Porous covalent organic frameworks in photocatalytic ROS-mediated processes

Abstract

Porous carbon-based frameworks represent an emerging class of nanostructured materials with variable crystallinity. In this family, a large number of bonding configurations lead to the growth of either graphitic carbon nitride, amorphous covalent organic polymers, metal–organic frameworks or covalent organic frameworks. The latter nanostructures have attracted a great deal of attention owing to their porous crystalline character, originating from the linking of monomeric units by strong covalent bonds for the development of extended conjugated networks. The simultaneous existence of the conjugation and spatial separation of electron donor–acceptor moieties are critical factors for enhanced photocatalytic efficiency. In this review, we aim to summarize the diversity of covalent organic frameworks, highlighting their different synthetic protocols, most importantly, giving rise to various building blocks that interact with each other through diverse linkages, thereby forming novel architectures. Due to the aforementioned structural and semiconductive properties, porous covalent organic frameworks exhibit promising photocatalytic performance in the generation of reactive oxygen species. Our goal is to shed some light on critical factors leading to the enhanced generation of either transient intermediates or neutral oxygen-containing substances. We have directed our discussion to the spatial separation of electron donor–acceptor moieties within a carbon network and extracted some helpful data on the structure–activity relationship for hydrogen peroxide production. Furthermore, we have described recent progress in the development of efficient photocatalytic systems for organic substance degradation using ROS-mediated redox processes.