Radiation-induced formation of Co3O4 nanoparticles from Co2+(aq): probing the kinetics using radical scavengers

The effects of the Co 2+ content and different radical scavengers on the kinetics of γ-radiation-induced Co 3 O 4 nanoparticle formation and growth were investigated. There are four distinct stages of particle formation with different oxidation rates. Scavengers and [Co 2+ ] 0 affect the oxidation kinetics in the different stages and consequently the final size of the particles formed. Radiolysis model calculations were performed to obtain the time-evolution of the concentrations of key oxidants and reductants, and the effect of scavengers on those concentrations. Based on the model results and experimental data a reaction mechanism for Co 3 O 4 particle formation by γ-irradiation of solutions containing Co 2+ (aq) is proposed. The main cobalt oxidation reaction changes with time. Oxidation of Co 2+ (aq) to Co 3+ (aq) by radiolytically produced &z.rad;OH occurs first in the solution phase. This is followed by spontaneous co-precipitation of mixed Co II /Co III hydroxide nucleate particles. Adsorption of Co II (ad) followed by surface oxidation of Co II (ad) to CoOOH(ad) by H 2 O 2 grows particles with a solid CoOOH(s) phase. In parallel, the solid-state transformation of CoOOH(s) and Co II (ad) to form Co 3 O 4 (s) occurs. The kinetics of γ-radiation-induced Co 3 O 4 nanoparticle formation occurs in four distinct stages. Scavengers and [Co 2+ ] 0 affect the kinetics in different stages, and consequently influence the final particle sizes. Radiolysis model calculations on the effects of radical scavengers provide insights into their role in controlling particle formation.