Enhanced visible light photocatalytic degradation of chlortetracycline over montmorillonite/g-C3N4 composite: kinetic insights, degradation pathways and ecotoxicity evaluation

Photocatalytic oxidation technology is recognized as an effective method for removing antibiotics from wastewater. In this work, a novel montmorillonite/graphitic carbon nitride (Mt/g-C3N4) composite was synthesized via a facile thermal polycondensation approach. The optimal 1% Mt/g-C3N4 photocatalyst demonstrated an excellent chlortetracycline (CTC) degradation rate of 0.0353 min-1 under visible light, which is about 42% higher than pristine g-C3N4. Electron spin resonance (ESR) and radical quenching experiments revealed that the •O2- plays the most significant role in the photocatalytic oxidation of CTC, while •OH, 1O2 and h+ also contribute, but not in dominant places. This study elucidates the mechanism by which the photocatalytic activity is enhanced. The improvements are ascribed to the extended absorption of visible light, efficient charge separation, and the inhibition of photo-induced electron-hole pair recombination, following the successful intercalation of g-C3N4 nanosheets into montmorillonite layers. Additionally, HPLC-QTOF-MS was employed to identify the transformation products of CTC, and the primary degradation pathways were elucidated. Furthermore, the ecotoxicity of the transformation products was evaluated using ECOSAR software.