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 -Irradiation of deaerated solutions in the presence of polyethyleneimine, polyacrylate, or polyvinyl sulfate gives stable metal sols containing spherical particles 2-4 nm in diameter. The optical absorption spectra of nickel nanoparticles 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 radiation-chemical reduction of Ni2+ ions by hydrated electrons and organic radicals (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, respectively. The nanoparticles are readily oxidized by O-2, H2O2 and other oxidants. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both nickel and silver in addition to silver nanoparticles.