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Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe.
Bin Ma1, Alejandro Fernandez-Martinez1, Sylvain Grangeon2
1Université Grenoble Alpes, CNRS, ISTerre , F-38041 Grenoble, France.
Environmental Science & Technology
|April 19, 2017
Summary
Layered double hydroxides (LDHs) remove molybdate from water via multiple mechanisms beyond simple anion exchange. This study reveals edge sorption, precipitation, and complex structural changes, offering new insights into environmental remediation strategies.
Area of Science:
- Environmental Science
- Materials Science
- Geochemistry
Background:
- Layered double hydroxides (LDHs) are effective for removing anionic contaminants from water.
- Anion exchange is considered the primary mechanism for contaminant removal by LDHs.
Purpose of the Study:
- To investigate molybdate (MoO42-) sorption mechanisms on CaAl LDHs.
- To elucidate the molecular-level processes governing anion uptake by LDHs.
Main Methods:
- Batch isotherm experiments were conducted to model molybdate sorption.
- X-ray techniques, including Mo K-edge X-ray absorption spectra and in situ time-resolved synchrotron-based X-ray diffraction, were employed.
- Advanced aqueous data modeling was used to interpret sorption isotherms.
Main Results:
- Sorption involves three mechanisms: edge site complexation, interlayer anion exchange, and CaMoO4 precipitation.
- Molybdenum (Mo) geometry changes from tetrahedral to octahedral and back to tetrahedral during sorption.
- In situ XRD confirmed anion exchange, aligning with isotherm data.
Conclusions:
- Anion uptake by LDHs is complex, involving edge sorption and interfacial dissolution-reprecipitation, not solely anion exchange.
- Changes in Mo geometry provide a molecular-scale probe for understanding anion uptake mechanisms.
- This research offers a new perspective on LDH-based environmental remediation.