The Ethylhexanoate route to metal oxide nanocrystals : synthesis of CoO nanooctahedra from Co¹¹2-Ethylhexanoate

Abstract

CoO nanocrystals were prepared by solvothermal processing of Co 2-ethylhexanoate in oleylamine at 250 °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 CO₃0₄ phase after heat treatment at 400 °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 CO₃0₄ phase obtained from the heat treatment at 400 °C was used to process chemoresistive sensors, which were able to detect ethanol under dry and humid conditions (0 and 50 % r.h. HO at 25 °C) at low temperatures (100 °C).