Bulk Synthesis of Monodisperse Ferrite Nanoparticles at Water-Organic Interfaces under Conventional and Microwave Hydrothermal Treatment and Their Surface Functionalization

Synthesis of monodisperse MFe2O4 (M =, Ni, Co, Mn) and gamma-Fe2O3 nanoparticles at a water-toluene interface under conventional as well as microwave hydrothermal conditions using readily available nitrate or chloride salts and oleic acid as the dispersing agent is described. The ensuing particles were monodispersed with a size distribution ranging from 5 to 10 nm. The process is atom-efficient and can be scaled up to a level of several grams without downsizing the size and shape. The modulation of solubility profile of the particles was accomplished via functionalization using organic moieties. X-ray diffraction confirmed the formation of cubic spinel nanostructures. Particle sizes calculated from the Scherrer formula and TEM micrographs were comparable. ICP-AES studies confirmed that the ratios of Fe to Ni, Mn, and Co were approximately equal to 2. FT-IR confirmed the presence of oleic acid moieties on the surface of the synthesized particles. At room temperature, the particles were found to be superparamagnetic with negligible coercivities equal to 11 - 12 Oe. The saturation magnetization values were in the range of 20-25 emu/g. To render them water-soluble, the particles were functionalized with organic moieties.