Configuration, Anion-Specific Effects, Diffusion, and Impact on Counterions for Adsorption of Salt Anions at the Interfaces of Clay Minerals

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• 作者：Xiong Li ; Hang Li ; Gang Yang
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 14, 2016
• 年：2016
• 卷：120
• 期：27
• 页码：14621-14630
• 全文大小：822K
• 年卷期：0
• ISSN：1932-7455

文摘

Interfacial interactions of clay minerals with salt solutions are ubiquitous and play a crucial role in a wide range of fields, where salt cations are the focus while anions are generally regarded as spectators. Here, molecular dynamics simulations show that the various anions are strongly adsorbed on the surfaces of clay minerals, and the resulting anion-specific effects are pronounced. Although constructing only H-bonds, anions form stable inner- and outer-sphere complexes with clay minerals, and F^– and OH^– can result in even more stable complexes than metal ions. The underlying anion-specific effects abide by the sequence OH^– > F^– > Cl^– > I^– and show apparent enhancements with increase of salt concentrations. OH^– is particular at relatively high concentrations, forming clusters and capturing metal ions at octahedral AlO₆ surfaces and approaching tetrahedral SiO₄ surfaces with help of metal ions in addition to the monodispersive inner- and outer-sphere species at octahedral AlO₆ surfaces that are similar for all anions. Diffusion coefficients of anions are the same order of magnitude as those of metal ions and are affected by counterions, concentrations, and distances to the surfaces of clay minerals. Diffusion coefficients of both inner- and outer-sphere anions decrease as I^– > Cl^– > F^– > OH^–. Adsorption of anions is affected by counterions (metal ions) and vice versa. Impact of anions on the adsorption of counterions also shows ion-specific effects that follow the sequence OH^– > F^– > Cl^– > I^–, and OH^– can even alter the adsorption structure and distribution of counterions.