Solvent-Free Synthesis of Covalent Organic Frameworks: Achievements and Challenges.

Abstract

Covalent organic frameworks (COFs) represent a powerful class of ordered porous materials, yet conventional solvothermal synthetic routes often hinder their practical implementation. Solvent-free strategies have emerged as attractive alternatives, not only for reducing the use of conventional solvents but also for creating distinct reaction environments for framework formation, crystallization, and materials processing. Mechanochemical activation, ionothermal media, melt- or flux-assisted polymerization, and vapor-assisted interfaces provide different modes of molecular transport and reaction regulation, thereby influencing bond formation, nucleation, crystal growth, and morphology evolution. This minireview summarizes recent advances in these strategies, with particular attention to their reaction characteristics, structural scope, and applicability to different COF systems. Selected approaches further enable the integration of framework construction with direct shaping into films, membranes, monoliths, foams, and platelets, as well as gram- to kilogram-scale production. Finally, we outline remaining challenges in crystallization pathways, structural integrity, and reproducible scale-up to guide the future industrial translation of COF technologies.