Shape Control in Iron Oxide Nanocrystal Synthesis, Induced by Trioctylammonium Ions

Faceted iron oxide nanoparticles with octahedral shape were synthesized through controlled modification of the iron oleate decomposition method. The key to this novel shape control is the in situ formation of trioctylammonium bromide (TOAHB) during the process, through decomposition of quaternary ammonium salts. This hypothesis was confirmed by carrying out the synthesis in the presence of preformed TOAHB, which again resulted in the formation of iron oxide octahedra. A detailed high-resolution transmission electron microscopy (HRTEM) analysis of the nanooctahedra was performed for shape analysis and structural characterization. X-ray photoelectron spectroscopy (XPS) indicates the presence of both metallic iron and iron oxide within the nanooctahedra. The results obtained by HRTEM and XPS are in agreement with magnetic analysis, which revealed the presence of several magnetic phases in the samples.