Enhancement of crystallinity of imine-linked covalent organic frameworks via aldehyde modulators

Organic additives known as modulators have been used to improve the crystallinity of covalent organic frameworks (COFs) and metal–organic frameworks (MOFs). Here, we demonstrate that benzaldehyde is an effective modulator for enhancing the crystallinity and porosity of imine-linked covalent organic frameworks (COFs). We varied the amount of benzaldehyde added during COF synthesis and found increased crystallinity and surface areas through powder X-ray diffraction (PXRD) and nitrogen gas adsorption measurements, respectively. The improved crystallinity and increased surface area were attributed to the reduced kinetics for COF nucleation and growth, which produced more ordered and crystalline COF materials. This work provides a simple, efficient and general way to improve the crystallinity and porosity of imine-linked COFs and furthers understanding of the role of modulators in the synthesis of COFs.