DFT studies of Cr(VI) complex adsorption on hydroxylated hematite (11¯02) surfaces

The adsorption structures of Cr(VI) species on hydroxylated α-Fe2O3(11¯02) were investigated using density functional theory within a periodic slab model. A broad structural survey of H2CrO4, HCrO4- and CrO42- 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 HCrO4-, a configuration that shows both H-bonding and Cr-O···H-O-Fe ion-dipole interaction is the most favored. In the case of CrO42-, 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, CrO42- displays the strongest interaction with the hydroxylated (11¯02) surface with no tendency toward reduction observed, in accordance with experiment.