Reduction of the copper ion to its metal and clusters in alcoholic media: A radiation chemical study

Abstract

Reduction of Cu 2+ ions with and without I − as a ligand was studied in N 2-purged alcoholic solutions by pulse radiolysis. In the absence of iodide ion, the initial rate constant for e − sol reaction with Cu 2+ was determined following the decay of solvated electrons in different alcohols; k bimol values are in the range of 0.8–1.1×10 10 dm 3 mol −1 s −1. In the presence of 10 −3 mol dm −3 KI, the respective k bimol remained almost same. Generally, on reduction, Cu(II) ion changes to Cu(I) ion initially and later it produces metallic copper (Cu°), and the stability of these intermediates depends on the conditions of the matrix. In the presence of I −, Copper ions such as Cu(II) or Cu(I) ions get reduced to metallic copper (Cu°) having initial absorption around 740 and below 400 nm. Later, at 100 μs time after the electron pulse, it gets transformed into a nanoparticle with an absorption band at 580 nm. Such formation of copper nanoparticle was observed only in 2-propanolic medium in the presence of iodide ions. During γ-radiolysis of N 2-purged 1.5×10 −4 CuSO 4 solutions in 2-propanol, reddish pink colored copper nanoparticles were formed, which are quite similar to those reported earlier in aqueous solution. But, in the presence of I − (2-propanolic solutions), such phenomenon was not noticed on γ-radiolysis. Interestingly, the formation of copper nanoparticle was observed also in the reactions of copper (II) ions with alcohol radicals formed during γ-radiolysis in N 2O-purged system, where e − sol were scavenged by N 2O. The nanoparticles generated both in N 2 and N 2O-purged alcoholic systems, viz. methanol, ethanol and 2-propanol, were found to be oxygen sensitive. The contradictory results from pulse and γ-radiolysis studies in the presence and absence of iodide ions are explained to account for the nanoparticle generation.