UiO-66金属有机框架从水中去除As（V）的计算洞察力,The Journal of Physical Chemistry C

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UiO-66金属有机框架从水中去除As（V）的计算洞察力
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2021-02-01 , DOI: 10.1021/acs.jpcc.0c09465
Claudia S. Cox ₁ , Valeria Cossich Galicia ₂ , Martina Lessio ₁

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金属有机骨架（MOF）（例如UiO-66）已显示出从水中去除有毒As（V）物种的巨大希望，但确切的吸附机理尚未得到很好的理解。在这项研究中，我们使用密度泛函理论计算和聚类模型来确定在不同pH条件（即砷酸和相关的氧阴离子）上存在的As（V）物种的吸附的准确能级和几何形状。作为此分析的结果，我们确定了一种新的吸附模式，其中两个As（V）分子以单齿的方式吸附在两个相邻的Zr开放金属位点上，这些位点由封端的配位体置换引起。该模式优于先前文献中在酸性和中性pH下提出的其他吸附模式。多齿吸附模式涉及单个As（V）分子在两个相邻的Zr位上的吸附，随着pH的增加，竞争变得越来越激烈，这与在碱性pH值下观察到的较低吸附性能一致。此外，我们研究了配位基团对Zr位点的影响对As（V）吸附热力学的影响。我们表明，氢氧化物-水配体对是最容易被吸附的As（V）物种取代的封端配体，这表明存在于水环境中的缺陷是As（V）物种吸附的理想位点。此外，我们发现磷酸氧阴离子的吸附可以在热力学上与As（V）吸附竞争，因此有可能解释了在存在磷酸盐的情况下观察到的As（V）吸附性能下降。

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Computational Insights into As(V) Removal from Water by the UiO-66 Metal–Organic Framework

Metal–organic frameworks (MOFs) such as UiO-66 have shown great promise for the removal of toxic As(V) species from water, but the precise adsorption mechanism is not yet well understood. In this study, we use density functional theory calculations and cluster models to determine accurate energetics and geometries for the adsorption of As(V) species present under varying pH conditions, namely, arsenic acid and related oxyanions. As a result of this analysis, we identify a new adsorption mode in which two As(V) molecules adsorb in a monodentate fashion on two neighboring Zr open metal sites resulting from capping ligand displacement. This mode is preferred over other adsorption modes previously proposed in the literature at acidic and neutral pH. Multidentate adsorption modes involving adsorption of a single As(V) molecule onto both neighboring Zr sites become more competitive as the pH increases, consistent with the lower adsorption performance observed at basic pH. Additionally, we study the influence of the ligands capping the Zr sites on As(V) adsorption thermodynamics. We show that the hydroxide–water ligand pair is the capping ligand most easily displaced by adsorbing As(V) species, suggesting that defects present in the aqueous environment are the ideal site for As(V) species adsorption. Furthermore, we find that adsorption of phosphate oxyanions can thermodynamically compete with As(V) adsorption, thus potentially explaining the observed decreased As(V) adsorption performance in the presence of phosphates. The molecular-level insights gained in this study are used to draw general design principles for the development of new MOFs that can be employed to remove toxic oxyanions from water.

更新日期：2021-02-11

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