Enhanced charge separation in n-n type sulfur-doped g-C3N4 nanosheets/NaBiS2 heterojunction photocatalyst: Insights into the preparation, characterization, and mechanism of photocatalytic degradation of methyl orange

The development and utilization of innovative, highly efficient photocatalysts have become a central focus in removing environmental pollutants. This study presents the novel creation of an n-n heterojunction comprised of NaBiS₂ and sulfur-doped g-C₃N₄ nanosheet, a metal-free semiconductor. This innovative photocatalyst is designed to be active under visible light and has been utilized for the first time for the photocatalytic degradation of methyl orange. To effectively use the prepared photocatalyst for environmental purification, the influence of various factors including the initial concentration of methyl orange, the differing weight ratios of the catalyst components, and the initial pH of the reaction medium on the photocatalytic process was examined. The findings revealed that under optimal conditions (30 % by weight of NaBiS₂, pH 3, and 5 mg L⁻¹ dye concentration), the degradation efficiency of methyl orange was obtained as 98.3 % within 150 min, which is significantly higher than that of NaBiS₂ and S-g-C₃N₄. This suggests a beneficial synergy between the two semiconductors, enhanced by sulfur doping, which promotes the separation of charge carriers. The improved photocatalytic efficiency can be primarily linked to the internal electric field that facilitates charge transfer between NaBiS₂ and S-g-C₃N₄, along with a prolonged charge carrier lifetime, as evidenced by photoluminescence and photocurrent analyses. Furthermore, findings from the inhibition tests and Mott-Schottky measurements suggest that the mechanism of heterogeneous charge transfer operates under an n-n-type model.