BiOI/Bi5O7I solid solution with S-scheme heterojunction as a high-efficiency photocatalyst for formaldehyde and Congo red degradation

Abstract

One effective strategy to eliminate formaldehyde (HCHO) pollution is the development of S-scheme heterojunction photocatalysts. Herein, the BiOI/Bi₅O₇I solid solution with S-scheme heterojunction photocatalyst was successfully prepared by calcining BiOI at 370 °C < T < 450 °C. Under visible light (λ > 400 nm), the removal rate of HCHO (0.16 mg/L) was 76% when 450-BiOI/Bi₅O₇I was irradiated for 60 min. The HCHO degradation rate constants of 450-BiOI/Bi₅O₇I (k = 0.0236 min⁻¹) were 4.1 and 3.8 times greater than those of pristine BiOI (k = 0.0058 min⁻¹) and Bi₅O₇I (k = 0.0063 min⁻¹). 450-BiOI/Bi₅O₇I also has good photodegradation performance for Congo red (CR), and the degradation rate reaches 90% after 180 min. The significant increase in photocatalytic performance is not only attributed to the uniformly distributed nanostructures but also to the S-scheme heterojunction. The S-scheme heterojunction collectively improves photocatalytic performance through its unique energy band structure matching, charge transfer mechanism, and synergistic interaction with the internal electric field (IEF). In addition, the formation of solid solutions can promote the efficiency of visible light harvesting and separation of photogenerated carriers, and endow the photogenerated holes with sufficient oxidation capacity. Therefore, BiOI/Bi₅O₇I solid solution with S-scheme heterojunction photocatalysts not only possess outstanding photocatalytic performance but also exhibit good photostability, which makes them promising photocatalysts for visible light environmental applications.