In situ surface modification of cerium oxide nanoparticles with catechol derivatives during supercritical hydrothermal synthesis

The attachment of organic molecules on the surface of metal oxide nanoparticles is known to change nanoparticle properties, including optical absorption, electrical conductivity, and magnetism. In this study, we examined the in situ surface modification of CeO 2 nanoparticles during synthesis to extend the possible range of changes in optical absorption by increasing the surface density of attached organic molecules. The surface-modified CeO 2 nanoparticles were hydrothermally synthesized in situ by heating Ce(OH) 4 precursors in water with surface modifier molecules, that is, either pyrocatechol or protocatechuic acid. As an alternative, we synthesized unmodified CeO 2 nanoparticles and performed conventional surface modification, where the unmodified CeO 2 nanoparticles were dispersed and stirred in an aqueous solution of the surface modifier. A comparison of the products revealed that in situ surface modification achieved approximately a twofold greater surface density of attached molecules than that obtained by conventional modification. Accordingly, the optical absorption of the in situ surface-modified CeO 2 nanoparticles was greater than that of the CeO 2 nanoparticles modified in the conventional manner. We believe that in situ surface modification provides an alternative way to tune the properties of metal oxide nanoparticles across a wide range.