Stable and Efficient Selective Photochemical Conversion of Nitric Oxide into Nitrates via Earth‐Alkaline‐Carbonate‐Doped N‐Rich Carbon Nitride

Abstract Achieving stable and selective photooxidation of NO x in air remains a significant challenge. Here, the study reports a doping strategy using alkaline‐earth carbonates to enhance the photocatalytic performance of N‐rich carbon nitride (C 3 N 5 ). The BaCO 3 ‐doped C 3 N 5 (BaCO 3 /C 3 N 5 ) composite demonstrates a remarkable NO removal efficiency of ≈60%, surpassing pristine BaCO 3 and N‐rich C 3 N 5 by factors of 60 and 12, respectively. This substantial enhancement is attributed to the synergistic effects of BaCO 3 doping, which promotes photogenerated carrier separation and transport, improves NO/O 2 adsorption and activation, and broadens visible‐light responsiveness. Notably, BaCO 3 /C 3 N 5 exhibits stable NO removal efficiency and high selectivity for nitrate (NO 3 ⁻ ) during ten consecutive cycles, as evidenced by in situ DRIFTS. Similarly, doping with CaCO 3 and SrCO 3 yields comparable improvements in performance. Furthermore, the NO removal efficiency per milligram of these composites and their effective suppression of toxic NO 2 intermediates surpass those of 36 reported C₃N x ‐based (X = 4, 5) and insulator‐based photocatalysts. This work provides valuable insights into the design of advanced photocatalysts for air pollution control, offering a sustainable pathway for mitigating NO x emissions.