A cation-responsive electrode system has been developed which incorporates aza-substituted crown ethers as ligands. In a novel application, uncomplexed crown ethers were used in the pelletized form for ionic transport. Electrodes have been produced which can be conditioned for a particular ion and following their use, be reconditioned and reused for other ions. Preparation method and lifetime studies are included. The responses of two crown ethers with plasticizers were evaluated for thirteen representative cations. The concentration range covered in each evaluation was 1 x 10-1 to 1 x 10-7 M. For those ions exhibiting Nernstian or near-Nernstian response, selectivity coefficients were derived.

Functional garments for physiological sensing purposes have been utilized in several disciplinesi.e. sports, firefighting, military and medical. In most of the cases textile electrodes (Textrodes)embedded in the garment are employed to monitor vital signs and other physiologicalmeasurements. Electrical Bioimpedance (EBI) is a non-invasive and effective technology that canbe used for detection and supervision of different health conditions. In some specific applicationssuch as body composition assessment EBIS has shown encouraging results proving good degreeof effectiveness and reliability. In a similar way Impedance Cardiography (ICG) is anothermodality of EBI primarily concerned with the determination of Stroke Volume SV, indices ofcontractility, and other aspects of hemodynamics.EBI technology in the previously mentioned modalities can benefit from a integration with agarment; however, a successful implementation of EBI technology depends on the goodperformance of textile electrodes. The main weakness of Textrodes is a deficient skin-electrodeinterface which produces a high degree of sensitivity to signal disturbances. This sensitivity canbe reduced with a suitable selection of the electrode material and an intelligent and ergonomicgarment design that ensures an effective skin-electrode contact area.This research work studies the performance of textile electrodes and garments for EBIspectroscopy for Total Body Assessment and Transthoracic Electrical Bioimpedance (TEB) forcardio monitoring. Their performance is analyzed based on impedance spectra, estimation ofparameters, influence of electrode polarization impedance Zep and quality of the signals using asreference Ag/AgCl electrodes. The study includes the analysis of some characteristics of thetextile electrodes such as conductive material, skin-electrode contact area size and fabricconstruction.The results obtained in this research work present evidence that textile garments with a dry skinelectrodeinterface like the ones used in research produce reliable EBI measurements in bothmodalities: BIS for Total Body Assessment and TEB for Impedance Cardiography. Textiletechnology, if successfully integrated, may enable the utilization of EBI in both modalities andconsequently implementing wearable applications for home and personal health monitoring. / <p>QC 20121213</p>

Dissertation (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study investigates the electrochemical oxidation of phenol. Phenol is a major toxin and water pollutant. In addition, during water treatment it reacts with chlorine to produce carcinogenic chlorophenols. lts treatment down to trace levels is therefore of increasing concern. For this purpose, dynamically stable anodes for the breakdown of phenols to carbon dioxide or other less harmful substances were developed and characterized. The anodes were prepared from mixed oxides of tin (Sn) and the precious metals ruthenium (Ru), tantalum (Ta) and iridium (Ir), which in tum were prepared using sol-gel techniques. This involved dip-coating the aqueous salts of the respective metals onto titanium substrates and heating to temperatures of several hundreds of degree Celsius. The properties of these mixed oxide thin films were investigated and characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), elemental dispersive energy X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and electrochemical measurements. A variety of different electrode materials including Til Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 and Ti/RhOx-Ir02 were developed and tested for their potential as oxidation catalysts for organic pollutants in wastewaters. Depending on the anode type, phenol was found to be electrochemically degraded, to different extents, on these surfaces during electrolysis. It was however found that the oxidation rate not only depended on the chemical composition but also on the oxide morphology revealed, resulting from the preparation procedure. The Ti/SnOz-Ru02-Ir02 film was found to be the most efficient surface for the electrolytic breakdown of phenol. This film oxidized phenol at a potential of 200 mV vs Ag/AgC!. The activity of the catalytic systems was evaluated both on the basis of phenol removal efficiency as well as the kinetics of these reactions. Phenol removal efficiency was more than 90% for all the film surfaces prepared and the rate of the reaction followed first order kinetics. A pathway for the electrochemical degradation of phenol was derived using techniques such as HPLC to identify the breakdown products. These pathway products included the formation of benzoquinone and the further oxidation of benzoquinone to the carboxylic acids malic, malonic and oxalic. / AFRIKAANSE OPSOMMING: Die onderwerp van hierdie studie is die elektrochemiese oksidasie van fenol deur nuwe gemengde-oksied elektrodes. Fenol is 'n belangrike gifstof en besoedelingsmiddel in water. Daarbenewens kan fenolook met chloor reageer tydens waterbehandeling om sodoende karsinogeniese chlorofenole te vorm. Dit is dus belangrik dat metodes ondersoek word wat die konsentrasie van fenol in water verminder. Hierdie studie behels die bereiding en karakterisering van nuwe dinamiese stabiele anodes (DSA) vir die afbreek van fenol tot koolstofdioksied en ander minder gevaarlike verbindings. Hierdie nuwe anodes is berei vanaf die gemengde-okside van die edelmetale tin (Sn), ruthenium (Ru), tantalum (Ta) en iridium (Ir), met behulp van sol-gel tegnieke. Die finale stap in die bereiding behels kalsinering van die oksides by temperature van "n paar honderd grade Celsius. Hierdie nuwe elektrodes is later gebruik om die oksidasie van fenol te evalueer. Die gemengde-oksied dunlae/anodes IS d.m.v. die volgende analitiesetegnieke gekarakteriseer: termiese-gravimetriese analise (TGA), skandeerelektronmikroskopie (SEM), atoomkragmikroskopie (AFM), elementverstrooiingsenergie- X-straalanalise (EDX), X-straaldiffraksie (XRD), Rutherford terug-verstrooiingspektroskopie (RBS), partikel-geinduseerde X-straal emissie (PIXE), en elektrochemiese metings. 'n Verskeidenheid elektrodes van verskillende materiale is berei en hul potensiaal as oksidasie-kataliste vir organiese besoedelingsmiddels in afloopwater bepaal. Hierdie elektrodes het die volgende ingesluit: Ti/Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 en Ti/RhOx-Ir02. Gedurende elektrolise is fenol elektrochemies afgebreek tot verskillende vlakke, afhangende van die tipe elektrode. Die oksidasietempo het egter nie alleen van die chemiese samestelling van die elektrode afgehang nie, maar ook van die morfologie van die okside, wat op hulle beurt van die voorbereidingsprosedure afgehang het. Daar is bevind dat die Ti/Sn02-Ru02-Ir02 elektrode die mees effektiewe oppervlakke vir die afbreek van fenol is. Hier het die oksidasie van fenol by 'n potensiaal van 200 mV plaasgevind. Die aktiwiteite van die katalitiese sisteme IS bepaal op grond van hulle fenolverwyderingsdoeltreffendheid. Die kinetika van die reaksies is ook bepaal. Al die elektrodes het >90% fenolverwyderingsdoeltreffendheid getoon en die reaksietempos was van die eerste-orde. Deur van analitiese tegnieke soos hoëdrukvloeistofchromatografie (HPLC) gebruik te maak is die afbreekprodukte van fenol geïdentifiseer en 'n skema vir die elektrochemiese afbreek van fenol uitgewerk. Daar is bevind dat bensokinoon gevorm het, wat later oksidasie ondergaan het om karboksielsure te vorm.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Please see fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

Σε αυτή την μελέτη διμεταλλικά ηλεκτρόδια Pt-TiO2 παρασκευάστηκαν και χαρακτηρίστηκαν με περίθλαση ακτίνων Χ (X-ray diffraction - XRD), με ηλεκτρονικό μικροσκόπιο σάρωσης (Scanning Electron Microscopy - SEM), φασματοσκοπία φωτοηλεκτρονίων από ακτίνες Χ (X-ray photoelectron spectroscopy - XPS), ηλεκτροχημικές τεχνικές και πειράματα ρόφησης-οξείδωσης μονοξειδίου του άνθρακα (CO stripping). Ερευνήθηκε η μείωση της περιεκτικότητας σε Pt χωρίς απώλειες της ηλεκτροκαταλυτικής ενεργότητας. Το TiO2 επιλέχθηκε λόγω της χημικής του σταθερότητας και του χαμηλού κόστους. Βρέθηκε ότι περιεκτικότητα σε TiO2 μέχρι 50% οδηγεί σε αύξηση της ηλεκτροχημικά ενεργής επιφάνειας (EAS) του ηλεκτροδίου.Η EAS του ηλεκτροδίου Pt(50%)-TiO2(50%) ήταν σχεδόν μια τάξη μεγέθους μεγαλύτερη από το ηλεκτρόδιο της καθαρής Pt, ενώ για περιεκτικότητα σε Pt χαμηλότερη από 30% η EAS μειώνεται δραματικά. Το παραπάνω συμπέρασμα στηρίχθηκε σε μετρήσεις του φορτίου της αναγωγικής κορυφής του οξειδίου της Pt και σε πειράματα ρόφησης-οξείδωσης του CO (CO stripping). Όλα τα δείγματα χρησιμοποιήθηκαν επίσης και ως άνοδοι κατά την διάρκεια ηλεκτροχημικής οξείδωσης μεθανόλης και αιθανόλης. Και στις δύο περιπτώσεις το ηλεκτρόδιο Pt(50%)-TiO2(50%) παρουσίασε τη μεγαλύτερη ηλεκτροκαταλυτική ενεργότητα. / In this study Pt-TiO2 binary electrodes were prepared by thermal decomposition of chloride precursors on Ti substrates, characterised by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), electrochemical techniques and CO stripping and used as anodes for alcohol oxidation. The minimization of the Pt loading without electrocatalytic activity losses was also explored. TiO2 was chosen due to its chemical stability, low cost and excellent properties as substrate for Pt dispersion. It was found that TiO2 loading up to 50% results in Electrochemically Active Surface (EAS) increase. The EAS of Pt(50%)-TiO2(50%) was found to be almost one order of magnitude higher than that of pure Pt while for Pt loadings lower than 30% the EAS was diminished. The above conclusion has been confirmed both by following the charge of the reduction peak of platinum oxide and by CO stripping experiments. All samples have been evaluated during the electrochemical oxidation of methanol and ethanol. In both cases the Pt(50%)-TiO2(50%) electrode exhibited better electrocatalytic activity than the pure Pt anode. The observed higher performance of the binary electrodes has been attributed to the enhanced Pt dispersion as well as to the formation of smaller Pt particles by the addition of TiO2.

No description available.

Voltammetric and spectroelectrochemical results are presented for the one-electron reduction of n-heptyl viologen on clean and silane-modified tin oxide, and on ion-beam modified, indium-tin oxide metallized plastic optically transparent electrodes (ITO MPOTE) surfaces. The use of viologens (dialkyl and diaryl 4,4' bipyridium compounds) in redox chromic displays is well known with a number of papers and patents discussing their use. The ability to vary the coloration rates of the electrochromic reaction of these compounds can be strongly influenced by the state of the electrode surface. Potential-step experiments, where the electrode potential is controlled at low overpotentials, has shown that the viologen reduction occurs through a nucleation process. The work here indicates that an "instantaneous nucleation" model appears to be the favored pathway for the n-heptyl viologen reaction. Chronoabsorptometric analysis of the nucleation process is made possible by monitoring the strongly absorbing viologen cation radical. Chronoabsorptometric data can be used to calculate the nucleation site density on an electrode surface. On silane-modified and ion-beam modified electrode surfaces, a more preferred nucleation site is found for the deposition of the first monolayers of viologen. Through the attachment of a silane or the ion-beam modification of an ITO metallized plastic film (ITO MPOTE), a nonpolar layer is created adjacent to the electrode surface. Prior to electrochemical reduction the n-heptyl viologen dication is partioned and concentrated into this nonpolar layer. The effect is a preconcentration of the viologen next to the electrode surface resulting in a fixed number of nucleation sites and an enhancement of the nucleation rate.

No description available.

No description available.

No description available.