A new role for surfactants in the formation of cobalt nanoparticles

During wet-chemical synthesis of nanoparticles it is believed that surfactants interact with the particles after their nucleation thereby controlling their crystal structure, shape and size. Contrary to this, our investigations presented in this paper reveal a new role for surfactants: influencing the reaction pathways, prior to nucleation, leading to the formation of cobalt nanoparticles. The results from the mechanistic investigation of the influence of various surfactants on the formation of cobalt nanoparticles carried out using time dependent FT-IR spectroscopy support this observation. The utilization of different surfactants such as oleic acid (OA), trioctylphosphine oxide (TOPO), octadecylamine (ODA), and trioctylphosphine (TOP) led to differences in reaction pathways and reaction intermediates, prior to the nucleation, leading to the formation of Co nanoparticles with very different properties. The particle size and size distribution were obtained from transmission electron microscopy (TEM). The electronic and geometric properties of the cobalt nanoparticles obtained were determined using synchrotron radiation based X-ray absorption spectroscopy (XAS) and the magnetic properties were measured using SQUID magnetometry.