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

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.