INFRARED STUDY OF ETHYL AND OCTYL XANTHATE IONS ADSORBED ON METALLIC AND SULFIDIZED COPPER AND SILVER SURFACES

Infrared reflection-absorption spectroscopy (IRAS) has-been used to study the adsorption of ethyl xanthate (EX) and octyl xanthate (OX) ions on copper and silver surfaces. The experimental reflection-absorption (RA) spectra are compared with simulated RA spectra based on the optical constants n(nu) and k(nu) derived from the transmission-absorption spectra of the corresponding metal alkyl xanthate salts. The good agreement between the experimental and simulated RA spectra for EX and OX ions adsorbed on copper and silver suggests that the ultimate chemical structure of the surface complexes formed is closely related to that of the metal salts. Alkyl xanthate ions directly bound to the surface are also observed for short adsorption times. The adsorption of EX and OX ions on copper and silver surfaces sulfidized by exposure to gas-phase H2S is also studied by IRAS. The rate of adsorption and the chemical structure of the adsorbed layer on sulfidized copper are the same as on metallic copper, presumably because of the presence of a thin Cu2O layer at the outermost surfaces of both substrates. On sulfidized silver surfaces the adsorption rate is noticeably reduced. The RA spectra of OX on sulfidized silver also display large variations in alkyl chain orientation and/or conformation with exposure time. We believe that the reduced rate of adsorption and the change in alkyl chain orientation and conformation at low exposures are due to a different pinning geometry caused by blocking of adsorption sites by adsorbed H2S. Furthermore, the rate of adsorption for OX is greater than for EX for all surfaces studied here.