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Naked magnetically recyclable mesoporous Au-γ-Fe2O3 clusters, combining the inherent magnetic properties of γ-Fe2O3 and the high catalytic activity of Au nanoparticles (NPs), are successfully synthesized. Hydrophobic Au-Fe3O4 dimers are first self-assembled to form sub-micrometer-sized Au-Fe3O4 clusters. The Au-Fe3O4 clusters are then coated with silica, calcined at 550 °C, and finally alkali treated to dissolve the silica shell, yielding naked-Au-γ-Fe2O3 clusters containing Au NPs of size 5-8 nm. The silica protection strategy serves to preserve the mesoporous structure of the clusters, inhibit the phase transformation from γ-Fe2O3 to α-Fe2O3, and prevent cluster aggregation during the synthesis. For the reduction of p-nitrophenol by NaBH4, the activity of the naked-Au-γ-Fe2O3 clusters is ≈22 times higher than that of self-assembled Au-Fe3O4 clusters. Moreover, the naked-Au-γ-Fe2O3 clusters display vastly superior activity for CO oxidation compared with carbon-supported Au-γ-Fe2O3 dimers, due to the intimate interfacial contact between Au and γ-Fe2O3 in the clusters. Following reaction, the naked-Au-γ-Fe2O3 clusters can easily be recovered magnetically and reused in different applications, adding to their versatility. Results suggest that naked-Au-γ-Fe2O3 clusters are a very promising catalytic platform affording high activity. The strategy developed here can easily be adapted to other metal NP-iron oxide systems. [ABSTRACT FROM AUTHOR]

A cost-efficient and scalable method is designed to prepare a SiOx–C composite with superior cyclability and excellent rate performance. The glucose addition in a two-step way induces a hierarchical structure, where individual SiOx nanoparticles are wrapped by a conductive carbon layer and these agglomerated particles are further wrapped by a carbon shell functioning as an electrolyte blocking layer. Instrumental analysis indicates that the SiOx domains are comprised of SiO2 and SiO. The SiOx–C anode exhibits a high reversible specific capacity of 674.8 mA h g−1 after 100 cycles at 100 mA g−1 with a capacity retention of about 83.5%. The excellent electrochemical performance is due to the hierarchical structure, the well-dispersed conductive carbon network, and the Li2O and Li4SiO4 generated in the initial discharge process, all of which can immensely relieve the volume expansion induced by the lithiation of silicon. This hierarchical SiOx–C composite has a promising prospect of practical application given its adequate storage capacity, good cycling stability, commercially available materials and simple equipment. [ABSTRACT FROM AUTHOR]