Continuous production of Cl-terminated MXenes by bubbling chemical vapor growth in molten salt

Although 2D transition-metal carbides (MXenes) are usually synthesized by selective etching and chemical vapor deposition approaches, they are limited by the slow reaction kinetics, resulting in their continuous production challenging. Here, we demonstrate a bubbling chemical vapor growth (BCVG) method to continuously produce Cl-terminated MXenes by the reaction of CH₄ and TiCl₄ chemical bubbles with titanium powder in a molten salt. In the molten reaction system, titanium powder would effectively react with TiCl₄ to form highly active [TiCl₆]^y– with low TiCl bond dissociation energies. The multivalent [TiCl₆]^y– could efficiently incorporate the carbon species from CH₄ to form [Ti₆CCl₁₈] clusters on the surface of bubbles in a low energy barrier, efficiently promoting the reaction kinetics. Subsequently, Cl-terminated MXenes were produced based on the following condensation reaction of [Ti₆CCl₁₈] clusters. The resultant MXene (Ti₂CCl_x) exhibits an expanded structure with strong interfacial polarization between its basal planes and the polymer matrix, delivering a good electromagnetic wave absorption performance with a minimum reflection loss (RL_min) value of –52.2 dB at a thin thickness of 2.84 mm.