Covalent Organic Frameworks via In Situ Monomer Release for Humid CO <sub>2</sub> Uptake
Arnab Sadhukhan, Shanmuk Srinivas Ravuru, Agnibha Das, Ekta Nehra, Satyadip Paul, Golam Rosul Khan, Matthew A. Addicoat, Yusuke Nishiyama, Snehasis Daschakraborty, Arvind Rajendran, Rahul Banerjee
Abstract
Achieving high crystallinity and porosity in covalent organic frameworks (COFs) remains a major challenge, particularly for robust azine-linked systems, where limited bond reversibility hinders framework ordering. While several strategies have improved the crystallinity in imine-linked COFs, analogous advances in azine-linked frameworks are still lacking. Here, we present a kinetic modulation strategy based on the in situ slow release of hydrazine via the trifluoroacetic acid (TFA)-mediated hydrolysis of a tetrazine precursor during the COF synthesis. Using this approach, we successfully synthesized two crystalline azine-linked COFs incorporating either a nonplanar bicarbazole or a planar pyrene core. This method enhances structural order, as evidenced by narrowed full width at half-maximum (FWHM) values in PXRD and higher surface areas compared to the COFs prepared with direct hydrazine hydrate addition. Time-resolved UV–vis and PXRD analyses elucidate the role of reaction kinetics in framework evolution. Notably, the resulting COFs exhibit S-shaped water vapor adsorption isotherms with minimal uptake below 40% relative humidity (RH), reflecting their hydrophobic backbones. More importantly, CO 2 uptake remains largely unaffected at 40% RH, and dynamic breakthrough experiments confirm that H 2 O does not interfere with CO 2 adsorption under these conditions. This work establishes a generalizable route for crystallinity enhancement in kinetically trapped COFs and offers promising materials for gas separation under humid environments.