Visible-light-driven concurrent activation of O₂ and N₂ for direct HNO₃ synthesis under ambient conditions

The activation of small molecules such as O₂ and N₂ to produce high-value-added chemicals under ambient conditions is of significant interest. The conventional synthetic process of HNO₃ from NH₃ and O₂ requires high temperatures and pressures. Here, we report the concurrent activation of O₂ and N₂ for direct HNO₃ synthesis in water under visible light irradiation at room temperature and atmospheric pressure, without requiring NH₃ and other additional additives. Organic polymers are used to prove this concept and realize the direct synthesis of HNO₃ from N₂ and O₂. The pyridyl-functionalized organic polymer not only achieves a remarkable H₂O₂ yield of 10,147.5 µmol·g_cat⁻¹ but also facilitates the synthesis of HNO₃ with a yield of 672.8 µmol·g_cat⁻¹. The final concentration of HNO₃ is 0.34 mM in water. Mechanistic studies, combining experimental observations and theoretical calculations, demonstrate a tandem reaction pathway involving O₂ reduction and N₂ oxidation. This work establishes a metal-free photocatalytic method for HNO₃ synthesis only using light, H₂O, N₂, O₂, and an organic polymer under ambient conditions.