Design of donor–acceptor type benzotrithiophene-based covalent organic frameworks for visible-light-driven overall water splitting

Benefitting from the abundant accessible catalytic sites and well-defined porous architectures enhancing mass transport, two-dimensional (2D) covalent organic frameworks (COFs) are emerging as promising photocatalysts for overall water splitting (OWS). However, the performance of many known COFs for this application remains unsatisfactory, primarily due to stringent requirements for precise band alignment, the limitation posed by overpotentials in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and mutual interference between the two half-reactions. Herein, we propose eight donor–acceptor (D–A) type 2D benzotrithiophene-based COFs (BTT-COFs), constructed from experimentally feasible building blocks via Schiff-base condensation reaction. By incorporating D–A pairs into the frameworks, these BTT-COFs exhibit enhanced intermolecular charge transfer characteristics as anticipated, thereby promoting efficient carrier separation during OWS. Concurrently, the D–A combinations enable precise modulation of the electronic structure, affording band gaps ranging from 2.35 to 2.89 eV with band-edge arrangements appropriately aligned for photocatalytic OWS under neutral conditions (pH = 7). Among them, the BTT-COF1 (incorporating benzotrithiophene and 1,3,5-triaminobenzene), BTT-COF2 (featuring benzotrithiophene and 2,4,6-triamino-1,3-diazine), and BTT-COF3 (consisting of benzotrithiophene and 2,4,6-triamino-1,3,5-triazine) are found to be capable of spontaneously driving OWS under their intrinsic photoinduced bias potentials. The remaining BTT-COFs require external bias to facilitate the reaction. Crucially, the theoretical solar-to-hydrogen (STH) conversion efficiencies of these materials range from 1.8 % to 10.0 %, highlighting their potential as efficient photocatalysts for OWS. Two-dimensional covalent organic frameworks (COFs) constructed from tailored donor-acceptor building blocks efficiently photocalalyze overall water splitting under visible light. • Eight experimentally feasible D–A type 2D BTT-COFs are constructed via Schiff-base condensation reaction. • Incorporating D–A pairs enhances intermolecular charge transfer within the frameworks. • BTT-COF1-3 exhibit spontaneous overall water splitting activity, while others require an external bias. • Theoretical solar-to-hydrogen conversion efficiencies of these BTT-COFs range from 1.8 % to 10.0 %.