Reduced Oxygenated g-C₃ N₄ with Abundant Nitrogen Vacancies for Visible-Light Photocatalytic Applications

A novel g-C₃ N₄ photocatalyst (RCNO) with abundant nitrogen vacancies and oxygen-containing electron-withdrawing groups was prepared. Oxygen was gradually introduced into the g-C₃ N₄ structure by a hydrothermal hydrolysis/condensation process, and nitrogen vacancies were produced with H₂ reduction. The presence of nitrogen vacancies reduced the conduction band energy of g-C₃ N₄ from -0.75 to -0.5 eV and introduced plenty of defect levels in the band gap (just below the conductive band with a width of 0.45 eV). The oxygenation of g-C₃ N₄ induced the formation of oxygen-containing functional groups, such as C=O and C-O, as well as effectively enhancing the separation efficiency of photogenerated carriers and reducing the valence band energy from 2.05 to 2.30 eV. Therefore, the photocatalytic activity and photocurrent responses of RCNO were about nine and eight times higher than that of g-C₃ N₄ , respectively.