Room temperature amine sensors enabled by sidewall functionalization of single-walled carbon nanotubes

A new series of sidewall modified single-walled carbon nanotubes (SWCNTs) with perfluorophenyl molecules bearing carboxylic acid or methyl ester moieties are herein reported. Pristine and functionalized SWCNTs (p-SWCNTs and f-SWCNTs, respectively) were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM). The nitrene-based functionalization provided intact SWCNTs with methyl 4-azido-2,3,5,6-tetrafluorobenzoate (SWCNT-N-C₆F₄CO₂CH₃) and 4-azido-2,3,5,6-tetrafluorobenzoic acid (SWCNT-N-C₆F₄CO₂H) attached every 213 and 109 carbon atoms, respectively. Notably, SWCNT-N-C₆F₄CO₂H was sensitive in terms of the percentage of conductance variation from 5 to 40 ppm of ammonia (NH₃) and trimethylamine (TMA) with a two-fold higher variation of conductance compared to p-SWCNTs at 40 ppm. The sensors are highly sensitive to NH₃ and TMA as they showed very low responses (0.1%) toward 200 ppm of volatile organic compounds (VOCs) containing various functional groups representative of different classes of analytes such as benzene, tetrahydrofurane (THF), hexane, ethyl acetate (AcOEt), ethanol, acetonitrile (CH₃CN), acetone and chloroform (CHCl₃). Our system is a promising candidate for the realization of single-use chemiresistive sensors for the detection of threshold crossing by low concentrations of gaseous NH₃ and TMA at room temperature.