Hybrid triazine-based g-C3N4(0 0 1)/anatase TiO2(0 0 1) heterojunction: Insights into enhanced photocatalytic mechanisms via DFT calculation

Understanding is far from satisfactory on the photocatalytic enhancement mechanism of g-C3N4/TiO2 composite by experimental methods. The objective of this study is to investigate the interface properties of the g-C3N4(0 0 1)/ TiO2(0 0 1) (remarked as CN/T/(0 0 1)) heterojunction by the density functional theory calculations for exploring the enhanced photocatalytic mechanisms. The calculated band structures revealed that the CN/T/(0 0 1) heterojunction was an indirect-gap semiconductor. The calculated energy gap (Eg) of the CN/T/(0 0 1) was much smaller than that of the TiO2(0 0 1) and g-C3N4(0 0 1) facet. Besides, the maximum value of valence band (VBM) and minimum value of conduction band (CBM) of CN/T/(0 0 1) was extended to a higher energy region than those of two side surfaces, suggesting the CN/T/(0 0 1) nanocomposite showed a longer redshift of absorption edge. A polarized field within the interface region was formed by the charge transfer between the TiO2(0 0 1) and g-C3N4(0 0 1) surface, which was beneficial to the separation of photo-generated carriers. These findings all indicated that the CN/T/(0 0 1) heterojunction demonstrated a type-II band alignment structure. The electronic structure analysis of TiO2(0 0 1), (1 0 1) and (1 0 0) facets indicated that the Fermi level of (0 0 1) and (1 0 1) facets occupied the position of conduction band. However, the Fermi level of (1 0 0) facets was still located at the top of the valence band. It is speculated that this is the reason why different crystal faces would construct different types of heterojunctions.