We study mechanism for combinet graphdiyne and graphene on TiO₂ which can improve the photocatalytic performance of TiO₂ by density functional theory with dispersion corrections (DFT-D) methods. Because of the different lattice parameters of graphdiyne, graphene and TiO₂(101), we used (1×1) graphdiyne supercell with (1×4) TiO₂(101) supercell to built the graphdiyne-TiO₂(101) composite, and (2×6) graphdiyne supercell with (1×5) TiO₂(101) supercell to built the graphene-TiO₂(101) composite. In detail, as the strong adsorption between carbon atom and the TiO₂ support, numbers of new high electron delocalization C—O covalent bonds were formed by O atom in TiO₂ surface and atop C atom in graphdiyne. While for the graphene-TiO₂(101) composite, the equilibrium distances between graphene and TiO₂ are so large that even the nearest C atoms were far as 2.869 ? to the TiO₂ planes, indicating the weak interaction between graphene and TiO₂ surface. The electron density, electron density difference were analyzed, the result shown that the graphdiyne combined with TiO₂(101) surface is beneficial to the charge transfer. The Mulliken charge population shows that the graphdiyne or graphene surface has a positive Mulliken charge, forming large opposite interface dipole at the interface, leading to a strong built-in electric field throughout the superlattice, which can resist the possibility of electron-hole recombination. Since the magnitude of charge accumulation in graphdiyne is larger than graphene surface, stronger electrons capture ability of graphdiyne- TiO₂(001) composite could be expected compared to graphene-TiO₂(001) composite. The electronic band structure shown that in the graphdiyne-TiO₂(101) composite, numbers of isolated energy levels were localized in the band gap which can reduce the electronic excitation energy from the isolated energy levels to the conductive band. The graphene-TiO₂(101) composite had no isolated energy level appeared in the band gap. The graphdiyne-TiO₂(101) composite has a lower valence band position than the graphene-TiO₂(101) composite ones, means compared with graphene composite, graphdiyne composite always shows higher oxidation ability, which induce a higher photocatalytic performance.

Key words: graphdiyne, graphene, first principles calculation, TiO₂