Phase-Controlled Iron Oxide Nanobox Deposited on Hierarchically Structured Graphene Networks for Lithium Ion Storage and Photocatalysis

The phase control, hierarchical architecturing and hybridization of iron oxide is important for achieving multifunctional capability for many practical applications. Herein, hierarchically structured reduced graphene oxide (hrGO)/alpha-Fe2O3 and gamma-Fe3O4 nanobox hybrids (hrGO/alpha-Fe and hrGO/gamma-Fe NBhs) are synthesized via a one-pot, hydrothermal process and their functionality controlled by the crystalline phases is adapted for energy storage and photocatalysis. The three-dimensionally (3D) macroporous structure of hrGO/alpha-Fe NBhs is constructed, while alpha-Fe2O3 nanoboxes (NBs) in a proximate contact with the hrGO surface are simultaneously grown during a hydrothermal treatment. The discrete alpha-Fe2O3 NBs are uniformly distributed on the surface of the hrGO/alpha-Fe and confined in the 3D architecture, thereby inhibiting the restacking of rGO. After the subsequent phase transition into gamma-Fe3O4, the hierarchical structure and the uniform distribution of NBs are preserved. Despite lower initial capacity, the hrGO/alpha-Fe NBhs show better rate and cyclic performances than those of commercial rGO/alpha-Fe due to the uniform distribution of discrete alpha-Fe2O3 NBs and electronic conductivity, macroporosity, and buffering effect of the hrGO for lithium ion battery anodes. Moreover, the catalytic activity and kinetics of hrGO/gamma-Fe NBhs are enhanced for photo-Fenton reaction because of the uniform distribution of discrete gamma-Fe3O4 NBs on the 3D hierarchical architecture.