Annealing Ti₃C₂T MXenes to Control Surface Chemistry and Friction

Although surface terminations (such as ═O, -Cl, -F, and -OH) on MXene nanosheets strongly influence their functional properties, synthesis of MXenes with desired types and distribution of those terminations is still challenging. Here, it is demonstrated that thermal annealing helps in removing much of the terminal groups of molten salt-etched multilayered (ML) Ti₃C₂T. In this study, the chloride terminations of molten salt-etched ML-Ti₃C₂T were removed via thermal annealing at increased temperatures under an inert (argon) atmosphere. This thermal annealing created some bare sites available for further functionalization of Ti₃C₂T. XRD, EDS, and XPS measurements confirm the removal of much of the terminal groups of ML-Ti₃C₂T. Here, the annealed ML-Ti₃C₂T was refunctionalized by -OH groups and 3-aminopropyl triethoxysilane (APTES), which was confirmed by FTIR. The -OH and APTES surface-modified ML-Ti₃C₂T are evaluated as a solid lubricant, exhibiting ∼70.1 and 66.7% reduction in friction compared to a steel substrate, respectively. This enhanced performance is attributed to the improved interaction or adhesion of functionalized ML-Ti₃C₂T with the substrate material. This approach allows for the effective surface modification of MXenes and control of their functional properties.