Enhanced optical absorption and photocatalytic water splitting of g-C₃N₄/TiO₂ heterostructure through C&B codoping : A hybrid DFT study

Our theoretical research indicate that the electric field are generated in the direction of (C doped) TiO₂ (101) surface to (B-doped) g-C₃N₄ monolayer for the pristine, C and B doped g-C₃N₄/TiO₂, and higher band-edge potential on the (C doped) TiO₂ (101) surface are observed compared to (B-doped) g-C₃N₄ monolayer. Thus, the pristine (2.591 eV), C-doped (2.663 eV) and B-doped (2.339 eV) g-C₃N₄/TiO₂ are Z-scheme heterostructures, which promotes charge separation and retains a prominent redox ability. After C doping, the C 2p energy level is introduced which facilitate the separation of photoexcited carriers. The B-doped g-C₃N₄/TiO₂ has a reduced bandgap and the mixing of B 2p and N 2p energy levels, promoting the red-shift of the optical absorption edge. The C&B codoped g-C₃N₄/TiO₂ follows type-II charge transfer mode because of their synergistic effect in C and B atoms, which changes the direction of the built-in electric field. It also has a narrow bandgap (1.309 eV) and effectively separate electron-hole pairs leading to strong optical absorption ability in the range of 360 nm–460 nm. The band-edges matching of the semiconductor photocatalyst and the direction of the built-in electric field jointly determine whether the charges are selected to be Z-scheme or II-type transfer mode. Based on g-C₃N₄/TiO₂ for C or/and B (co)doping, their different charge transfer modes have been established and they are expected to show promising photocatalytic water splitting performance.