Porous poly(triazine-heptazine)s: low-temperature solvothermal synthesis, *HCO intermediate activation and photocatalytic CO₂ reduction to CH₄

High-temperature ionothermal synthesis has been proven effective in preparing environment-friendly carbon nitride (CN)-based photocatalysts in either triazine or heptazine form for CO₂ reduction reaction (CO₂RR). However, such a process is usually energy-intensive and suffers from partial carbonization that results in non-porous catalysts and degenerating their activities. Herein, we report the preparation of highly porous CN polymers (porous C₆N₇, C₃N₃, C_4.5N₅) through a low-temperature solvothermal polymerization of cyameluric chloride itself or cyanuric chloride itself, or both, respectively. As such, it avoids unfavorable carbonization and allows for fine control of its chemical structure and significantly enlarged surface area (up to 669 m² g⁻¹). The pincer-like 2,2′-bipyridine sites of porous C₆N₇ alter the photocatalytic CO₂ reduction pathways via stabilizing the *HCO intermediates, which promotes further hydrogenation to produce CH₄ in a high selectivity. Benefiting from the carbonization-free polymerization, high porosity, and *HCO intermediate activation, porous C₆N₇ gave a superior CO₂RR to CH₄ performance (17.18 µmol g⁻¹ h⁻¹) as well as high stability (5 successive cycles), outperforming the bulk and state-of-the-art counterparts of CN. This opens an avenue for the rational construction of efficient porous CN-based photocatalytic systems, demonstrating their great potential in energy conversion reactions.