Highly crystalline porous carbon nitride with electron accumulation capacity: Promoting exciton dissociation and charge carrier generation for photocatalytic molecular oxygen activation

Abstract

Exciton effects play an important role in many polymeric photocatalytic systems, yet to date have largely been neglected in photocatalytic reactions over graphitic carbon nitride (g-CN). Since an exciton consists of a bound electron and hole, strategies that can boost the dissociation of exciton to generate a hot electron and hole should lead to enhanced photocatalytic activity. Herein, by using crystalline porous carbon nitride (CPCN) as a model, we demonstrate that grafting CPCN with electron accumulation capacity can efficiently facilitate the dissociation of exciton. Density functional theory (DFT) calculation shows that the introduced cyano group (CN) in CPCN can distort the structure of carbon nitride and result in an energy disordered interface, thus, the electron in exciton can be extracted by CN and then stabilized by K+. Benefited from this electron accumulation process, the exciton in CPCN is effectively dissociated and the formed hot electron and hole is rapidly transferred. Specifically, the average lifespan (τave) is reduced from 3.76 ns (bulk carbon nitride, BCN) to 2.65 ns (CPCN), while the surface charge transfer efficiency (ηt) is increased from 36.6% (BCN) to 50.8% (CPCN). As a result, the obtained CPCN displays excellent performance for photocatalytic molecular oxygen activation. This work sheds light on the development of advanced carbon nitride-based photocatalysts for contaminant degradation and energy conversion through excitonic engineering.