Synthesis of two-dimensional titanium nitride Ti₄N₃ (MXene)

We report on the synthesis of the first two-dimensional transition metal nitride, Ti₄N₃-based MXene. In contrast to the previously reported MXene synthesis methods-in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions-here a molten fluoride salt is used to etch Al from a Ti₄AlN₃ powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti₄N₃T_x, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti₄N₃ and terminated Ti₄N₃T_x were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti₄N₃ are predicted to be metallic. Bare Ti₄N₃ is expected to show magnetism, which is significantly reduced in the presence of functional groups.