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

Abstract

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.