A novel Z-scheme Bi4O5Br2 nanosphere/Bi2S3 nanorod heterojunction with rich oxygen vacancy enhanced the photoreduction of Cr (VI) based on efficient charge separation

The yield and effective separation of the photosensitive charge carriers are the main factors that can improve the photocatalytic efficiency of the semiconductors. Here, we proposed a novel Z-scheme Bi4O5Br2 nanosphere/Bi2S3 nanorod heterojunction containing oxygen vacancies (OVs), prepared by two steps synthesis, involving alcoholysis and anion exchange. The photocatalytic performance of Bi4O5Br2/Bi2S3 composites with different Bi2S3 content on Cr (VI) under Xe lamp irradiation was investigated. Compared with the pristine BiOBr, monophase Bi4O5Br2, and defect-free BiOBr/Bi2S3-2, Bi4O5Br2/Bi2S3 composites exhibited outstanding photoreduction activity. The optimal Bi4O5Br2/Bi2S3-2 composite reduced 91.3% Cr (VI) under neutral conditions within 80 min. The effects of catalyst dosage, chromium concentration, pH and added electrolyte were discussed in detail. The stability tests involving 5 cycles of photocatalytic experiments indicated that Bi4O5Br2/Bi2S3-2 maintained over 70% of its efficiency. The high-efficiency photocatalytic performance of Bi4O5Br2/Bi2S3-2 was attributed to excellent light-trapping ability and the efficient migration and separation of the carrier through a Z-scheme. The OVs on the surface captured the light-excited electrons to act on the photodegradation of Cr (VI). These results enriched the heterojunction engineering dealing with BiOBr and could provide new insights for solving the problem of Cr (VI) pollution in the environment.