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

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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 simila...