An infrared spectroscopic study of carbonate adsorption to zirconium dioxide sol-gel films from aqueous solutions

Internal reflection infrared spectroscopy has been used to investigate the formation and nature of surface carbonates on ZrO2 sol-gel films. Films prepared in atmospheres of CO2 and air exhibited an enhancement of bands in the 1600-1300 cm(-1) spectral region compared to films prepared in an Ar atmosphere. This is due to formation of surface carbonates from the reaction of atmospheric CO2 with the metal oxide film. Both bidentate carbonate and bidentate bicarbonate surface species are formed. For in situ solution adsorption studies, ZrO2 sol-gel films were pretreated with an alkaline wash to remove surface contaminants. Adsorption from dilute aqueous (HCO3-)-C-12 solutions resulted in the appearance of strong infrared absorptions at 1551 and 1349 cm(-1) as well as other absorptions at 1091, 1052, 849, and 761 cm(-1). The strong absorptions shifted to 1505 and 1304 cm(-1) with adsorption from dilute (HCO3-)-C-13 Solutions. The adsorbed species has been assigned to a bidentate carbonate from existing infrared absorption data for both zirconium carbonato complexes and previously assigned surface carbonate species. Adsorption isotherms were determined from in situ infrared spectral measurements of adsorbate absorbances as a function of bicarbonate solution concentration. A Langmuir isotherm analysis was used to obtain an equilibrium constant for adsorption of 2 x 10(5) M-1, indicating a strongly bound surface complex.