Facile synthesis of Bi12O17Br2 and Bi4O5Br2 nanosheets: In situ DRIFTS investigation of photocatalytic NO oxidation conversion pathway

Bi12O17Br2 and Bi4O5Br2 visible-light driven photocatalysts, were respectively fabricated by hydrothermal and room-temperature deposition methods with the use of BiBr3 and NaOH as precursors. Both Bi12O17Br2 and Bi4O5Br2 were composed of irregular nanosheets. The Bi4O5Br2 nanosheets exhibited high and stable visible-light photocatalytic efficiency for ppb-level NO removal. The performance of Bi4O5Br2 was markedly higher than that of the Bi12O17Br2 nanosheets. The hydroxyl radical (•OH) was determined to be the main reactive oxygen species for the photo-degradation processes of both Bi12O17Br2 and Bi4O5Br2. However, in situ diffuse reflectance infrared Fourier transform spectroscopy analysis revealed that Bi12O17Br2 and Bi4O5Br2 featured different conversion pathways for visible light driven photocatalytic NO oxidation. The excellent photocatalytic activity of Bi4O5Br2 resulted from a high surface area and large pore volumes, which facilitated the transport of reactants and intermediate products, and provided more active sites for photochemical reaction. Furthermore, the Bi4O5Br2 nanosheets produced more •OH and presented stronger valence band hole oxidation. In addition, the oxygen atoms of NO could insert into oxygen-vacancies of Bi4O5Br2, which provided more active sites for the reaction. This work gives insight into the photocatalytic pollutant-degradation mechanism of bismuth oxyhalide.