Facile synthesis, phase transfer, and magnetic properties of monodisperse magnetite nanocubes

The monodisperse Fe₃O₄ nanocubes with controllable sizes from 6.5 to 30.0 nm have been synthesized in organic phase. By the formation of surfactant bilayers with charged hydrophilic ions of α-cyclodextrin, Fe₃O₄ nanocubes were successfully "pulled" into water from hexane for a possible biomedical application. The Fe₃ O₄ nanocubes with the surfactant bilayers show a good stability in aqueous solution compared with those in aqueous solution which were transferred from organic phase by ligand exchange using PVP with strong binding group. The hysteresis loop at 300 K of Fe₃O₄ nanocubes with different sizes reveals that a size-dependent behavior of saturation magnetization and the nanocubes with a size less than 25 nm show a typical superparamagnetic behavior at room temperature. The comparison of magnetization of the hydrophilic Fe₃ O₄ nanocubes in CD and PVP aqueous solution reveals that the surfactant bilayers can provide a good stability of magnetization.