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.

Keywords:

• Ammonia
• electrochemistry
• polypyrrole
• single-walled carbon nanotubes (SWCNTs)

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Tapan Sarkar acknowledges financial assistance from the Scientific and Engineering Research Board (SERB) through grant EEQ/2018/000715.