A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water.

Abstract

Constructing powerful photocatalytic system that can achieve the carbon dioxide (CO2) reduction half-reaction and the water (H2O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust -C=C- bond linkages. The charge separation ability is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge separation enables the photogenerated electron-hole pairs separated by intramolecular charge transfer process to form photogenerated electrons involved in CO2 reduction and photogenerated holes participated in H2O oxidation simultaneously. The powerful viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate of 190.6 μmol g-1 h-1 with about 100% selectivity and oxygen (O2) evolution of 90.2 μmol g-1 h-1 among all the porous materials in CO2 reduction with H2O as sacrificial agents. Therefore, a powerful photocatalytic system is successfully achieved, and this catalytic system exhibits excellent stability in the catalysis process for 50 hours. Meanwhile, the structure-function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.