Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe.
Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe.
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DOI：
10.1021/acs.est.7b00946
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发表时间：
2017-04
影响因子：
11.4
通讯作者：
B. Ma;A. Fernández-Martínez;S. Grangeon;C. Tournassat;N. Findling;F. Claret;Ayumi Koishi;N. Marty-N.-Mart
中科院分区：
文献类型：
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作者：
B. Ma;A. Fernández-Martínez;S. Grangeon;C. Tournassat;N. Findling;F. Claret;Ayumi Koishi;N. Marty-N.-Mart
层状双氢氧化物（LDH）被认为是修复水生环境的有效相，主要通过阴离子交换机制去除阴离子污染物。在这里，结合批量等温实验和 X 射线技术来研究随着钼酸盐负载量的增加，CaAl LDH 上的钼酸盐 (MoO42-) 吸附机制。水数据的高级建模表明，吸附等温线可以通过三种保留机制来解释，包括两种类型的边缘位点复合物、层间阴离子交换和 CaMoO4 沉淀。同时，Mo 几何形状在边缘从四面体演变为八面体，并在较高的 Mo 负载量下回到四面体配位，由 Mo K 边缘 X 射线吸收光谱表明。此外，在两种 CaAl LDH 上进行阴离子交换过程后，进行原位时间分辨同步加速器 X 射线衍射，与吸附等温线非常一致。这种详细的分子视图表明，不同的吸收机制（边缘吸附、界面溶解-再沉淀）在环境相关条件下发挥作用并控制阴离子吸收，这与阴离子交换作为主要保留机制的经典观点形成鲜明对比。这项工作通过使用 Mo 几何形状的变化作为强大的分子尺度探针，全面审视了所有这些机制，为 LDH 相吸收阴离子机制的复杂相互作用提供了新的见解。
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 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.