Surface Chemistry-Driven Oxidation Mechanisms in TiCT MXenes
arXiv:2503.07896 · doi:10.1002/smsc.202500209
Abstract
TiCT is a leading compound within the MXenes family and can find host in widespread applications. It is synthesized by selectively etching layers from the TiAlC precursor, and this process typically introduces surface terminations, T, such as OH, O, or F. However, the aggressive chemical conditions required for its preparation, as well as exposure to air, humidity, and heat, can lead to impurity phases that potentially compromise its desirable properties. We reveal a two-step oxidation process during heat treatment, where initial oxidation occurs between layers without altering the integrity of the TiC layered structure, followed by the formation of anatase TiO at elevated temperatures. The process was carefully monitored using \emph{in situ} Raman spectroscopy and \emph{in situ} microwave conductivity measurements, employed to TiCT prepared using various etching techniques involving concentrated HF, LiF + HCl, and HF + HCl mixtures. The oxidation process is heavily influenced by the synthesis route and surface chemistry of TiCT, with fluoride and oxyfluoride groups playing a pivotal role in stabilizing the anatase phase. The absence of these groups, in contrast, can lead to the formation of rutile TiO.