Abstract:

The size of nanoparticles plays a crucial role in their performance. In this article, three methods, i.e., direct impregnation, homogeneous oxidative precipitation with hydrogen peroxide, and ammonia-catalyzed hydrolysis, were applied to synthesize iron, cobalt, and nickel metal oxide nanoparticles supported on graphene. The influence of the three deposition methods on particle size distribution was investigated. Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the catalysts. The highest dispersion and the most uniform particle size distribution were obtained by the hydrogen peroxide homogeneous oxidative precipitation method. Hydrogen peroxide favors the maximization of the oxygen-containing groups on graphenes, thereby providing sufficient absorption and nucleation sites to give a high dispersion of nanoparticles. In contrast, ammonia accelerates the nucleation speed and results in the largest particle size and inhomogeneity. The catalytic properties of the graphene-supported metal oxide nanoparticles were tested with the oxidation of benzyl alcohol as a probe reaction. The reaction activity decreased in the following order: catalysts prepared by hydrogen peroxide-assisted deposition > direct impregnation > ammonia-catalyzed hydrolysis. The decrease in reaction activity was consistent with the order of increasing catalyst particle sizing shown in transmission electron microscopy images. The catalytic relevance of the particle size showed a necessity for the development of effective methods for size-controlled nanocatalyst synthesis on graphenes.

Key words: Particle size, Graphene, Metal oxide, Hydrogen peroxide, Benzyl alcohol