Facilely tuning the triazine-heptazine ratios in crystalline g-C3N4 for efficient photo-degradation of tylosin

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Intrinsically, g-C3N4 has high-density defects, insufficient efficiencies of photogenerated charge carrier separation and transfer, and inadequate photocatalytic ability against antibiotics. A facile crystallinity engineering on g-C3N4 assisted by molten-salts and simultaneously fine-tuning the triazine-heptazine ratio led to forming type-II homojunctions, without introducing foreign atoms and being metal-free. It was successfully achieved through modulating the calcination temperatures and using KCl-LiCl. The salts accelerated deamination reaction kinetics, tuned the unit ratio, and improved the degree of carbon nitride polymerization. At a triazine-heptazine ratio of 74:26 obtained at 450 °C, 10 mg/L of tylosin was completely mitigated within 9 min by the catalyst. Active radicals including O2− and OH were boosted from charge carriers under visible light, and the recombination of photogenerated excitons was relieved on the interfaces of the homojunctions. Breaking glycosidic bonds and dropping off deoxyglycosyl moieties are considered the main degradation mechanism. The cytotoxicity and acute toxicity of the degradation product are classified as harmless. In addition, 3D-molecular docking between the transformation products and target proteins (L4 and L22) in ribosome confirms toxicity reduction. This work paves a way for efficient and harmless photocatalytic degradation of tylosin by facilely modulating the unit ratio and enhancing the crystallinity of carbon nitride without introducing foreign atoms.