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.  In this work, we present a new synthesis and processing route to produce crystalline hydrazone-linked COF gels and aerogels with hierarchical porosity.  We implemented this method to produce a series of hydrazone-linked COFs with different alkyl side-chain substituents and demonstrate that we can control 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, we demonstrate a method for additive manufacturing of hydrazone-linked COFs using hydroxymethylcellulose as a sacrificial additive.  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.