ADSORBED THIOSULFATE INTERMEDIATE OF CADMIUM-SULFIDE AQUEOUS PHOTOCORROSION DETECTED AND CHARACTERIZED BY IN-SITU INFRARED-SPECTROSCOPY

In situ infrared spectroscopy has been used to show that aqueous cadmi um sulfide photocorrosion leads to solution sulfate via an adsorbed th iosulfate intermediate. Infrared spectra were recorded from thin films of colloidal cadmium sulfide deposited on zinc selenide internal refl ection elements and in contact with aqueous solutions. Infrared absorp tions at 1005 and 1152 cm(-1) have been ascribed to adsorbed thiosulfa te by comparisons with the corresponding absorptions in solution. Simu ltaneous in situ photolysis and infrared spectroscopy showed that adso rbed thiosulfate was initially formed but gradually converted to sulfa te. Adsorption isotherm data, derived from absorbances in the infrared spectra, showed that thiosulfate is strongly adsorbed and that sulfat e is weakly adsorbed to cadmium sulfide. This accounts for the lack of detection of thiosulfate in solution when photocorrosion occurs.