Duke Orata

Virtues of composite structures in electrode modification. Preparation and properties of poly (aniline)/nafion composite films

Poly(aniline) (PA) is electropolymerized within thin films of precast Nafion on gold or glassy carbon electrodes. The quartz crystal microbalance (QCM) is used to aid in identification of the ionic species that undergo transport during switching of the PA between its insulating and conducting forms. The QCM frequency changes observed in solutions containing various cationic species suggest that cation transport is dominant for these composite structures. In acidic solution, a consequence of the high transport number for the proton in the composite films is shown to be an enhanced switching rate relative to the simple (non-composite) PA film. The composite PA films appear to be less resistive and therefore more electrochemically well behaved over a wider pH range than the simple PA films.

Electrodeposition of polyaniline on acidified clay montmorillonite modified electrode

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.

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

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.

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

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.

Electrochemical degradation of a metallated polyaniline

Abstract Cyclic voltammetric analysis of the degradation of metal modified polyaniline show that lead deposition in polyaniline suppress the latters electrochemical degradation (or formation of quinones) at positive potentials above ∼0.7 V (SCE). Tin modified polyaniline appears to show improved conductivity. Modification of polyaniline by deposition of silver does not result in a substantial change in the polyaniline electrochemical characteristics.

Allen-Hickling equation applied to the quasi-reversible polyaniline redox system

Abstract We have applied the Allen–Hickling equation to compute α, K and io from polyaniline cyclic voltammetric response. The data give an insight into the faradaic and double-layer components of the total charge. The presence of a bidentate ligand 2,2′-bipyridyl is shown to reverse the shifts in oxidation potential as a function of external solution pH. The results obtained also indicate that the capacitive currents (iDL) are independent of external solution pH.

Charge-state trapping at a conducting polymer-redox ion-exchanger interface - a bilayer electrode

Abstract The results presented in this paper highlight the use of Amberlite, a commercial cation-exchange resin as a material for electrode modification. We also show that when a redox centre is attached to the cation-exchange resin and an interface developed between it and a conducting polymer (polyaniline), electrochemical features characteristic of bilayer electrodes such as charge ‘trapping’ are observed

Electroanaysis of Unconventional (herbal) Drugs Using Surface Modified Electrodes in Conjunction with Cycic Votammetry

In this paper we report on the use of surface modified electrodes in conjunction with cyclic voltammetry to study the redox profiles of quinine in unconventional drugs-herbal medicine. The unconventional drugs used in the study include cinchona bark and malbet. The results show quinine in cinchona is redox active with the oxidation and reduction potentials on bare carbon graphite electrode occurring at 0.495V and 0.345V respectively. The oxidation/reduction potential on bentonite modified electrode occurred at 0.450V/ (0.345V and -0.030V). It was observed that, when in contact with the bentonite over along period, quinine in cinchona is physi-sorbed. The redox process of the quinine extract is diffusion limited. In the case of malbet the quinine in Alstonia scholaris was detected . The other natural products in malbet appear not to be electroactive. The oxidation and reduction peak potential for quinine in alstonia scholaris appeared at 0.540V and 0.225V in 1M H2SO4 and 0.525V and 0.330 V in HCl.The malbet appears to ingress into bentonite lattice and is pre-concentrated in the bentonite hence, giving enhanced redox signals.The electrochemical signal obtained in malbet is attributed to quinine in Alstonia scholaris.

Electro-Characterization of Polypyrolle Electrosynthesized on a Montmorillonite Host-Matrix, in Aqueous Media Containing Sulphuric Acid as Supporting Electrolyte

In this paper polypyrolle has been electrosynthesised from an aqueous media containing the pyrolle monomer and sulphuric acid as the supporting electrolyte. The redox properties of polypyrolle on carbon graphite working electrode and on a clay montmorillonite host matrix has also been reported. The results obtained from plots of oxidative and reductive peak currents yield redox efficiencies above 95% for the polypyrolle redox process. The polypyrolle redox process is also shown to be diffusion limited. The reduction in the rate of electrodeposition of polypyrolle on a polyaniline loaded clay montmorillinite host- matrix, is a veiled confirmation of intercalation of the polyaniline in montmorillonite matrix.

Surface Modified Electrodes Used in Cyclic Voltammetric Profiling of Quinine an Anti-Malarial Drug

In this paper electrochemical profiling of quinine, an effective anti- malarial drug administered to humans, was done using primarily the very versatile electrochemical technique- cyclic voltammetry. In the electro-analysis, the main supporting electrolyte used was sulphuric acid. The surface of the working electrode was modified using electronically conducting polymer- polyanailine and a clay montmorillonite- bentonite. Quinine and metal cation Cu 2+ , Co 2+ , Zn 2+ and Sn 2+ were also used to modify the electrode surface.The results obtained showed that quinine oxidation /reduction potential on bare carbon graphite electrode occured at 0.495V/0.300V and 0.015V (0.25M H2SO4 supporting electrolyte). Bentonite modified electrode gave 0.434V/0.480V (1M H2SO4 supporting electrolyte) and 0.360V/0.345V (1M HCl supporting electrolyte). A mechanistic pathway for the oxidation of quinine has also been proposed. It was also observed from the results obtained from studies on the effect of consumables such as tea, glycine and milk on quinine, that milk totally suppressed the redox process in quinine. Amino acids which are the building blocks in proteins and which is an important macromolecule in humans, does not affect significantly the redox process in quinine. Cyclic voltammetric profiling of quinine interaction with metal cations such as Cu 2+ , Co 2+ , Zn 2+ and Sn 2+ and All solutions were prepared using de-ionized water. The clay montmorillonite, bentonite (sourced from Athi River Mining Company Ltd., Kenya) was purified as described by Bard(18-19). It has a mesh size ranging from 150 to 200 um, cation exchange capacity (CEC) 1.18-1.22 mM/g and a pH range of 8.4-9.6. The density of the bentonite is 1.25g/cm3 which are comparable to other clay minerals from different parts of the world (18). It has a solvent retention capacity of 22.5% and 4.8% for water and organic solvents respectively, while its moisture content is 8.5%. It swells by a factor of 1.7 and 1.4 in water and organic solvents respectively In generating the cyclic potential scans, two sets of instruments were used. These comprised of a Princeton Applied Research (PAR) model 173 pontentiostat/galvanostat, a logarithmic current converter model 369 that controlled the current, a PAR model 175 universal programmer and a PAR RE 0089 X-Y recorder.