Two-dimensional Ti3C2Tx MXenes combine high electrical conductivity with chemically active surfaces, but their susceptibility to oxidation limits long-term stability while also offering a route to functional TiO2-based materials. Although defects, surface chemistry and processing conditions are known to influence MXene degradation, how deliberate defect enrichment and cation treatment govern both oxidation progress and TiO2 polymorph evolution remains unclear.
Here, we compare the air oxidation of pristine, defect-rich, Na-treated and BaCl2-treated Ti3C2Tx under identical thermal conditions. Thermogravimetric analysis was combined with powder X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy of products recovered at successive temperatures to track oxidation kinetics, structural transformation, carbon evolution and changes in Ti chemical states. The defect-rich precursor oxidized earlier and more rapidly than pristine Ti3C2Tx. Both untreated materials initially formed anatase, followed by mixed anatase–rutile products and ultimately predominantly rutile at higher temperatures. Cation treatment did not prevent TiO2 formation but altered its phase evolution. At equivalent temperatures, NaCl-treated MXene retained more anatase than the corresponding untreated defect-rich precursor, although rutile remained the dominant phase. BaCl2-treated MXene showed a stronger effect, with substantially less rutile and greater anatase persistence than the corresponding untreated material.
These findings show that precursor modification affects different aspects of Ti3C2Tx oxidation. Structural defects promote oxidative conversion, whereas Na and Ba treatment modify the subsequent anatase-to-rutile evolution. The results provide a basis for controlling MXene degradation and tailoring the phase composition of MXene-derived TiO2 through defect and cation engineering.