Effect of Cationic Exchange on the Hydration and Swelling Behavior of Ti3C2Tz MXenes

MXenes, two-dimensional transition-metal carbides, have shown great promise as materials for capacitive energy storage, electromagnetic interference shielding, transparent electrodes, among many other applications. Colloidal suspensions are usually processed to design materials for these applications. However, the mechanisms underlying MXene exfoliation into single or few nanosheets after etching with hydrochloric acid and lithium fluoride are not well understood. Herein, the structural changes induced by the cationic exchange in the interlayer space of Ti3C2Tz during washing are investigated. We also show, mostly by X-ray diffraction of Ti3C2Tz multilayers, that cationic exchange between H3O+ ions, on the one hand, and Li+, K+, or Mg2+, on the other, is occurring reversibly. The presence of Li+ is a necessary condition for the crystalline swelling observed to ≈16 Å and the subsequent exfoliation of Ti3C2Tz into single layers.