Donor–acceptor hetero[6]radialene-based three-dimensional covalent organic frameworks for organic pollutant adsorption, photocatalytic degradation, and hydrogen production activity

Abstract

Covalent organic frameworks (COFs) are promising photocatalysts for treating organic pollutants and solar-to-hydrogen conversion; however, their suboptimal energy band structure and rapid charge recombination limit their photocatalytic performance. Herein, we synthesized two donor–acceptor hetero[6]radialene-based TFP 3D COFs, TFP-Py and TFP-BF, with a unique [3,4]-linked ffc topological structure for the adsorptive and photocatalytic degradation of the rhodamine B (RhB) dye and photocatalytic hydrogen production from water. The acceptor is hetero[6]radialene and the donors are planar pyrene (Py) and twisted bifluorenylidene (BF). TFP 3D COFs surpass previously reported COFs in removing RhB from water in 10 min with a maximum adsorption capacity (Q_m) of 840 mg g⁻¹. Interestingly, the incorporation of the twisted BF structure into the hetero[6]radialene-based 3D COF backbone improved the band gap structure, charge transport, and photoinduced electron and hole isolation. The TFP-BF 3D COF degrades organic dye (RhB) with 1.4-fold greater catalytic activity (1.5 × 10⁻² min⁻¹) than the planar pyrene donor-derived TFP-Py 3D COF (1.1 × 10⁻² min⁻¹). It demonstrates a hydrogen evolution (HER) rate of 21.04 mmol g⁻¹ h⁻¹, obviating the need for a Pt cocatalyst, the highest COF-specific capacity ever recorded. This study illuminates how electron donor topology and hetero[6]radialene 3D structure affect photocatalysis.