ATR-FTIR and Density Functional Theory Study of the Structures, Energetics, and Vibrational Spectra of Phosphate Adsorbed onto Goethite
ATR-FTIR and Density Functional Theory Study of the Structures, Energetics, and Vibrational Spectra of Phosphate Adsorbed onto Goethite
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DOI：
10.1021/la303111a
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发表时间：
2012-10-16
期刊：
影响因子：
3.9
通讯作者：
Strongin, Daniel R.
中科院分区：
文献类型：
--
作者：
Kubicki, James D.;Paul, Kristian W.;Strongin, Daniel R.
采用周期平面波密度泛函理论（DFT）和分子簇杂化分子轨道密度泛函理论（MO-DFT）对α-FeOOH（010）、（001）、（101）和（210）表面的磷酸盐表面复合物模型进行了计算。单齿和双齿HPO 42-表面复合物的结合能进行了比较H2 PO 4-外层复合物。使用DFT分子动力学（DFT-MD）模拟和能量最小化的平均势能来估计每种构型的吸附能。从周期系统的能量最小化结构中提取分子团簇，并用MO-DFT进行能量再最小化和频率分析。模型化的P-O和P-Fe距离是一致的与EXAFS数据的砷酸盐含氧阴离子，这是一个类似的磷酸盐，和原子间的距离预测的集群是类似的周期性模型。然后将这些簇的计算振动频率与观察到的红外波段相关联。导致有利的吸附能，也被发现产生的理论振动频率，以及与实验相关。单齿与双齿构型的相对稳定性是所考虑的针铁矿表面的函数。总的来说，我们的结果表明，磷酸盐吸附到针铁矿上是以各种表面复合物的形式发生的，这取决于矿物的习性（即，先前的IR光谱研究可能难以解释，因为观察到的光谱平均了具有多个表面的任何给定样品上的三种或更多种构型的结构性质。
Periodic plane-wave density functional theory (DFT) and molecular cluster hybrid molecular orbital-DFT (MO-DFT) calculations were performed on models of phosphate surface complexes on the (100), (010), (001), (101), and (210) surfaces of alpha-FeOOH (goethite). Binding energies of monodentate and bidentate HPO42- surface complexes were compared to H2PO4- outer-sphere complexes. Both the average potential energies from DFT molecular dynamics (DFT-MD) simulations and energy minimizations were used to estimate adsorption energies for each configuration. Molecular clusters were extracted from the energy-minimized structures of the periodic systems and subjected to energy reminimization and frequency analysis with MO-DFT. The modeled P-O and P---Fe distances were consistent with EXAFS data for the arsenate oxyanion that is an analog of phosphate, and the interatomic distances predicted by the clusters were similar to those of the periodic models. Calculated vibrational frequencies from these clusters were then correlated with observed infrared bands. Configurations that resulted in favorable adsorption energies were also found to produce theoretical vibrational frequencies that correlated well with experiment. The relative stability of monodentate versus bidentate configurations was a function of the goethite surface under consideration. Overall, our results show that phosphate adsorption onto goethite occurs as a variety of surface complexes depending on the habit of the mineral (i.e., surfaces present) and solution pH. Previous IR spectroscopic studies may have been difficult to interpret because the observed spectra averaged the structural properties of three or more configurations on any given sample with multiple surfaces.