title: Investigation of chromate coordination on ferrihydrite by in situ ATR-FTIR spectroscopy and theoretical frequency calculations.
abstract: Chromate mobility, reactivity, and bioavailability in soil environments are affected by adsorption reactions on iron oxide minerals, but the adsorption mechanisms remain controversial. In this study, we employed in situ attenuated total reflectance Fourier transform infrared spectroscopy and theoretical frequency calculations to characterize chromate adsorption on 2-line ferrihydrite. The effects of pH, aqueous chromate concentration, ionic strength, and deuterium exchange were investigated. Results suggest the formation of monodentate and bidentate surface complexes. It was determined that monodentate complexes are dominant at low surface coverage and pH ≥ 6.5 and that bidentate complexes form at high surface coverage and pH < 6. Deuterium exchange experiments indicated that the inner-sphere complexes are not protonated. Difference spectra revealed that monodentate complexes are particularly susceptible to ionic strength effects under acidic conditions.
authors.affiliation: Department of Civil and Environmental Engineering, University of Connecticut, Storrs, Connecticut 06269, United States.
authors.forename: Chad P
authors.initials: CP
authors.lastname: Johnston
authors.forename: Maria
authors.initials: M
authors.lastname: Chrysochoou
mesh_terms: D000327:Adsorption; D002840:Chromates / Q000737:chemistry*; D004777:Environment; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D009994:Osmolar Concentration; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D014732:Vibration; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D002840:Chromates; D005290:Ferric Compounds; D014874:Water Pollutants, Chemical; C000499:ferric oxide; C092844:ferric oxyhydroxide