Insights into cation exchange selectivity of a natural clinoptilolite by means of dielectric relaxation spectroscopy |
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Authors: | Gerardo Rodríguez-Fuentes Sabine Devautour-Vinot Sekou Diaby François Henn |
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Institution: | 1.Instituto de Ciencia y Tecnología de Materiales,Universidad de La Habana,La Habana,Cuba;2.Equipe Physicochimie des Matériaux Désordonnés et Poreux, Institut Charles Gerhardt, UMR 5253 CNRS,Université Montpellier 2,Montpellier Cedex 5,France;3.Laboratoire de Chimie-Physique, UFR-SSMT (Unité de Formation et de Recherche en Sciences des Structures de la Matière et Technologie),Université de Cocody-Abidjan,Abidjan 22,C?te d’Ivoire |
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Abstract: | Purified natural clinoptilolite from the Tasajeras deposit, Cuba, and some of its metal exchanged forms are studied, at the
dehydrated state, by means of dielectric relaxation spectroscopy (DRS) using two different modus operandi: complex impedance
spectroscopy and dielectric dynamic thermal analysis. Data analysis yields the determination of the extra-framework cation
(EFC) population into the various possible crystallographic sites of the zeolitic framework as well as of the activation energy
characterizing the localized hopping mechanism of EFC. First, it is shown that the DRS responses obtained here match well
with the previous reported data, which were previously localized EFCs in positions close to M1 and M2 sites when the clinoptilolite
is modified to almost homoionic form. From this outcome, it can be concluded that all EFCs are in the same crystallographic
situation regarding solvation or, in other terms, that no steric effect can be taken into account to explain cationic selectivity.
Second, based on the assumption that the activation energy for EFC hopping is directly connected to the EFC/framework interaction
and on simple thermodynamics consideration, we show this interaction does not govern the EFC exchange reaction. So, it is
emphasized that EFC/H2O interaction is the key factor for cation exchange selectivity. |
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