Chlorine-Doped Graphitic Carbon Nitride for Enhanced Photocatalytic Degradation of Reactive Black 5: Mechanistic and DFT Insights into Water Remediation.

Photocatalysts are recognized as eco-friendly technologies that exhibit significant potential for removing organic pollutants upon exposure to light. Herein, we successfully modified graphitic carbon nitride (CNM) by chlorine (Cl) doping through a calcination process to enhance the photocatalytic degradation of Reactive Black 5 (RB5) under visible-light irradiation. The Cl-doping efficiency was comprehensively assessed, with CNM-Cl(0.4) demonstrating the best photocatalytic performance, achieving a rate constant of 0.199 min , which is 1.76 times higher than that of undoped CNM. The observed enhancement can be ascribed to the improved photocurrent response and the narrowing of the bandgap, both of which result from the incorporation of chlorine into the CNM framework. The incorporation of Cl into CNM resulted in more than double the photocurrent generation compared to bare CNM, promoting rapid charge carrier separation and significantly reducing charge recombination. This was further supported by BET surface area analysis, where Cl doping led to a ∼4-fold increase in specific surface area, facilitating more active sites for pollutant adsorption. Additional information about the electronic characteristics of CNM and CNM-Cl was obtained through first-principles density functional theory (DFT) calculations, which confirmed the experimental findings. The photocatalytic degradation mechanism is carried out by the production of reactive oxygen species, such as hydroxyl radicals (•OH) and superoxide anions (•O ). The results of this study show that chlorine doping greatly improves the photocatalytic performance of carbon nitride materials (CNM). This modification makes CNM a very promising metal-free photocatalyst for environmental remediation and water purification under visible light irradiation, especially considering its high stability, reusability, and eco-friendly synthetic approach.