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.

A coordination nanosheet composed of [Fe(tpy)₂]²⁺ (tpy = 2,2':6',2''-terpyridine) units, showing reversible electrochromism at the ligand-based cathodic potential, has been prepared through a liquid/liquid interfacial synthesis. The noble metal-free nanosheet exhibited a CO evolution rate of 114.3 mmol·g⁻¹·h⁻¹ with the selectivity up to 99.3% under visible light irradiation in the presence of water, which is in the front rank of heterogeneous catalysis for CO₂ photoreduction. Such robust photocatalytic performance is due to efficient ligand-based electron transfer through long-lived π radical anion tpy^·− with a lifetime more than 25 min, as evidenced by in situ electron paramagnetic resonance (EPR) and ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy studies. Fe(II) cation in [Fe(tpy)₂]²⁺ mainly contributes to enhancing reduction potentials of ligand and stabilizing π radical anion tpy^·−. This ligand-based electron transfer with the aid of metal cation represents a promising strategy for selective CO₂ photoreduction, especially towards gaining CO from CO₂.