Salicylaldehyde-Grafted g-C3N4 for Enhanced Photocatalytic Degradation of Diclofenac and Antibiotics

Abstract In this study, salicylaldehyde-grafted modified graphitic carbon nitride (modified g-C3N4, denoted CNX) was synthesized via a mild, green solvent-assisted grafting strategy. The covalent incorporation of salicylaldehyde─rationally designed to leverage its aromatic and hydroxyl dual-functionality to modulate the donor–acceptor microenvironment─significantly enhanced the photocatalytic efficiency by overcoming the inherent limitations of pristine CN, such as limited visible-light utilization and rapid recombination of photogenerated charge carriers. These materials were employed for the removal of emerging organic contaminants, particularly diclofenac (DCF) and various antibiotics, from aquatic environments. The optimized catalyst, CN2.5, achieved a high 99% degradation of DCF within only 25 min under 405 nm LED irradiation, following pseudo-first-order kinetics with a reaction rate constant 1.5 times higher than that of pristine CN. Furthermore, CN2.5 demonstrated high stability and recyclability over five cycles and maintained stable performance in complex matrices, such as tap water and lake water. Mechanistic investigations revealed that the synergistic effect between salicylaldehyde and the g-C3N4 framework facilitates charge separation and promotes the generation of reactive species, primarily superoxide radicals (·O2–). This work provides valuable structural and mechanistic insights into the design of advanced g-C3N4-based materials as an effective and sustainable strategy for the efficient removal of pharmaceutical pollutants.