First-Principles Study on New Photocatalytic Materials Graphdiyne-TiO2

Abstract

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 x 1) graphdiyne supercell with (1 x 4) TiO2(101) supercell to built the graphdiyne-TiO2(101) composite, and (2 x 6) graphdiyne supercell with (1 x 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 A 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(101)composite could be expected compared to graphene-TiO2(101) 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.