High Photocatalytic Activity of Heptazine-Based g-C3N4/SnS2 Heterojunction and Its Origin: Insights from Hybrid DFT

The g-C3N4-based composite structure exhibits excellent photocatalytic performance. However, their photogenerated carrier transfer and photocatalytic reaction mechanism were unclear. In this study, a 2D/2D g-C3N4/SnS2 heterojunction was systematically investigated by a hybrid density functional approach. Results indicated that the g-C3N4/SnS2 heterojunction was a staggered band alignment structure, and band bending occurred at the interface. A built-in electric field from the g-C3N4 surface to the SnS2 surface was formed by interfacial interaction. During visible-light irradiation, excited electrons in the conduction band maximum (CBM) of SnS2 easily recombined with the holes in the VBM of g-C3N4 under the electric field force. As a result, photogenerated electrons and holes naturally accumulate at the CBM of g-C3N4 and the valence band maximum (VBM) of SnS2, respectively. The effective separation of holes and electrons in space was advantageous to them participating in catalytic reactions on a different surface. Consequently, a direct Z-scheme photocatalytic reaction mechanism was established to enhance the photocatalytic activity of the g-C3N4/SnS2 heterojunction. Our results not only reveal the photocatalytic reaction mechanism of the g-C3N4/SnS2 heterojunction but also provide a theoretical guidance for the design and preparation of novel g-C3N4-based composite structures.