Construction of dual S-scheme Ag2CO3/Bi4O5I2/g-C3N4 heterostructure photocatalyst with enhanced visible-light photocatalytic degradation for tetracycline

In recent years, the construction of step-scheme (S-scheme) heterojunction has proved to be a promising method to improve the degradation performance of photocatalysts. Importantly, S-scheme heterojunction system shows great potential in accelerating the separation and transformation of photogenerated carriers and obtaining strong light oxidation ability. In this paper, Ag2CO3/Bi4O5I2/g-C3N4 dual S-scheme heterojunction material was designed and constructed by heat treatment and subsequent in-situ wet chemistry. Compared with the original Bi4O5I2 and g-C3N4, Ag2CO3/Bi4O5I2/g-C3N4 hybrid catalyst showed remarkably enhanced photocatalytic performance in tetracycline degradation. The tetracycline degradation rate constant of Ag2CO3/Bi4O5I2/g-C3N4 is 0.03892 min−1, which is about 2.09, 5.80 and 13.33 times higher than that of pure Ag2CO3 (0.01865 min−1), Bi4O5I2 (0.00671 min−1) and g-C3N4 (0.00292 min−1), respectively. The apparent enhancement of photocatalytic activity is not only due to the formation of ternary complex, which can enlarge the visible light response of g-C3N4, but also due to the S-scheme heterojunction. When the interface is illuminated by visible light, the establishment of the built-in electric field and the resulting bending of the band edge promote the recombination of photogenerated carriers with weaker redox ability in the composite while retaining electrons and holes with stronger redox ability. Therefore, the residual electrons and holes with high reducing and oxidizing properties endow the composite with extremely high redox ability. In addition, the driving force and mechanism of charge transfer and separation in dual S-scheme heterojunction photocatalyst were studied and discussed. This study expands the application range of g-C3N4 material, and also discusses the reaction mechanism of Ag2CO3/Bi4O5I2/g-C3N4 composite material in dual S-scheme reaction system in detail.