Morphotaxial Halogenation of Solution-Processed Two-Dimensional Indium Selenide

Morphotaxy, a process by which a 2D material is chemically modified while retaining its original physical dimensions, is an emerging strategy for synthesizing unconventional materials at the atomically thin limit. Morphotaxy is typically implemented by vapor-phase reactions on mechanically exfoliated or vapor-deposited 2D van der Waals (vdW) materials. Here we report a method for converting solution-processed films of 2D InSe into InI₂ and InBr₂ using dilute I₂ and Br₂ solutions, respectively. The converted materials retain the physical dimensions of the original 2D flakes, providing access to non-vdW indium halides in ultrathin form. Liquid-phase exfoliation directly enables this morphotaxial reaction by producing nanosheets with high surface areas and introducing residual polyvinylpyrrolidone that stabilizes the flake morphology and slows the reactivity of I₂ and Br₂. Overall, this work presents a versatile strategy for achieving atomically thin metal halides and offers mechanistic insights relevant to the morphotaxial halogenation of other solution-processed 2D materials.