Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Environ Sci Technol. 2012 Oct 16;46(20):11154-61. doi: 10.1021/es302879y. Epub 2012 Oct 3.
Uranyl adsorption at the muscovite (mica)/water interface was studied by second harmonic generation (SHG). Using the nonresonant χ(3) technique and the Gouy-Chapman model, the initial surface charge density of the mica surface was determined to be -0.022(1) C/m(2) at pH 6 and in the presence of dissolved carbonate. Under these same conditions, uranyl adsorption isotherms collected using nonresonant χ(3) experiments and resonantly enhanced SHG experiments that probe the ligand-to-metal charge transfer bands of the uranyl cation yielded a uranyl binding constant of 3(1) × 10(7) M(-1), corresponding to a Gibbs free energy of adsorption of -52.6(8) kJ/mol, and a maximum surface charge density at monolayer uranyl coverage of 0.028(3) C/m(2). These results suggest favorable adsorption of uranyl ions to the mica interface through strong ion-dipole or hydrogen interactions, with a 1:1 uranyl ion to surface site ratio that is indicative of monovalent cations ((UO(2))(3)(OH)(5)(+), (UO(2))(4)(OH)(7)(+), UO(2)OH(+), UO(2)Cl(+), UO(2)(CH(3)COO(-))(+)) binding at the interface, in addition to neutral uranyl species (UO(2)(OH)(2) and UO(2)CO(3)). This work provides benchmark measurements to be used in the improvement of contaminant transport modeling.
水镁石（云母）/水界面的铀酰吸附通过二次谐波产生（SHG）进行了研究。使用非共振 χ(3)技术和 Gouy-Chapman 模型，在 pH 6 和存在溶解的碳酸盐的情况下，确定云母表面的初始表面电荷密度为-0.022(1) C/m(2)。在相同条件下，使用非共振 χ(3)实验和共振增强 SHG 实验收集铀酰吸附等温线，探测铀酰阳离子的配体-金属电荷转移带，得到铀酰结合常数为 3(1) × 10(7) M(-1)，对应于吸附的吉布斯自由能为-52.6(8) kJ/mol，单层铀酰覆盖时的最大表面电荷密度为 0.028(3) C/m(2)。这些结果表明，铀酰离子通过强离子偶极或氢键有利地吸附到云母界面上，铀酰离子与表面位点的比例为 1:1，表明界面上存在单价阳离子 ((UO(2))(3)(OH)(5)(+)、(UO(2))(4)(OH)(7)(+)、UO(2)OH(+)、UO(2)Cl(+)、UO(2)(CH(3)COO(-))(+)）结合，此外还有中性铀酰物种 (UO(2)(OH)(2) 和 UO(2)CO(3))。这项工作提供了基准测量值，可用于改进污染物输运模型。
