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The Effect of Substrate Type and 2,2′-Bipyridine on the Sorption of Copper(II) on Silica and Alumina

Published online by Cambridge University Press:  10 February 2011

Sing-Foong Cheah ,
Gordon E. Brown Jr.  and
George A. Parks
Sing-Foong Cheah
Affiliation:
Department of Geological and Environmental SciencesStanford University, Stanford, CA 94305-2115, USA
Gordon E. Brown Jr.
Affiliation:
Department of Geological and Environmental SciencesStanford University, Stanford, CA 94305-2115, USA Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305-2115, USA
George A. Parks
Affiliation:
Department of Geological and Environmental SciencesStanford University, Stanford, CA 94305-2115, USA
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Abstract

We have studied the co-adsorption of Cu(II) and an organic ligand, 2,2′-bipyridine (bipy), on amorphous silica (am-SiO2) and γ-Al2O3 (γ-alumina). This study focuses on two fundamental questions: (1) how bipy affects the macroscopic uptake behavior and molecular-scale characteristics of Cu(II) sorption complexes formed on each oxide; and (2) how and why the uptake behavior and the characteristics of Cu(II) sorption complexes differ for the two oxides. Solution uptake experiments and X-ray Absorption Fine Structure (XAFS) spectroscopy were used to answer these questions.

In the absence of bipy and at a surface loading of approximately 0.05 μM/m2, Cu(II) adsorbs predominantly as a dimeric complex on am-SiO2 surfaces but as a monomeric complex on γ-Al2O3. At low Cu(II) to solid ratio, bipy shifts the pH of Cu(II) sorption on am-SiO2 to lower values, but it shifts the pH of Cu(II) sorption on γ-Al2O3 to higher values. Uptake experiments and XAFS measurements on the wet sorption samples indicate that sorption of aqueous Cu(bipy)2 on γ-Al2O3 displaces one bipy from the aqueous Cu(bipy)2 complex, while sorption on am-SiO2 does not disrupt the complex. More detailed XAFS analysis suggests an innersphere Cu(bipy)1 complex on γ-Al2O3 and a stronger Cu-surface oxygen interaction when Cu(bipy)2 adsorbs on γ-Al2O3 than am-SiO2.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 432: Symposium S – Aqueous Chemistry and Geochemistry of Oxides , 1996 , 231
Copyright
Copyright © Materials Research Society 1997

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