Esma Sezer

Oxidative polymerization of N‐substituted carbazoles

Poly(N-vinylcarbazole), poly(N-carbazole) and poly(N-ethylcarbazole) powders were chemically synthesized by the reaction of ceric ammonium nitrate (CAN) with N-vinylcarbazole carbazole and N-ethylcarbazole in acetonitrile. Products were characterized by elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and viscosity, X-ray fluorescence and four-probe conductivity measurement. It is found that when a suitable concentration of CAN is used in the polymerization process, the conductivity of chemically synthesized polymers can be improved further by controlling the CAN addition.

Electrosynthesis and study of carbazole–acrylamide copolymer electrodes

Abstract Polymerisation of N-carbazoles in the presence of acrylamide has been studied by electrochemical polymerisation onto platinum and indium tin oxide (ITO), electrodes from an acetonitrile solution of the monomers and tetraethylamonnium perchlorate-supporting electrolyte. The influence of polymerisation conditions such as electrode potential, monomer concentration, type of solvent and supporting electrolyte on the mechanical and electrochemical properties of final polymers have been studied. The redox behaviour of the polymer-coated electrodes was checked in solution containing ferrocene and dopamine solution by cyclic voltammetry. Depending on the conditions the electrode response may be reversible or quasi reversible. Cationic polymerisation of monomer is initiated either by the monomer cation radical or by the proton generated by the coupling reaction of the cation radical of carbazole. For the characterisation of copolymers Cyclic Voltammetry, UV–vis and FT-IR spectrophotometric, solid state conductivity and SEM measurements were used.

An Electrochemical Study of Homopolymer, Copolymer and Composite Electrodes of Polypyrrole and Polycarbazoles

Abstract Copolymer and composites of pyrrole with carbazole were synthesized on a platin substrate and an electrochemical study of polymeric films was performed. The characterization of homopolymer, copolymer and composite films was performed by electrochemical methods (i.e., polarization curves and cyclovoltammetric measurements), morphological and elemental analyses, solid-state conductivity measurements and spectrophotometric methods comparatively. The reversibility of electrodes was checked by ferrocene in nonaqueous media. The stability of films was also tested both with corrosion and residual discharge capacity measurements in acidic aqueous solution.

Electro-induced oxidative polymerization of N-vinylcarbazole

WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW In this study, a novel procedure to increase the yield of the non-crosslinked, photoconductive, white form of linear poly(N-vinylcarbazole) (LPVCz) is reported. The yield of LPVCz is increased (up to 53%) by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of Nvinylcarbazole in a divided electrochemical cell. The concentration of Ce(IV) remained constant during the polymerization since Ce(III) is readily oxidized to Ce(IV) electrochemically. Since the electrochemical oxidation of Ce(III) to Ce(IV) took place simultaneously at the anode, the deposition of dark green crosslinked polyvinylcarbazole on the electrode surface, which hinders the formation of white LPVCz, can be prevented. The Fourier transform infrared, ultraviolet±visible and fluorescence spectra of white LPVCz showed that the structures of polymers are the same as those produced by conventional polymerization. Copyright  1999 John Wiley & Sons, Ltd.

Electrochemically induced redox polymerization of acrylamide

Polymerization of acrylamide (AA) has been studied in aqueous solution in the presence of Ce(IV) salt-oxalic acid initiator system in an electrochemical cell with and without separation of anolyte and catholyte. For reactions that required the cathode and anode sections to be analyzed individually, a cell whose compartments were divided by a sintered glass disk of the medium porosity was employed. Polymerization was initiated by a free radical that is formed by the fast reaction of oxalic acid and Ce(IV). The electrolysis of the reaction solution results in regeneration of Ce(IV), which can oxidize oxalic acid to produce radicals. The effect of sulfuric acid and cerium (IV) salt concentration and temperature on the yield of electroinitiated polymerization in different cell designs and structural identification of products were performed. Reaction was also followed by cyclic voltametric measurements, and a mechanism was proposed. Results indicated that the electrolysis method with a divided cell (85% conversion) shows advantages, compared with nonelectrolytic (5% conversion) and with undivided electrochemical cell (25% conversion) methods where a high concentration of initiator was used.

Determination of nitroaromatic and nitramine type energetic materials in synthetic and real mixtures by cyclic voltammetry.

Nitro-explosives contain reducible aromatic -NO2 groups or cyclic >N-NO2 bonds that may undergo reductive cleavage. This work reports the development of a cyclic voltammetric (CV) assay for nitro-aromatics (trinitrotoluene (TNT), dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) using a glassy carbon electrode. This determination was first used for these energetic materials by resolving current responses of reduction potentials primarily due to one constituent but partly contributed by other constituents. Calibration curves of current intensity versus concentration were linear in the range of 30-120 mg L(-1) for RDX with a limit of detection (LOD) of 10.2 mg L(-1), 40-120 mg L(-1) for HMX (LOD=11.7 mg L(-1)), 40-120 mg L(-1) for TNT (LOD=11.2 mg L(-1)), and 40-140 mg L(-1) for DNT (LOD=10.8 mg L(-1)). Results showed that the CV method could provide a sensitive approach for the simultaneous determination of RDX and TNT in synthetic and real mixtures. Deconvolution of current contributions of mixtures at peak potentials of constituents was performed by multiple linear regression. The proposed method was successfully applied to the analysis of military explosives comp A5 and octol, and method validation was performed both against HPLC on a comp B (TNT+RDX) sample and against GC-MS on real post-blast residual samples containing both explosives.

N‐Vinylcarbazole‐Acrylamide Copolymer Electrodes Electrochemical Response to Dopamine

Copolymers of N-vinylcarbazole and acrylamide were synthesized by the free radical polymerization using AIBN as initiator. Copolymer electrodes were prepared by casting from 3% solution on platinum and stainless steel substrate. Solvent was removed by heating at 1 10°C in vacuum 10 - Pa for 5 h. The response of electrodes to dopamine was tested by cyclic voltammetry and results suggest that depending on conditions (i.e., scan rates, thickness of film, composition of copolymer), the electrode shows reversible and stable behavior during the 14 days and it seems to he a suitable sensor electrode to dopamine. Stability of copolymer coating was investigated for stainless steel electrodes in sulfuric acid and it is found that copolymer coating can inhibit the corrosion of stainless steel up to 94%.

Combination of a poly(3,4-ethylene-dioxythiophene) electrode in the presence of sodium dodecyl sulfate with centri-voltammetry

A poly(3,4-ethylene-dioxythiophene) (PEDOT) electrode was prepared by electropolymerization of 3,4-ethylene-dioxythiophene (EDOT) in the presence of sodium dodecyl sulfate (SDS). The electrode was combined with centri-voltammetry for the first time and applied for dopamine (DA) detection. Under the experimental conditions, SDS provides a high density of negative charges to the PEDOT electrode and by this way the electrode attracts the positively charged DA. Also by applying centrifugation, effective accumulation of DA onto the electrode surface was achieved. Two linear ranges 1 × 10−9 M to 1 × 10−5 M and 2 × 10−5 M to 1 × 10−1 M with two LOD values of 5.9 nM and 3.1 nM were found for the developed system. Sample application and interference study were also conducted.

Centri-voltammetric dopamine detection

Centri-voltammetry, which includes the combination of centrifugal forces and voltammetry, is a kind of new method. In this work, centri-voltammetry was applied for the detection of the very important biological molecule Dopamin (DA) for the first time. After optimization of centrifugal parameters, a linear range was obtained between 5 × 10−9 M and 5 × 10−6 M DA with the equation y = 7.8206x − 0.3575 and correlation coefficient R2 = 0.997. The RSD value was calculated for 10−7 M DA (n = 5) and found to be 1.37%. LOD (3 s m−1) and LOQ (10 s m−1) values were also calculated and found to be 1.007 × 10−9 M and 1.023× × 10−9 M, respectively. Also the detection of DA in the presence of ascorbic acid (AA) has been conducted and it has been found that in the presence of 100 fold AA, it is possible to obtain accessable DA peaks.

AN ELECTROCHEMICAL STUDY OF SOLUBLE COPOLYMER OF ETHYL CARBAZOLE WITH N-METHYL PYRROLE AND 3-METHYL THIOPHENE

Copolymers of N-ethyl Carbazole (ECZ) with N-Methyl Pyrrole (N-MPy) and 3-Methyl Thiophene (3-MTh) were synthesized on platinum substrate and electrochemical investigation of polymeric films was performed. The characterization of homopolymer and copolymer films was performed by electrochemical methods (i.e. polarization curves and cyclovoltammetric measurements), solid-state conductivity measurements and spectrophotometric methods comparatively. A possible scheme for the copolymerization has been suggested. Solid state conductivity of PECz can be improved by inclusion of 3MTh and NMPy into chain. The ionization potentials, Ip, electron affinity, Ea, optical band gap, Eg, peak potentials, Ep, and doping degrees, y, of copolymer electrodes were calculated from these measurements. Copolymer electrodes have lower Ip, Eg, Ep values and better switching properties in accordance with homopolymer electrodes. Presence of alkyl group gives solubility to copolymers obtained both chemically and electrochemically.