Iron/cobalt/nickel regulation for efficient photocatalytic carbon dioxide reduction over phthalocyanine covalent organic frameworks

Using solar photocatalytic CO2 reduction to produce high-value-added products is a promising solution to environmental problems caused by greenhouse gases. Metal phthalocyanine COFs possess a suitable band structure and strong light absorption ability, making them a promising candidate for photocatalytic CO2 reduction. However, the relationship between the electronic structure of these materials and photocatalytic properties, as well as the mechanism of photocatalytic CO2 reduction, is still unclear. Herein, the electronic structure of three MPc-TFPN-COFs (M = Ni, Co, Fe) and the reaction process of CO2 reduction to CO, HCOOH, HCHO and CH3OH were studied using DFT calculations. The calculated results demonstrate that these COFs have a good photo response to visible light and are new potential photocatalytic materials. Three COFs show different reaction mechanisms and selectivity in generating CO2 reduction products. NiPc-TFPN-COFs obtain CO through the reaction pathway of CO2 → COOH → CO, and the energy barrier of the rate-determining step is 2.82 eV. NiPc-TFPN-COFs and FePc-TFPN-COFs generate HCHO through CO2 → COOH → CO → CHO → HCHO, and the energy barrier of the rate step is 2.82 eV and 2.37 eV, respectively. Higher energies are required to produce HCOOH and CH3OH. This work is helping in understanding the mechanism of photocatalytic reduction of CO2 in metallophthalocyanine COFs.