Fluorine-free synthesis of ambient-stable delaminated Ti2CTx (MXene)

Abstract

Compared with the widely used star material Ti₃C₂T_x, Ti₂CT_x, as a representative of thin layer MXenes, has unique and attractive performance in many fields, yet its development is severely hampered by its poor environmental instability. The nature of MXenes is closely related to the terminal groups, where the stability is no exception. Understanding the effect of different terminal groups on the stability of MXenes is of great significance to fundamentally improve the stability of MXenes. Herein, both experiment and theory results proved that compared with F terminal, the surface of Ti has higher oxidation state after bonding with O groups; thus, O terminal MXenes have better stability. Futhermore, a simplified and effective method to prepare fluorine-free Ti₂CT_x with oxygen-rich terminals (O-Ti₂C) is proposed, which greatly improves the stability of delaminated Ti₂C aqueous solution. The delaminated O-Ti₂C aqueous solution can be stably stored for 30 days, much longer than that of HCl and LiF etched F-terminated Ti₂C (F-Ti₂C) (completely oxidized within 24 h). Furthermore, O-Ti₂C as a humidity sensor shows excellent performance with high response and good repeatability. This work greatly prolongs the shelf life of the Ti₂CT_x solution, which will lay the foundation for the large-scale application and performance improvement of O-Ti₂C MXenes.