Novel ZnFe2O4/Bi2S3 high-low junctions for boosting tetracycline degradation and Cr(VI) reduction

The fabrication of photocatalysts with high reaction activity for decomposition of pharmaceutical contaminants and detoxication of heavy metal ions in wastewater is challenging. In this study, novel ZnFe2O4/Bi2S3 high-low junctions with different work functions and tight interface were constructed by the growth of Bi2S3 over ZnFe2O4 under hydrothermal conditions, and the content of ZnFe2O4 was optimized. The optimal 12 % ZnFe2O4/Bi2S3 sample exhibited the best visible-light photocatalytic performance of 91.6 % tetracycline removal at solution pH of 4.72 and 96.7 % reduction efficiency of Cr(VI) at solution pH of 5.51 within 2 h. Holes (h+), hydroxyl radicals (OH) and superoxide radicals (O2−) jointly attacked tetracycline, leading to efficacious decomposition of tetracycline and sharp toxicity reduction. The toxicity prediction of degradation intermediates by ECOSAR software and E. coli growth further confirmed the significant role of ZnFe2O4/Bi2S3 high-low junction in toxicity reduction of tetracycline. The photogenerated electrons were involved in Cr(VI) reduction. The relationship between structure and photocatalytic activity was set forth from the view of light absorption, band structure, internal electric field at interface, charge separation and migration behaviors. Importantly, the photocatalytic mechanism of ZnFe2O4/Bi2S3 high-low junctions with different work functions and intimate interface was first provided based on edge energy offset. This work will provide new insights for the preparation and application of high-low junction photocatalytic materials based on CB/VB edge energy shift and unique photogenerated charge transfer mechanism.