Ultra-stable Bi4O5Br2/Bi2S3 n-p heterojunctions induced simultaneous generation of radicals •OH and •O2- and NO conversion to nitrate/nitrite species with high selectivity under visible light

Advancement of photocatalytic systems that restricted formation and emission of toxic by-product NO2 remained a great challenge regarding NO removal. To circumvent this issue, in this study composites Bi4O5Br2/Bi2S3 were constructed through a facile anion exchange route that sulfurized pure Bi4O5Br2 (BB) in CS2 under room temperature. In-situ formed Bi2S3 (BS) was identified and intimately connected with BB to form n-p heterojunctions. Under visible light, n-p heterojunction composites BB-BS showed significantly improved NOx removal and selectivity for NO2-/NO3- comparing to BB, although photocatalytic removal over NO was almost identical. Specifically, NOx removal by the best candidate BB-BS60 was 1.5 times that of BB, while selectivity for NO2-/NO3- increased from 60% to 90%, causing extremely low formation of NO2. The generation of NO2-/NO3- was identified by FT-IR spectra and XPS analyses. The variation of photocatalytic performance and relevant selectivity was systemically discussed and mainly related to boosting generation of radicals center dot OH and center dot O-2(-), strengthened visible-light absorption, and well-matched band structures of both components in the Z-scheme mode. Eventually, these ultra-stable composites could be utilized for successive five runs and catalytic performance was well preserved without surface cleaning. This work might shed light on the construction of suitable photocatalytic systems with significant improvement of total NOx removal and avoidance of toxic by-product NO2 formation or emission.

Automated summary

The study developed composite Bi4O5Br2/Bi2S3 through anion exchange to improve NOx removal while avoiding toxic NO2 formation. The composites showed enhanced selectivity and efficiency under visible light due to improved radical generation, light absorption, and band structure matching in the Z-scheme mode. The ultra-stable composites could be used for multiple runs without loss of catalytic performance, offering a promising solution for total NOx removal without NO2 formation or emission.