Understanding mineral-water interface reactivity is imperative due to its relation to geochemical processes such as cycling, bioavailability, and fate of nutrients and contaminants in water. All of these processes entail sorption of molecular and ionic species at mineral interfaces. However, methods to characterize the structures and energetics of sorption are limited, in particular how to relate density functional theory (DFT) modeling to experimental observables. In the present work, the inner-sphere adsorption of a number of oxyanions on the (001) and (012) surfaces of α-Al2O3 have been investigated using a DFT-based thermodynamics model. We also studied the inner-sphere adsorption of alkali and alkaline earth cations on the (101) and (001) surfaces of α-SiO2. Periodic boundary conditions were applied to mimic the extended crystalline characteristics of the substrates. Double Numerical Polarized (DNP) basis sets were employed as describe the atomic orbitals for the periodic GGA-PBE calculations. Specifically, energetics, pH dependence, and vibrational properties of these surfaces were examined in the presence of hydration effects for all of the abovementioned surfaces. A systematic inspection of various adsorption modes of oxyanions on the (001) and (110) surface of α-Al2O3 was also performed. Optimized geometries, phonons, and energetics were utilized to interpret and complement the experimental calorimetric measurements. We use the varying surface terminations to analyze the role of surface functional groups and charging on the energetics and strength of adsorption. Different inner-sphere adsorption cases on the (001) surface were modelled to examine the competitive effect of various species present in the natural aqueous environment. These variables were studied by coupling the DFT results with thermodynamics modelling that includes terms for different environmental variables such as pH.

DFT + solvent ion model applied to inner-sphere adsorption

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.