Direct Z-scheme heterojunctions with perylenetetracarboxylic diimide decorated amino-rich porous g-C3N4 nanosheets for metal-free photocatalytic N2 fixation

Photocatalytic nitrogen fixation is a green, sustainable ammonia synthesis method in artificial nitrogen fixation technology. However, activating inert nitrogen molecules requires a great deal of energy, and the design of stable and efficient nitrogen-fixing photocatalysts is of great research value and challenge. In this paper, g-C₃N₄ nanosheets (10H-CN_v) containing nitrogen-vacancy curled porous ammonia-rich structure and perylenetetracarboxylic diimide (PDI) are covalently combined bonded by the in-situ condensation to construct direct Z-scheme heterojunction photocatalysts. Among them, the nitrogen vacancies and the curled porous morphology endow 10H-CN_v with more active sites for N₂ adsorption. The direct Z-scheme heterojunction is constructed with an enhanced internal built-in electric field, effectively promoting the selective accumulation of photogenerated electrons and holes in the 10H-CN_v and PDI components. Sufficient redox potentials provide a potential driving force for lowering the activation energy barrier of inert nitrogen molecules. In addition, the direct Z-scheme heterojunction in charge transfer mode enables efficient spatial separation of photogenerated electrons and holes. The average yields of 30 % PDI/10H-CN_v photocatalyzed direct conversion of N₂ molecules to ammonia and nitrate are 519.2 and 135.9 μmol g⁻¹h⁻¹, respectively. This work gives valuable guidelines for directly constructing Z-scheme heterostructures of photocatalysts for their application in nitrogen fixation.