(510g) Finding Properties Effecting Selectivity of SeO42- Removal from Water Containing Se/S/P Oxo-Anions Using Adsorption on Metal Oxide: DFT Study with Hybrid Solvent Method.

Selenium is highly soluble in water as selenate and selenite and is toxic to human and aquatic life even at very low concentration (TWA 0.2 mg/m³). Adsorption is a promising remediation strategy; however existing metal oxides have low selectivity towards Se and As oxoanions. Here we use first principal calculations to study the facet and material dependent behavior of Se(IV), Se(VI), S(VI), P(III) and P(V) adsorption. We delineate material properties affecting the adsorption characteristics such as valance electrons, and bond lengths, and surface properties such as interfacial water network, oxo-anion surface configuration, pH, etc. We find that the water network has significant control over adsorption behavior. Since number of H on the surface and oxo-anion directly control the water network, Al₂O₃ is not selective adsorbent towards selenate as compared to sulphate. The adsorption is highest at low pH, as the surface is concentrated with excess H. The facet dependent adsorption is also related to changes in water network over the surface. The adsorbents electronegativity also affects the adsorption energy of oxo-anion. The hematite binds Se(VI) and Se(IV) more strongly than Al₂O₃ surfaces because the Fe atoms are able to donate electrons to oxoanion-surface bonds . The adsorbent material has stronger effect on oxo-anions in inner sphere configuration. The potential adsorbent material, therefore, needs to bind the oxo-anion in inner sphere configuration, for highly selective adsorption.