Exploring the full potential use of heterojunction photocatalysts containing bismuth has attracted considerable interest in recent years. Fabrication of well-defined heterojunction photocatalysts with precise modulation of their chemical composition is crucial for tuning their optical properties and photocatalytic activity. In this study, we fabricated nanoplate α-Bi₂O₃/(BiO) ₂CO₃ heterojunctions through in situ thermal treatment of (BiO) ₂CO₃ nanoplates synthesized using a facile hydrothermal process. Characterization results showed that the as-prepared Bi₂O₃/(BiO) ₂CO₃ heterojunctions possessed distinct crystal interface and exhibited pronounced structural and optical modulation, resulting in significant improvement of their photocatalytic activity for NO removal under simulated solar light irradiation compared with pristine (BiO) ₂CO₃. Electron spin resonance spectroscopy showed that ⋅OH radicals were the major reactive species involved in NO degradation, which is consistent with the theoretical analysis. The heterojunction formation can not only broaden the light absorption range but also improve the charge separation of photo-induced electron–hole pairs. This study is an important advancement in the development of semiconductor heterojunctions towards achieving functional photocatalysts. Copyright © 2016 Macmillan Publishers Limited.