Visible-light activation of persulfate by a Z-scheme photocatalyst Fe-C3N4/Bi2Sn2O7 for tetracycline degradation

A Z-scheme photocatalyst Fe-C3N4/Bi2Sn2O7 was prepared and used to couple with persulfate oxidation in order to realize high efficient degradation of tetracycline. The results indicated that, under visible light irradiation, 100 mL of 20 mg·L−1 tetracycline could be efficiently decontaminated in 30 min with 0.5 g/L photocatalyst and 2 mM persulfate. The first-order kinetic constant was 6.04 and 16.13 times that of single photocatalytic oxidation by Fe-C3N4/Bi2Sn2O7 and single persulfate oxidation, respectively. With the help of the Z-scheme heterojunction between Fe-C3N4 and Bi2Sn2O7, more electrons were photogenerated to participate in the Fe2+/3+ cycle reaction, synergistically improving the activation of persulfate. Meanwhile, the holes thereby ensured the high photocatalytic oxidation performance in the coupling system. The analysis of electron spin resonance verified that·OH,·O2-, h+, 1O2, and·SO4- had positive impacts on the tetracycline degradation. Additionally, the operation mechanism of the coupling system and the possible degradation pathway were proposed.