Ammonium Peroxydisulfate In Aqueous Solution Research Articles

Synthesis and characterization of polyaniline–camphorsulphonic acid nanotube film

Polyaniline (PANI) nanotubes were prepared in the bulk solution and as films using the aniline oxidation with ammonium peroxydisulfate in aqueous solutions of camphorsulfonic acid (CSA). The in situ PANI films produced during the oxidation of aniline in CSA and also in hydrochloric acid solutions were followed by monitoring the frequency changes of quartz crystal microbalance (QCM). The kinetics of the film formation were discussed. The scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) showed PANI nanotubes. In addition, nanorods and nanoflowers composed from nanofibers and nanoflakes are also present to some extent. The nanotubes were characterized using UV–Vis spectroscopy.

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water – FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.

The chemical oxidative polymerization of aniline in water: Raman spectroscopy

AbstractThe structural changes of aniline oligomers and polyaniline, associated with oxidation of aniline with ammonium peroxydisulfate in aqueous solutions without any added acid, were studied. The reaction was quenched at various times and the films deposited on silicon windows have been studied in detail by Raman spectroscopy, at excitation wavelengths 633 and 514 nm. The presence of substituted phenazine structural units, in addition to ordinary benzenoid, quinonoid, and semiquinonoid structures, has been proved by the appearance of characteristic Raman bands at 1645–1630, 1420–1400, 1380–1365, ∼575, and ∼415 cm−1. The remarkable differences of the Raman spectra of oligoanilines, precipitated in the first phase of oxidative polymerization, and polyaniline nanotubes and nanorods, formed in the second stage of reaction, are discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Synthesis of nanostructured conducting polyaniline in the presence of 5-sulfosalicylic acid

Oxidative polymerizations of aniline with ammonium peroxydisulfate in aqueous solution of 5-sulfosalicylic acid (SSA), were performed at the constant molar ratio [oxidant]/[monomer] = 1.25, by using various initial molar ratios of SSA to aniline. It was shown that the ratio [SSA]/[aniline] has a crucial influence on the molecular structure, morphology, and conductivity of synthesized polyaniline5-sulfosalicylate (PANI-SSA), as well as on the yield and temperature profile i.e. the mechanism of polymerization process. The yield of PANI-SSA was 80 - 86% for [SSA]/[aniline] ratios in the range 0.25-1.0. Granular PANI-SSA was obtained by the oxidative polymerization of in situ formed anilinium 5-sulfosalicylate ([SSA]/[aniline] = 1.0). The initial induction period was followed by the rapid exothermic polymerization of aniline during the oxidation of anilinium 5-sulfosalicylate with peroxydisulfate. Nanostructured PANI-SSA was synthesized by the oxidation of the mixture of dianilinium 5-sulfosalicylate and aniline ([SSA]/[aniline] = 0.25), which proceeds in two exothermic phases well separated with an athermal period. The presence of nanocylinders (nanorods, possibly nanotubes), with the average diameter of 95-250 nm and the length of 0.5-1.0 ?m has been revealed by scanning electron microscopy. It was concluded that PANI nanocylinders are formed when reaction solution has the initial pH > 3.5. Electroconductivity of synthesized polyanilines was in the range 0.01-0.17 S cm-1, and it increases with increasing molar ratio of SSA to aniline. Molecular structure of synthesized polyanilines was investigated by FTIR spectroscopy. Besides the characteristic bands of standard PANI in emeraldine form (benzenoid, quinonoid, and semiquinonoid units), the band attributable to substituted phenazine structural units was observed at -1415 cm-1 in the FTIR spectrum of nanostructured PANI-SSA sample.

Polyaniline and polypyrrole: A comparative study of the preparation

Aniline and pyrrole have been oxidized with ammonium peroxydisulfate in aqueous solutions, in the presence of equimolar quantities of hydrochloric acid. The oxidation of pyrrole was faster; the induction period typical of aniline oxidation was absent in the case of pyrrole. As the proportion of oxidant-to-monomer molar concentration increased up to 1.5, the yield increased in both cases. Similarities between the two oxidations are illustrated and discussed. The oxidant-to-monomer molar ratio 1.25 is proposed to be the optimum stoichiometry, in the accordance with the data published in the literature. The conductivities of the polymers prepared were only slightly dependent on the oxidant-to-monomer ratio in the range 0.3–1.5, and were of the order of 10 0 S cm −1 for polyaniline and ∼10 −2–10 −1 S cm −1 for polypyrrole. Outside this interval, the conductivity of both polymers was reduced. Polyaniline having conductivity ∼10 S cm −1 was produced in solutions of phosphoric acid of various concentrations. On the contrary, the conductivity of polypyrrole was reduced as the concentration of phosphoric acid became higher. The type of protonation is discussed with the help of FTIR spectra by analyzing the ammonium salts obtained after deprotonation. Sulfate or hydrogen sulfate anions produced from peroxydisulfate always constitute a part of the counter-ions.

Evolution of Polyaniline Nanotubes: The Oxidation of Aniline in Water

The course of aniline oxidation with ammonium peroxydisulfate in aqueous solutions has been investigated. The reaction was terminated at various times and the intermediates collected. Besides the precipitates, the films deposited in situ on silicon windows have also been studied. The kinetic course of polymerization is controlled by the acidity level, which changes during the polymerization from pH 8 to a final value close to pH 1. It has two distinct exothermic phases. Gel-permeation chromatography indicates that aniline oligomers are produced at first at high pH, while polyaniline follows after the pH becomes sufficiently low. The growth of polyaniline nanotubes was observed by optical microscopy and confirmed by electron microscopy. The molecular structure of the reaction intermediates was studied in detail by FTIR spectroscopy. Oxidation products are markedly sulfonated, and they contain phenazine units. Aniline oligomers are more soluble in chloroform than the polymer fraction, which contains nanotubes.

Polyaniline nanotubes: conditions of formation

AbstractThe courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm−1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry