Adsorption of Some Copper(II)-Amino Acid Complexes at the Solid-Solution Interface. Effect of Ligand and Surface Hydrophobicity

The adsorption characteristics of Cu(II) in the presence of amphiphilic (polar-nonpolar) amino acids onto two fundamentally different solid surfaces, viz., alumina (γ-Al₂O³) and activated carbon, were investigated. Adsorption at the relatively hydrophilic alumina surface was governed primarily by hydrogen bonding. Electrostatic repulsion between the adsorbate and the alumina surface prevented adsorption. The sequence of adsorption of Cu(II)-amino acid complexes on activated carbon corresponded directly to the ligand hydrophobicity: Cu-Phe >Cu-Leu >Cu-Val >Cu-Ala >Cu-Gly. This demonstrates the possibility of removing metals from aqueous solution by ligand complexation followed by adsorption onto an appropriate solid surface. The ligand must be bifunctional, possessing both a hydrocarbon and a polar moiety. The latter provides a complexation site for the metal ion; the hydrocarbon provides the wherewithal for hydrophobic bonding to the surface.