Achieving Macroscopic V4C3Tx MXene by Selectively Etching Al from V4AlC3 Single Crystals

Hexagon-like MAX-phase V4AlC3 single crystals grown by a plane 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 V4AlC3 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 V4AlC3 single crystals between 300 and 1473 K in air were clarified. Importantly, we carefully investigated the room-temperature corrosion behaviors of V4AlC3 single crystals in concentrated acids [HCl, H2SO4, hydrofluoric acid (HF), and HNO3] and alkalis (NaOH and KOH). V4AlC3 single crystals are stable in concentrated HCl, H2SO4, and NaOH but unstable and even dissolved completely in concentrated KOH and HNO3. In particular, our XRD, RS, FE-SEM, and EDX results have confirmed that HF can dissolve the Al layers of V4AlC3 single crystals but cannot corrode V4C3 layers at room temperature, which eventually led to the formation of macroscopic V4C3Tx MXene. This reported approach of macro-sized V4C3Tx 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.