COLLOIDAL COPPER IN AQUEOUS-SOLUTIONS - RADIATION-CHEMICAL REDUCTION, MECHANISM OF FORMATION, AND PROPERTIES

Colloidal copper has been obtained by gamma-irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When Cu-II is not entirely incorporated into the complex with PEI, disproportionation of Cu-I aqua complexes formed affords the metal, along with Cu2O. Reduction of the PEI complex of Cu-I by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.