| Abstract
| - Interfacial processes can control the transport, speciation, and ultimate fate of aqueous pollutants in groundwater.Here, we apply resonantly enhanced second harmonic generation as well as the χ(3) technique to study theinteraction of chromium(VI) with the (11̄02) α-Al2O3−water interface. Adsorption isotherm measurementsyield free energies of adsorption that are consistent with a hydrogen-bonding mechanism mediated throughthe outer-sphere solvation shell of chromium(VI). Results from measurements regarding the charge state ofthe α-Al2O3−water interface as well as the chromium(VI) saturation surface coverages and the pH-dependenceof the chromium(VI) equilibrium binding constants are used to develop a thermodynamic and mass-balancedmodel that describes the interfacial interactions on the molecular level. Special attention is paid to the interfacialspeciation state of chromium(VI) as a function of bulk solution pH. Scaling up, we estimate the mobility ofchromium(VI) in alumina-rich soils by using the Kd model. This work presents a significant advancement inour understanding of the molecular-level interactions between chromium(VI) and α-Al2O3 and improves ourability to predict the environmental mobility, speciation, and ultimate fate of chromium(VI).
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