Mechanistic Insights into Simultaneous Oxygen-Doped and Defect-Engineered Carbon Nitride as a Multifunctional Photocatalyst for Tetracycline Degradation, N₂ Fixation, and H₂O₂ Production

The ease of synthesis of affordable photocatalysts activated by visible light and exhibiting exceptional photocatalytic performance is highly advantageous for addressing energy and environmental problems. Herein, simultaneous oxygen-doped and defect-engineered carbon nitride (ACN) was easily prepared via thermal calcination using ammonium oxalate as the chemical functionalization agent. The photocatalytic experimental studies claimed a maximum tetracycline degradation of 88% in 60 min of visible light irradiation. The ACN displayed 721 μM of H2O2 and 316 μM of ammonia generation in 60 min of visible light illumination. The remarkable efficiency of the ACN photocatalyst is linked to its enhanced visible light utilization, achieved by modifying the bandgap. Also, its increased surface area facilitates better charge carrier separation, while defect formation and concurrent oxygen doping work to suppress charge carrier recombination. Scavenger studies highlighted the critical role of superoxide radicals and electrons in the photocatalysis process. Nitrogen defects and oxygen heteroatoms facilitate effective charge separation by forming electron–hole pairs within the delocalized system under visible light, which promotes interfacial contact and the decomposition of tetracycline. A metal-free, chemically functionalized carbon nitride photocatalyst, enriched with defects and doped with oxygen, was employed as an affordable, efficient, and environmentally friendly material for energy and environmental remediation.