RESUMEN
A selective preparation and the formation mechanism of hexagonal and cubic CoO nanoparticles from the reaction of [Co(acac)(2)] (acac=acetylacetonate) and amine have been investigated. CoO nanoparticles with a hexagonal pyramidal shape were yielded under decomposition conditions with amine. Importantly, the addition of water altered the final phase to cubic and comprehensively changed the reaction mechanism. The average sizes of the hexagonal and cubic CoO nanoparticles could be controlled either by changing the amine concentration or by using different reaction temperatures. Detailed formation mechanisms are proposed on the basis of gas chromatography-mass spectrometry data and color changes of the reaction mixture. The hexagonal CoO phase is obtained through two distinct pathways: solvolysis with C-C bond cleavage and direct condensation by amine. On the other hand, the cubic CoO nanoparticles were synthesized by strong nucleophilic attack of hydroxide ions from water and subsequent C-C bond breaking. The resulting caboxylate ligand can stabilize a cobalt hydroxide intermediate, leading to the generation of a thermodynamically stable CoO phase.
RESUMEN
Monodisperse Pt and PtRu/C(60) hybrid nanoparticles with controlled diameters were synthesized by the reduction of metal precursors in the presence of C(60); the resulting metal/C(60) hybrid nanocatalyst exhibited a remarkable enhancement of methanol oxidation activity over commercial E-TEK catalysts.
RESUMEN
Highly crystalline, phase- and size-controlled CoO nanocrystals of hexagonal and cubic phases have been prepared by thermal decomposition of Co(acac)3 in oleylamine under an inert atmosphere. Kinetic and thermodynamic control for the precursor formation leads to two different seeds of hexagonal and cubic phases at higher temperatures. The crystal size of both CoO phases can be easily manipulated by changing the precursor concentration and reaction temperature.