Synthesis, Engineering, and Characterization of Covalent Organic Framework-Based Composite Aerogels

Covalent organic frameworks (COFs) are a recently discovered class of nanoporous polymeric materials with ultra-high specific surface areas, which makes them highly attractive for applications in nanofiltration, gas capture and storage, and catalysis. However, the macroscopic morphology of COFs is maintained by relatively weak physical interactions between crystallites, which limits the applications of COFs where they may experience significant physical stresses. Herein, fillers are added to three-dimensional TAPB-PDA COF aerogels synthesized to improve the mechanical strength and functionality through the formation of a composite material by physically implanting the fillers in the macropores present in the gel network. Boron nitride loading is shown to double the Young’s modulus of the aerogel, from 11 kPa to 22 kPa, at 20 relative weight percent loading, while only causing a 10% decrease in accessible nanoporous surface area, normalized to the mass of COF in the sample. Poly(acrylic acid) added at 5 relative weight percent loading and crosslinked increases the Young’s modulus to 21 kPa and simultaneously increases the elastic limit of the aerogel from 10% to 65% strain, while inducing a 38% decrease in accessible nanoporous surface area, normalized to the mass of COF in the sample. This work demonstrates the potential for macroscopic composites with COFs forming the majority phase of the material, showing the possibility for mechanical reinforcement without significant hinderance of the adsorbent functionality of the material.