DFT studies of Cr(VI) complex adsorption on hydroxylated hematite () surfaces

The adsorption structures of Cr(VI) species on hydroxylated α-Fe2O3( 1 1 ¯ 0 2 ) were investigated using density functional theory within a periodic slab model. A broad structural survey of H2CrO4, HCrO 4 - and CrO 4 2 - adsorbed on different surface sites was carried out. Chromate species adsorb on the hydroxylated surface via an outer-sphere mechanism through H-bonding and ion–dipole attraction. The most stable structure for H2CrO4 reveals strong H-bonding to surface and between adsorbates. For HCrO 4 - , a configuration that shows both H-bonding and Cr–O···H–O–Fe ion–dipole interaction is the most favored. In the case of CrO 4 2 - , the most favored adsorption configuration shows the complex standing on the surface with a Cr–O bond aligned on OH, presenting the strongest Cr–O···H–O–Fe interaction. In these three species, CrO 4 2 - displays the strongest interaction with the hydroxylated ( 1 1 ¯ 0 2 ) surface with no tendency toward reduction observed, in accordance with experiment.