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.