Advancing n→π* Electron Transition of Carbon Nitride Nanotubes for H₂ Photosynthesis

Melon-based carbon nitride (g-C3N4) is a promising metal-free and sustainable material for photocatalytic water splitting. In principle, pristine carbon nitride only exhibits moderate activity due to the insuficient visible light absorption and fast charge recombination. To enhance the solar-to-energy efficiency of g-C3N4, it depends on the rational design of the morphology and electronic structure. Herein, we report on self-assembly of g-C3N4 nanotubes by co-polycondensation of urea and oxamide with their similar structure and reactivity to optimize the texture and electronic properties. Unlike pristine g-C3N4, the obtained copolymers exhibit clear optical absorption above 465 nm, which is ascribed from the n[rightward arrow][small pi]* electron transition involving lone pairs of the edge nitrogen atoms of the heptazine units. Besides, the charge carrier mobility was also optimized in the spatially seperated nanotube structure, which is contributed to generate more hot electrons. The optimized copolymers show dramatically enhanced H2 evolution activities especially with green light. The achieved apparent quantum yield (AQY) of optimal CN-OA-0.05 for H2 evolution with green LED ([small lambda] = 525 nm) reaches 1.3 %, which is about 10 times higher than that of pure CN with state-of-the-art activity in this wavelength region