The wide bandgap of BiOCOOH (BCH) limits its application in the visible-light region. To solve this problem, a series of carbon quantum dots (CQDs)/BCH composites is synthesized using a simple hydrothermal approach. The incorporation of CQDs extends the light absorption range of BCH from the UV to the visible region, thereby enabling it to convert NO into less toxic products efficiently. From the theoretical calculations, an ohmic junction is formed between CQDs and BCH due to the difference in their work functions, which promotes the directional transfer of photogenerated electrons to CQDs, enhancing the separation effi- ciency of the photogenerated carriers to improve photocatalytic performance. As a result, the optimized 3-CQDs/BCH composite exhibits a high NO conversion rate, 54.5%, which is 14.7 times that of pure BCH under visible-light irradiation (λ ≥ 420 nm), besides a low NO2 generation concentration (<10 ppb). After five cycles of use, the photocatalytic efficiency shows almost no decrease, demonstrating favorable stability and practical potential efficiency for the gaseous hazards. Finally, the reaction mech- anism and plausible pathways involved in the photocatalytic conversion of NO over 3-CQDs/BCH were elucidated using electron paramagnetic resonance and in situ diffuse reflectance infrared Fourier transform spectroscopy.
