Ammonia gas sensor based on electrosynthesized polypyrrole films.

Inkjet-printed films of the conductive polymer polypyrrole have been used for vapour sensing at room temperature. The electrical properties, sensitivity, reproducibility and stability of the polymer chemiresistors are reported. A significant increase in conductivity was observed on the exposure of the films to the vapours of simple alcohols. The value of the fractional resistance change, Δ R / R , of the films increased linearly with increasing concentrations of both ethanol and methanol. A relatively high Δ R / R value, approximately 90%, was obtained on exposure to 5000 parts per million of methanol. The response time of the inkjet-printed sensors to polar vapours was generally shorter than that for non-polar compounds. It is suggested that the increase in conductivity may be related to a vapour-induced change in the transfer of charge carriers between the polymer chains.

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Inkjet-printed polypyrrole thin films for vapour sensing

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the UB3LYP/6-31G(d) level have been performed to investigate the tunable nature, i.e., doping and dedoping processes, of polypyrrole (PPy). The calculated theoretical data show strong correlation with the recent experimental reports, which validates our computational protocol. The calculated properties are extrapolated to the polymer (PPy) through a second-order polynomial fit. Changes in band gap, conductivity, and resistance of nPy and nPy-X (where n = 1–9 and X = +, NH3, and Cl) were studied and correlated with the calculated vibrational spectra (IR) and electronic properties. Upon doping, bridging bond distance and internal bond angles decrease (decrease in resistance over polymer backbone), whereas dedoping results in increases in these geometric parameters. In the vibrational spectrum, doping is characterized by an increase in the band peaks in the fingerprint region and/or red shifting of the spectral bands. Dedoping (9...

Doping and Dedoping Processes of Polypyrrole: DFT Study with Hybrid Functionals

A nano-composite core–shell Ag@SnO 2 material was synthesized by chemical reduction and characterized by temperature-programmed reduction (TPR), UV–visible reflective spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDS). SnO 2 , Ag/SnO 2 and Ag@SnO 2 were used to sense ethanol (C 2 H 5 OH) in an ethanol gas detection system. The SnO 2 material under 200 ppm ethanol gas exhibited a sensor response ( S  =  R air / R ethanol  = (resistance of sensor signal of air)/(resistance of sensor signal of ethanol gas)), response time ( t 90 ) and recovery time ( t R90 ) were 1.54, 54 s and 85 s, respectively. Ag@SnO 2 materials had an improved sensor response of 2.24, with a shortened response time ( t 90 ) and recovery time ( t R90 ) of 34 s and 68 s, respectively. The bond strength between ethanol gas and the Ag@SnO 2 on which was adsorbed, determined by van der Waal's forces, and was calculated for a case in which more than 20 molecules were adsorbed. The mechanism of the sensing of ethanol gas, based on its adsorption, its reaction on the surface and its desorption is presented.

Ag@SnO2 core–shell material for use in fast-response ethanol sensor at room operating temperature

A series of polypyrrole (PPy)/titanium dioxide (TiO2) nanocomposites were prepared in different polymerization conditions by ‘in situ’ chemical oxidative polymerization. The nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectra (XPS), and UV–Vis diffuse reflectance spectra. The photocatalytic degradation of methyl orange (MO) was chosen as a model reaction to evaluate the photocatalytic activities of TiO2/PPy catalysts. The results show that a strong interaction exists at the interface between TiO2 and PPy, the deposition of PPy on TiO2 nanoparticles can alleviate their agglomeration, PPy/TiO2 nanocomposites show stronger absorbance than neat TiO2 under the whole range of visible light. The obtained PPy/TiO2 nanocomposites exhibit significantly higher photocatalytic activity than the neat TiO2 on the degradation of MO aqueous solution under visible and UV light illumination. The reasons for improving the photocatalytic activity were also discussed.

Photocatalytic activity of polypyrrole/TiO2 nanocomposites under visible and UV light

We discuss the use of polymeric blends formed by the controlled growth of doped polypyrrole chains in the interior of films of different dielectric polymers as sensors of the presence of representative examples of volatile organic compounds. The dielectric films (of either (poly(caprolactone), poly(ethylene oxide), poly(methyl-methacrylate), poly(vinyl alcohol), or poly(vinyl-acetate)) containing an appropriate oxidizing agent were prepared atop a conducting glass substrate and the polymerization of polypyrrole was induced through the vapor phase technique, after exposure of the desired matrix to pyrrole vapor. The UV–vis–NIR spectra of the films were used to monitor the increase of their conductive character through the assessment of the intensity of the polaron band characteristic of the doped form of polypyrrole. The change of conductivity upon exposure to the volatile compounds used (methanol, ethanol, carbon tetrachloride and benzene) was adopted as a measure of the corresponding sensitiveness of the films. Differently to the previous case in which doped films of polypyrrole were examined as sensors (when a similar low level of response was found towards apolar compounds), now we have found that some of the blends (PMMA/PPY and PVA/PPY, in special) exhibit a particular sensitiveness to the polarity of the molecule of the vapor tested. We therefore suggest that the simultaneous use of such polypyrrole blends in an arrangement pattern can improve the efficiency of electronic nose devices.

L.F.B. de Lira

Papers

Use of conducting polypyrrole blends as gas sensors