Visible-Light-Driven Photocatalytic Degradation of Methylene Blue Using a Graphene Oxide/Sulfur Carbon Nitride (GO/SCN) Nanocomposite

The development of efficient visible-light-responsive photocatalysts for the removal of persistent organic pollutants from wastewater remains an important challenge in environmental remediation. In this study, a graphene oxide/sulfur carbon nitride (GO/SCN) nanocomposite was synthesized and evaluated for the photocatalytic degradation of methylene blue (MB) under visible-light irradiation. Structural, morphological, and optical properties of the synthesized materials were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and Brunauer–Emmett–Teller (BET) surface area analysis. XRD results confirmed the preservation of the graphitic carbon nitride structure with slight peak broadening after GO incorporation, while FTIR spectra indicated the presence of characteristic C–N heterocyclic vibrations and oxygen-containing functional groups from graphene oxide. SEM analysis revealed a layered and interconnected morphology with well-dispersed GO sheets within the SCN matrix. UV–Vis DRS analysis showed enhanced visible-light absorption with a red shift of the absorption edge from approximately 455 nm for pristine SCN to 475 nm for the GO/SCN composite. The optical band gap decreased from 2.72 eV for SCN to 2.58 eV for GO/SCN, indicating improved visible-light utilization. BET analysis demonstrated an increase in specific surface area from 32.6 m² g⁻¹ for SCN to 68.9 m² g⁻¹ for the GO/SCN nanocomposite, providing additional active sites for photocatalytic reactions. Photocatalytic experiments revealed that the GO/SCN nanocomposite achieved 96.4% degradation of methylene blue within 100 min under visible-light irradiation, significantly outperforming pristine SCN. Kinetic analysis showed that the degradation process followed pseudo-first-order reaction kinetics with an apparent rate constant of 0.032 min⁻¹. Radical scavenger experiments indicated that superoxide radicals (•O₂⁻), hydroxyl radicals (•OH), and photogenerated holes were the primary reactive species responsible for dye degradation. Furthermore, the photocatalyst exhibited excellent stability, maintaining over 90% degradation efficiency after five consecutive cycles. The enhanced photocatalytic performance is attributed to the synergistic interaction between graphene oxide and sulfur carbon nitride, which promotes efficient charge separation, improved electron transport, and increased adsorption of dye molecules. These findings demonstrate that GO/SCN nanocomposites represent promising metal-free photocatalysts for sustainable wastewater treatment and environmental purification applications.