Designing of covalent organic framework/2D g-C₃N₄ heterostructure using a simple method for enhanced photocatalytic hydrogen production

Designing heterostructure photocatalysts is a promising approach for developing highly efficient photocatalysts for hydrogen energy production. In this work, we synthesized a series of a covalent organic framework (COF)/g-C₃N₄ (CN) heterojunction photocatalysts, denoted as x % COF/CN (in which x indicates the weight % of COF and x = 5, 10, 20, 30, 40, 50, 90, 95, 100), for hydrogen production. The COF, which is a key component of the photocatalyst, was prepared by assembling benzothiadiazole (BT) and pyrene (Py) derivatives as building blocks. Integrating COF rods into the two-dimensional (2D) layered g-C₃N₄ structure significantly improved photocatalytic H₂ production. The hybrid system (30 % COF/CN) displayed an outstanding hydrogen evolution rate (HER) of 27540 ± 805 μmol g⁻¹h⁻¹, outperforming most known COFs and g-C₃N₄-based photocatalysts, besides exhibiting stable photocatalytic performance. Moreover, the apparent quantum yield (AQY) was 15.5 ± 0.8 % at 420 nm. Experimental techniques and density functional theory (DFT) calculations demonstrated that the 30 % COF/CN heterostructure has broad visible-light absorption, adequate band energy levels, and the best chemical reactivity descriptors compared to the individual components, resulting in effective carrier separation and excellent performance. Our findings offer a valuable strategy for developing highly efficient and stable heterojunction photocatalysts for visible-light-driven H₂ evolution.