Paul Scherrer Institut, General Energy Research, Laboratory for Bioenergy and Catalysis, CH-5232 Villigen PSI, Switzerland.
J Phys Chem A. 2013 Sep 5;117(35):8368-76. doi: 10.1021/jp404272e. Epub 2013 Aug 26.
Sulfur K-edge X-ray absorption spectroscopy (XAS) has been used to distinguish between aqueous and solid sulfates and to investigate changes in their speciation. Data have been collected for tetrahedrally coordinated S in K2SO4 and KHSO4 solids and aqueous solutions. With a first qualitative analysis of the X-ray absorption near-edge structure (XANES) spectra, it has been observed that those for solids are much more structured and distinguishable from those of aqueous solutions. The protonation state has a strong effect on the white line of sulfates and has been assigned to the different charge delocalization in the samples, the effect of the solvating water molecules and multiple scattering effects. In the extended X-ray absorption fine structure (EXAFS) spectra, the backscattering from the first O shell dominated the EXAFS fine structure function, χ(k), but the nonlinear multiple scattering contributions occurring in the first coordination shell are significant and must be considered in the EXAFS analysis. The intensity of these contributions strongly depend on the symmetry of the system. For a distorted tetrahedron, the intensity of the multiple scattering contributions is less than that found in a regular tetrahedron. The FEFF code has been used to model the contributions of the multiple-scattering processes. The observed experimental evidence in the XAS data can be used to distinguish between sulfates in solids and liquids. This is applicable to many chemical, geochemical, and biological systems.
硫 K 边 X 射线吸收光谱（XAS）已被用于区分水相和固相硫酸盐，并研究其形态变化。已经收集了 K2SO4 和 KHSO4 固体和水溶液中四面体配位 S 的数据。通过对 X 射线吸收近边结构（XANES）光谱进行初步定性分析，观察到固体的光谱结构更加复杂，与水溶液的光谱明显不同。质子化状态对硫酸盐的白线有很强的影响，并归因于样品中不同的电荷离域、溶剂水分子的影响和多次散射效应。在扩展 X 射线吸收精细结构（EXAFS）光谱中，来自第一 O 壳层的反向散射主导了 EXAFS 精细结构函数 χ(k)，但在第一配位壳层中发生的非线性多次散射贡献是显著的，在 EXAFS 分析中必须考虑这些贡献。这些贡献的强度强烈依赖于体系的对称性。对于扭曲的四面体，多次散射贡献的强度小于规则四面体中的强度。FEFF 代码已被用于模拟多次散射过程的贡献。XAS 数据中的观察到的实验证据可用于区分固体和液体中的硫酸盐。这适用于许多化学、地球化学和生物学系统。
