G. P. Karpacheva

Electroactivity of chemically synthesized polyaniline in neutral and alkaline aqueous solutions: Role of self-doping and external doping

The electroactivity of chemically synthesized polyaniline and its copolymer with metanilic acid has been investigated in a wide pH range. It was found that the external doping of PAn with camphorsulfonic acid extends the electroactivity in neutral and alkaline media. Additional ring substitution with sulfo-groups does not further extend the electroactivity, but improves the stability upon cycling in neutral and alkaline media.

Polyaniline-modified cholinesterase sensor for pesticide determination.

Cholinesterase sensors based on glassy carbon and planar epoxy graphite electrodes modified with processed polyaniline have been developed and examined for pesticide detection. The modification of electrode surface with polyaniline provides high operational stability and sensitivity towards the pesticides investigated. The detection limits found (coumaphos, 0.002, trichlorfon, 0.04, aldicarb, 0.03, methiocarb, 0.08 mg l(-1)) make it possible to detect the pollutants in the waters on the level of limited threshold levels without sample preconcentration.

Carbon nanostructures based on IR-pyrolyzed polyacrylonitrile

For the first time, it is shown that IR pyrolysis of a composite based on polyacrylonitrile and gadolinium chloride produces a metal-carbon nanocomposite where metal particles with a size of 4–11 nm form a fine dispersion in the structure of the carbon matrix. The carbon phase of the composite is a carbon-carbon nanocomposite with a structure in which carbon nanoparticles (bamboolike carbon nanotubes, carbon nanospheres, or octahedral carbon nanoparticles) are incorporated into the matrix graphite-like material.

New polyaniline-based potentiometric biosensor for pesticides detection

A cholinesterase potentiometric sensor based on a glassy carbon electrode modified with processible polyaniline has been developed and explored for the detection of organophosphorus and carbamic pesticides. Acetyl- and butyryl-cholinesterase from various sources were immobilized on the surface of a polyaniline modified electrode by cross-linking with glutaraldehyde. Polyaniline modification made it possible to obtain a reversible pH response of about 86-mV/pH unit and to improve the analytical and operational characteristics of substrate and inhibitor detection. The sensitivity of pesticide detection depends on both the source of the enzyme and its activity and on pesticide hydrophobicity. The detection limits of the pesticides investigated (Trichlorfon, 1.5/spl middot/10/sup -7/ mol/l, Coumaphos, 5/spl middot/10/sup -9/ mol/l, Methiocarb, 8/spl middot/10/sup -7/ mol/l, Aldicarb, 2/spl middot/10/sup -7/ mol/l) were found lower than those obtained with other similar cholinesterase sensors. The possibility for the detection of the trace amounts of pesticides in river waters and grape juice with cholinesterase sensors developed has been established on model samples.

Oxidative polymerization of diphenylamine: A mechanistic study

The mechanism of oxidative polymerization of diphenylamine is considered. The kinetic study of diphenylamine polymerization and of the structure and molecular-mass characteristics of the reaction products has shown that the degree of oxidation of intermediates plays the key role in polyrecombination. The relationship between the polymerization procedure and the molecular mass of polydiphenylamine was revealed.

Oxidative Polymerization of Diphenylamine: Synthesis and Structure of Polymers

Three procedures for the chemical oxidative polymerization of diphenylamine, namely, in solutions of sulfuric acid, in an H2SO4-tert-butanol mixture, and via the interfacial process, are considered. It was shown that the highest molecular mass products are formed by the interfacial process. Oxidative hydrolysis and chain termination reactions predominate in a homogeneous medium. The effects of polymerization conditions, such as the concentration of reagents, their ratio, and the reaction temperature, on the yield and molecular-mass characteristics of polydiphenylamine were studied. The structure of reaction products was investigated by UV spectroscopy. It was demonstrated that, even when ammonium persulfate is in excess, the degree of oxidation of polydiphenylamine is rather small and chain propagation proceeds as a C-C rather than N-C addition as in the case of aniline.

Thermal stability of polydiphenylamine synthesized through oxidative polymerization of diphenylamine

The thermal stability of polydiphenylamine synthesized through the oxidative polymerization of diphenylamine has been studied. It has been established that the main processes of thermal and thermooxidative degradation of polydiphenylamine begin at 600–650 and 450°C, respectively. It has been shown that, in the course of thermal oxidation of the doped polydiphenylamine, the elimination of a dopant takes place first. With a further increase in temperature, the behavior of this material becomes similar to that of the neutral polymer.

New approaches to synthesizing electroactive polymers

The chemical oxidative polymerization of aniline in a heterophase system is studied. In the presence of a solid substrate, the aniline polymerization involves two kinetically and chemically independent processes, namely, the polymerization in the bulk solution and at the substrate surface. The growth of the polyaniline coating at the substrate surface includes three successive processes: interfacial polymerization, adsorptive polymerization, and destruction of the polymer chain. The interfacial oxidative polymerization of diphenylamine and phenothiazine is examined. The yield and chemical structure of polymers is shown to depend on the polymerization conditions.

The formation of Pt-Ru alloy nanoparticles in a carbon matrix under IR pyrolysis conditions

Nanosized Pt-Ru alloy and Pt13Ru27 intermetallic compound particles dispersed in a carbon matrix were obtained for the first time directly during the preparation of the composite. The alloying of the Pt and Ru particles occurred at IR pyrolysis intensities corresponding to temperatures above 700°C over the whole homogeneity range of solid solutions based on platinum. Metallic nanoparticles were round-shaped (the mean size 6–8 nm) and had a narrow particle-size distribution.

Oxidative polymerization of diphenylamine-2-carboxylic acid: Synthesis, structure, and properties of polymers

Polymers of diphenylamine-2-carboxylic acid are synthesized for the first time via chemical oxidative polymerization. The effects of the concentration of reagents, their ratio, and the temperature and time of reaction on the yield and chemical structure of poly(diphenylamine-2-carboxylic acid) are studied by IR and UV spectroscopy. It is shown that the growth of polymer chains proceeds through the C-C addition in the para position of phenyl rings relative to nitrogen. During the thermal oxidation of poly(diphenylamine-2-carboxylic acid), COOH groups and dopant molecules are successively eliminated; with a further increase in temperature, the polymer behaves as polydiphenylamine. The main processes of thermooxidative degradation of poly(diphenylamine-2-carboxylic acid) begin at 570°C. This value is 120°C higher than the corresponding parameter in the case of polydiphenylamine.