Synergistic photodegradation of Remazol Black B dye using sulfur-doped g-C3N4/rGO composite: The dual role of thiourea

Abstract

The increasing contamination of azo dye compounds, such as Remazol Black B (RBB), in aquatic environments is a pressing issue. Therefore, developing efficient and environmentally safe photocatalysts is crucial. In this study, we successfully fabricated a sulfur-doped g-C₃N₄/rGO composite using a one-step facile hydrothermal method and investigated its photocatalytic activity in degrading RBB under ultraviolet (UV) light irradiation. Moreover, this metal-free photocatalyst offers a promising solution by minimizing potential environmental toxicity. Our results demonstrate the dual role of thiourea in introducing sulfur and reducing GO in the S-g-C₃N₄/rGO composite. X-ray diffraction (XRD) analysis revealed that sulfur incorporation enhances the crystallinity of the composites. Brunauer-Emmett-Teller (BET) measurements demonstrate that the S-g-C₃N₄/rGO-5 composite achieves a significantly higher specific surface area of 114.34 m²g⁻¹, supporting its enhanced photocatalytic performance. The introduction of sulfur and rGO into g-C₃N₄ enhances light absorption efficiency, narrowing the band gap from 2.71 eV for pristine g-C₃N₄ to 2.07 eV for S-g-C₃N₄/rGO-5. Furthermore, Photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) analyses reveal reduced intensity and imaginary impedance after sulfur doping and rGO incorporation, suggesting a suppressed charge recombination rate. Under UV light irradiation, the optimized S-g-C₃N₄/rGO-5 composite achieved 98.75 % RBB removal within 60 min and retained 37 % degradation efficiency under visible light. Additionally, the photocatalyst showed good stability, maintaining 87 % of its initial performance after five cycles. These findings highlight the potential of S-g-C₃N₄/rGO composites as efficient and sustainable photocatalysts for environmental remediation.