Formation and absorption spectrum of copper nanoparticles from the radiolytic reduction of Cu(CN)(2)(-)

Colloidal copper particles (20-100 nm) are Formed in the gamma-irradiation of aqueous solutions of KCu(CN)(2); which also contain methanol or 2-propan ol as OH scavenger. The radiation chemical yield is of the order of 0.1 Cu atoms formed per 100 eV absorbed radiation energy and decreases with increa sing concentration of excess KCN. A reduction mechanism is proposed, in whi ch the hydrated electron reacts with Cu(CN)(2)(-) whereas organic radicals attack,2 copper-I species, possibly colloidal Cu2O, present in low concentr ation by partial hydrolysis of Cu(CN)(2)(-). Free copper atoms do not appea r as intermediates in this mechanism. The optical absorption spectrum of Cu particles of different size is also reported; it contains the plasmon band in the 560-580 nm region and a UV band at 222 nm and becomes flatter with increasing particle size. The copper particles have almost spherical shape when formed at high irradiation dose rates but exhibit very pronounced poly hedra and rodlike contributions at low-dose rates.