Insights into the thermal and chemical stability of multilayered V2CTx MXene

Abstract

We report on the thermal stability of multilayered V₂CT_x MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to elucidate and monitor the molecular, electronic, and structural changes of both the surface and bulk of the V₂CT_x MXene which has recently received much attention. The MXene samples were heated up to 600 °C in inert (N₂), oxidative (CO₂, air), and reductive (H₂) environments under similar conditions. In situ Raman showed that the VO vibration for two-dimensional vanadia is preserved up to 600 °C under N₂, while its intensity reduces under H_2. When heated above 300 °C under either CO₂ or air, V₂CT_x slightly oxidizes or transforms into V₂O₅, respectively. Furthermore, SEM revealed the presence of an accordion-like layered structure for the MXene under N₂ and H₂, while under CO₂ and air the layered structure collapses and forms VO₂ (V⁴⁺) and V₂O₅ (V⁵⁺) crystals, respectively. XPS reveals that, regardless of the gas, surface V species oxidize above 300 °C during the dehydration process. Finally, we demonstrated that the partial dehydration of V₂CT_x results in the partial oxidation of the material, and the total dehydration is achieved once 700 °C is reached. We believe that our methodology is a unique alternative to tune the dehydration, oxidation, and properties of V₂CT_x, which allows for the expansion of applications of MXenes.