One-step synthesis and characterization of ultrastable and amorphous Fe₃O₄ colloids capped with cysteine molecules

A one-step sonochemical synthesis of a uniformly dispersed aqueous solution of amorphous Fe₃O₄ nanoparticles capped with DL-cysteine (cys) has been achieved. During the sonication, several processes or chemical reactions occurred: the decomposition of iron pentacarbonyl (Fe(CO)5), the formation of amorphous Fe₃CO₄ nanoparticles, the capping of the Fec with cysteine molecules, the formation of a surface chemical bond of Fe-S between Fe₃O₄ particles and sulfur from cysteine, and the formation of cystine by linking two cysteine molecules. These capping cystine and cysteine molecules acted both as antioxidants and stabilizers, and the capped Fe₃O₄ colloids could be stable as long as 3 months at room temperature. Usually, the size of the amorphous Fe ₃O₄ nanoparticles capped with Cys was found to be 20-30 nm. The products were characterized by a number of analytical techniques, such as XRD, DSC, TGA, XPS, TEM, HRTEM, Raman Spectroscopy, magnetic measurements, and spot tests.