How Cation–Silica Surface Interactions Affect Water Dynamics in Nanoconfined Electrolyte Solutions

Abstract

Probing electrolyte behavior at the atomic level provides valuable insights into understanding the reactive transport of electrolyte solutions in nanoconfinement and help explain and predict the macroscopic properties of industrial or natural nanoporous materials. In this study, we focused on the behavior of water and ions in silica nanocylinders with a pore diameter of 2.6 nm filled with electrolyte solutions, XCl at 1 M with X = Li, Na, and Cs, monovalent cations presenting various kosmotropic/chaotropic properties. Using a combination of experiments and theoretical modeling, we analyzed the water dynamics based on three primary effects: the confinement, the electrolyte, and the interfacial ion−porous material surface interaction. Comparing the water dynamics obtained with those of divalent cations previously studied by Baum et al. (Dynamical and Structural Properties of Langmuir 35 (2019) 10780−10794. https://doi.org/10.1021/acs.langmuir.9b01434), we highlight that monovalent cations present weaker interactions with silica surfaces than divalent cations. This significantly impacts the water dynamics in addition to the confinement and electrolyte effects. This study pinpoints the importance of ion behavior within the interfacial layer and its impact on water transport in nanoconfinement.