Adsorption of Pb(II) on the kaolinite(001) surface in aqueous system: A DFT approach

A systematic first-principles model study of Pb(II) adsorption on the basal hydroxylated (0 01) surface of kaolinite in aqueous environment was carried out using periodic DFT slab calculations. The effective coordination number, coordination geometry, preferred adsorption position and adsorption type of Pb(II) complex were examined, with two different types of surface sites (O-u with "up" hydrogen and O-1 with "lying" hydrogen) considered. Complexes in mono-, bi- and tri-dentate modes exhibit coordination number of 3-5 within the hemidirected tendency geometry. The monodentate complex on "O-u" site and the tridentate complex on "O-u-O-u-O-1" site of two neighboring Al centers are found to be the major adsorption species. Hydrogen bonding interaction of surface O-1 with hydrogen of aqua ligands acts as the key factor for the stability of complex. Partial density of state (PDOS) projections combining with Mulliken bond populations show that coupling of Pb 6p with the antibonding Pb 6s-O 2p states is the dominant orbital interaction of Pb(II) with aqua oxygen (O-w) or surface oxygen (O-s). Different from the covalent Pb-O-w, bond of Pb-O-s, displays strong ionic characters. (C) 2015 Elsevier B.V. All rights reserved.