Mechanistic Insights into the Formation of Nanofibrous Covalent Organic Frameworks (COFs) and their Promotion to the Catalysis of Hydrodechlorination

Abstract

The nanoscale morphologies of COFs deeply affect their performance in practical applications. However, it still lacks studies to well understand their formation mechanism for guiding and controlling the synthesis for desired nanomorphology. To achieve more mechanistic insights into the formation of nanofibrous COFs, herein a series of nanofibrous and non-fibrous COFs are synthesized and the intrinsic relationships among the morphology, chemical constituent, structure planarity, and the DFT calculated interlayer stacking energy are investigated comprehensively. The study reveals the planarity of building monomers is not decisive for forming the nanofibrous COFs. The presence of electron-withdrawing triazine group in amine monomers and the electron-donating ─OH group in aldehyde monomers are essential for suppressing the growth of COF crystallites in x-y plane and promoting the stacking in z-direction to form nanofibrous COFs. The COF morphology can be modulated by the functional groups in monomers by regulating the competition between lateral reaction activity and interlayer stacking energy. The prepared nanofibrous COFs exhibited two-fold increased catalytic activity and better stability than the non-fibrous counterpart in hydrodechlorination. The new insights and proposed mechanism here can help open up a domain for precise designing and modulating the COF nanomorphology from molecular level for specific application.