Triphasic synthesis of MXenes with uniform and controlled halogen terminations
Dongqi Li, Wenhao Zheng, Mahdi Ghorbani-Asl, Juliane Scheiter, Kamil Sobczak, Silvan Kretschmer, Josef Polčák, Pranjali Hirasing Jadhao, Paweł Piotr Michałowski, Ruoling Yu, Jiaxu Zhang, Jinxin Liu, Jingwei Du, Quanquan Guo, Ehrenfried Zschech, T. Šikola, Mischa Bonn, Nicolás Pérez, Kornelius Nielsch, Arkady V. Krasheninnikov, Hai I. Wang, Minghao Yu, Xinliang Feng
Abstract
Abstract Surface terminations critically govern the properties of two-dimensional transition metal carbides and/or nitrides (MXenes), yet a universal strategy to obtain MXenes with uniform and controllable terminations remains elusive. Here we introduce a ‘gas–liquid–solid’ triphasic etching strategy that employs iodine vapour, halide molten salts and MAX phases to produce MXenes with pure and precisely tunable halogen terminations (Cl, Br, I or their combinations). In this process, halide molten salts dissolve iodine via interhalogen anion formation while efficiently transporting etching by-products. The resulting MXenes retain excellent structural integrity, yielding uniformly ordered surfaces. As a representative example, Ti 3 C 2 Cl 2 shows a 160-fold enhancement in macroscopic conductivity and a 13-fold enhancement in terahertz conductivity relative to conventional Cl/O-terminated Ti 3 C 2 , attributed to minimized electron trapping and scattering. Beyond single-halogen terminations, the gas–liquid–solid approach enables dual- and triple-halogen termination control, providing a general platform for tailoring MXene surface chemistry towards advanced (opto)electronic applications.