Synthesis and surface modification of deagglomerated superparamagnetic nanoparticles

A method for the preparation of aminosilane coated, chemically stable, agglomerate-free superparamagnetic iron oxide nanoparticles (ferrites, e.g. Fe3O4 and gamma-Fe2O3) has been developed. These nanocomposite particles posess core-shell structure. The well crystallized core particles are prepared by precipitation from aqueous salt solutions (primary particle size 10 nm). The surface modification of the weakly agglomerated core particles with aminiosilane (e.g. gamma-aminopropyl-triethoxysilane) leads to deagglomerated particles, covered by a thin polymerized aminosilane shell. A stron dependency of the particle/agglomerate size on the silane/iron oxide-ratio as well as on the disintegration time was found. A ratio of aminosilane to iron oxide of 0.8 (weigth ratio) and a disintegration time of 72h result in overall particle sizes in the range of 10-15 nm. After surface modification, aminogroups are present on the particle surface (IEP of 9.5). The particles show superparamagnetic behaviour (saturation magnetization 68 EMU/g) and aqueous suspensions are stable against agglomeration. A desorption of the coating in aqueous suspensions (pH 3 to 11) is not observed