Novel inorganic/organic Z-scheme heterojunction rGO@PANI/SnO2 with enhanced photocatalytic activity for degradation of sulfadiazine

As the persistent contamination of water sources with antibiotics poses a growing environmental challenge, effective strategies for the degradation of such pollutants are urgently needed. Herein, a novel organic-inorganic Z-scheme heterojunction material, reduced Graphene Oxide (rGO)@PANI/SnO 2 , was prepared for the photocatalytic degradation of sulfadiazine (SD). When the PANI/SnO 2 with PANI doping amount of 1% was loaded on 1% rGO, the catalyst showed the best photocatalytic activity, with a reaction rate constant of 0.184   h -1 , which was 32.8 and 7.19 times higher than that of PANI and SnO 2 , respectively. The improved photocatalytic activity was mainly due to the high electrical conductivity of rGO and the formation of a Z-scheme heterojunction between PANI and SnO 2 , which effectively facilitated the transfer of photogenerated carriers. Quenching experiments showed that ·OH is the main active species. Besides, Density Functional Theory (DFT) calculations found that the sulfonamide bond and pyrimidine heterocyclic were vulnerable site in the SD. Then, four possible degradation pathways were proposed, primarily involving the breaking of the sulfonamide bond and the ring-opening of the pyrimidine heterocycle. The response surface method (RSM) was used to confirm that the removal of SD was affected by the single factor of initial SD concentration, pH value and catalyst dosage, and the magnitude of the effect of different parameters was in the order of pH > catalyst dosage > SD concentration. It was found that Cl - and SO 4 2- inhibited the photocatalytic process, whereas HCO 3 - facilitated the process through its ability to produce ·OH by hydrolysis and provide a weakly alkaline environment. This work provides novel ideas for the preparation of organic-inorganic heterojunction photocatalysts and enhances the application of organic materials in the photocatalytic degradation of antibiotics in water.