One-Step Synthesis of Honeycomb-Like Carbon Nitride Isotype Heterojunction as Low-Cost, High-Performance Photocatalyst for Removal of NO

Carbon nitride (CN) is a metal-free conjugated semiconductor photocatalyst, but it is limited by its low activity mainly because of a high rate of charge carrier recombination. Here, we synthesized a honeycomb-like CN isotype heterojunction photocatalyst, made of a single substrate, by thermal treatment of thiourea and urea mixing with ultrapure water. This new photocatalyst can remove a low concentration of NO (600 ppb) effectively, and its maximum efficiency is 68% under visible-light irradiation. This catalytic efficiency is much better than the previously reported literature. We attributed the high performance to the formation of a heterojunction and efficient charge separation and transfer. Their interfaces of the honeycomb-like CN isotype heterojunction are not mutually exclusive because of almost no difference in their chemical composition. Furthermore, the honeycomb structure likely increased the absorption of light energy and improved the photocatalytic properties owing to multiple reflections within the porous structure. Finally, a Z-scheme photocatalytic mechanism is put forward and explained based on electron spin resonance experiments and calculations of the energy bands.