Shifting of the band edge and investigation of charge carrier pathways in the CdS/g-C₃N₄ heterostructure for enhanced photocatalytic degradation of levofloxacin

We investigated charge carrier pathways and the generation of an electric field at the interface of a CdS/g-C₃N₄ heterojunction for better understanding of the photocatalytic mechanism and photocatalytic performance. A rapid and uniform microwave-assisted method was used to form a CdS/g-C₃N₄ heterojunction by coupling CdS nanoparticles with g-C₃N₄ nanosheets. The charge carrier pathways of electrons and holes were examined using a near-band-edge single light activation strategy combined with XPS and UV-vis DRS data. Degradation of the antibiotic levofloxacin was used to confirm the suggested behavior and to evaluate the photocatalytic efficiency. The results showed that the band gap value in the composite structure narrowed, resulting in longer excited-state lifetime. Electron injection pathways were confirmed by comparing data obtained from degradation in the presence of coupled samples and physically mixed samples. The results further indicated that the band positions shifted due to the generation of an electric field at the composite sample interface, allowing electrons to travel from the conduction band in CdS to the conduction band in g-C₃N₄ and not the opposite, as usually discussed. These findings clarify the disagreement among different cases considered in the literature.