Metal-free thiophene-based covalent organic frameworks achieve efficient photocatalytic hydrogen evolution by accelerating interfacial charge transfer

Abstract

Photocatalysis is widely recognized as an efficient and environmentally friendly pathway for the conversion of solar energy into chemical energy. In recent years, designing efficient hydrogen evolution to obtain green clean energy has been one of the major challenges faced by researchers. Covalent organic frameworks (COFs) are considered as new and effective photocatalyst due to the inherent porosity, high crystallinity and structural adjustability. In this study, two metal-free thiophene-based covalent organic frameworks (JLNU-308 and JLNU-309) were constructed by solvothermal method through effective modulation sites. Because JLNU-COFs has a narrow band gap and good absorption capacity in the spectral range, the interfacial charge transfer speed is accelerated to solve the problem of low charge separation efficiency. Remarkably, JLNU-309 displays an impressive hydrogen evolution rate of 2868.57 μmol g−1 h−1 under visible light irradiation (λ > 420 nm). The superior hydrogen evolution reaction (HER) activity is due to the triazine units, which have high visible light absorption capacity, one-dimensional nanochannels of two-dimensional COFs and synergy with charge mobility. The photoelectrochemical measurements and calculation of density functional theory (DFT) supports the accuracy of the experiment. This work opens an avenue for constructing functional covalent organic frameworks for environmentally relevant critical applications. In addition, the simple synthesis process, excellent activity and high chemical stability indicate that JLNU-COFs are promising photocatalytic hydrogen production materials.