: rational design and excellent catalytic performance in 4-nitrophenol reduction.

A unique and rational design was presented to fabricate Ni/SiO2@Au magnetic hollow microspheres (MHMs) with interesting structures and well-dispersed metal nanoparticles. Hierarchical nickel silicate hollow microspheres were synthesized using silica colloidal spheres as a chemical template. Then, Ni/SiO2 MHMs with well-dispersed Ni nanoparticles were prepared via an in situ reduction approach. Ni/SiO2@Au MHMs were finally obtained by immobilizing uniform Au nanoparticles onto Ni/SiO2 support through a low-temperature chemical reduction process. It was found that Ni/SiO2@Au MHMs inherit the shape and uniformity of the original silica scaffold, and Ni NPs and Au NPs, which were less than 5 nm in size, were well dispersed on the mesoporous silica shell with narrow size distribution. Both Ni/SiO2 and Ni/SiO2@Au MHMs showed excellent catalytic activity in the 4-nitrophenol reduction reaction. Importantly, introduction of a small amount of Au NPs onto Ni/SiO2 MHMs markedly improved the catalytic activity. In particular, Ni/SiO2@Au MHMs showed high conversion even after re-use for several cycles with magnetic separation. The unique structure, high catalytic performance, and ease of separation make Ni/SiO2@Au MHMs highly promising candidates for diverse applications.