Density functional theory characterization of phosphate and sulfate adsorption on Fe-(hydr)oxide: Reactivity, pH effect, estimation of Gibbs free energies, and topological analysis of hydrogen bonds

► The chemical reactivity suggests that the inner-sphere complexation occurs via a ligand exchange. ► Thermodynamic favorability of inner-outer sphere adsorption is directly related to the pH. ► Bidentate binuclear complexes are the most thermodynamically favorable mode of adsorption. ► The hydrogen bonds were classified and characterized using the QCT method. ► OH⋯O hydrogen bonds nature is electrostatic in all structures.