Porphyrin-based conjugated organic polymer with dual metal sites for highly active and selective visible-light-driven reduction of CO2 to CO

Abstract

A porphyrin-based conjugated organic polymer (COP) was constructed from 5,10,15,20-tetrakis(4-bromophenyl)porphyrin copper (CuTBPP) and 5,5′-bis-ethynyl-2,2′-bipyridine (BPY) via Sonogashira coupling. Its complex Co/CuTBPP–BPY–COP (with dual metal sites composed of copper porphyrin and a cobalt BPY unit) was prepared by coordination with Co²⁺. All of the prepared CuTBPP–BPY–COP and Co/CuTBPP–BPY–COP compounds exhibited excellent photocatalytic performance toward CO₂ reduction under visible-light irradiation without another sacrificial reagent but only H₂O. Co/CuTBPP–BPY–COP (dual metal sites) exhibited better photocatalytic activity than CuTBPP–BPY–COP (a single metal site). Co/CuTBPP–BPY–COP retained a higher photocatalysis capacity for CO₂ reduction after 10 consecutive cycles. The total quantity of CO product was 263.2 μmol g⁻¹ after 10 h of irradiation. Theoretical studies indicate that introducing Co metal centers and nitro groups are more favorable for the photoreduction catalysis of CO₂ compared with that using CuTBPP–BPY–COP.