XPS studies on the electronic structure of bonding between solid and solutes: Adsorption of arsenate, chromate, phosphate, Pb2+, and Zn2+ ions on amorphous black ferric oxyhydroxide

The adsorption of three anions (AsO43-, PO43-, and CrO42-) and two cations (Zn2+ and Pb2+) has been determined on a new form of amorphous black ferric oxyhydroxide that resembles in local structure beta-FeOOH, akaganeite. The nature of the interaction between FeOOH substrate and the above mentioned adsorbates is characterised with X-ray photoelectron spectroscopy on the co re and valence band levels of trivalent iron and oxygen using frontier mole cular orbital theory as theoretical framework. Our findings indicate that s ubstantial and variable charge transfer occurs in which the FeOOH substrate can function either as a Lewis acid or base in its interaction with differ ent adsorbates. Our findings suggest that the valence band spectra can be u sed to estimate qualitatively the energy level separation between the highe st occupied molecular orbital (HOMO) and lowest unoccupied molecular orbita l (LUMO) of the surface complexes and to assess the chemical affinity betwe en substrate and adsorbate. Copyright (C) 2000 Elsevier Science Ltd.