Removal Mechanisms of Phosphate by Lanthanum Hydroxide Nanorods: Investigations using EXAFS, ATR-FTIR, DFT, and Surface Complexation Modeling Approaches
Removal Mechanisms of Phosphate by Lanthanum Hydroxide Nanorods: Investigations using EXAFS, ATR-FTIR, DFT, and Surface Complexation Modeling Approaches
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DOI：
10.1021/acs.est.7b03803
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发表时间：
2017-11-07
影响因子：
11.4
通讯作者：
Lo, Irene M. C.
中科院分区：
文献类型：
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作者：
Fang, Liping;Shi, Qiantao;Lo, Irene M. C.
镧基材料是有效的螯合水中的磷酸盐，然而，其去除机制仍不清楚，环境相关因素的影响尚未进行研究。因此，本研究采用扩展X射线吸收光谱（EXAFS）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）、密度泛函理论（DFT）和化学平衡模型，探讨了La（OH）（3）去除磷酸盐的机理。结果表明，La（OH）（3）表面络合是去除磷酸盐的主要机理，在酸性条件下，La（OH）（3）表面存在双质子化的单核双齿（BM-H2）和双核双齿（BB-H2）磷酸盐。当pH值增加到7时，BM-H1和BB-H2是控制La（OH）（3）对磷酸盐吸附的两种主要构型，而BB-H1是pH值为9时磷酸盐吸附的主导构型。随着磷酸盐负载量的增加，La（OH）（3）上的磷酸盐构型从二元BM-H1和BB-H2转变为BB-H1。在Ca存在下形成无定形Ca-3（PO 4）（2），导致在碱性条件下增强的磷酸盐去除。不同机制的整体除磷的贡献，成功地模拟了化学平衡模型，是符合光谱结果。该研究为La（OH）（3）去除磷酸盐的分子水平机理提供了新的见解。
Lanthanum-based materials are effective for sequestering phosphate in water, however, their removal mechanisms remain unclear, and the effects of environmentally relevant factors have not yet been studied. Hereby, this study explored the mechanisms of phosphate removal using La(OH)(3) by employing extended X-ray absorption spectroscopy (EXAFS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), density functional theory (DFT) and chemical equilibrium modeling. The results showed that surface complexation was the primary mechanism for phosphate removal and in binary phosphate configurations, namely diprotonated bidentate mononuclear (BM-H2) and bidentate binuclear (BB-H2), coexisting on La(OH)(3) in acidic conditions. By increasing the pH to 7, BM-H1 and BB-H2 were the two major configurations governing phosphate adsorption on La(OH)(3), whereas BB-H1 was the dominant configuration of phosphate adsorption at pH 9. With increasing phosphate loading, the phosphate configuration of on La(OH)(3) transforms from binary BM-H1 and BB-H2 to BB-H1. Amorphous Ca-3(PO4)(2) forms in the presence of Ca, leading to enhanced phosphate removal at alkaline conditions. The contributions of different mechanisms to the overall phosphate removal were successfully simulated by a chemical equilibrium model that was consistent with the spectroscopic results. This study provides new insights into the molecular-level mechanism of phosphate removal by La(OH)(3).