An artificial photosynthesis system comprising a covalent triazine framework as an electron relay facilitator for photochemical carbon dioxide reduction

Natural photosystem II, which utilizes multiple photosensitizers, is essentially an organic-inorganic hybrid system, and comprises electron transfer relay processes. The relay processes can facilitate charge transfer and reduce charge recombination. Thus it can significantly improve photocatalytic performance. Such a strategy has rarely been studied for CO₂ reduction in conjugated porous polymers. Here we report a new organic-inorganic hybrid material, which constitutes an electron transfer relay photocatalytic system for CO₂ reduction using a porous framework as a relay facilitator. The system was fabricated by decorating a new porphyrin-based covalent triazine framework (Por-CTF) with α-Fe₂O₃ nanoparticles using an in situ strategy, which was then coupled with a Ru complex photosensitizer. Owing to the formation of an electron transfer relay system, the ternary system exhibits a sharp enhancement in photocatalytic activity towards CO₂ reduction to CO as compared with the binary system. The best performance given by the electron transfer relay system (α-Fe₂O₃@Por-CTF-10×/Ru(bpy)₃Cl₂) produces a catalytic CO evolution rate of 8.0 μmol h^-1 with 93% CO selectivity, which is obviously superior to that of the binary system. The highest apparent quantum efficiency was also evaluated as 1.43% at 450 nm. This work provides a prototype model system for the design of an artificial photocatalytic system for photochemical CO₂ reduction.