Ti3C2 Sheets with an Adjustable Surface and Feature Sizes to Regulate the Chemical Stability.

Tuning the feature sizes and surface moiety groups of a two-dimensional (2D) sheet material has been regarded as the most effective strategy for achieving desired physical and chemical properties. The newly emerging transition-metal carbide or nitride sheets, generally referred to as MXenes, are of interest to the research community owing to their versatile behavior. While the chemical stability of MXenes is of pivotal importance to their real applications, a systematic study of examining the effect of their surface and lateral size on the resulting chemical stability is still lacking. Herein, by systematically varying the synthesis parameters, we obtained both regular and ultrasmall Ti3C2 sheets with different surfaces, namely, Al oxyanions or OH/F. To investigate the chemical stability and sustainability of each Ti3C2 sheet in an oxidizing environment, including an ambient atmosphere and a H2O2 medium, the evolution of phase, morphology, and optical behavior was carefully studied. The sheets covered with Al oxyanions had greater structural stability than those covered with the other species considered in this study, which may be due to the Al oxyanions acting like a shield and passivating the surface in the oxidizing atmosphere. Regarding the effect of feature size, thinner sheets or those with smaller lateral dimensions showed improved oxidation resistance, which could be due to the difficulty encountered in the structural recrystallization from Ti3C2 to oxidized product TiO2. This study provides a deeper understanding of MXenes and a method to efficiently engineer structures with desired performances.