Dual‐Hydrogen Bond Donor‐Functionalized Carbon Nanotube Fibers: Enhancing Anion‐Sensing Performance Through Functionalization Approaches

Abstract In this study, chemiresistive anion sensors are developed using carbon nanotube fibers (CNTFs) functionalized with squaramide‐based dual‐hydrogen bond donors (SQ1 and SQ2) and systematically compared the sensing properties attained by two different functionalization methods. Model structures of the selectors are synthesized based on a squaramide motif incorporating an electron‐withdrawing group. Anion‐binding studies of SQ1 and SQ2 are conducted using UV–vis titrations to elucidate the anion‐binding properties of the selectors. These studies revealed that the chemical interaction with acetate (AcO⁻) induced the deprotonation of both SQ1 and SQ2. Selectors are functionalized onto the CNTFs using either covalent or non‐covalent functionalization. For covalent functionalization, SQ1 is chemically formed on the surface of the CNTFs, whereas SQ2 is non‐covalently functionalized to the surface of the CNTFs assisted by poly(4‐vinylpyridine). The results showed that non‐covalently functionalized CNTFs exhibited a 3.6‐fold higher sensor response toward 33.33 mm AcO⁻ than covalently functionalized CNTFs. The selector library is expanded using diverse selectors, such as TU‐ and CA‐based selectors, which are non‐covalently functionalized on CNTFs and presented selective AcO⁻‐sensing properties. To demonstrate on‐site and real‐time anion detection, anion sensors are integrated into a sensor module that transferred the sensor resistance to a smartphone via wireless communication.