Dysprosium-Doped Carbon Nitride Activating Sulfite for Synergistic Photocatalytic Degradation of Methylene Blue

Abstract

The sulfate radical-based advanced oxidation process (SR-AOP) combined with photocatalytic has garnered increasing attention for enhancing the efficiency of pollutant treatment. Improving photocatalytic efficacy and exploring novel SO4 •- generation methods remain critical for boosting the integrated system's catalytic capability. Herein, the degradation of methylene blue (MB) was investigated by preparing dysprosium-doped modified g-C3N4 materials (xDy-CN) to activate sulfites, in combination with visible light. xDy-CN was synthesized via thermal polymerization and characterized using techniques such as SEM, XRD, FTIR, XPS, and BET. The influence of pH, xDy-CN dosage, sulfite dosage, and coexisting anions on the removal of MB were examined, and a degradation pathway for MB was also proposed. The results demonstrated that under conditions of a catalyst dosage of 0.4 g/L and a sulfite concentration of 0.5 mM, 95% of MB was degraded within 40 minutes. The reaction rate constant of 0.3Dy-CN in the SO3 2-/vis synergistic system (0.055 min -1 ) was approximately 2.8 times higher than that of g-C3N4 (0.0199 min -1 ). Dysprosium doping can reduce the bandgap width of g-C3N4, increase the material's specific surface area, and enhance the degradation efficiency of MB. Free radical quenching experiments and EPR analysis revealed that O2 •-played a dominant role in MB degradation, while •OH, SO4 •-and 1 O2 made secondary contributions, and h + had no direct effect. Ultimately, MB was degraded by these abundant active substances into CO2, H2O and small molecule intermediates.