Titanium Carbide MXene Synthesis by Etching of Titanium Aluminum Carbide in Acetic Acid Solution

Ti-MXene (Ti3C₂Tz) is the most common member of a larger family of 2D materials widely explored due to a variety of possible applications. MXenes are mostly synthesized using strong acids like HF and HCl or using procedures that require elevated temperatures. Here, we present a new method for Ti₃C₂Tz preparation with a weak acid solution, which is more beneficial for mass production with reduced environmental impact. It is demonstrated that aluminum can be etched from titanium aluminum carbide (Ti₃AlC₂) using ammonium fluoride (NH₄F) dissolved in an aqueous solution of acetic acid (CH₃COOH). Optimization of the balance between amounts of water and acetic acid in the etching solution allows for complete etching of Al atoms yielding partially nitrogen terminated MXene in addition to common -O/-OH and -F termination. The mechanism of MXene formation was investigated by the in situ synchrotron radiation X-ray diffraction (XRD), allowing characterization of "pristine" MXene structure forming directly in the process of Ti₃AlC₂ reaction with NH₄F/CH₃COOH. In situ XRD analysis also enables identification of the reaction byproducts, thus providing information about the mechanism of MXene formation.