Some insights in the sonochemical preparation of cobalt nano-particles

The preparation of cobalt nano-particles from a solution of Co(CO)(3)(NO) in n-decane under ultrasonication with a frequency of 20 kHz yielded cobalt particles of a size of ca. 5 nm. The presence of either silica or oleic acid in the solution reduced the particle size to ca. 3 and 2 nm, respectively. The resulting particle size is independent of the ultrasonication time, initial Co(CO)(3)(NO) concentration, ultrasound intensity and solution temperature. It is postulated that bubble collapse generates multiple nucleation sites resulting in the formation of cobalt particles with a rather uniform particle size distribution.