Facet-dependent and defect-enhanced vanadate adsorption on Mg(OH)2 surface: A combined study of DFT calculations and batch experiments

Vanadium contamination has gained increasing attention around the world and it is urgent to develop feasible approach to tackle this growing pollution (e.g., vanadate). Herein, density functional theory (DFT) calculations combined with batch experiments were used to systematically evaluate the capacity of Mg(OH) 2 to adsorb vanadate , by investigating the impacts of different exposed facet and surface OH defect on the structure configurations, adsorption energy and the efficiency of vanadate adsorption. DFT calculations suggested that although the capacity of vanadate adsorption on the facets of Mg(OH) 2 would be obviously influenced by the formation of various coordination complex (e.g., monodentate, bidentate and tridentate) on each facet, the capacity for these facets of Mg(OH) 2 towards vanadate adsorption followed the order: (100) > (001). Moreover, such a vanadate adsorption was further enhanced by the presence of surface OH defect, owing to altered densities of states (DOS) of the adsorption site. Batch experiments verified the defect-rich Mg(OH) 2 was favorable to adsorb vanadate, and both (001) and (100) facet play the great roles. This molecular-level understanding of the facet-dependent and defect-enhanced adsorption behavior of Mg(OH) 2 toward vanadate provides a useful insight into designing and applying effective adsorbents for the removal of heavy metal oxyanions.