Effect of Etching Temperature and Time on In Situ HF-Generating (NH4F) Synthesis of Ti3C2Tx MXene

MXenes are a family of two-dimensional transition-metal carbides and nitrides, produced by selectively etching the “A” layer from a layered MAX-phase ceramic precursor. Ti3C2Tx MXene was synthesised from Ti3AlC2 via microwave-assisted, in situ HF-generating etching using NH4F/HCl as a safer alternative to concentrated HF. The etching temperature was first varied (40–100 °C, 30 min), and then the duration (30–90 min) was varied at the most favourable temperature. Samples were characterised by SEM, EDS, XRD, and Raman spectroscopy. SEM showed a non-monotonic relationship between temperature and morphology, with the most uniform accordion-like layering at 80 °C before fragmentation and edge erosion at 100 °C; duration showed a similar pattern, with 30 min at 80 °C being most uniform and heterogeneity increasing at 60 and 90 min. XRD, using a composite residual-MAX-phase index, placed the MAX-to-MXene crossover between 60 and 80 °C, consistent with SEM. EDS showed fluorine content and aluminium removal decoupling with etching time, with fluorine declining sharply beyond 30 min without a corresponding recovery in aluminium removal. Raman confirmed the characteristic Ti3C2Tx fingerprint at every condition. Thus, 80 °C/30 min was identified as the most favourable processing window; however, given the coarseness of the parameter grid, the true optimum may lie within intermediate, untested conditions.