Study of the Ion Interclation Mechanism in Mxene Membrane for the Water Treatment Applications

Abstract

MXene membrane consists of free-standing layers of a 2D material, namely MXene, which is attracting growing interest due to its conductivity and well-defined interlayer distance and slit-like channels, making it attractive in applications like energy storage and water treatment applications. Unfortunately, these membranes can swell and shrink when in contact with water or under high temperatures. MXene (Ti3C2) is a two-dimensional early transition metal carbide-derived by the etching of MAX (Ti3AlC2) phases in fluoride-containing solutions, and it can be intercalated with cations due to its surface termination that makes MXene sheets Negatively charged. The conventional characterization was used to examine the successful intercalation of cations between MXene membrane layers utilizing SEM, TEM, XPS, and elemental mapping by EDS. The contact angle revealed that higher hydration radius cations decrease the hydrophilicity of the MXene membranes when intercalated. This thesis is comprised of four chapters. Chapter one consists of the introduction and literature review, which provides an overview of the current conventional technology in water treatment applications and how the two-dimensional nanomaterial can improve it. The high water flow of 2D membrane stems from the well-defined nanometer channels that exhibit low friction for the water flow making high water flux membranes. This chapter also addresses the synthesis, fabrication, and structure of MXene membranes. Furthermore, the chapter discusses the ionic intercalation in aqueous for these membranes and compares the ionic sieving mechanism between GO and MXene membranes as well as discusses the stability of MXene membranes under different environmental conditions. The second chapter introduces the systems in detail and outlines the materials used in this study. Chapter three presents the results of the investigation by showing the synthesis and fabrication of the membranes and the successful intercalation of cations between MXene layers. Furthermore, the effect of different intercalated cations under various temperatures and relative humidity values are investigated using in-situ ESEM and XRD capabilities. A conclusion of the study is provided in the final chapter. Here, using in-situ X-ray diffraction (XRD) analysis, the effect of intercalated cations such as Na-Ti3C2, Ca-Ti3C2, and Al-Ti3C2 between MXene membranes on its crystal structure (namely d-space) under different temperatures are investigated. The study found that the higher the hydration enthalpies of the intercalated cations, the less stable the MXene membrane becomes under increased high temperatures. The same observation was true in the in-situ environmental scanning electron microscope (ESEM) study, where the cross-section of these cations suffers a significant decrease compared with lower hydration enthalpy cations. Moreover, an in-situ (ESEM) was utilized to observe the effect of different hydration enthalpy cations on membrane thickness under changes in relative humidity. Higher hydration enthalpy intercalated cation MXene membranes had fewer changes in their cross-section thickness compared with lower hydration enthalpy cations. This thesis provides a detailed study of the ion intercalation mechanism in MXene membrane for applications related to water treatment.