Engineered g-C3N4/N-TiO2 heterostructure for enhanced visible-light photocatalytic degradation of chloramphenicol: Mechanistic insight and ecotoxicological assessment of the treated effluent

Abstract

This study presents the development and evaluation of a graphitic carbon nitride/N-doped titanium dioxide heterostructure for the visible-light photocatalytic degradation of chloramphenicol, a persistent pharmaceutical contaminant. The graphitic carbon nitride/N-doped titanium dioxide heterostructures were synthesized via a low-temperature evaporation method and extensively characterized by Wide Angle X-Ray Diffraction, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, Brunauer-Emmett-Teller surface area analysis, photoluminescence spectroscopy, and scanning electron microscopy. The optimized graphitic carbon nitride/N-doped titanium dioxide sample demonstrated superior photocatalytic efficiency, achieving 81 % chloramphenicol removal after 180 min at an initial pollutant concentration of 25 mg/ L, with a kinetic rate constant of 0.0092 min⁻¹ . Mechanistic investigations, including radical scavenging experiments and band structure analysis, revealed that the photocatalytic process follows an S-scheme charge transfer pathway, in which photogenerated electrons in the conduction band of graphitic carbon nitride and holes in the valence band of N-dopedTiO 2 are preserved as the main active species. Superoxide radicals were identified as dominant, while hydroxyl radicals also contributed to the degradation process. The material exhibited excellent reusability and stability over five cycles. High-resolution mass spectrometry identified five major degradation intermediates, suggesting pathways involving dehydroxylation, oxidative cleavage, and ring-opening. Furthermore, additional tests conducted at a more environmentally relevant chloramphenicol concentration (100 µg/L) confirmed the photocatalyst’s effectiveness, achieving substantial pollutant removal in both distilled and tap water matrices. confirmed the photocatalyst’s effectiveness in both distilled and tap water matrices. Although chloramphenicol was substantially degraded, ecotoxicity tests revealed residual toxicity in the effluents, likely due to partial mineralization and the intrinsic toxicity of the suspended photocatalyst. These results demonstrate that the graphitic carbon nitride/N-doped titanium dioxide heterostructure is a highly efficient and energy-saving photocatalyst. However, the persistence of ecotoxicological effects underscores the need for additional post-treatment steps aimed at both removing transformation products and mitigating catalyst-related toxicity. • The g-C₃N₄/N-TiO₂ heterostructure efficiently degrades CAP under visible light. • Optimal CAP removal (81 %) was achieved using g-C₃N₄(30)/N-TiO₂ at 3 g/L dosage. • Superoxide radicals were identified as the main species responsible for CAP removal. • The g-C₃N₄(30)/N-TiO₂ heterostructure showed good reusability under visible light. • Toxicity and degradation pathway of CAP transformation products were assessed

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