A metal-free covalent organic framework as a photocatalyst for CO2 reduction at low CO2 concentration in a gas–solid system

Abstract

A β-ketoenamine-based COF is used as a photocatalyst to convert CO₂ and H₂O into CO and O₂ under visible-light irradiation without using additional photosensitizers and sacrificial agents in a gas–solid system. When CO₂ concentration was controlled at 30.0% at 80 °C, TpBb-COF exhibited a CO production rate of 89.9 μmol g⁻¹ h⁻¹, which was higher than that (52.8 μmol g⁻¹ h⁻¹) in pure CO₂, indicating that low concentrations of CO₂ are conducive to the photocatalytic reduction of CO₂. DFT calculations indicate that the adsorption of H₂O on TpBb-COF was more preferential, which promoted the adsorption and reduction of CO₂. In light of this finding, the mechanism or reaction pathway was explored. The rate equation of CO₂ photocatalytic reduction was derived to correlate the association of the CO₂ concentration and CO production rate, which is consistent with the experimental results and theoretical calculations.