Two-Dimensional Transition Metal Carbides

TLDR

MAX phases are a large family of layered, machinable transition metal carbides, nitrides, and carbonitrides. The study reports the synthesis of two‑dimensional transition metal carbides and carbonitrides by immersing selected MAX phase powders in hydrofluoric acid. The authors exfoliate various MAX phases—including Ti₂AlC, Ta₄AlC₃, (Ti₀.₅Nb₀.₅)₂AlC, (V₀.₅Cr₀.₅)₃AlC₂, and Ti₃AlCN—by immersing powders in HF at room temperature for 10–72 h followed by sonication. Exfoliation removes the A layer, producing MXenes whose sheet resistances are comparable to multilayer graphene and whose surfaces are hydrophilic.

Abstract

Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti(2)AlC, Ta(4)AlC(3), (Ti(0.5),Nb(0.5))(2)AlC, (V(0.5),Cr(0.5))(3)AlC(2), and Ti(3)AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the "A" group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.