Sonochemical synthesis of functionalized amorphous iron oxide nanoparticles

Sonochemical decomposition of Fe(CO)(5) was carried out in the presence of different surfactants. The reactions give stable colloids of undecenoate, d odecyl sulfonate, and octyl phosphonate coated Fe2O3 nanoparticles of 5-16 nm in diameter. The ionic binding of the surfactants to the nanoparticle su rfaces was confirmed by FTIR spectroscopy. Electron paramagnetic resonance measurements, magnetization curves, and zero-field cooled and field cooled studies indicate that the as-prepared amorphous nanoparticles are superpara magnetic. These studies show that the phosphonate-coated nanoparticles beha ve in a strikingly different manner from the other particles. It is propose d that the extra negative charge on the phosphonate, as compared to the car boxylate and sulfonate groups, makes it a strong bridging bidentate ligand, resulting in the formation of strong ionic bonds to the surface Fe3+ ions, which decreases the number of unpaired spins, possibly through a double su perexchange mechanism through a Fe3+-O-P-O-Fe3+ pathway.