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Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe

Abstract : Layered double hydroxides (LDHs) have been considered as effective phases for the remediation of aquatic environments, to remove anionic contaminants mainly through anion exchange mechanisms. Here, a combination of batch isotherm experiments and X-ray techniques was used to examine molybdate (MoO42-) sorption mechanisms on CaAl LDHs with increasing loadings of molybdate. Advanced modeling of aqueous data shows that the sorption isotherm can be interpreted by three retention mechanisms, including two types of edge sites complexes, interlayer anion exchange, and CaMoO4 precipitation. Meanwhile, Mo geometry evolves from tetrahedral to octahedral on the edge, and back to tetrahedral coordination at higher Mo loadings, indicated by Mo Kedge X-ray absorption spectra. Moreover, an anion exchange process on both CaAl LDHs was followed by in situ time-resolved synchrotron-based X-ray diffraction, remarkably agreeing with the sorption isotherm. This detailed molecular view shows that different uptake mechanisms edge sorption, interfacial dissolution-reprecipitation are at play and control anion uptake under environmentally relevant conditions, which is contrast to the classical view of anion exchange as the primary retention mechanism. This work puts all these mechanisms in perspective, offering a new insight into the complex interplay of anion uptake mechanisms by LDH phases, by using changes in Mo geometry as powerful molecular-scale probe.
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https://hal-brgm.archives-ouvertes.fr/hal-01849363
Contributeur : Myriam Chergui <>
Soumis le : jeudi 26 juillet 2018 - 10:00:22
Dernière modification le : vendredi 11 septembre 2020 - 14:54:34

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Bin Ma, Alejandro Fernandez-Martinez, Sylvain Grangeon, Christophe Tournassat, Nathaniel Findling, et al.. Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe. Environmental Science & Technology, American Chemical Society, 2017, 51 (10), pp.5531 - 5540. ⟨10.1021/acs.est.7b00946⟩. ⟨hal-01849363⟩

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