A two-stage strategy of “Incubation and Driven growth” for synthesizing covalent organic frameworks with enhanced lateral growth and layer stacking at ambient condition

A two-stage strategy of “Incubation and Driven growth” was developed for synthesizing crystalline imine-linked covalent organic frameworks (COFs) at ambient condition. At the first stage, COF crystallites were incubated by slow nucleation and growth under the modulation of inhibitor. At the second stage, the water-soluble modulator and solvent were gradually removed by salt-water extraction, breaking the polycondensation reaction equilibrium to drive the growth and assembly of COF crystallites. With this strategy, six representative [3+3] and [3+2] COFs were successfully synthesized, indicating its universality. The crystallinity and porosity of the synthesized COFs are similar or better than those reported in literature. Notably, the COFs exhibited larger-sized morphologies with stronger lateral growth and vertical layer stacking compared with those synthesized by other 1-stage method. The effect of time-dependent, temperature and modulator on the crystallinity and morphology revealed the process of growth and assembly could be well controlled. The distinctive inner structures endowed the COFs exceptional iodine adsorption capability, better than those prepared by traditional solvothermal method and 1-stage method. This work also provides a concept and mechanistic basis for tuning the inner structure and morphology of COFs for specific application.