Metalloporphyrin-based covalent organic frameworks composed of the electron donor-acceptor dyads for visible-light-driven selective CO2 reduction

The visible-light-driven photocatalytic CO2 reduction with high efficiency is highly desirable but challenging. Herein, we present porphyrin-tetraphenylethene-based covalent organic frameworks (MP-TPE-COF, where M=H2, Co and Ni; TPE=4,4′,4″,4‴-(ethane-1,1,2,2-tetrayl) tetrabenzaldehyde; COF=covalent organic framework) as ideal platforms for understanding photocatalytic CO2 reduction at molecular level. Experimental and theoretical investigations have demonstrated crucial roles of metalloporphyrin units in selective adsorption, activation and conversion of CO2 as well as in the separation of charge carriers and electron transfer, thus allowing for flexible modulation of photocatalytic activity and selectivity. CoP-TPE-COF exhibits high CO evolution rate of 2,414 µmol g−1 h−1 with the selectivity of 61% over H2 generation under visible-light irradiation, while NiP-TPE-COF provides CO evolution rate of 525 µmol g−1 h−1 and 93% selectivity with superior durability. Moreover, the photocatalytic system is feasible for the simulated flue gas, which provides CO evolution rate of 386 µmol g−1 h−1 and selectivity of 77%. This work provides in-depth insight into the structure-activity relationships toward the activation and photoreduction of CO2.