Porphyrin, graphene and polymers: smart combinations for selective nanofibrous chemosensors for gas and VOCs

Abstract

Polymer-carbon nanomaterials composites properties sound so attractive in various areas to have become a great challenge, too, in chemical sensors investigation. Here, a thin nanofibrous layer, composed of two insulating and eco-friendly thermoplastics (polystyrene-PS and polyhydroxibutyrate-PHB), a known percentage of nanofillers of mesoporous graphitized carbon (MGC) and a free-base tetraphenylporphyrin (H2TPP), has been deposited onto an interdigitated Micro-Electrode (IDE) by electrospinning technology and in a single step (Figure). The effects of the combination of a porphyrin with the composite system graphene-polymers appeared evident whenmnanofibrous layers, with- and without porphyrin, were compared about their morphology, electrical and sensing parameters. Both the resulting sensors wereconductive at room temperature and could work between 40 and 70-80 ◦C without an apparent degradation. Therefore porphyrindoped fibers appeared smoother and thinner (d: ≈175 nm) than porphyrin-free ones (d: ≈550 nm). The latter, indeed, looked extremely rough on the surface and decorated with brighter islands. However, both of them were more resistive at lower temperature, but became much more conductive when temperature rose to 60-70 °C. Porphyrin had a key role in adsorption and diffusion of chemicals, depending on its combination inside the composite fiber, since the response rates dramatically increased (toluene, acetic acid) with temperature. Conversely, the porphyrin-free sensor resulted highly sensitive and selective to acetic acid at 40◦C but the sensitivity fell down when the sensor operated at 80 ◦C. On the other hand, the same sensor increased its sensitivity only to NO2 when worked at 80°C, reporting a ~2 ppb limit of detection (LOD), thus confirming that temperature, as well as the free-base porphyrin, were two key players in driving the selectivity of the designed nanocomposite polymeric sensors.