Pore-Wall Decorated Covalent Organic Frameworks for Selective Vapor Sensing

Covalent organic frameworks (COFs) are an attractive class of materials for sensing applications due to their inherent crystallinity, high surface area, and designable framework functionalities. While the majority of COFs have high electrical resistance, making it difficult to harness these materials for electronic sensors, real-time impedance spectroscopy can enable gas and vapor sensing of a much wider range of COFs. Herein, a set of post-synthetically modified (PSM) COFs are explored though a straightforward one-step substitution reaction by reacting phenol moieties on the pore wall, with alkyl bromides, to embed alkyl, aryl, or alcohol groups into the framework. This modular approach provides access to improved sensor properties toward the detection of volatile organics, acids, and potentially harmful gases. Sensor results indicate that post-synthetically modified COFs offer better sensitivity toward NO2 and acetic acid, with the aryl functionalized COF having an NO2 detection limit of 10 ppm. Furthermore, modified COFs also show higher selectivity toward isopropanol and toluene. This work highlights the importance of methods that facilitate post-synthetic modification of COFs so that functional groups and COF properties can be tuned. A series of covalent organic frameworks (COFs) derivatives are synthesized by the straightforward post-synthetic modification of a phenolic COF and studied as electronic sensors for harmful gases and volatile organic compounds using real-time impedance spectroscopy. This creative approach is leveraged to explore structure-property correlations and obtain COF-based gas sensor measurements of capacitance and resistance simultaneously. image