One-step scalable synthesis of honeycomb-like g-C3N4 with broad sub-bandgap absorption for superior visible-light-driven photocatalytic hydrogen evolution

Abstract

Integration of a nanostructure design with a sub-bandgap has shown great promise in enhancing the photocatalytic H₂ production activity of g-C₃N₄via facilitating the separation of photogenerated charges while simultaneously increasing the active sites and light harvesting ability. However, the development of a synthetic route to generate an ordered g-C₃N₄ structure with remarkable sub-bandgap absorption via a scalable and economic approach is challenging. Herein, we report the preparation of a honeycomb-like structured g-C₃N₄ with broad oxygen sub-bandgap absorption (denoted as HOCN) via a scalable one-pot copolymerization process using oxamide as the modelling agent and oxygen doping source. The morphology and sub-bandgap position can be tailored by controlling the oxamide to dicyandiamide ratio. All HOCN samples exhibit remarkable enhancement of photocatalytic H₂ production activity due to the synergistic effect between the sub-bandgap and honeycomb structure, which results in strong light absorption extending up to 1000 nm, fast separation of photogenerated charge carriers, and rich photocatalytic reaction sites. In particular, HOCN4 exhibits a remarkable photocatalytic H₂ production rate of 1140 μmol h⁻¹ g⁻¹ under visible light irradiation (>420 nm), which is more than 13.9 times faster than the production rate of pristine g-C₃N₄. Moreover, even under longer wavelength light irradiation (i.e., >500 and >800 nm), HOCN4 still exhibits a high H₂ production rate of 477 and 91 μmol h⁻¹ g⁻¹, respectively. In addition, HOCN4 possesses an apparent quantum yield (AQY) of 4.32% at 420 nm and 0.12% at 800 nm. These results confirm that the proposed synthesis strategy allow for scalable production of g-C₃N₄ with an ordered nanostructure via electronic modulation, which is beneficial for its practical application in photocatalytic H₂ production.