Ternary [Al(2)O(3)-electrolyte-Cu(2+)] species: EPR spectroscopy and surface complexation modeling.
Cu(2+) binding on gamma-Al(2)O(3) is modulated by common electrolyte ions such as Mg(2+), SO(4)(2-), and PO(4)(3-) in a complex manner: (a) At high concentrations of electrolyte ions, Cu(2+) uptake by gamma-Al(2)O(3) is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg(2+) and Cu(2+) ions for the SO(-) surface sites of gamma-Al(2)O(3). (b) At low concentrations of electrolyte ions, Cu(2+) uptake by gamma-Al(2)O(3) can be enhanced. This is due to synergistic coadsorption of Cu(2+) and electrolyte anions, SO(4)(2-) and PO(4)(3-)(.) This results in the formation of ternary surface species (SOH(2)SO(4)Cu)(+), (SOH(2)PO(4)Cu), and (SOH(2)HPO(4)Cu)(+) which enhance Cu(2+) uptake at pH<6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH<<pH(PZC), Cu(2+) coordinates to one SO(-) group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH>>pH(PZC) Cu(2+) may coordinate to two SO(-) groups. At pH<<pH(PZC) electrolyte ions SO(4)(2-) and PO(4)(3-) are bridging one O-atom from the gamma-Al(2)O(3) surface and one Cu(2+) ion forming ternary [gamma-Al(2)O(3)/elecrolyte/Cu(2+)] species.
Papadas
Ioannis T
IT
Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece.
Kosma
Chariklia
C
Deligiannakis
Yiannis
Y