Harvesting Solar Light with Crystalline Carbon Nitrides for Efficient Photocatalytic Hydrogen Evolution

TLDR: This method successfully enables a substantial amount of visible light to be harvested for H2 evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts.

Abstract: Described herein is the photocatalytic hydrogen evolution using crystalline carbon nitrides (CNs) obtained by supramolecular aggregation followed by ionic melt polycon- densation (IMP) using melamine and 2,4,6-triaminopyrimi- dine as a dopant. The solid state NMR spectrum of 15 N- enriched CN confirms the triazine as a building unit. Control- ling the amount and arrangements of dopants in the CN structure can dramatically enhance the photocatalytic perfor- mance for H2 evolution. The polytriazine imide (PTI) exhibits the apparent quantum efficiency (AQE) of 15 % at 400 nm. This method successfully enables a substantial amount of visible light to be harvested for H2 evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts. Producing hydrogen, an environmentally benign energy carrier with a high energy density, from water splitting is a primary goal of modern chemistry. (1) The rational design and synthesis of abundant, sustainable, and efficient metal-free photocatalytic materials that operate with visible light con- tinue to be challenges in this field. Recently, the polymeric carbon nitride (CN) semiconductor g-C3N4 has attracted significant attention because this catalyst exhibited stable performance in the photocatalytic water-splitting reaction (half reaction) under visible light. (2) The semiconductor properties of g-C3N4 result from the formation of an extended p-conjugated system from s-triazine units and largely rely on the extent of their polymerization. A structural character- ization revealed the presence of unreacted amino and/or cyano functionalities owing to incomplete polymerization. (3)