Synthesis and characterization of aggregated nano-cobalt particles by bottom up approach

Abstract

This paper reports a novel process for the synthesis of nano-sized cobalt particles by a bottom-up approach. Cobalt chloride has been reduced using hydrazine as the precursor, in a basic medium maintained at 70⁰C. Other factors studied in this research were the combined effect of using an anionic surfactant – sodium dodecyl sulphate (SDS) and a cationic polymer-polyvinylpyrrolidone (PVP) in the formation of nano-sized agglomerated Co particles. Further particle size reduction (less than 5nm) was achieved by using this combination of SDS with PVP. These nano-aggregated cobalt particles were characterized by using high resolution electron microscopes HRSEM/HRTEM with EDX facilities. On the basis of electron microscopic observations a model is postulated: in the absence of SDS/PVP the cobalt atoms get aggregated and form a natural oxide layer around them, with time further aggregation occur they meet up with more Co particles. When both SDS and PVP are present, PVP is able to form a polymeric coating around the aggregated cobalt particles already oxidized and stops further agglomeration. The PVP-polymeric layer is able to hinder the formation of further agglomeration of Co atoms hence a dramatic reduction in the particle sizes are obtained.

Keywords: Bottom-up, SDS/PVP, Co particles, 5nm