Reduction of Ni2+ by hydrazine in solution for the preparation of nickel nano-particles

Abstract

The reduction of Ni2+ by hydrazine in solution for the preparation of nickel nano-particles has been studied. It was found that the reactions occur in two stages. The first stage is the reduction of Ni2+ by N2H4 according to 2Ni2+ + N2H4 + 4OH− = 2Ni↓ + 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 nickel nano-particles. The reaction for the formation of nickel is also catalyzed by nickel 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. Kinetic study reveals that the reaction orders with respect to Ni2+, N2H4 and Ni are 1, 0 and 1, respectively. Thus, the increase of the initial concentration of Ni2+ and the amount of inducing agent used accelerate the reaction rate and decrease the consumption of N2H4 significantly. Pure nickel nano-particles with high surface areas are produced and the surface area can increase from 18 to 79 m2/g with the increase of concentration of Ni2+ used. The fully understanding of the reaction between Ni2+ and hydrazine in solution may provide a new optimized technique to prepare the nickel catalysts with high surface areas, in addition to the currently available techniques for the preparation of Raney nickel and supported nickel catalysts.