Highly efficient photocatalytic degradation of ofloxacin coupling with Cr(VI) reduction by m-PDI/BiOI organic–inorganic S-scheme heterojunction catalysts

The combined pollution toxicity of hexavalent chromium heavy metal (Cr(VI)) and antibiotics (such as ofloxacin, OFL) is much higher than that of a single pollutant, posing a serious challenge to the ecological environment. Photocatalytic technology can achieve the removal of both single pollutants and composite pollutants. It is urgent to develop catalysts with high carrier separation efficiency and photocatalytic degradation performance. In this work, we successfully prepared m-PDI/BiOI heterojunction catalysts (mPB-3) with tight contact interfaces using the continuous ion layer adsorption and reaction method, and applied them to the synergistic removal of OFL and Cr(VI). The results showed that mPB-3 exhibited a bidirectional enhancement effect. The degradation rate of OFL reached more than 99.5 % within 40 min, the corresponding reduction efficiency of Cr(Ⅵ) reached 63.7 % at pH = 9. Furthermore, the influence of different environmental factors on the degradation process have also been clarified, indicating that mPB-3 has good stability and adaptability. The system characterization results confirmed that a S-scheme heterojunction has been formed. This can accelerate the rapid migration of electrons from m-PDI to BiOI, achieving efficient charge separation, and ultimately enhancing the photocatalytic activity. Finally, the degradation intermediate products and degradation mechanism were analyzed. This study provides a feasible solution for the design of efficient photocatalytic materials and their application in the combined pollution treatment of OFL and Cr(VI). Environmental implication Cr(VI) and OFL coexisting in water bodies pose significant ecological risks due to their enhanced combined toxicity. Traditional treatment techniques often struggle to effectively address such complex pollution systems. This study demonstrates that the m-PDI/BiOI heterojunction photocatalyst can efficiently synergistically remove both contaminants under environmentally relevant conditions (e.g., pH = 9), providing a practical strategy to mitigate composite pollution challenges. The S-scheme charge separation mechanism offers insights for designing advanced catalysts to tackle emerging multi-pollutant threats in aquatic ecosystems, supporting sustainable water treatment solutions.