(514h) Impact of Solvated Water on Adsorption of Selenium Oxo-Anion on <012> Hematite and Alumina Surface

Metals such as Cr, As and Se, in their soluble oxo-anion forms, are toxic to human and aquatic life at very low concentrations. Increased usage of these metals in industries threatens to further increase the concentrations of these species in our water resources. Adsorption on metal oxide surfaces provides an method to remove these oxo-anions from water without large treatment plants, which is particularly important in rural areas. However, adsorption is not selective and exacerbated because of higher concentrations of competitive oxo-anions, for e.g., sulfur oxo-anions are present in higher concentration as compared to Selenium oxo-anions. This increases the financial burden to quickly replenish the adsorbent. Recent adsorption experiments of selenium oxoanion of different hematite surface found that selenate and selenite have higher selectivity on [012] and [110] hematite facet respectively. Here we use first principle calculations to study the facet dependent behavior of hematite-based adsorption. Adsorption energies are calculated for varying oxo-anion configuration including inner and outer sphere complexes on [012] surface. In this work, we delineate the most important effects controlling adsorption, including surface configuration, pH, solvation, etc. We find the solvation configuration directed by the surface controls the adsorption behavior. The model is extended to calculate energies on [012] alumina surface to understand the effects of metal oxide surfaces on adsorption capabilities. In addition to shedding light on this particular adsorbing species, this work highlights the criticality of correctly considering solvation, and outer sphere adsorption, in first principles analysis of oxoanion adsorption.