Metal-free 3D donor–acceptor COF with low exciton binding for solar fuel production based on CO2 reduction

Abstract

A recent upsurge in developing organic materials as photocatalysts for CO₂ reduction is observed owing to their low cost, tunable band gap, and high selectivity compared to inorganic semiconductors. Herein, we have reported an imine-based 3D covalent organic framework (TT-COF) based on tris(4-aminophenyl)amine (TAPA) and an aldehyde derivative of tetraphenylethylene (TFTPE(CHO)₄) where TAPA unit acts as a donor and TPE moiety plays the role for the acceptor. The TT-COF possesses worthy band alignment, visible range light absorption, and good CO₂ uptake of 29 mL g⁻¹ at room temperature, which renders it a promising metal-free photocatalyst towards visible light (400–750 nm)-driven CO₂ reduction reaction (CO₂RR). After 26 h of photo-irradiation in the presence of TEA, TT-COF enabled the production of CO with a yield of 6.45 mmol g⁻¹ with 83% selectivity. The presence of continuous self-organized donor–acceptor components in the interpenetrating network facilitates charge transfer as well as decreases the exciton binding energy (E_b = 84.2 meV), which leads to efficient charge separation and photocatalytic activity. The transient intermediate species formed during the CO₂ reduction process was monitored by in situ DRIFT study and a plausible mechanism was derived based on DFT calculations.