Effects of vacancies on the electronic structures and photocatalytic properties of g-C3N4

The geometric structures, electronic structures and photocatalytic properties of g-C3N4 with different vacancies are studied by the first-principles calculations. These calculations suggest that introducing different vacancies can cause the relaxation of these adjacent atoms, the formation of dangling bonds, and the deformation of these building blocks. And these band gaps of the heptazine-based graphitic C3N4 sheets are narrowed by different vacancies. The energetic preferability of the heptazine-based g-C3N4 sheets with different vacancies is assessed as functions of the environmental factors, including nitrogen partial pressure and temperature. It is indicated that VC2 and VN2 are the respectively stable vacancies over the investigated nitrogen partial pressure. A transition from VN2 to VC2 should occur at ultrahigh vacuum pN2≥∼10−23atm at 1000 K, and move to higher nitrogen partial pressure with the increasing temperature. According to the calculated absorption coefficient, these g-C3N4 sheets with VC2 and VN2 vacancies have larger absorption than the perfect structure over the visible wavelength range, suggesting that vacancies can increase the catalytic efficiency of graphitic C3N4. These results show that introducing defects, especially vacancies, is an effective approach to enhance the sunlight absorption efficiency of graphitic carbon nitride.