Aqueous solutions of colloidal nickel: radiation-chemical preparation, absorption spectra, and properties

Radiation-chemical reduction of Ni2+ ions in aqueous solutions of Ni(ClO4)( 2) containing sodium formate or isopropyl alcohol was studied. gamma -Irrad iation of deaerated solutions in the presence of polyethyleneimine, polyacr ylate, or polyvinyl sulfate gives stable metal sols containing spherical pa rticles 2-4 nm in diameter. The optical absorption spectra of nickel nanopa rticles exhibit a band with a maximum at 215+/-5 nm (epsilon (215) = 4.7.10 (3) L mol(-1) cm(-1)) and a shoulder at 350 nm. A mechanism for the radiati on-chemical reduction of Ni2+ ions by hydrated electrons and organic radica ls (CO2.- radical anions in the case of HCOONa and (Me2COH)-O-. radicals in the case of (PrOH)-O-i). The redox potentials of the Ni2+/Ni-0 and Ni+/Ni- 0 pairs (Ni-0 is a nickel atom) are approximately -2.2 and -1.7 V, respecti vely. The nanoparticles are readily oxidized by O-2, H2O2 and other oxidant s. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both nickel and silver in addition to silver nano particles.