Metalloporphyrin-based covalent triazine frameworks for efficient photocatalytic CO2 cycloaddition at ambient conditions

The sunlight-driven CO₂ fixation into high value-added industrial products constitutes a promising approach to mitigating global warming, offering an alternative to traditional thermally-driven fixation requiring high temperature and/or high pressure. Herein, we design and synthesize four isostructural porphyrinic covalent triazine frameworks (Por-CTFs) including metal-free Por-CTF (H2Por-CTF) and metallized Por-CTFs (MPor-CTFs, M = Co, Zn, Cu) and their photocatalytic activity in CO₂ cycloaddition. All Por-CTFs exhibit wide light adsorption range in visible region via introducing porphyrins into the covalent triazine frameworks (CTFs) skeleton. Different metal ions which are well anchored in the MPor-CTFs skeleton not only offer Lewis acidic sites for substrate interaction but also apparently endow photocatalysts with longer photogenerated carrier lifetimes and higher electron-hole separation efficiency. Encouragingly, under visible light-assisted and mild conditions, the CoPor-CTF exhibits excellent photocatalytic performance achieving a reaction rate of 62.22 mmol g⁻¹ h⁻¹, which is among the state-of-the-art cases for photocatalytic CO₂ cycloaddition and outperforms two other MPor-CTFs. This work demonstrates that the photophysical and electronic properties of Por-CTFs can be rationally tuned by incorporating various metal ions into porphyrin units to achieve effective photocatalysts for CO₂ cycloaddition.