Abstract：The cobalt nanoparticles have been prepared by reduction of Co2＋ with hydrazine in ethanol-aqua system at room temperature. It was found that the overall reaction occurs in two stages. The first stage is the reduction of Co2＋ by N2H4 according to 2Co2＋＋N2H4＋4OH－＝2Co¯＋N2＋4H2O, while the second stage consists of two side reactions, the decomposition of hydrazine (N2H4＝N2＋2H2) and the disproportionation of hydrazine (3N2H4＝N2＋4NH3) catalyzed by the formed cobalt nanoparticles. The reaction for the formation of cobalt is catalyzed by cobalt as an autocatalytic reaction. Accordingly, a small amount of inducing agent, NaBH4 can be added to initiate the reaction that can then proceed continuously at 288 K. The kinetic equation of the reaction for the reduction of Co2＋ by hydrazine has been derived by monitoring the volume of gases evolved versus time. It reveals that the reaction orders with respect to Co2＋, N2H4 and Co are 1, 0 and 1, respectively. Thus, the increase of the initial concentration of Co2＋ and the amount of inducing agent used accelerate the reaction rate and decrease the consumption of N2H4 significantly. The activation energy of the autocatalytic reaction was found to be about 89 kJ•mol－1. Change of initial concentration of Co2＋ might alter the surface area of Co nanoparticles from 11 to 25 m2/g, corresponding to the particles with average diameters from 60 to 30 nm.
李智渝,韩承辉,沈俭一. 溶液中肼还原钴离子制备纳米金属钴的反应动力学[J]. 化学学报, 2006, 64(4): 295-300.
LI Zhi-Yu1,2, HAN Cheng-Hui1,2, SHEN Jian-Yi*,1. Reaction Kinetics of Reduction of Co2＋ by Hydrazine in Solution for the Preparation of Cobalt Nanoparticles. Acta Chimica Sinica, 2006, 64(4): 295-300.