State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Environ Sci Technol. 2011 Mar 1;45(5):1873-9. doi: 10.1021/es1035283. Epub 2011 Jan 31.
The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO(2) interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average ∼4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn-O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments.
水合锌(II)在水-TiO(2)界面上的局部配位结构通过扩展 X 射线吸收精细结构 (EXAFS) 和 X 射线吸收近边结构 (XANES) 光谱结合密度泛函理论 (DFT) 计算来确定。通过 EXAFS 分析得到了中心 Zn 原子周围平均约 4.5 个 O 原子的非整数配位数。DFT 计算表明，这种配位结构与 4 配位的双齿双核 (BB) 和 5 配位的双齿单核 (BM) 亚稳平衡吸附 (MEA) 态的混合物一致。BB 络合物具有 4 配位的 Zn，而单齿单核 (MM) 络合物具有 6 配位的 Zn，在 BM 吸附模式下发现了 5 配位的吸附 Zn。DFT 计算的能量表明，较低配位的 BB 和 BM 模式在热力学上比较高配位的 MM MEA 状态更有利。实验观察到的 XANES 指纹提供了 4 配位和 5 配位 Zn-O 模式的额外直接光谱证据。总体光谱和计算证据表明，由于空间位阻效应，Zn(II)可以在不同的 MEA 状态下以 4、5 和 6 个氧配位的位点存在，并且不同的 MEA 状态的共存形成了多种配位环境。
