Adsorption Mechanism of Hydrated Pb(OH)+ on the Kaolinite (001) Surface

The adsorption behavior of Pb(OH)(+) on the basal octahedral (001) surface of kaolinite has been investigated using the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) of density functional theory with periodic slab models, where the water environment was considered. The coordination geometry, coordination number, preferred adsorption position, and adsorption type were examined, with binding energy estimated. All the monodentate and bidentate complexes exhibited hemi-directed geometry with coordination numbers of 3-5. Site of "O-u" with "up" hydrogen was more favorable for monodentate complex than site of "O-l" with "lying" hydrogen. Monodentate complexation of "O-u" site with a high binding energy of -182.60 kJ center dot mol(-1) should be the most preferred adsorption mode, while bidentate complexation on "OuOl" site of single Al center was also probable. The stability of adsorption complex was found closely related to the hydrogen bonding interactions between surface O-l and H in aqua ligands of Pb(II). Mulliken population and density of states analyses showed that coupling of Pb 6p with the antibonding Pb 6s-O 2p states was the primary orbital interaction between Pb(II) and the surface oxygen. Hydrogen complexation occupied a much large proportion in the joint coordination structure of bidentate complex, where bonding state filling predominated for the Pb-O-I interaction.