Tuning the strength of built-in electric field in 2D/2D g-C₃N₄/SnS₂ and g-C₃N₄/ZrS₂ S-scheme heterojunctions by nonmetal doping

Single photocatalysts usually exhibit unsatisfactory performance due to the serious recombination of photogenerated electron‒hole pairs. Combining two photocatalysts to construct S-scheme heterojunction could solve this problem. In S-scheme mechanism, the interfacial built-in electric field (IEF) provides a vital driving force for efficient charge separation. Modifying the IEF is a feasible strategy to further improve the photocatalytic activity. Herein, a novel idea of tuning the strength of IEF in 2D/2D graphitic carbon nitride (g-C₃N₄)/MS₂ (M = Sn, Zr) S-scheme heterojunctions by nonmetal doping was developed by employing density functional theory calculation. Three nonmetal elements (O, P, and S) were severally introduced into g-C₃N₄/MS₂ composites. Charge density difference suggested that O and S doping led to increased interfacial electron transfer, while P doping had minimal influence. As expected, the calculated field strength of O- and S-doped g-C₃N₄/MS₂ composites was significantly larger than that of pristine and P-doped g-C₃N₄/MS₂ composites. Therefore, O and S doping endowed g-C₃N₄/MS₂ S-scheme heterojunctions with enhanced IEF and more thorough charge transfer. Correspondingly, the experimentally synthesized O-C₃N₄/SnS₂ composite exhibited better photocatalytic H₂-production activity than g-C₃N₄/SnS₂ composite. This work proposed an original idea of employing proper nonmetal doping to magnify the advantage of S-scheme heterojunction in accelerating charge separation.