Solubilization, dispersion and stabilization of magnetic nanoparticles in water and non-aqueous solvents: recent trends

Recent achievements in the solubilization and stabilization of magnetic nanoparticles (MNPs) are reviewed. The majority of reported MNPs correspond to iron-based {nZVI, superparamagnetic iron oxides (SPIONs), core-shell Fe/Au or FexOy/Au nanoparticles and ferrites} nanoparticles, with a few numbers corresponding to MnO and cobalt nanoparticles. Magnetic nanoparticles can be solubilized in water or non-aqueous solvents for short or long time periods. The main approaches for MNP solubilization are discussed, namely, suitable choice of precursors, pH, surfactants/coating agents, and solvents, as well as functionalizing agents. MNPs are generally solubilized by functionalization with water-soluble compounds/moieties (in particular, sulfonic acid disodium salts, soluble polymers, porphyrins and calixarenes), under conditions of the thermal decomposition of low stability metal complexes, coprecipitation, microwave heating, and by ultrasonication. The polyol strategy is frequently applied to increase MNP solubility. The stabilization of MNPs in solutions could be achieved with the help of inorganic, monomeric and polymeric compounds.