Mechanistic Insights\ninto Simultaneous Oxygen-Doped\nand Defect-Engineered Carbon Nitride as a Multifunctional Photocatalyst\nfor Tetracycline Degradation, N<sub>2</sub> Fixation, and H<sub>2</sub>O<sub>2</sub> Pr

The ease of synthesis of affordable photocatalysts activated\nby\nvisible light and exhibiting exceptional photocatalytic performance\nis highly advantageous for addressing energy and environmental problems.\nHerein, simultaneous oxygen-doped and defect-engineered carbon nitride\n(ACN) was easily prepared via thermal calcination using ammonium oxalate\nas the chemical functionalization agent. The photocatalytic experimental\nstudies claimed a maximum tetracycline degradation of 88% in 60 min\nof visible light irradiation. The ACN displayed 721 μM of H<sub>2</sub>O<sub>2</sub> and 316 μM of ammonia generation in 60\nmin of visible light illumination. The remarkable efficiency of the\nACN photocatalyst is linked to its enhanced visible light utilization,\nachieved by modifying the bandgap. Also, its increased surface area\nfacilitates better charge carrier separation, while defect formation\nand concurrent oxygen doping work to suppress charge carrier recombination.\nScavenger studies highlighted the critical role of superoxide radicals\nand electrons in the photocatalysis process. Nitrogen defects and\noxygen heteroatoms facilitate effective charge separation by forming\nelectron–hole pairs within the delocalized system under visible\nlight, which promotes interfacial contact and the decomposition of\ntetracycline. A metal-free, chemically functionalized carbon nitride\nphotocatalyst, enriched with defects and doped with oxygen, was employed\nas an affordable, efficient, and environmentally friendly material\nfor energy and environmental remediation.