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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. [ABSTRACT FROM AUTHOR]

Binary metal oxide MnCo2O4 nanosheets wrapped on a hollow activated carbon shell (C@MnCo2O4) were successfully synthesized through a facile hydrothermal method followed by a calcination process. The novel structure of a flower-like C@MnCo2O4 composite, which consists in a good conductive carbon shell and well interconnected nanosheets, can efficiently facilitate electrolyte penetration and offers an expedite transport path for ions and electrons. Notably, the large surface of the hybrid composite (347 m² g-1) can provide a large amount of active sites, which evidently accommodates the strain during cycling. Benefiting from this elegant combination and the effectively mesoporous structure, the specific capacitance of the C@MnCo2O4 composite can be achieved as high as 728.4 F g-1, which is, to the best of our knowledge, the highest value so far reported for MnCo2O4 based electrode materials. In addition, the C@MnCo2O4 composite exhibits enhanced rate capability and an excellent cycling stability of 95.9% retention after 1000 cycles at a high current density of 8 A g-1. Therefore, the desirable integrated electrical performance allows it to be a promising electrode material for supercapacitor applications. [ABSTRACT FROM AUTHOR]