Carbon dots as heterojunction transport mediators effectively enhance BiOI/g-C₃N₄ synergistic persulfate degradation of antibiotics

In this work, a ternary structured photocatalyst carbon dots (CDs) modified BiOI/g-C₃N₄ (CDs@BiOI/g-C₃N₄) was prepared by a simple one-pot in situ coprecipitation method using ethylene glycol as chelating agent. Under LED irradiation, CDs@BiOI/g-C₃N₄, especially in coordination with persulfate (PS), exhibited excellent photocatalytic performance and cycling stability for tetracycline (TC) mineralization. Even after five cycles, the removal rate of TC still remained around 80%. Meanwhile, the mechanism of enhanced photocatalytic activity and its photogenerated carriers transfer was elucidated by optical, electrochemical and energy band structure characterization. The deformation of band structure made the interfaces of g-C₃N₄ and BiOI generate Schottky barrier with CDs, respectively. CDs acted as an electron transfer and storage medium, facilitating the separation and migration of electron-hole pairs (e⁻-h⁺) at the interface of the heterojunction structure. The photocatalytic experiments with PS showed that the CDs@BiOI/g-C₃N₄/PS advanced oxidation system achieved 82.7% removal of TC, which was 6.7, 3.1, and 1.2 times higher than that of pure g-C₃N₄, BiOI, and BiOI/g-C₃N₄ photocatalysts. The degradation of TC intermediates was further discussed by liquid chromatography-mass spectrometry (LC-MS).