Catechol as a new electron hot spot of carbon nitride

Abstract

Graphitic carbon nitride (CNx) is a promising photocatalyst with visible-light sensitivity, attractive band-edge positions, tunable electronic structure, and eco-friendliness. However, their applications are limited by a low catalytic activity due to inefficient charge separation and insufficient visible-light absorption. Here we show a new method to generate the electron polarization of CNx toward the edge via the chemical conjugation of catechol to CNx for enhanced photochemical activity. The electron-attracting property of catechol/quinone pairs induces the accumulation of photo-excited electrons at the edge of conjugated catechol-CNx hybrid nanostructure (Cat-CNx), serving as an electron hot spot. The accumulation is demonstrated by positive open-circuit photovoltage and increases electron transfer through the conjugated catechol while suppressing charge recombination in the CNx. The catechol conjugation also widens the photoactive spectrum via the larger range delocalization of π-electrons. Accordingly, Cat-CNx reveals a 6.3 times higher reductive photocurrent density than CNx. Gold ion reduction dramatically increased due to the enhanced electron transfer activity of Cat-CNx in cooperation with the inherent hydrophilicity and metal chelating property of catechols. Cat-CNx exhibits a 4.3 times higher maximum adsorption capacity for gold ions under simulated sun light illumination compared to CNx. This work suggests that the post-modification of CNx’s π-conjugated system is a promising route to handle varied shortcomings and broaden availability of CNx.