Synthesis of Chlorine-Terminated MXenes by Dry Selective Extraction with TiCl₄

Despite rapid research progress in the field of MXenes over the past decade, this new family of nanomaterials still faces challenges in terms of scalable manufacturing and control over surface chemistry, which determines many of their physicochemical properties. This work demonstrates titanium tetrachloride (TiCl₄) as a new type of gas-phase etchant for the dry selective extraction of the A-element (Al) from MAX phases, providing MXenes with uniform chlorine surface terminations. Our approach eliminates the need for extensive washing, which is required in the cases of wet-chemical and molten salt etching. Computational data suggest that TiCl₄ reacts with the MAX phases directly to extract AlCl₃ rather than forming any intermediate phases. One of the resulting MXenes, Ti₃C₂Cl₂, was then delaminated into few-layer flakes by intercalating lithium ions from an organic solvent. Some of the hydrophobic delaminated flakes were discovered to roll into a tubular shape, forming 1-dimensional nanoscrolls. Our dry etching process provides opportunities for the scalable synthesis of halogen-terminated Ti- and Nb-based MXenes with two to four M-element layers and controlled surface chemistry.