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

Abstract

The g-C 3 N 4 -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-C 3 N 4 /SnS 2 heterojunction was systematically investigated by a hybrid density functional approach. Results indicated that the g-C 3 N 4 /SnS 2 heterojunction was a staggered band alignment structure, and band bending occurred at the interface. A built-in electric field from the g-C 3 N 4 surface to the SnS 2 surface was formed by interfacial interaction. During visible-light irradiation, excited electrons in the conduction band maximum (CBM) of SnS 2 easily recombined with the holes in the VBM of g-C 3 N 4 under the electric field force. As a result, photogenerated electrons and holes naturally accumulate at the CBM of g-C 3 N 4 and the valence band maximum (VBM) of SnS 2 , 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-C 3 N 4 /SnS 2 heterojunction. Our results not only reveal the photocatalytic reaction mechanism of the g-C 3 N 4 /SnS 2 heterojunction but also provide a theoretical guidance for the design and preparation of novel g-C 3 N 4 -based composite structures.

Unraveling the Interfacial Charge Migration Pathway at the Atomic Level in a Highly Efficient Z‐Scheme Photocatalyst

“…This hypothesis suggests that for the CdS/CoS 2 composite, the electrons would be transferred from CdS via the interface states into the lower valence‐band edge of CoS 2 . Considering that the interface states come from the Co–S 5.8 transition layer, we can conclude that an electron migration pathway transfers electrons from CdS to CoS 2 , as further confirmed by X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS; see Figures S15 and S16). Furthermore, the carrier density for CdCoS ( N d =1.62×10 30 cm −3 ; see the Supporting Information) increased as compared to CdS ( N d =6.91×10 29 cm −3 ), as determined from the slope of the Mott–Schottky plot (see Figure S17), which provides evidence for the boosting of electron transfer.…”

Nature and Role of Surface Junctions in BiOIO3 Photocatalysts

“…In fact, charge flow across the junction can result in an interface dipole and consequent band bending near the interface. Figure 4b reports the calculated charge density difference ( Δρ ), defined as Δρ = ρ (010)/(100) − ρ (010) − ρ (100) , [ 64 ] where it can be appreciated that for Model III a relevant charge density accumulation and depletion occurs, as a consequence of the strong chemical interaction at the interface. Model I is characterized by a very poor charge density difference from the isolated components, and Model II has only a weak chemical interaction.…”

Review on DFT calculation of s‐triazine‐based carbon nitride

“…In summary, the above two examples provided two possible methods to elucidate the transfer of photogenerated electrons and photocatalytic mechanism, and it was difficult to affirm or negate anyone of these two methods. Nevertheless, the latter method has been extensively employed in other computational research on g-C 3 N 4 -based composites, [91][92][93][94][95][96][97] which will be further discussed below. Of note, the photocatalytic mechanism deduced by the latter method can either be traditional type Ⅱ or direct Z-scheme heterostructure.…”