Metal complex formation on the surface of amorphous aluminium hydroxide Part V. Interaction of copper (II) with aluminium hydroxide in the presence of o-, m- and p-tyrosine and dopa

Abstract

Electron spin resonance (ESR) spectra of amorphous aluminium hydroxide gels after adsorption of copper (II) from aqueous solution in the presence of the title compounds (pH range 4–8 metal-to-ligand ratios 1:2 or 1:20) showed the formation of surface complexes between the adsorbed ligand and the metal ion. The metal adsorption behaviour, the extent of complexation and the composition of the surface species were dependent on the nature of ligand and the composition of the exchange solution. All ligands formed two complexes with 1:1 and 2:1 ligand-metal stoichiometry, respectively, but only dopa was really effective in yielding the 2:1 species. The structure of complexes involved primarily bonding to surface through the phenolic groups and chelation of metal through the amino acid donor set. Furthermore, the metal sorption in the presence of tyrosines, while still showing a pH-dependence of the metal-like type, was lower compared with that in the absence of ligand. In contrast, a maximum of adsorption was observed at about pH 6 in the presence of dopa. The adsorption behaviour may be explained by the differing ability of the ligands to form bonds with the surface.