SPECTROSCOPIC STUDIES ON COPPER SULFIDE SOLS

The conversion of a "golden-brown" copper sulfide sol (particle diameter approximately 80-120 angstrom) to a "green" form has been studied by use of optical spectroscopy, scanning tunneling microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results indicate that the golden-brown sol is a poorly crystalline form of covellite, which converts to crystalline covellite (the "green" form) at a rate that depends upon the temperature and oxygen concentration of the sol. The valency of copper in the poorly crystalline golden-brown sol is found to be exclusively copper(I), while the green sol has a component of copper(II), which accounts for an absorption band observed in the visible and near-infrared region. The reactions involved in the conversion, and other side reactions occurring during the conversion process, are discussed.