Graphene-Coated Metal Oxide Nanocrystals (M <sub><b><i>x</i></b> </sub> O <sub><b><i>y</i></b> </sub> @C) Form during the Liquid-Phase Thermal Decomposition of Metal Oleates.

Abstract

Materials combining graphitic carbon with metal oxide nanoparticles are critical for applications in water treatment, catalysis, and energy storage. These composites leverage carbon's electrical conductivity and chemical resilience to enhance the catalytic, electronic, and magnetic properties of metal oxide nanoparticles. Previous approaches to synthesizing such materials have relied on high-temperature (>600 °C) pyrolysis of powders, a process that can alter nanoparticle size, composition, and morphology. Alternative lower-temperature routes in solution yield amorphous carbon, which lacks the conductivity and chemical resistance of graphitized carbon. This study presents a route to form graphitic carbon coatings on iron, manganese, and cobalt oxide nanoparticles at temperatures below 400 °C. The synthetic process exploits the thermal decomposition of metal carboxylates, which generates carbon monoxide (CO) within the reaction environment that further disproportionates to elemental carbon on the nanoparticle surface. Gas chromatography confirms CO evolution, and electron microscopy reveals the formation of core-shell structures with graphitic coatings of varying thickness. Iron oxide nanoparticles coated via this method exhibit exceptional chemical resistance, remaining intact in strong acids while maintaining their magnetic properties. This advancement enables the production of size-tunable nanoparticle-graphite suspensions via conventional solution-phase chemistry. These findings suggest a scalable approach for producing graphitized carbon-metal oxide composites without the need for extreme temperatures, broadening the potential applications of these materials in energy storage and environmental remediation.