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An Electron Paramagnetic Resonance Spectroscopy Investigation of the Retention Mechanisms of Mn and Cu in the Nanopore Channels of Three Zeolite Minerals

Published online by Cambridge University Press:  01 January 2024

Daniel R. Ferreira ,
Cristian P. Schulthess ,
James E. Amonette  and
Eric D. Walter
Daniel R. Ferreira*
Affiliation:
Department of Biology and Chemistry, Southern Polytechnic State University, Building E, Suite 183, 1100 South Marietta Pkwy, Marietta, GA 30060, USA
Cristian P. Schulthess
Affiliation:
Department of Plant Science and Landscape Architecture, University of Connecticut, 1376 Storrs Road, Storrs, CT 06269-4067, USA
James E. Amonette
Affiliation:
Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland, WA 99352, USA
Eric D. Walter
Affiliation:
Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999 Richland, WA 99352, USA
*
*E-mail address of corresponding author: [email protected]
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Abstract

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The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than in that of ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium-sized nanopore channels or smaller.

Keywords

AdsorptionCopperEPRInner-sphereIon ExchangeManganeseNanoporesNISEOuter-sphereZeolites
Type
Article
Information
Clays and Clay Minerals , Volume 60 , Issue 6 , December 2012 , pp. 588 - 598
Copyright
Copyright © Clay Minerals Society 2012

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