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Characterization of Electrochemical Behaviour and Adsorption of Methyl Viologen on Boron Doped Diamond Electrodes Depending on Their Surface Pre-treatment
Fořtová, Lucie ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
In this study we focused on the electrochemical and adsorptive behaviour of methyl viologen on electrode of boron doped diamond (BDD) possessing different termination as result of electrochemical or mechanical pretreatment. Namely was performed anodic activation applying +2.4 V in 0.5 mol L-1 sulphuric acid and cathodic pretreatment in the same solution at -2.4 V to obtain predominantly H-terminated surface. While the O- terminated surface is relatively hydrophilic with low surface conductivity, the H-terminated surface is hydrophobic with certain surface conductivity, which results typically in faster heterogenous electron transfer (HET) kinetics. Fast HET kinetics was observed on polished surfaces, that were obtained by polishing with alumina suspension. Methyl viologen (MV), a widely used herbicide, was used as a model compound because its quasireversible redox transformations result in charge changes of the molecule which includes neutral (MV0 ) or positively charged (MV+ , MV2+ ) forms. Adsorption was connected with MV0 form. The pilot experiments were performed in aqueous media using cyclic voltammetry (CV). The results indicate that adsorption of MV occurs not only on H-terminated surface, but also on the polished and O-terminated surface. Adsorption of MV0 was observed on anodic peaks on...
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Determination of selected elements in potato tubers by atomic absorption spectrometry
Fořtová, Lucie ; Hraníček, Jakub (advisor) ; Kozlík, Petr (referee)
The main aim of this bachelor thesis was a determination of the elements K, Mg, Ca, Na, Zn and Fe in the potato tubers and in their boiled solution using the method of flame atomic absorption spectrometry. The chosen samples were late consumer potato tubers of Granada cultivar (boiling type B). It was necessary to optimize working conditions before the sample analysis. The optimal flow rate of acetylene ranged from 2.0 to 2.5 l/min using the flame acetylene-air. The flame acetylene-nitrous oxide was used only for calcium with flow rate 6.0 l/min. The optimal height of a beam above the burner edge was measured in interval 5 to 7 pieces of defined scale mentioned in a manual for spectrometer GBC 933 AA. Using the optimal conditions, the basic characteristics for individual methods of determination were characterized (LOD, LOQ, LDR, sensitivity, repeatability). Limits of quantification were following: 78, 31, 7.0, 8.0, 190 and 71 μg/l for K, Na, Mg, Ca, Fe and Zn, respectively. The optimal conditions were used for the determination of the selected elements in samples. The solutions were prepared from diversely processed potato tubers (whole, whole without skin, chopped without skin, skin) by boiling into deionized water. After the samples had cooled down, the concentrated nitric acid was added...
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