Self-Controlled Growth of Covalent Organic Frameworks by Repolymerization

The growth of covalent organic frameworks (COFs) normally goes through a fast polymerization process, which quickly forms amorphous powder and then slowly crystallizes to obtain nanometer-sized crystals. Until now, it is still a challenge to modulate the growth process of COFs, which hampers the controllable synthesis for practical applications. Here, we develop a repolymerization strategy which realizes the self-controlled growth of COFs for the first time. COFs powder is used as starting material that can slowly decompose and release monomers and oligomers. At a self-established equilibrium state of reversible polymerization-decomposition-repolymerization reactions, the monomers and oligomers controllably repolymerize to form a thin crystalline COF film on substrates. The resulting COF film can be directly used as the sensing interface of graphene transistor sensors, which detect NH3 down to 100 ppt, showing the great potential of this strategy in future applications.