Gordana Ćirić-Marjanović

Conducting carbonized polyaniline nanotubes

Conducting nitrogen-containing carbon nanotubes were synthesized by the carbonization of self-assembled polyaniline nanotubes protonated with sulfuric acid. Carbonization was carried out in a nitrogen atmosphere at a heating rate of 10 degrees C min(-1) up to a maximum temperature of 800 degrees C. The carbonized polyaniline nanotubes which have a typical outer diameter of 100-260 nm, with an inner diameter of 20-170 nm and a length extending from 0.5 to 0.8 microm, accompanied with very thin nanotubes with outer diameters of 8-14 nm, inner diameters 3.0-4.5 nm and length extending from 0.3 to 1.0 microm, were observed by scanning and transmission electron microscopies. Elemental analysis showed 9 wt% of nitrogen in the carbonized product. Conductivity of the nanotubular PANI precursor, amounting to 0.04 S cm(-1), increased to 0.7 S cm(-1) upon carbonization. Molecular structure of carbonized polyaniline nanotubes has been analyzed by FTIR and Raman spectroscopies, and their paramagnetic characteristics were compared with the starting PANI nanotubes by EPR spectroscopy.

Carbonised polyaniline and polypyrrole: towards advanced nitrogen-containing carbon materials

Polyaniline (PANI) and polypyrrole (PPY) undergo carbonisation in an inert/reduction atmosphere and vacuum, yielding different nitrogen-containing carbon materials. This contribution reviews various procedures for the carbonisation of PANI and PPY precursors, and the characteristics of obtained carbonised PANI (C-PANI) and carbonised PPY (C-PPY). Special attention is paid to the role of synthetic procedures in tailoring the formation of C-PANI and C-PPY nanostructures and nanocomposites. The review considers the importance of scanning and transmission electron microscopies, XPS, FTIR, Raman, NMR, and EPR spectroscopies, electrical conductivity and adsorption/desorption measurements, XRD, and elemental analyses in the characterisation of C-PANIs and C-PPYs. The application of C-PANI and C-PPY in various fields of modern technology is also reviewed.

Synthesis and characterization of conducting polyaniline 5-sulfosalicylate nanotubes

Conducting polyaniline 5-sulfosalicylate nanotubes and nanorods were synthesized by the template-free oxidative polymerization of aniline in aqueous solution of 5-sulfosalicylic acid, using ammonium peroxydisulfate as an oxidant. The effect of the molar ratio of 5-sulfosalicylic acid to aniline on the molecular structure, molecular weight distribution, morphology, and conductivity of polyaniline 5-sulfosalicylate was investigated. The nanotubes, which have a typical outer diameter of 100-250 nm, with an inner diameter of 10-60 nm, and a length extending from 0.4 to 1.5 microm, and the nanorods, with a diameter of 80-110 nm and a length of 0.5-0.7 microm, were observed by scanning and transmission electron microscopies. The presence of branched structures and phenazine units besides the ordinary polyaniline structural features was revealed by infrared and Raman spectroscopies. The stacking of low-molecular-weight substituted phenazines appears to play a major role in the formation of polyaniline nanorods. The precipitation-dissolution of oligoaniline templates as a key element in the formation of polyaniline nanotubes is proposed to explain the crucial influence of the initial pH of the reaction mixture and its decrease during the course of polymerization.

Synthesis and characterization of self-assembled polyaniline nanotubes/silica nanocomposites.

Self-assembled semiconducting, paramagnetic polyaniline nanotubes have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in aqueous medium in the presence of colloidal silica particles of an average diameter approximately 12 nm, without added acid. The electrical conductivity of polyaniline nanotubes/silica nanocomposites is in the range (3.3-4.0)x10(-3) S cm(-1). The presence of paramagnetic polaronic emeraldine salt form of polyaniline and phenazine units in nanocomposites was proved by FTIR, Raman, and EPR spectroscopies. The influence of the initial silica/aniline weight ratio on the morphology of polyaniline/silica nanocomposites was studied by scanning and transmission electron microscopies. Nanocomposites synthesized by using the initial weight ratio silica/aniline<or=0.2 contain polyaniline nanotubes which have a typical outer diameter of 100-250 nm and an inner diameter of 10-80 nm, and nanorods with a diameter of 60-100 nm, accompanied with polyaniline/silica nanogranules, while the nanocomposite synthesized at weight ratio silica/aniline approximately 2 contains polyaniline/silica nanogranules with an average diameter of 35-70 nm. The evolution of molecular and supramolecular structure of polyaniline in the presence of colloidal silica is discussed.

Synthesis and Characterization of Conducting Self-Assembled Polyaniline Nanotubes/Zeolite Nanocomposite

Self-assembled conducting, paramagnetic polyaniline nanotubes have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in aqueous medium in the presence of zeolite HZSM-5, without added acid. The influence of initial zeolite/aniline weight ratio on the conductivity, molecular and supramolecular structure, paramagnetic characteristics, thermal stability, and specific surface area of polyaniline/zeolite composites was studied. The conducting (approximately 10(-2) S cm(-1)), semiconducting (3 x 10(-5) S cm(-1)), and nonconducting (5 x 10(-9) S cm(-1)) composites are produced using the zeolite/aniline weight ratios 1, 5, and 10, respectively. The coexistence of polyaniline nanotubes, which have a typical outer diameter of 70-170 nm and an inner diameter of 5-50 nm, accompanied by nanorods with a diameter of 60-100 nm and polyaniline/zeolite mesoporous aggregates, distinct from the morphology of microporous zeolite HZSM-5, was proved in the conducting nanocomposite by scanning and transmission electron microscopies. FTIR spectroscopy confirmed the presence of polyaniline in the form of conducting emeraldine salt and suggested significant interaction of polyaniline with zeolite. The evolution of molecular and supramolecular structure of polyaniline in the presence of zeolite was discussed.

Chemical Oxidative Polymerization of Aminodiphenylamines

The course of oxidation of 4-aminodiphenylamine with ammonium peroxydisulfate in an acidic aqueous ethanol solution as well as the properties of the oxidation products were compared with those of 2-aminodiphenylamine. Semiconducting oligomers of 4-aminodiphenylamine and nonconducting oligomers of 2-aminodiphenylamine of weight-average molecular weights 3700 and 1900, respectively, were prepared by using an oxidant to monomer molar ratio of 1.25. When this ratio was changed from 0.5 to 2.5, the highest conductivity of oxidation products of 4-aminodiphenylamine, 2.5 x 10 (-4) S cm (-1), was reached at the molar ratio [oxidant]/[monomer] = 1.5. The mechanism of the oxidative polymerization of aminodiphenylamines has been theoretically studied by the AM1 and MNDO-PM3 semiempirical quantum chemical methods combined with the MM2 molecular mechanics force-field method and conductor-like screening model of solvation. Molecular orbital calculations revealed the prevalence of N prim-C10 coupling reaction of 4-aminodiphenylamine, while N prim-C5 is the main coupling mode between 2-aminodiphenylamine units. FTIR and Raman spectroscopic studies confirm the prevalent formation of linear N prim-C10 coupled oligomers of 4-aminodiphenylamine and suggest branching and formation of phenazine structural units in the oligomers of 2-aminodiphenylamine. The results are discussed with respect to the oxidation of aniline with ammonium peroxydisulfate, leading to polyaniline, in which 4-aminodiphenylamine is the major dimer and 2-aminodiphenylamine is the most important dimeric intermediate byproduct.

Interfacial Synthesis of Gold-Polyaniline Nanocomposite and Its Electrocatalytic Application.

Gold-polyaniline (Au-PANI) nanocomposite was prepared using a simple interfacial polymerization method, performed in an immiscible water/toluene biphasic system using tetrachloroaurate, AuCl4(-) as an oxidant. The formation of Au nanoparticles (AuNPs) or Au-PANI nanocomposite can be controlled to a certain degree by varying the ratio of initial Au(+) and aniline concentrations. Under optimal condition (HAuCl4/aniline ratio is 1:2), green dispersion of Au-PANI nanocomposite is produced in aqueous phase, whose morphology, structure and physicochemical properties are investigated in details. The nanocomposite shows granular morphology with mostly rodlike AuNPs embedded in polymer. It was found that polyaniline in the composite is in the conducting emeraldine salt form, containing high amount of Au (28.85 wt %). Furthermore, the electrical conductivity of the nanocomposite was found to be four-fold higher than that of the polymer itself. In addition, the nanocomposite powder, isolated from the as-prepared aqueous dispersion, can later be easily redispersed in water and further used for various applications. Moreover, the obtained Au-PANI nanocomposite showed excellent electrocatalytic performance toward the electrochemical oxygen reduction reaction (ORR), with high ORR onset potential and good selectivity. This makes it a promising candidate for a new class of Pt-free ORR catalyst.

Revised mechanism of Boyland-Sims oxidation.

New computational insights into the mechanism of the Boyland-Sims oxidation of arylamines with peroxydisulfate (S(2)O(8)(2-)) in an alkaline aqueous solution are presented. The key role of arylnitrenium cations, in the case of primary and secondary arylamines, and arylamine dications and immonium cations, in the case of tertiary arylamines, in the formation of corresponding o-aminoaryl sulfates, as prevalent soluble products, and oligoarylamines, as prevalent insoluble products, is proposed on the basis of the AM1 and RM1 computational study of the Boyland-Sims oxidation of aniline, ring-substituted (2-methylaniline, 3-methylaniline, 4-methylaniline, 2,6-dimethylaniline, anthranilic acid, 4-aminobenzoic acid, sulfanilic acid, sulfanilamide, 4-phenylaniline, 4-bromoaniline, 3-chloroaniline, and 2-nitroaniline) and N-substituted anilines (N-methylaniline, diphenylamine, and N,N-dimethylaniline). Arylnitrenium cations and sulfate anions (SO(4)(2-)) are generated by rate-determining two-electron oxidation of primary and secondary arylamines with S(2)O(8)(2-), while arylamine dications/immonium cations and SO(4)(2-) are initially formed by two-electron oxidation of tertiary arylamines with S(2)O(8)(2-). The subsequent regioselectivity-determining reaction of arylnitrenium cations/arylamine dications/immonium cations and SO(4)(2-), within the solvent cage, is computationally found to lead to the prevalent formation of o-aminoaryl sulfates. The formation of insoluble precipitates during the Boyland-Sims oxidation of arylamines was also computationally studied.

Insight into the template effect of vesicles on the laccase-catalyzed oligomerization of N -phenyl-1,4-phenylenediamine from Raman spectroscopy and cyclic voltammetry measurements

We report about the first Raman spectroscopy study of a vesicle-assisted enzyme-catalyzed oligomerization reaction. The aniline dimer N-phenyl-1,4-phenylenediamine (= p-aminodiphenylamine, PADPA) was oxidized and oligomerized with Trametes versicolor laccase and dissolved O2 in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) vesicles (80–100 nm diameter) as templates. The conversion of PADPA into oligomeric products, poly(PADPA), was monitored during the reaction by in situ Raman spectroscopy. The results obtained are compared with UV/vis/NIR and EPR measurements. All three complementary methods indicate that at least some of the poly(PADPA) products, formed in the presence of AOT vesicles, resemble the conductive emeraldine salt form of polyaniline (PANI-ES). The Raman measurements also show that structural units different from those of “ordinary” PANI-ES are present too. Without vesicles PANI-ES-like products are not obtained. For the first time, the as-prepared stable poly(PADPA)-AOT vesicle suspension was used directly to coat electrodes (without product isolation) for investigating redox activities of poly(PADPA) by cyclic voltammetry (CV). CV showed that poly(PADPA) produced with vesicles is redox active not only at pH 1.1–as expected for PANI-ES–but also at pH 6.0, unlike PANI-ES and poly(PADPA) synthesized without vesicles. This extended pH range of the redox activity of poly(PADPA) is important for applications.

Hydrogen peroxide sensing at MnO2/carbonized nanostructured polyaniline electrode

Manganese dioxide modified carbonized nanostructured polyaniline (MnO2/Carb-nanoPANI) was prepared via a novel hydrothermal procedure. The synthesized material was characterized using XRD, SEM and TG-DTA analysis. Furthermore, MnO2/Carb-nanoPANI was examined as electrode material for potential application in the field of electroanalysis. It showed a high electrocatalytic activity for the sensing of hydrogen peroxide in an aqueous media.