Duke Orata

Bio: Duke Orata is an academic researcher from University of Nairobi. The author has contributed to research in topics: Polyaniline & Cyclic voltammetry. The author has an hindex of 6, co-authored 26 publications receiving 651 citations. Previous affiliations of Duke Orata include University of Wyoming.

Determination of ion populations and solvent content as functions of redox state and pH in polyaniline

Abstract: The piezoelectric quartz crystal microbalance (QCM) is used to investigate the ion populations and solvent content of thin films of polyaniline (PA) on electrode surfaces as functions of redox state and pH. The data are shown to be consistent with a model for PA in which the initial oxidation at a potential of ca. 0.2 V vs. SCE to give the conductive form of the polymer creates charged sites by oxidation of amine moieties along the polymer chains. Higher potentials cause further (pH dependent) oxidation with cumulative removal of exactly one electron per ring to produce a polymer containing imine groups which can hydrolyze to form quinone and quinone/imine types of structures. The initial oxidation process is accompanied by proton expulsion at low pH values, indicating partial protonation of the PA amine nitrogens in the reduced form with loss of these protons on oxidation. In addition to the proton expulsion, anion insertion also takes place during oxidation under all conditions that were studied. Data from such measurements as a function of pH allow estimation of the pK/sub a/ values of the reduced (insulating) and oxidized (conducting) forms of PA, which are given as ca. -0.3 and 3. respectively. Experiments inmore » strong (10 M) acid solutions reveal changes in solvent content during oxidation which are observed to influence the electrochemical response of PA. The ability to measure both electrochemical and gravimetric data simultaneously is shown to greatly constrain possible models for systems such as PA, leading to less ambiguity in their description.« less

Electrodeposition of polyaniline on acidified clay montmorillonite modified electrode

Abstract: In this paper, we have presented results obtained on derivatization of the working electrode surface with clay montmorillonites treated with varying amounts of acid. The resultant changes in the population of Bronsted and Lewis acid sites is shown to affect the redox properties of conducting polymer, polyaniline.

Bentonite (clay montmorillonite) as a template for electrosynthesis of thyroxine

Abstract: The results discussed in this paper show that modification of the working electrode surface with clay montmorillonite (bentonite) enhances the iodine redox process and electrosynthesis of thyroxine. This is observed from the well defined quasi-reversible redox peaks obtained in the case of a modified surface as compared to bare carbon. These improvements in redox properties are attributed to the effect of pre-concentration and electrocatalysis. Orientation of clay plates also plays an important role.

A comparative study of the electrochemical/electro-degradation of polyaniline from aniline loaded in a clay-mineral/polyaniline composite matrix to that of the bulk solution

Abstract: Polyaniline was electrodeposited on an insulating-host matrix, Bentonite (clay mineral). Cyclic voltammetry was used to characterize the electrochemical response. Results show that aniline was trapped in the Bentonite/Polyaniline composite matrix and that the rate of polyaniline electrodeposition from this trapped aniline is different from that of the bulk solution. The electrochemical degradation rates are also different.

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction.

Abstract: Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers: the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.