Probing Specific Adsorption of Electrolytes at Kaolinite–Aqueous Interfaces by Atomic Force Microscopy

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Adsorption of electrolytes (ions) at solid-liquid interfaces alters the physical and chemical properties of materials and hence plays a critical role in manufacturing and processing of nanomaterials featuring large surface or interfacial areas of desired structures and morphology. Many experiments and theoretical calculations using various electrical double layer (EDL) models have been conducted to understand how and where ions adsorb at charged surfaces in a liquid. However, conclusions from previous research remain inconclusive because of model-dependent approaches to studying ion adsorption at diverse solid-liquid interfaces. In this study, atomic force microscopy is used to image in liquids the surface lattice structure of two kaolinite basal planes in the presence and absence of monovalent and divalent cations. Distinct adsorption of ions through different mechanisms (such as electrostatic attraction and specific adsorption) is identified through atomic resolution imaging without the assumption of an EDL structure.