Tuning of Morphological and Antibacterial Properties of Poly(3,4-ethylenedioxythiophene):Peroxodisulfate by Methyl Violet.

This study demonstrates a one-step synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) in the presence of the methyl violet (MV) dye. The structural properties of PEDOT:peroxodisulfate were studied using Raman and MALDI-TOF spectroscopies. The use of the MV dye in the polymerization process resulted in a change in the typical irregular morphology of PEDOT:peroxodisulfate, leading to the formation of spherical patterns. SEM and TEM analyses revealed that increasing the dye concentration can produce larger spherical aggregates probably due to the hydrophobic and π-π interactions. These larger aggregates hindered the charge transport and reduced the electrical conductivity. Interestingly, at higher dye concentrations (0.05 and 0.075 M), the PEDOT:peroxodisulfate/MV films exhibited significantly improved antibacterial activity against Staphylococcus aureus and Escherichia coli. Furthermore, the PEDOT:peroxodisulfate films with the incorporated MV dye exhibited a well-defined and repeatable redox behavior. The remarkable amalgamation of their optical, electrochemical and antibacterial properties provides the PEDOT:peroxodisulfate/MV materials with an immensely diverse spectrum of applications, including in optical sensors and medical devices.

Polypyrrole Aerogels: Efficient Adsorbents of Cr(VI) Ions from Aqueous Solutions.

Three-dimensional and porous polypyrrole (PPy) aerogels were prepared using a facile two-step procedure in which cryogels were synthesized via the cryopolymerization of pyrrole with iron (III) chloride in the presence of supporting water-soluble polymers (poly(N-vinylpyrrolidone), poly(vinyl alcohol), gelatin, methylcellulose or hydroxypropylcellulose), followed by freeze-drying to obtain aerogels. The choice of supporting polymers was found to affect the morphology, porosity, electrical conductivity, and mechanical properties of PPy aerogels. PPy aerogels were successfully used as adsorbents to remove toxic Cr(VI) ions from aqueous solutions.

Effect of a Zr-Based Metal-Organic Framework Structure on the Properties of Its Composite with Polyaniline.

Composites of polyaniline (PANI) and Zr-based metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were synthesized by the oxidative polymerization of aniline in the presence of MOF templates with the MOF content in the resulting materials (78.2 and 86.7 wt %, respectively) close to the theoretical value (91.5 wt %). Scanning electron microscopy and transmission electron microscopy showed that the morphology of the composites was set by the morphology of the MOFs, whose structure was mostly preserved after the synthesis, based on the X-ray diffraction data. Vibrational and NMR spectroscopies pointed out that MOFs participate in the protonation of PANI and conducting polymer chains were grafted to amino groups of UiO-66-NH2. Unlike PANI-UiO-66, cyclic voltammograms of PANI-UiO-66-NH2 showed a well-resolved redox peak at around ≈0 V, pointing at the pseudocapacitive behavior. The gravimetric capacitance of PANI-UiO-66-NH2, normalized per mass of the active material, was also found to be higher compared to that of pristine PANI (79.8 and 50.5 F g-1, respectively, at 5 mV s-1). The introduction of MOFs into the composites with PANI significantly improved the cycling stability of the materials over 1000 cycles compared to the pristine conducting polymer, with the residual gravimetric capacitance being ≥100 and 77%, respectively. Thus, the electrochemical performance of the prepared PANI-MOF composites makes them attractive materials for application in energy storage.

Synthesis and Impedance Spectroscopy of Poly(p-phenylenediamine)/Montmorillonite Composites.

Poly(p-phenylenediamine)/montmorillonite (PPDA/MMT) composites were prepared by the oxidative polymerization of monomers intercalated within the MMT gallery, using ammonium peroxydisulfate as an oxidant. The intercalation process was evidenced by X-ray powder diffraction. The FT-IR and Raman spectroscopies revealed that, depending on the initial ratio between monomers and MMT in the polymerization mixture, the polymer or mainly oligomers are created during polymerization. The DC conductivity of composites was found to be higher than the conductivity of pristine polymer, reaching the highest value of 10-6 S cm-1 for the optimal MMT amount used during polymerization. Impedance spectroscopy was performed over wide frequency and temperature ranges to study the charge transport mechanism. The data analyzed in the framework of conductivity formalism suggest different conduction mechanisms for high and low temperature regions.

Effect of PAMAM Dendrimers on Interactions and Transport of LiTFSI and NaTFSI in Propylene Carbonate-Based Electrolytes.

Poly(amidoamine) (PAMAM)-based electrolytes are prepared by dissolving the PAMAM half-generations G1.5 or G2.5 in propylene carbonate (PC), either with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salts. The solutions, designed for ion battery applications, are studied in terms of ions transport properties. Raman Spectroscopy reveals information about the interactions between cations and PAMAM dendrimers as well as full dissociation of the salts in all solutions. Pulsed-field gradient Nuclear Magnetic Resonance (PFG NMR), measured as a function of both temperature and PAMAM concentration, are obtained for the cation, anion, solvent, and dendrimer molecules using lithium (7Li), sodium (23Na), fluorine (19F), and hydrogen (1H) NMR, respectively. It was found that lithium diffusion is slow compared to the larger TFSI anion and decreases with PAMAM concentration due to interactions between cation and dendrimer. Comparison of conductivities calculated from diffusion coefficients using the Nernst-Einstein equation, with conductivity measurements obtained from Impedance Spectroscopy (IS), shows slightly higher IS conductivities, caused among others by PAMAM conductivity.

Role of p-Benzoquinone in the Synthesis of a Conducting Polymer, Polyaniline.

Polyaniline (PANI) and 2,5-dianilino-p-benzoquinone both are formed by oxidation of aniline in an acidic aqueous environment. The aim of this study is to understand the impact of addition of p-benzoquinone on the structure of PANI prepared by the oxidation of aniline hydrochloride with ammonium peroxydisulfate and to elucidate the formation of low-molecular-weight byproducts. An increasing yield and size-exclusion chromatography, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy, and nuclear magnetic resonance analyses of the products show that p-benzoquinone does not act as a terminating agent in the synthesis of PANI and the content of 2,5-dianilino-p-benzoquinone increases with the increasing molar concentration of p-benzoquinone in the reaction mixture, [BzQ]. Regarding the structure of PANI, Raman and UV-visible spectra show that the doping level and the charge delocalization both decrease with the increase of [BzQ], and the FTIR spectra of the PANI bases indicate an increased concentration of benzenoid units at higher [BzQ]. We explain these observations by an increasing concentration of structural defects in PANI chains and propose a 2,5-dianilino-p-benzoquinone-like structure of these defects present as pendant groups. The bands typical of 2,5-dianilino-p-benzoquinone-like moiety are observed even in the vibrational spectra of the sample prepared without addition of p-benzoquinone. This confirms in situ oxidation of aniline to p-benzoquinone within the course of the oxidation of aniline hydrochloride to PANI.

Tailoring of carbonized polypyrrole nanotubes core by different polypyrrole shells for oxygen reduction reaction selectivity modification.

By using methyl orange template, polypyrrole nanotubes were obtained by the oxidative polymerization of pyrrole. The nanotubes were carbonized in inert atmosphere to nitrogen-enriched carbon nanotubes. These were subsequently coated with 20 wt% of polypyrrole prepared in the absence or the presence of anionic dyes (methyl orange or Acid Blue 25). The morphology of all the samples was examined by the electron microscopies, FTIR and Raman spectroscopies. Moreover, X-ray photoelectron spectroscopy and elemental analysis were used to prove the chemical structure and the successful coating process. Electron paramagnetic resonance analysis was used to calculate the spin concentrations. Significant impact of coating method is evidenced with neat polypyrrole coating providing a two-fold capacitance increase compared to uncoated nanotubes, while coating in the presence of Acid Blue 25 decreasing it slightly. With respect to oxygen reduction reaction, coatings irreversibly transformed in the first few cycles in the presence of the products of O2 reduction, presumably hydrogen peroxide, altering the oxygen reduction mechanism. This transformation allows the tailoring of the polymeric shell, over ORR active carbonaceous core, and tuning of the catalyst selectivity and optimization of materials performance for a given application - from alkaline fuel cells to hydrogen peroxide generation.

Polypyrrole Nanotubes and Their Carbonized Analogs: Synthesis, Characterization, Gas Sensing Properties.

Polypyrrole (PPy) in globular form and as nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the absence and presence of methyl orange, respectively. They were subsequently converted to nitrogen-containing carbons at 650 °C in an inert atmosphere. The course of carbonization was followed by thermogravimetric analysis and the accompanying changes in molecular structure by Fourier Transform Infrared and Raman spectroscopies. Both the original and carbonized materials have been tested in sensing of polar and non-polar organic vapors. The resistivity of sensing element using globular PPy was too high and only nanotubular PPy could be used. The sensitivity of the PPy nanotubes to ethanol vapors was nearly on the same level as that of their carbonized analogs (i.e., ~18% and 24%, respectively). Surprisingly, there was a high sensitivity of PPy nanotubes to the n-heptane vapors (~110%), while that of their carbonized analog remained at ~20%. The recovery process was significantly faster for carbonized PPy nanotubes (in order of seconds) compared with 10 s of seconds for original nanotubes, respectively, due to higher specific surface area after carbonization.

Spectroscopic study of the highly homogeneous polyaniline film formation on gold support.

The oxidation of aniline with ammonium peroxydisulfate in the aqueous solution of acetic acid has two subsequent phases: the oxidation of the neutral aniline molecules at low acidity, which was followed by the oxidation of the anilinium cations after the acidity became higher. The final polyaniline film deposited on immersed surfaces is usually contaminated with semi-crystalline oligomers which precipitated during induction period from the reaction medium. To obtain a homogeneous film, which is important in the fabrication of many molecular electronic devices, we have studied the course of aniline oxidation in a view of new experimental evidence. In the unique series of experiments, the silicon or gold supports have been immersed in the reaction mixture at crucial stages of oxidation reaction, and the deposits at the end of the reaction were analyzed. The growth of a highly homogenous film on the gold-coated glass substrate immersed in the reaction mixture at the end of the polymerization period has been observed. The molecular structure of the products was monitored with UV-visible, infrared, and Raman spectroscopies. The possible mechanism of the film formation and the molecular mechanism of the surface interaction of chemisorbed aniline oligomers with gold support are proposed.

Detection of aniline oligomers on polyaniline-gold interface using resonance Raman scattering.

In situ deposited conducting polyaniline films prepared by the oxidation of aniline with ammonium peroxydisulfate in aqueous media of various acidities on gold and silicon supports were characterized by Raman spectroscopy. Enhanced Raman bands were found in the spectra of polyaniline films produced in the solutions of weak acids or in water on gold surface. These bands were weak for the films prepared in solutions of a strong acid on a gold support. The same bands are present in the Raman spectra of the reaction intermediates deposited during aniline oxidation in water or aqueous solutions of weak or strong acids on silicon removed from the reaction mixture at the beginning of the reaction. Such films are formed by aniline oligomers adsorbed on the surface. They were detected on the polyaniline-gold interface using resonance Raman scattering on the final films deposited on gold. The surface resonance Raman spectroscopy of the monolayer of oligomers found in the bulk polyaniline film makes this method advantageous in surface science, with many applications in electrochemistry, catalysis, and biophysical, polymer, or analytical chemistry.

Self-assembly of aniline oligomers.

A great number of nano/microscaled morphologies have recently been prepared during the oxidation of aniline. At the early stage of oxidation, aniline oligomers are obtained, often in spectacular morphologies depending on reaction conditions. Herein, the flower-like hierarchical architectures assembled from aniline oligomers by a template-free method are reported. Their formation process is ascribed to the self-assembly of oligoanilines through non-covalent interactions, such as hydrogen bonding, hydrophobic forces, and π-π stacking. The model of directional growth is offered to explain the formation of petal-like objects and, subsequently, flowers. In order to investigate the chemical structure of the oligomers, a series of characterizations have been carried out, such as matrix-assisted laser desorption ionization, time-of-flight mass spectrometry, gas chromatography coupled with mass spectrometry analysis, X-ray diffraction, and UV/Vis, Fourier-transform infrared, and Raman spectroscopies. Based on the results of characterization methods, a formation mechanism for aniline oligomers and their self-assembly is proposed.