Theoretical Study Of Monolayer Metal Doped Graphitic-phase Carbon Nitride?g-C₃N₄?

Because the band gap of graphitic-phase carbon nitride?g-C₃N₄? is about 2.70 eV, the photocatalytic efficiency of pristine g-C₃N₄ is restricted by its limited light absorption. The absorption edge in the whole spectrum occurs at 450 nm. Therefore, various protocols such as texture modification, doping with metal and nonmetal elements and copolymerization have been employed to enhance the photocatalytic performance of g-C₃N₄. Transition metals?TMs? can deposit on the top of the single-layered sheets for strong modification of the electronic properties of g-C₃N₄. In this paper, M/g-C₃N₄?M=Mn, Cu, Au? have been optimized theoretically by embedding Mn, Cu, Au atoms in the cavity of the g-C₃N₄ sheet, respectively. The stability and electronic band structure of the M/g-C₃N₄?M=Mn, Cu, Au? monolayer nanosheet have been explored by using ab initio density functional theory?DFT? method at the B3LYP/6-31 G level. The result demonstrates the energy gap of g-C₃N₄ is 2.77 eV,which is very close to the theoretical value of 2.70 eV, indicating that the calculation method and basis set were proper for the system. Furthermore, the energy gaps of M/g-C₃N₄?M=Mn, Cu, Au? are decreased by doping metal atom to enhance absorption invisible light. The binding energies demonstrated that the stable order is Mn/g-C₃N₄, Cu/g-C₃N₄,Au/g-C₃N₄, which origin from the metal atomic radius, electronegativity as well as the charge distribution around the central metal atom. For further studing the effects of doping metal atom on photoelectronic properties of g-C₃N₄, the electronic band structure, the density of states?DOS? and the partial density of states?PDOS? of monolayer Au/g-C₃N₄ have been calculated by using hybrid functional HSE06. The results show that Au/g-C₃N₄ remains an indirect semiconductor, which has a perfect two-dimensional structure, and the single atom Au inserts into the cavity surrounded by N and C atoms on the monolayer g-C₃N₄. Moreover, the new energy levels on the top of the valence band come from the orbital of the single atom Au, which will further promote the migration of photon-generated carrier and the photocatalysis reaction. Bader charge analysis shows that thesingle atom Au shows a positive valance of +2, which will possibly further improve the optical catalysis for this new material. Remarkably, the Au/g-C₃N₄ has high stability and relatively stronger optical harvesting ability in the visible region. All calculations were inplemented in Gaussian 09 and VASP packages.Based on these extensive density functional calculations, here we present a new kind of compound of monolayer M/g-C₃N₄ with good stability and the light absorptioncapacity. Thus our approach provides new routes to fabricate stable and beautiful two-dimensional optical catalyst materials.