title: Contaminant adsorption on nanoscale particles: structural and theoretical characterization of Cu2+ bonding on the surface of Keggin-type polyaluminum (Al30) molecular species.
abstract: The adsorption of contaminants onto metal oxide surfaces with nanoscale Keggin-type structural topologies has been well established, but identification of the reactive sites and the exact binding mechanism are lacking. Polyaluminum species can be utilized as geochemical model compounds to provide molecular level details of the adsorption process. An Al30 Keggin-type species with two surface-bound Cu(2+) cations (Cu2Al30-S) has been crystallized in the presence of disulfonate anions and structurally characterized by single-crystal X-ray diffraction. Density functional theory (DFT) calculations of aqueous molecular analogues for Cu2Al30-S suggest that the reactivity of Al30 toward Cu(2+) and SO4(2-) shows opposite trends in preferred adsorption site as a function of particle topology, with anions preferring the beltway and cations preferring the caps. The bonding competition was modeled using two stepwise reaction schemes that consider Cu2Al30-S formation through initial Cu(2+) or SO4(2-) adsorption. The associated DFT energetics and charge density analyses suggest that strong electrostatic interactions between SO4(2-) and the beltway of Al30 play a vital role in governing where Cu(2+) binds. The calculated electrostatic potential of Al30 provides a theoretical interpretation of the topology-dependent reactivity that is consistent with the present study as well as other results in the literature.
authors.affiliation: Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
authors.forename: Samangi
authors.initials: S
authors.lastname: Abeysinghe
authors.forename: Katie W
authors.initials: KW
authors.lastname: Corum
authors.forename: Diane L
authors.initials: DL
authors.lastname: Neff
authors.forename: Sara E
authors.initials: SE
authors.lastname: Mason
authors.forename: Tori Z
authors.initials: TZ
authors.lastname: Forbes
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D053758:Nanoparticles / Q000737:chemistry*; D011789:Quantum Theory; D013499:Surface Properties
chemical_list: D003300:Copper; D000535:Aluminum