Surfactant assisted reactive crystallization of cobalt oxide nanoparticles in a tubular microreactor: effects of precursor concentrations and type of surfactants

Abstract

Cobalt oxide (CoO) nanoparticles were synthesized via a surfactant assisted reactive crystallization route using cobalt chloride hexahydrate (CoCl₂·6H₂O) and sodium borohydride (NaBH₄) in an indigenous lab-scale tubular microreactor. The effects of the precursors' concentrations, flow rate and type of surfactants on particle size distribution, average particle size (d_Avg) and aggregation of synthesized CoO nanoparticles were investigated. The initial molar ratios of the precursors' concentrations (CoCl₂·6H₂O : NaBH₄) were kept as 1 : 3 and 1 : 5 by varying the CoCl₂·6H₂O concentrations in the range of 0.0025–0.01 M. CTAB and Tween 80 were used as surfactants. Results revealed that Tween 80 as a superior surfactant to CTAB for both the molar ratios, in combination with dilute precursors (0.0025 M CoCl₂·6H₂O) and minimum flow rates, yields CoO nanoparticles with d_Avg < 10 nm with narrow size distributions.