Aging of 2D MXene nanoparticles in air: An XPS and TEM study

Different batches of Ti3C2OxFx MXene were prepared, and their stability in air and argon was studied. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) in multiple modes (bright field imaging, energy-dispersive X-ray analysis, and selected-area electron diffraction) was employed to study the chemical and morphological changes in two-dimensional (2D) MXene exposed to air for several days and months. We observed the progressive development of the Ti4+ state accompanied by the development of TiO2 formation, which lead to a slow disintegration of the 2D MXene nanosheets, although their overall morphology and crystalline structure can persist for several months. The presence of water is found to play an important role in the hydrolysis and degradation reactions during MXene aging. Our XPS and TEM studies show how the surface chemistry changes during aging in air and which surface termination groups are indicative of stable Ti3C2OxFx MXene and which storage conditions can stabilize MXene for more than 337 days.