Molecular Simulation of Structure and Diffusion at Smectite鈥揥ater Interfaces: Using Expanded Clay Interlayers as Model Nanopores
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- 作者：Jeffery A. Greathouse ; David B. Hart ; Geoffrey M. Bowers ; R. James Kirkpatrick ; Randall T. Cygan
- 刊名：Journal of Physical Chemistry C
- 出版年：2015
- 出版时间：July 30, 2015
- 年：2015
- 卷：119
- 期：30
- 页码：17126-17136
- 全文大小：841K
- ISSN：1932-7455
文摘
In geologic settings relevant to a number of extraction and potential sequestration processes, nanopores bounded by clay mineral surfaces play a critical role in the transport of aqueous species. Solution structure and dynamics at clay鈥搘ater interfaces are quite different from their bulk values, and the spatial extent of this disruption remains a topic of current interest. We have used molecular dynamics simulations to investigate the structure and diffusion of aqueous solutions in clay nanopores approximately 6 nm thick, comparing the effect of clay composition with model Na-hectorite and Na-montmorillonite surfaces. In addition to structural properties at the interface, water and ion diffusion coefficients were calculated within each aqueous layer at the interface, as well as in the central bulk-like region of the nanopore. The results show similar solution structure and diffusion properties at each surface, with subtle differences in sodium adsorption complexes and water structure in the first adsorbed layer due to different arrangements of layer hydroxyl groups in the two clay models. Interestingly, the extent of surface disruption on bulk-like solution structure and diffusion extends to only a few water layers. A comparison of sodium ion residence times confirms similar behavior of inner-sphere and outer-sphere surface complexes at each clay surface, but 鈭?% of sodium ions adsorb in ditrigonal cavities on the hectorite surface. The presence of these anhydrous ions is consistent with highly immobile anhydrous ions seen in previous nuclear magnetic resonance spectroscopic measurements of hectorite pastes.