10.1021/acs.est.7b00946.s001 Bin Ma Bin Ma Alejandro Fernandez-Martinez Alejandro Fernandez-Martinez Sylvain Grangeon Sylvain Grangeon Christophe Tournassat Christophe Tournassat Nathaniel Findling Nathaniel Findling Francis Claret Francis Claret Ayumi Koishi Ayumi Koishi Nicolas C. M. Marty Nicolas C. M. Marty Delphine Tisserand Delphine Tisserand Sarah Bureau Sarah Bureau Eduardo Salas-Colera Eduardo Salas-Colera Erik Elkaïm Erik Elkaïm Carlo Marini Carlo Marini Laurent Charlet Laurent Charlet Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe American Chemical Society 2017 edge sites complexes sorption isotherm CaMoO 4 precipitation Mo geometry anion uptake mechanisms CaAl LDHs batch isotherm experiments control anion uptake time-resolved synchrotron-based X-ray diffraction Mo K-edge X-ray absorption spectra anion exchange mechanisms anion exchange process Layered Double Hydroxides Multiple Sorption Modes Structural Probe Layered interlayer anion exchange 2017-04-18 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Evidence_of_Multiple_Sorption_Modes_in_Layered_Double_Hydroxides_Using_Mo_As_Structural_Probe/4928681 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 (MoO<sub>4</sub><sup>2–</sup>) 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 CaMoO<sub>4</sub> precipitation. Meanwhile, Mo geometry evolves from tetrahedral to octahedral on the edge, and back to tetrahedral coordination at higher Mo loadings, indicated by Mo K-edge 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.