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 the interaction of chromium(VI) with the (11̄02) α-Al 2O3-water interface. Adsorption isotherm measurements yield free energies of adsorption that are consistent with a hydrogen-bonding mechanism mediated through the outer-sphere solvation shell of chromium(VI). Results from measurements regarding the charge state of the α-Al 2O3-water interface as well as the chromium(VI) saturation surface coverages and the pH-dependence of the chromium(VI) equilibrium binding constants are used to develop a thermodynamic and mass-balanced model that describes the interfacial interactions on the molecular level. Special attention is paid to the interfacial speciation state of chromium(VI) as a function of bulk solution pH. Scaling up, we estimate the mobility of chromium(VI) in alumina-rich soils by using the Kd model. This work presents a significant advancement in our understanding of the molecular-level interactions between chromium(VI) and α-Al2O3 and improves our ability to predict the environmental mobility, speciation, and ultimate fate of chromium(VI).
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films