Synthesis and Additive Manufacturing of Hydrazone‐Linked Covalent Organic Framework Aerogels

Covalent Organic Frameworks (COFs) are crystalline, porous organic materials. Recent studies have demonstrated novel processing strategies for COFs to form adaptable architectures, but these have focused primarily on imine‐linked COFs. This work presents a new synthesis and processing route to produce crystalline hydrazone‐linked COF gels and aerogels with hierarchical porosity. The method was implemented to produce a series of hydrazone‐linked COFs with different alkyl side‐chain substituents, achieving control of the hydrophilicity of the final aerogel. Variation in the length of the alkyl substituents yielded materials with controllable form factors that can preferentially adsorb water or nonpolar organic solvents. Additionally, a method for additive manufacturing of hydrazone‐linked COFs using hydroxymethylcellulose as a sacrificial additive is presented. This work demonstrates an effective and simple approach to the fabrication of hydrazone COF aerogels and additive manufacturing to produce hydrazone COFs of desired shape. Fast gelation and crystallization of hydrazone linked COFs enable processing into hierarchically porous aerogels with tunable solvent adsorption properties. Additionally, the fast reaction kinetics facilitate a reactive 3D printing technique with a sacrificial polymer binder to produce 3D printed structures of COF aerogel material.