Synthesis of Rhombic Dodecahedral Fe₃O₄ Nanocrystals with Exposed High-Energy {110} Facets and Their Peroxidase-like Activity and Lithium Storage Properties

Large quantities of monodispersed single-crystal rhombic dodecahedral (RD) Fe₃O₄ nanocrystals (NCs) bounded by high-energy {110} facets were prepared by using a one-pot toluene–water two-phase interfacial reaction method. By adjusting the Fe­(acac)₃ concentration and the volume of hydrazine hydrate, their sizes could be controlled in the range from 60 to 100 nm. The formation of these RD Fe₃O₄ NCs with exposed high-energy {110} surfaces might be the result of selective stabilization of such unstable facets by the C₁₇H₃₃­COO^– based on FT-IR analysis. The magnetic measurement revealed that the saturation magnetization (<i>M</i>_s) of the RD Fe₃O₄ NCs was 85 emu/g at room temperature. When used as peroxidase mimetics, the prepared RD Fe₃O₄ NCs showed excellent peroxidase-like catalytic activity toward oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine and degradation of the aniline compound methylene blue dye in the presence of H₂O₂. When tested as anode materials for lithium-ion batteries, these as-obtained RD Fe₃O₄ NCs showed a high initial discharge capacity of 1147 mA h g^–1 at the current density of 0.2 C, a good cycle performance (362 mA h g^–1 at 0.2 C after 100 cycles and 191 mA h g^–1 at 1 C up to 130 cycles), and good rate capability at high current rates of 1–4 C