Size Control of Cobalt Nanoparticles Through Synthesis Parameter Variation

Abstract

In the present work, cobalt nanoparticles were synthesised in the range of 4 to 72 nm through the chemical reduction method, in which cobalt nitrate, oleic acid and sodium borohydride were used as the precursor, stabiliser and reducing agent, respectively. The syntheses were carried out by varying the synthesis parameters, such as the amount of reducing agent, amount of stabiliser and turbulence level of the reaction medium, with the aim of evaluating their influence on the control of cobalt nanoparticle size distribution. The nanoparticles size decrease with high concentrations of reducing agent and stabiliser, due to an increase in the reaction rate and viscosity of the medium, respectively. It was also verified that the high level of turbulence used during the synthesis could provide anomalous diffusion of cobalt nanoparticles in the reaction medium. Under this condition, the growth kinetics may vary significantly with regards to two distinct reaction paths, causing opposite growth behaviour in relation to the synthesis occurring in the normal distribution of the nanoparticles.