The Ethylhexanoate Route to Metal Oxide Nanocrystals: Synthesis of CoO Nanooctahedra from Co-II 2-Ethylhexanoate

CoO nanocrystals were prepared by solvothermal processing of Co 2-ethylhexanoate in oleylamine at 250 degrees C. The obtained products, identified as CoO by X-ray diffraction, had an octahedral shape, as seen by transmission electron microscopy, reflecting the cubic symmetry of the CoO crystallographic phase. The materials were converted into the Co3O4 phase after heat treatment at 400 degrees C. The nanocrystal evolution was investigated by FTIR spectroscopy. It was concluded that weak oleylamine bonding to the nanocrystal surface during the synthesis step favored the exchange with 2-ethylhexanoato ligands, and that the interplay between the two ligands favored the kinetic control of the growth, resulting in the finally observed octahedral morphology. The Co3O4 phase obtained from the heat treatment at 400 degrees C was used to process chemoresistive sensors, which were able to detect ethanol under dry and humid conditions (0 and 50% r.h. H2O at 25 degrees C) at low temperatures (100 degrees C).