Electrochemically Functionalized Single-Walled Carbon Nanotubes With Polypyrrole for the Detection of Sub-Part-per-Million Concentrations of Ammonia

Abstract

Here we report a facile method of functionalization of single-walled carbon nanotubes (SWNTs) with polypyrrole and making a chemiresistive sensor using the functionalized nanomaterial for sub-part-per-million detection of ammonia gas at room temperature. The sensor fabrication involves three steps: (i) immobilization of SWNTs by dip coating method on a silane-treated silicon/silicon dioxide substrate, (ii) printing of two parallel lines of conducting silver paste 5 mm apart as source and drain to define the source and the drain electrode, and (iii) in-situ electrochemical polymerization to functionalize the SWNTs with polypyrrole. The functionalization of SWNT was confirmed using electrochemical current-voltage measurements. The functionalized SWNTs exhibited several folds higher sensitivity to ammonia gas than the pristine SWNTs. A charge density of 0.85 C.cm−2 was optimum for electrochemical functionalization, providing maximum sensing response toward ammonia. The functionalized SWNTs showed a large measurable response starting from 50 to 750 part-per-billion (ppb) of ammonia with a sensitivity of ∼1.55% per ppb, and a limit of detection of 5 ppb of ammonia. Almost complete recovery of the sensor and an average response time of ∼9 min was also observed.