Catechol Quinone as an Electron-Shuttling Spot Conjugated to Graphitic Carbon Nitride for Enhancing Photocatalytic Reduction

Abstract

Carbon nitride (CN) has emerged as a promising photocatalyst, recognized for its visible-light sensitivity, high conduction band-edge position, tunable electronic configuration, and environmental friendliness. Despite these attributes, the practical application of CN is hindered by challenges such as inefficient charge carrier separation, a narrow light absorption range, and inherent n-type characteristics due to nonstoichiometry. Here, we introduce a new postsynthetic functionalization strategy that modifies CN with catechol quinone (CQ) to substantially improve its photocatalytic performance through light-induced electron polarization and extended light absorption. The key mechanism involves promoted spatial charge separation at the CN-CQ interface, leveraging the light-triggered oscillation of CQ between its electron donor and acceptor states, corroborated by density functional theory calculations. Moreover, CN-CQ conjugation broadens the photoactive range of CN across the full spectrum of visible light due to lower-energy electronic excitations arising from the midgap states introduced by CQ. Under sunlight illumination, the CN-CQ conjugation increased the photocatalytic activities of CN 2-fold for photochemical gold ion reduction and hydrogen evolution. Our findings suggest that postsynthetic functionalization with a redox-active moiety is a promising strategy for enhancing the photocatalytic activity of CN.