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

Abstract

With molecularly well-defined and tailorable two-dimensional structures, covalent organic frameworks (COFs) have emerged as leading material candidates for diverse applications including chemical sensing, storage, separation, and catalysis. In many of these contexts, the ability to directly and deterministically print COFs into arbitrary geometries would enable rapid optimization and deployment. However, previous attempts to print COFs have been restricted by low spatial resolution and/or post-deposition polymerization that complicates processing or limits the range of compatible COFs. Here, we overcome these limitations with a pre-synthesized, solution-processable colloidal ink that enables aerosol jet printing of COFs with micron-scale resolution. A key component of the ink formulation is the low-volatility solvent benzonitrile, which is critical to obtaining homogeneous printed COF film morphologies. The 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 the temperature sensing performance of the COFs. In particular, the printed COF-CNT nanocomposite films show high in-plane COF crystallinity and exhibit tunable electrical conductivity as a function of CNT loading, COF pore size, and temperature, 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 can accelerate the incorporation of COFs into technologically significant applications. This article is protected by copyright. All rights reserved.