Single-Walled Carbon Nanotube–Poly(porphyrin) Hybrid for Volatile Organic Compounds Detection

Porphyrins due to their unique and interesting physicochemical properties have been widely investigated as functional materials for chemical sensor fabrication. However, their poor conductivity is a major limitation toward the realization of porphyrin-based field-effect transistor/chemiresistor sensor. The issue of conductivity can be overcome by exploiting the excellent electrical property of single-walled carbon nanotubes (SWNTs) to make a SWNTs-based hybrid device in which SWNTs would act as a transducer and porphyrin as a sensory layer. The present attempt was to fabricate a SWNTs–poly­(tetraphenylporphyrin) hybrid through electrochemical route and to evaluate its potential as a low-power chemiresistor sensor for sensing acetone vapor as a model for volatile organic compounds. Functionalization of SWNTs with porphyrin polymer by the electrochemical method resulted in a fuller coverage of SWNTs surface compared to a partial coverage by adsorption and thereby higher sensitivity. SWNTs were coated with poly­(tetraphenylporphyrin) of different thickness by applying different charge density to optimize sensing performance. Differences in sensing performance were noticed for hybrids fabricated at varying charge densities, and the optimum sensing response was found at 19.65 mC/cm². The hybrid exhibited a wide dynamic range for acetone vapor sensing from 50 to ∼230 000 ppm with a limit of detection of 9 ppm. The field-effect transistor studies showed a negative threshold voltage shift and almost constant transconductance when exposed to air/analyte, indicating electrostatic gating dominated sensing mechanism. Further, the results confirmed a good stability of the device over a period of 180 days. The long-term device stability along with the sensing capability at low analyte concentration with a wide dynamic range and easily scalable fabrication technique signify the potential of SWNT–poly­(porphyrin) hybrid for volatile organic compound sensing applications