Achieving Macroscopic VCT MXene by Selectively Etching Al from VAlC Single Crystals.

Hexagon-like MAX-phase VAlC single crystals grown by a high-temperature flux method were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX). We report, for the first time, the first-order Raman spectra (RS) of VAlC single crystals experimentally and theoretically. Via the combination of the results of thermogravimetric analysis, differential scanning calorimetry, XRD, FE-SEM, and EDX, the oxidation performance and mechanism of VAlC single crystals between 300 and 1473 K in air were clarified. Importantly, we carefully investigated the room-temperature corrosion behaviors of VAlC single crystals in concentrated acids [HCl, HSO, hydrofluoric acid (HF), and HNO] and alkalis (NaOH and KOH). VAlC single crystals are stable in concentrated HCl, HSO, and NaOH but unstable and even dissolved completely in concentrated KOH and HNO. In particular, our XRD, RS, FE-SEM, and EDX results have confirmed that HF can dissolve the Al layers of VAlC single crystals but cannot corrode VC layers at room temperature, which eventually led to the formation of macroscopic VCT MXene. This reported approach of macro-sized VCT MXene can be adapted for obtaining other macroscopic MXenes and will inspire plenty of theoretical and experimental investigations to explore their intrinsic nature and applications, especially for electronic and photonic applications.