Atomic structure, comparative stability and electronic properties of hydroxylated Ti2C and Ti3C2 nanotubes

Recently, hydroxylated and fluorinated graphene-like titanium carbide TiCx layers have been solvothermally fabricated in large amounts from so-called MAX phase Ti3AlC2. We assume, that a wide family of novel planar and tubular forms of titanium carbides may exist and design the atomic models for monolayers and nanotubes with nominal stoichiometry Ti2C, Ti3C2 and for their hydroxylated forms Ti2C(OH)2, Ti3C2(OH)2. The stability and electronic properties of these nanostructures are examined by means of density-functional theory tight-binding method depending on the composition and the type of OH arrangement. We reveal that the type of OH termination plays a minor role in the variation of nanotubes’ strain energies, but causes a difference in the relative stability of their parent planar phases. The electronic structure for all nanotubes studied has metallic-like character, while their precursors (planar layers) demonstrate either metallic-like or semiconducting behavior depending on the arrangement of the surface OH groups.