Tartaric Acid‐Engineered g‐C 3 N 5 Nanosheets With Improved Charge Separation for Visible‐Light‐Driven Degradation of Tetracycline

ABSTRACT The rational design of metal‐free photocatalysts with high activity and stability is critical for addressing antibiotic contamination in wastewater. Here, a series of tartaric acid‐modified carbon nitride (g‐C 3 N 5 –TA–x) photocatalysts were synthesized and evaluated for the degradation of tetracycline hydrochloride (TCH) under visible‐light irradiation. Among them, g‐C 3 N 5 –TA–9 exhibited the best performance, achieving 79.85% TCH removal within 120 min, with an apparent rate constant ( k app ) of 0.0129 min —1 , 2.3 times higher than pristine g‐C 3 N 5 . The photocatalytic activity was strongly pH dependent, with optimal performance near neutral condition, consistent with the surface charge characteristics of the catalyst and the ionization states of TCH. Radical‐trapping experiments identified superoxide radicals ( • O 2 − ) and photogenerated holes (h + ) as the dominant reactive species. The catalyst also demonstrated good structural stability and recyclability across multiple runs. LC–MS analysis revealed key intermediates and indicated that degradation proceeds via dealkylation, dehydroxylation, and ring‐opening reactions, ultimately producing smaller, less toxic species. This study highlights that TA modification effectively tunes the surface properties and electronic structure of g‐C 3 N 5 , offering a promising metal‐free strategy for sustainable antibiotic removal in water treatment.