Synergistic Adsorption and Photocatalysis over Ag2CO3/Coca-Cola-Modified g-C3N4 for Antibiotic Wastewater Treatment

Considering the limitations of traditional adsorption and standalone photocatalytic technologies, as well as the environmental hazards posed by antibiotics, a novel Ag2CO3/CCN S-scheme heterojunction was fabricated by coupling Ag2CO3 with Coca-Cola-modified g-C3N4 (designated as CCN) via ultrasonic stirring. Coca-Cola serves as an easily accessible and unique three-in-one precursor (carbon, phosphorus, and pore-forming CO2) for simultaneously reconstructing the morphology and modulating the electronic structure of g-C3N4. Under the optimal conditions involving a catalyst dosage of 1.4 g/L, levofloxacin hydrochloride (LEV) concentration of 15 mg/L, and natural pH, the Ag2CO3/CCN composite achieved 95.1% LEV removal following 30 min in the dark and 80 min under visible light. The reaction rate constant of Ag2CO3/CCN was 0.00315 min-1, which is 33.08 times that of g-C3N4, 10.09 times that of CCN-3, and 1.54 times that of Ag2CO3. Furthermore, Ag2CO3/CCN exhibited excellent versatility and salt tolerance properties. The characterization results indicate that the improved photocatalytic performance of Ag2CO3/CCN stems from two factors. First, the specific surface area increase of CCN enhances its adsorption capacity. Second, the S-scheme heterojunction formed between Ag2CO3 and CCN facilitates the separation of photogenerated carriers. The possible degradation pathways of LEV were elucidated using HPLC-MS, Fukui index calculations and charge transfer analysis. The toxicity of the degradation intermediates was predicted using the ECOSAR software. Finally, a plausible electron transfer mechanism for the S-scheme heterojunction was proposed. The present work offers fresh perspectives on the design of integrated adsorption-photocatalytic systems for the purification of antibiotic-containing wastewater.