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

Hexagon-like MAX-phase V₄AlC₃ 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 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 V₄C₃T_x MXene. This reported approach of macro-sized V₄C₃T_x 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.