Construction of S-scheme cyano-modified g-C3N4/TiO2 film with boosted charge transfer and highly hydrophilic surface for enhanced photocatalytic degradation of norfloxacin

Developing highly efficient and recyclable photocatalysts has been regarded as an attractive strategy to solve antibiotic contaminants. Herein, we designed and fabricated Cy-C3N4/TiO2 S-scheme heterojunction film with boosted charge transfer and a highly hydrophilic surface. The as-prepared heterojunction exhibited outstanding removal efficiency on tetracyclines and fluoroquinolone antibiotics (more than 80% within 90 min). The removal rate of 300-Cy-C3N4/TiO2 on norfloxacin (NOR) was 2.12, and 1.59 times higher than that of pristine TiO2, C3N4/TiO2, respectively. The excellent photocatalytic performance of 300-Cy-C3N4/TiO2 was attributed to the highly hydrophilic surface and effective transfer and separation of carriers. Moreover, the NOR degradation pathways were proposed based on the results of density functional theory (DFT), and liquid chromatography-mass spectrometry. The toxicity assessment indicated the toxicity of intermediates can be remarkably alleviated. The DFT calculation and selective photo-deposition experiment demonstrated that an internal electric field was formed at the heterojunction interface, and the charge carriers migrated between Cy-C3N4 and TiO2 following an S-scheme transfer pathway. This research not only provides a promising method for tracking charge distribution on thin-film heterojunction photocatalysts but also helps us to design high-efficiency, and recyclable heterojunctions to solve antibiotic contaminants.