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 (C₃N₅). The BaCO₃-doped C₃N₅ (BaCO₃/C₃N₅) composite demonstrates a remarkable NO removal efficiency of ≈60%, surpassing pristine BaCO₃ and N-rich C₃N₅ by factors of 60 and 12, respectively. This substantial enhancement is attributed to the synergistic effects of BaCO₃ doping, which promotes photogenerated carrier separation and transport, improves NO/O₂ adsorption and activation, and broadens visible-light responsiveness. Notably, BaCO₃/C₃N₅ exhibits stable NO removal efficiency and high selectivity for nitrate (NO₃^⁻) during ten consecutive cycles, as evidenced by in situ DRIFTS. Similarly, doping with CaCO₃ and SrCO₃ yields comparable improvements in performance. Furthermore, the NO removal efficiency per milligram of these composites and their effective suppression of toxic NO₂ 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.