Synthesis of two-dimensional carbide Mo2CTx MXene by hydrothermal etching with fluorides and its thermal stability

In this study, highly pure Mo2CTx MXene was successfully synthesized from Mo2Ga2C by etching in hydrothermal conditions for 24 h at 140-180 degrees C. The etching solutions were lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF) or ammonium fluoride (NH4F) mixed with hydrochloric acid (HCl). The temperature to obtain pure Mo2CTx MXene in NH4F + HCl solution was 140 degrees C, lower than that in other etching solutions. The thickness of as-prepared monolayer Mo2CTx nanosheet was measured to be 1.5 +/- 0.3 nm by atomic force microscope. From thermogravimetry and differential thermal analysis, Mo2CTx MXene was found to be stable in argon atmosphere at a temperature of up to 500 degrees C. As the temperature increased, Mo2CTx MXene gradually transformed, and beta-Mo2C/MoC/Mo3C2 was eventually formed to coexist with Mo2CTx MXene at 700 degrees C. In air atmosphere, Mo2CTx MXene was stable at 200 degrees C. At 590 degrees C, Mo2CTx MXene was completely oxidized to MoO3.