Post-synthesis surface-modified silicas as adsorbents for heavy metal ion contaminants Cd(II), Cu(II), Cr(III), and Sr(II) in aqueous solutions

► Wide pore silica gels have larger adsorption capacities than narrow pore silica. ► Adsorption free energies are generally more favorable for narrow pore silica. ► Multiple amino groups can result in more favorable adsorption free energies suggesting chelation. ► Reductions in surface area are less pronounced for the EDTrA organosilane derivative. ► Cr(III) adsorption on EDTrA-modified silica results in a carboxylate band shift to higher energy.