Metal-free azo-bridged porphyrin porous organic polymers for visible-light-driven CO2 reduction to CO with high selectivity

Abstract

Two nitrogen-rich azo-bridged porphyrin porous organic polymers (Azo-Por-Bpy-POP and Azo-Por-Dadp-POP) with high surface areas were prepared by coupling 5,10,15,20-tetra(p-nitrophenyl)-porphyrin with the aromatic amines of 2,2′-bipyridine-5,5′-diamine (Bpy) and diaminodiphenyl (Dadp). Azo-Por-Bpy-POP and Azo-Por-Dadp-POP display high photocatalytic reduction activity for CO₂ to CO under visible-light irradiation without a sacrificial reagent or metal co-catalyst. Azo-Por-Bpy-POP exhibits the highest photoreduction for CO₂ with CO as the only carbonaceous reduction product with a production rate of 38.75 μmol g⁻¹ h⁻¹. Theoretical investigations indicate a stronger electrostatic interaction between CO₂ and Azo-Por-Bpy-POP than Azo-Por-Dadp-POP, which favors CO₂ photoreduction.