Morphology study of metal oxide nanoparticles and aerogels produced via thermal decomposition of metal carbonyls in supercritical carbon dioxide

Abstract

In this work, a process of thermal decomposition of metal carbonyls in oxygen-enriched supercritical carbon dioxide was studied. Manganese, iron, cobalt, and tungsten carbonyls were found to be soluble in supercritical CO2 at relatively mild conditions. For each metal carbonyl studied in this work, the thermal decomposition led to the formation of branched agglomerated structures throughout the high-pressure vessel. More specifically, for manganese and iron carbonyls, the procedure yielded partially monolithic aerogel-like structures, while for cobalt and tungsten carbonyls, the formation of branched aggregates was observed. The morphology of all the obtained metal oxides was studied by means of TEM. The study revealed that all materials consisted of individual nanoparticles with sizes between 2 and 40 nm. Pore structure was investigated by analyzing N2 adsorption/desorption curves. The specific surface area varied greatly depending on the type of oxide from 10 m2/g for CoOx to 130 m2/g for MnOx.