Few-Layer Clayenes for Material and Environmental Applications

Here, we coined the term "clayene" for a single layer of clay and "few-layer clayene" for clays with 2-10 layers. Few-layer clayenes, which are Fe²⁺-rich and mica-type, were prepared hydrothermally at 200 °C and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM)/high-resolution transmission electron microscopy (HRTEM) to determine the crystalline phases and morphology, respectively. Chemical composition by energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy confirmed the iron-rich mica composition, and the latter also revealed the presence of both Fe²⁺ and Fe³⁺. Mössbauer spectroscopy further confirmed the presence of Fe²⁺ and Fe³⁺ and their proportions in the mica-type few-layer clayenes. All of the synthesized mica-type few-layer clayenes except one exhibited high specific surface areas (SSAs) ranging from 94 to 149 m²/g as determined by N₂ adsorption-desorption isotherms and the Brunauer-Emmett-Teller (BET) equation. The high surface areas are in conformity with the crystal sizes calculated from XRD peaks and also as revealed by HRTEM. Taking advantage of the interfacial reactions of the high surface area of few-layer clayenes, two potential applications of clayenes were demonstrated in materials and environmental fields.