Aerosol-Jet-Printable Covalent Organic Framework Colloidal Inks and Temperature-Sensitive Nanocomposite Films

With molecularly well-defined and tailorable 2D structures, covalent organic frameworks (COFs) have emerged as leading material candidates for chemical sensing, storage, separation, and catalysis. In these contexts, the ability to directly and deterministically print COFs into arbitrary geometries will enable rapid optimization and deployment. However, previous attempts to print COFs have been restricted by low spatial resolution and/or post-deposition polymerization that limits the range of compatible COFs. Here, these limitations are overcome with a pre-synthesized, solution-processable colloidal ink that enables aerosol jet printing of COFs with micron-scale resolution. The ink formulation utilizes the low-volatility solvent benzonitrile, which is critical to obtaining homogeneous printed COF film morphologies. This ink formulation is also compatible with other colloidal nanomaterials, thus facilitating the integration of COFs into printable nanocomposite films. As a proof-of-concept, boronate-ester COFs are integrated with carbon nanotubes (CNTs) to form printable COF-CNT nanocomposite films, in which the CNTs enhance charge transport and temperature sensing performance, ultimately resulting in high-sensitivity temperature sensors that show electrical conductivity variation by 4 orders of magnitude between room temperature and 300 °C. Overall, this work establishes a flexible platform for COF additive manufacturing that will accelerate the incorporation of COFs into technologically significant applications.