Cu2+ Interaction with Microcrystalline Gibbsite. Evidence for Oriented Chemisorbed Copper Ions

M. B. McBride1, A. R. Fraser and W. J. McHardy
The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen AB9 2QJ, United Kingdom
1 Department of Agronomy, Cornell University, Ithaca, New York 14853

Abstract: The ability of a high surface-area gibbsite to adsorb Cu2+ was studied using a Cu2+ ion-selective electrode, electron spin resonance, infrared spectroscopy, and electron microscopy. The gibbsite chemisorbed small amounts of monomeric Cu2+ (<0.5 mmole/100 g) which was oriented with its z-axis perpendicular to the (001) plane of the mineral. The proposed chemisorption sites are at gibbsite crystal “steps” observed by electron microscopy. Although Cu2+ adsorption on gibbsite as a function of pH was largely reversible, exposure of the chemisorbed Cu2+ to NH3 did not result in desorption from the surface despite the displacement of several OH or H2O ligands by NH3. The results indicate that at least one Cu-O-Al bond is formed in the process of chemisorption.

At pH > 5, the gibbsite appeared to promote the hydrolysis and polymerization of Cu2+, with further adsorption at the surfaces. Infrared spectroscopy revealed no effect of the adsorption on the (001) surface hydroxyl groups, although the anisotropic diffusion of protons in the gibbsite structure was verified from deuteration studies.

Key Words: Adsorption • Chemisorption • Copper • Electron spin resonance • Gibbsite • Infrared spectroscopy

Clays and Clay Minerals; February 1984 v. 32; no. 1; p. 12-18; DOI: 10.1346/CCMN.1984.0320102
© 1984, The Clay Minerals Society
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