Oligomer‐Incorporated Polymeric Layer Framework of Graphitic Carbon Nitride for Effective Photocatalytic Hydrogen Evolution

Abstract

AbstractThis paper presents a structural design of graphitic carbon nitride (CN) for use as an active photocatalyst in H2 evolution reactions. The active photocatalyst is synthesized by subjecting a CN sample to consecutive annealing and ammonia treatments. The CN sample is produced through urea condensation. The annealing treatment destroys the polymeric CN to form a defective polymeric layer framework incorporating 1,3,4,6,7,9,9b‐Heptaazaphenalene‐2,5,8‐triamine (melem) oligomers. The annealed CN exhibits a wide absorption range in visible light because the distorted structure causes conjugation of the π‐orbital with a nitrogen nonbonding state. The subsequent ammonia treatment of the annealed CN repairs the nitrogen vacancies and bridges the polymeric framework and melem oligomers. The repaired and bridged sample (N‐aCN) provides viable pathways for charge separation and transport, and active amino sites are introduced in the sample for electron injection in order to produce H2. When Pt is deposited, the CN and N‐aCN samples catalyze H2 evolution from aqueous triethanolamine solution at quantum yields of 3.7 and 17%, respectively, under 420 nm monochromatic irradiation. The high activity of N‐aCN demonstrates that the oligomer‐incorporated polymeric layer framework effectively harvests light and mediates charge transport in CN materials for photoenergy conversion.