sp2 Carbon-Conjugated Covalent Organic Frameworks (sp2c-COFs): Synthesis and Application in Photocatalytic Water Splitting

Preparation of irreversible sp² carbon-conjugated covalent organic frameworks (sp²c-COFs) with specific porosity, easy structural functionalization, high chemical stability, and unique π-electron conjugation structure (especially the combination of π–π stacking interactions and conjugation system), can remove the barrier of electron transfer and provide a unique advantage for photocatalytic water splitting. Herein, based on three kinds of reactions (Aldol condensation reaction, Knoevenagel condensation reaction, and Horner-Wadsworth-Emmons reaction) and guided by the precise modulation of ligand structure and topology, this review summarizes the synthesis of sp²c-COFs and their applications in photoelectrocatalytic water splitting (hydrogen evolution and oxygen evolution reactions). Furthermore, challenges and possible research directions for sp²c-COFs in photocatalytic water splitting are also provided.