Co particles were synthesized with mean particle sizes in the range of 3.2-171.4 nm in ambient atmosphere by reduction of cobalt salt with sodium borohydride as the reducing reagent, a combination of alcohols as solvents and a triblock copolymer P123 (EO20PO70EO20) as the surfactant. The particle size and its distribution were controlled by varying the synthesis parameters such as the viscosity of the medium, the amount of alcohols or P123 in the reaction system. FT-IR and X-ray photoelectron spectroscopy (XPS) measurements confirmed the interaction between the oxygen atoms of P123 and Co2+ or Co-0. Detailed surface analyses by XPS and HRTEM revealed that the synthesized particles consisted of Co-0 metal surrounded by amorphous CoO, Co2B and chemisorbed P123. (C) 2008 Elsevier B. V. All rights reserved.