(BiO)₂CO₃ single-crystal nanosheets were successfully fabricated via an eco-friendly aqueous process using CO₂ and bismuth nitrate as raw materials under mild conditions within 30 min. Compared with previous preparation methods, this facile method avoids treatment at high temperatures, the use of organic precursors and the production of undesirable organic byproducts during the synthesis process. The as-prepared samples were characterized by XRD, SEM, TEM, BET-BJH measurement, UV-vis DRS, FT-IR and time-resolved ns-level PL in detail. It was found that the size and the thickness of the (BiO)₂CO₃ nanosheets can be influenced by the reaction temperature and CO₂ concentration. The as-prepared (BiO)₂CO₃ nanosheets were applied to the photocatalytic removal of NO_x under artificial UV-vis and UV light irradiation and showed an admirable photocatalytic performance. Significantly, (BiO)₂CO₃ nanosheets can be directly fabricated using the CO₂ in air without extra separation process, and the as-prepared (BiO)₂CO₃ nanosheets exhibited an efficient and durable photocatalytic performance for NO_x removal. The present work developed a novel method utilizing CO₂ to produce functional (BiO)₂CO₃ nanosheets with potential applications in environment and energy, which is expected to fabricate other functional metal carbonates.