Carbon doped TiO₂ and ZnO S-scheme heterojunction synergistically enhance the photocatalytic degradation performance of tetracycline

Tetracycline is a commonly used broad-spectrum antibiotic widely used in medicine and agriculture, but its improper use leads to a large amount of residual drugs being discharged into natural water bodies with wastewater, causing adverse effects on the environment. Polyacrylonitrile (PAN)@ZnO/TiO₂ was prepared by one-step hydrothermal method, and the tubular composite catalyst ZnO/C-TiO₂ was prepared by high temperature calcination. The catalysts were characterized by XRD, SEM, TEM, XPS, and FTIR, which demonstrated the successful preparation of carbon-doped TiO₂ and ZnO heterojunction. The results of optical and photoelectrochemical characterization show that ZnO/C-TiO₂ has the best visible light absorption capacity and photogenerated electron-hole separation ability. The degradation performance of the catalyst for tetracycline under visible light irradiation was investigated using tetracycline as the target pollutant. The results show that ZnO/C-TiO₂ has the best photocatalytic degradation efficiency (74.29%) for 40 mg/L tetracycline. The improvement of photocatalytic activity is attributed to the construction of S-scheme ZnO/C-TiO₂ heterojunction, which accelerates the separation of photogenerated electrons and holes. In addition, the composites can also effectively degrade methylene blue, methyl orange, rhodamine B and other dyes. At the same time, the stability experiment shows that ZnO/C-TiO₂ has good stability after 5 cycles.