XPS Study of Pb(II) Adsorption on γ-Al2O3 Surface at High pH Conditions

Abstract

Lead(II) adsorption on γ-Al2O3 at high pH condition (11 <pH<13) was studied in NaNO3 solutions. With increasing pH from 11, Pb(II) uptake by γ-Al2O3 was decreased regardless to sodium concentration (0.1 and 1.0 M). XPS spectra showed no chemical shifts occurred in substrate Al (2s, 2p) and O (1s) binding energy by Pb(II) adsorption. Binding energy of adsorbed Pb (4f) had no dependence on pH and adsorption density and was higher than that of orthorhombic yellow PbO and Pb(NO3)2. Molecular orbital (MO) calculation revealed lowest unoccupied molecular orbital (LUMO) energy of Pb(OH)- 3 was about 6 eV higher than that of Pb(OH)2, and suggested Pb(OH)- 3 was less reactive than Pb(OH)2 with deprotonated surface hydroxyl ligand. These results suggest that Pb(II) is adsorbed on γ-Al2O3 as inner-sphere surface complex form at high pH condition. Although Pb(II) is adsorbed on γ-Al2O3 as inner-sphere surface complex, bonding between Pb(II) and γ-Al2O3 shows less covalent nature.