Graphitic carbon nitride (g-C3N4 ) is a useful photocatalyst applied in various areas. However, it has some disadvantages that limit its applications. Therefore, doping and the construction of a heterojunction are beneficial methods to overcome these drawbacks. ZnS is one of the photocatalysts that can be combined with g-C3N4 . The sulfur vacancy defect in ZnS enhances its ability to adsorb visible light compared to bare ZnS. In this work, we theoretically investigated bulk g-C3N 4 (g-C3N4 -B), monolayer g-C3N4 (g-C3N4 -M), ZnS, and defective ZnS (ZnS-D) using the SIESTA package. Subsequently, the position of the conduction band minimum (CBM) and valence band maximum (VB) of g-C 3N4 -B and g-C3N4 -M were plotted relative to the CBM and VBM of ZnS-B and ZnS-D. The results showed that the g-C3N4 /ZnS heterojunction is more suitable than g-C3N4/ZnS-D. This heterojunction is a Z-scheme type, which increases the lifetime of the carriers. On the other hand, it is a narrow gap semiconductor that can be used in thermoelectric devices, and the value of the Seebeck coefficients confirms that the heterojunction enhances the thermoelectric properties of the photocatalysts. Our results demonstrate that the Z-scheme mechanism enhances the lifetime of carriers and thermoelectric properties.

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