Polymeric Carbon Nitride with Localized Aluminum Coordination Sites as a Durable and Efficient Photocatalyst for Visible Light Utilization

The development of efficient and yet economic photocatalysts that can utilize solar light is crucial for the sustainable future. We report a simple approach to introduce a bidentate type of metal coordination site in polymeric carbon nitride (PCN) by an in situ keto enol cyclization route of acetylacetone and urea to incorporate a metal chelating pyrimidine derivative into the molecular framework of PCN. The resulting new metal coordination sites provide both N- and O-complexing ligands unlike the unmodified PCN that has N-ligands only. As a proof-of-concept experiment, we introduced Al3+ ions into these coordination sites, which induced significant enhancements in visible light photocatalytic activities for organic pollutant degradation and H-2 evolution as compared to those of bulk PCN and the conventional "nitrogen pot" metal coordinated PCN. The optimized Al loading was as low as 0.32 wt %. The photocatalytic activities sensitively depended on the Al incorporation, and the Al-incorporated sample demonstrated an excellent stability in water with showing little sign of metal leaching. While the aluminum ions complexed in the nitrogen pot little influenced the photocatalytic activity, Al3+ ions complexed by both N and O ligands in the alternative coordination sites significantly enhanced the photocatalytic activity of PCN. This study demonstrates a facile and scalable synthesis of PCN with alternative metal coordination sites for efficient solar energy conversion.