Selective Discrimination among Benzene, Toluene, and Xylene: Probing Metalloporphyrin-Functionalized Single-Walled Carbon Nanotube-Based Field Effect Transistors

Single-walled carbon nanotubes have been noncovalently functionalized with metalloporphyrins. Iron tetraphenyl porphyrin and cobalt tetraphenyl porphyrin were independently employed to functionalize aligned nanotubes network that formed the channel material for chemical field effect transistor-based sensors. The primary aim of the study was to achieve discrimination among structurally similar aromatic hydrocarbons, benzene, toluene, and xylene, and derive possible role of the central metal ions present in the metalloporphyrins in defining sensor selectivity. Currentvoltage and field effect transistor measurements have confirmed formation of the efficient charge transfer complex during functionalization. The sensors were validated in respect to the analyte atmosphere within a concentration window of 500 ppb to 10 ppm. A clear affinity of the sensors toward toluene was recorded; however, the iron tetraphenyl porphyrin functionalized sensors exhibited a clear response (change in normalized resistance = 0.728) at lowest concentration validated, approximately 30% sensitivity (500 ppb to 10 ppm concentration) and excellent linearity (R-2 =0.94) with figures that are significantly better than cobalt tetraphenyl porphyrin-based devices. Observed behavior of the sensors have been rationalized in terms of vacant d orbitals of the central metal ions of metalloporphyrins and the side substituents present in the structure of the hydrocarbons validated.