First principles investigation of the electronic properties of graphitic carbon nitride with different building block and sheet staggered arrangement

The electronic properties of g-C3N4 with different building block and sheet staggered arrangement are studied by using first-principles calculations. The calculated lattice constants and band gaps of bulk g-C3N4 with different space group P-6m2, R3m, Cmcm and P6(3)/mmc consistent well with the previous results. The hybrid functional HSE06 is performed to evaluate the electronic properties of graphitic carbon nitride, and it is suggested that the HSE06 hybrid functional could predict more reasonable band gap than the traditional functional. The band gaps of bulk g-C3N4 with P-6m2, R3m, Cmcm and P6(3)/mmc structure are about 2.8 eV, 2.6 eV, 2.6 eV and 2.4 eV, respectively. The electronic properties of monolayer triazine-and heptazine-based structure for g-C3N4 are also studied, and the corresponding band gaps are 3.0 eV and 2.7 eV, respectively. Compared to the monolayer g-C3N4, the decreasing band gaps of bulk structures should be attributed to the band overlapping among the neighboring graphitic CN sheets. The thermodynamic properties of bulk g-C3N4 are also investigated, and the results show that the heptazinebased structures have larger thermal expansion coefficient and relatively smaller thermal conductivity compared to the triazine-based structures. These calculated results are suggested that not only building block but also sheet staggered arrangement has important effect on the electronic properties of g-C3N4. Furthermore, the charge density of monolayer g-C3N4 shows that C and N atoms of g-C3N4 sheets with different building block are all sp(2) hybridization, which is similar to that of graphite. Our results unveil that the building block and sheet staggered arrangement are effective factors to tune the electronic structure and enhance the sunlight absorption efficiency of g-C3N4. (C) 2017 Elsevier B.V. All rights reserved.