Reduced Form Of Polyaniline Research Articles

Role of Graphite Oxide (GO) and Polyaniline (PANI) in NO2 Reduction on GO-PANI Composites

Graphite oxide−polyaniline (GO-PANI) composites were obtained by mixing graphite oxide with a polyaniline salt. The extent of surface reduction of the GO and polyanline (emeraldine) was increased by calcination at 350 °C. The surface characterization was done using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, potentiometric titration, elemental analysis, and adsorption of nitrogen at its boiling point. The materials were exposed to NO2 to evaluate their activity for NO2 retention/reduction on the surface. On all samples with the reduced form of polyaniline (emeraldine), a high efficiency for NO2 reduction was observed. This efficiency was governed by the presence of PANI. Moreover, the presence of N-methylformamide solvent in the composite was determined to be an increasing factor for NO retention on the surface via its hydrogen bonding to the solvent that is interacting with the surface functional groups of graphite oxide. The calcination of GO-PANI at 350 °C reduced the GO surface, resulting in a physical mixture of graphite particles and reduced polyaniline (emeraldine). This happened because of the low thermal stability of compounds formed via the reactions of emeraldine with epoxy and carboxylic groups.

Kinetic Studies for the Electrocatalytic Reduction of Bis(2-mercapto-1,3,4-thiadiazoyl)-5,5‘-disulfide at a Poly(3,4-ethylenedioxythiophene) Film-Modified Electrode via Rotating-Disk Electrode Voltammetry

We have carried out a thorough study of the electron exchange reaction between 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), which dramatically accelerates the redox reactions of DMcT at room temperature. A qualitative analysis of the electron exchange reaction was carried out via UV/vis spectroelectrochemistry, while a quantitative study focused on the charge transfer from the reduced form of PEDOT, (PEDOT)red, to the DMcT dimer (diDMcT) using rotating-disk electrode (RDE) voltammetry. The kinetic model employed to estimate the charge-transfer rate was based on the analysis previously proposed by Savéant and co-workers (J. Electroanal. Chem. 1982, 131, 1), which takes into account charge propagation in a polymer film on an electrode surface and diffusion of a substrate through the polymer film. Thus, such an analysis is appropriate for the system investigated in this study, in which charge propagation occurs in a PEDOT film via self-exchange and diDMcT is incorporated and partitioned into the PEDOT film. Specifically, we found that the so-called “SR” model, in which the overall process of a system is controlled by the catalytic reaction and the diffusion of a substrate through a film, is the most appropriate one to describe the diDMcT/PEDOT system. This was based on the fact that diDMcT is incorporated and partitioned into the PEDOT film and not directly reduced at the glassy carbon electrode (GCE) surface (at potentials where PEDOT catalyzes the reactions) and that charge propagation through the PEDOT film is sufficiently rapid that the slope of the concentration profile of PEDOT is essentially zero over the film’s thickness under the conditions employed in this study. On the basis of such an analysis, the second-order rate constant for the charge-transfer reaction from (PEDOT)red to diDMcT was estimated as 32 M-1 s-1. This value is significantly larger than that previously obtained for the charge-transfer reaction from the reduced form of polyaniline (PAn) to diDMcT (0.03 M-1 s-1), indicating the high electrocatalytic activity of PEDOT toward the redox reactions of DMcT. Moreover, a comparison of the standard rate constants, k0, for the DMcT/diDMcT redox couple obtained at bare and PEDOT film-modified GCEs indicates that the redox reaction is accelerated by a factor of approximately 12 000 at the PEDOT film-coated GCE. These results demonstrate that the use of conducting polymers, such as PEDOT, as efficient electrocatalysts for the redox reactions of DMcT, is a promising strategy to utilize organosulfur compounds as energy-storage materials in lithium-ion rechargeable batteries.

Determination of Cr(VI) in Water with Amperometric Detection at Conductive Polymer Electrodes

Electrochemical sensors can provide sensitive detection for monitoring of contaminant leakage from storage areas, plume movement in ground and surface water, and residual contamination following cleanup using inexpensive, portable equipment. While hexavalent chromium, Cr(VI), exhibits slow electron transfer kinetics at most electrodes, it is catalytically reduced by the reduced form of polyaniline (PANI). In the present device, the reduction of PANI oxidized by Cr(VI) provides an analytical signal proportional to Cr(VI) concentration in aqueous samples, allowing amperometric detection of Cr(VI) with ppb detection limits. Calibration curves, limits of detection, S/N ratios, and effects of interferences on the sensor response in a flow injection analysis configuration are presented.

Filament-like structure formation in vacuum thermally evaporated thin films of polyaniline during oxidation in nitric acid

Oxidation of vacuum thermally evaporated thin films of polyaniline by aqueous nitric acid results in autocatalytic formation of filament-like heterogeneous dissipative structures in the oxidized areas due to non-equlibrium reactions between the reduced form of polyaniline and the oxidant.

Optical, structural and fluorescence microscopic studies on reduced form of polyaniline: The leucoemeraldine base

Electrochemically deposited thin films of emeraldine salt (ES) on indium-tin-oxide (ITO) glass plate and [111] silicon crystal were treated chemically with a phenyl hydrazine (PNH) solution in order to obtain a leucoemeraldine base (LB) form of polyaniline (PANI). The NMP-treated PANI films were washed using different organic solvents. ES, LB and air-oxidized LB films were examined using UV-visible, optical microscopy, X-ray diffraction and fluorescence microscopic techniques. The obtained results showed a direct correlation in the optical, structural and fluorescence behaviour of the LB form of PANI. An X-ray diffraction study revealed the partial crystallinity in the ES, whereas the LB and the air-oxidized LB showed amorphous structures. The first evidence of high fluorescence microscopic behaviour in the LB form of PANI has been observed. The gradual decrease in fluorescence signal as a function of time for the LB film has been interpreted as being due to the diffusion phenomenon in relation to the contact of the complex of the phenyl ring with O 2 molecules.

Electrochemical Oxidation of Polyaniline in Nonaqueous Electrolytes: "In Situ" Raman Spectroscopic Studies

Spectroelectrochemical behavior of polyaniline in nonaqueous electrolytes has been studied by Raman spectroscopy using two excitation lines : blue (457 nm) and infrared (1064 nm). It has been demonstrated that in the electrolytic solution consisting of tetrabutylammonium tetrafluoroborate/diphenyl phosphate/acetonitrile both oxidation processes (oxidation of leucoemeraldine to emeraldine and emeraldine to pernigraniline) can be investigated by Raman spectroscopy. The blue excitation line is very insensitive to the oxidation and protonation changes occurring during the first oxidation process and reveals only the reduced segments of polyaniline chains. However in the second oxidation process significant changes in the Raman spectra occur, consistent with the formation of pernigraniline units accompanied by deprotonation of the polymer. No Raman spectrum can be recorded for the most reduced form of polyaniline using the infrared excitation line. However gradual oxidation of the polymer results in the appearance of the Raman bands characteristic of the oxidized units which are strongly resonantly enhanced. The infrared line is extremely sensitive toward the existence of protonated segments and allows for direct monitoring of the deprotonation processes occurring during the second oxidation process (i.e. the oxidation of emeraldine to pernigraniline).