Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
Langmuir. 2012 Jun 12;28(23):8637-50. doi: 10.1021/la300032h. Epub 2012 May 25.
The interfacial structure between the muscovite (001) surface and aqueous solutions containing monovalent cations (3 × 10(-3) m Li(+), Na(+), H(3)O(+), K(+), Rb(+), or Cs(+), or 3 × 10(-2) m Li(+) or Na(+)) was measured using in situ specular X-ray reflectivity. The element-specific distribution of Rb(+) was also obtained with resonant anomalous X-ray reflectivity. The results demonstrate complex interdependencies among adsorbed cation coverage and speciation, interfacial hydration structure, and muscovite surface relaxation. Electron-density profiles of the solution near the surface varied systematically and distinctly with each adsorbed cation. Observations include a broad profile for H(3)O(+), a more structured profile for Li(+) and Na(+), and increasing electron density near the surface because of the inner-sphere adsorption of K(+), Rb(+), and Cs(+) at 1.91 ± 0.12, 1.97 ± 0.01, and 2.26 ± 0.01 Å, respectively. Estimated inner-sphere coverages increased from ~0.6 to 0.78 ± 0.01 to ~0.9 per unit cell area with decreasing cation hydration strength for K(+), Rb(+), and Cs(+), respectively. Between 7 and 12% of the Rb(+) coverage occurred as an outer-sphere species. Systematic trends in the vertical displacement of the muscovite lattice were observed within ~40 Å of the surface. These include a <0.1 Å shift of the interlayer K(+) toward the interface that decays into the crystal and an expansion of the tetrahedral-octahedral-tetrahedral layers except for the top layer in contact with solution. The distortion of the top tetrahedral sheet depends on the adsorbed cation, ranging from an expansion (by ~0.05 Å vertically) in 3 × 10(-3)m H(3)O(+) to a contraction (by ~0.1 Å) in 3 × 10(-3) m Cs(+). The tetrahedral tilting angle in the top sheet increases by 1 to 4° in 3 × 10(-3) m Li(+) or Na(+), which is similar to that in deionized water where the adsorbed cation coverages are insufficient for full charge compensation.
采用原位反射 X 射线反射法测量了白云母（001）表面与含有单价阳离子（3×10(-3) m Li(+)、Na(+)、H(3)O(+)、K(+)、Rb(+)或 Cs(+)，或 3×10(-2) m Li(+)或 Na(+)）的水溶液之间的界面结构。还通过共振反常 X 射线反射法获得了 Rb(+)的元素特异性分布。结果表明，吸附阳离子覆盖率和形态、界面水合结构以及白云母表面弛豫之间存在复杂的相互依存关系。表面附近溶液的电子密度分布随吸附的每种阳离子而系统且明显地变化。观察结果包括 H(3)O(+)的宽轮廓、Li(+)和 Na(+)的更结构化轮廓以及由于 K(+)、Rb(+)和 Cs(+)的内球吸附而导致表面附近电子密度增加，分别为 1.91 ± 0.12、1.97 ± 0.01 和 2.26 ± 0.01 Å。估计的内球覆盖率分别从0.6 增加到 0.78 ± 0.01 到0.9 每单位细胞面积，对于 K(+)、Rb(+)和 Cs(+)，阳离子水合强度依次降低。Rb(+)覆盖的 7%至 12%以外壳物种存在。在表面40 Å 范围内观察到白云母晶格垂直位移的系统趋势。这些趋势包括向界面方向移动的层间 K(+)的0.1 Å 位移，该位移衰减到晶体中，并且除了与溶液接触的顶层之外，四面体-八面体-四面体层都发生了膨胀。与溶液接触的顶层的扭曲取决于吸附的阳离子，范围从 3×10(-3) m H(3)O(+)中的膨胀（垂直方向约为 0.05 Å）到 3×10(-3) m Cs(+)中的收缩（约 0.1 Å）。顶层四面体的倾斜角在 3×10(-3) m Li(+)或 Na(+)中增加 1 至 4°，这与在去离子水中的情况相似，在去离子水中，吸附阳离子的覆盖率不足以完全补偿电荷。
