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Electrochemical behaviour of {110}-oriented single crystal boron-doped diamond electrode for electroanalysis
Poláková, Jana ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
This bachelor thesis deals with the study of the electrochemical behavior of the neurotransmitter dopamine on mechanically polished single crystal boron-doped diamond electrodes with crystal orientation {110} and the boron-to-carbon (B/C) ratio in the gas phase during the chemical vapor deposition process at 250, 500, 1000 and 2000 ppm. Measurements were carried out on mechanically polished, O-terminated and H-terminated electrodes. The redox inner-sphere markers [Fe(CN)6]3−/4− and dopamine/dopamine-o-quinone and the outer- sphere marker [Ru(NH3)6]3+/2+ were used for electrochemical characterization of the polished electrode surface by cyclic voltammetry. As the B/C ratio increases for inner-sphere redox systems, ΔEp values decrease due to the acceleration of heterogeneous electron transfer kinetics. The high values of potential differences indicated that DA behaves quasi-reversibly at BDD electrodes. The ΔEp values for [Ru(NH3)6]3+/2+ showed no trend, confirming the independence of this marker at the doping level. Repeatability was further investigated when several measurements are performed in succession, with the DA solution being stirred before each measurement. It was found that when the solution is stirred, the current response does fluctuate (sr = 9.20), but the potential shows very low...
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Influence of surface termination of boron-doped diamond electrode on the electrochemical behaviour of phenol and its derivatives
Nedvěd, Michal ; Schwarzová, Karolina (advisor) ; Gabriel, Jiří (referee)
This thesis is devoted to the study of electrochemical oxidation of meta-substituted phenolic substances on a boron-doped diamond electrode. In the first phase, it was studied the effect of pH on their electrochemical oxidation by the methods of classical "direct current" voltammetry (DCV) and differential pulse voltammetry (DPV). The study was performed on three types of boron doped diamond (BDD) surfaces: polished, anodic and cathodically activated. In the second phase, attention was paid to the Hammett correlation to study the effect of the substituent on the potential of electrochemical oxidation of selected phenolic compounds. Among the substituents studied were (-H, -CH3, -OCH3, -(CH2)2COOH, -COOH a -NO2). In general, the oxidation potentials were lower in the basic medium than in the acidic medium on all studied surfaces. An exception was the studied phenolic acids, which could not be detected in an alkaline medium on the O-terminated BDD, probably due to electrostatic repulsion between the partially negative electrode surface and the acid dianion. The highest correlation coefficient for the dependence composed of all studied phenols was obtained for the polished and H-terminated surface at pH 11, ie the dissociated form of phenolic substances. The high electron density leads to easy...
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The width of potential window of boron doped diamond electrodes in dependence on their pretreatment and composition of the mixed electrolyte solution
Dvořáková, Klára ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The diploma thesis focuses on the range of the potential window of the BDD electrode in dependence on the composition of the mixed electrolyte solution and the treatment of the electrode surface. The measurements were performed on a polished (p-BDD) and O-terminated (O-BDD) electrode by the method of linear sweep voltammetry (LSV) in a three-electrode system. It was confirmed that in an environment with a suitable organic solvent, the range of the potential window widens. The measured solutions consisted of deionized water containing sodium perchlorate with a concentration of 1 mmol l−1 and one organic solvent in which sodium perchlorate with a concentration of 1 mmol l−1 was also dissolved. Acetonitrile, methanol, N,N-dimethylformamide and isopropanol were used in solutions (0 %, 1 %, 5 %, 10 %, 50 %, 70 %, 90 %, 95 %, 99 % or 100 % volume percent). Expansion, or the shortening of the potential window range was evaluated separately for each solvent in the anodic and cathodic regions. The expansion of the window on both sides was confirmed in acetonitrile as the concentration of the solvent increases, so it is based on this experiment as a universal solvent suitable for the determination of reducing and oxidizing analytes, from measurements on O-BDD and also on p-BDD. In the case of the remaining...
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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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Study of surface modifications of boron doped diamond electrode for voltammetric detection of dopamine and serotonin
Eremina, Anna ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
This diploma thesis deals withthe studyof electrochemical behaviorand detection of two structurally different neurotransmitters, dopamine (DA) and serotonin (5-HT), in solutions commonly used for neuron cultivation, namely Neurobasal (NB), NB with phenol red and in phosphate buffer (PB) of a pH close to the physiological value. An electrode based on boron-doped diamondwas used for the study, examiningtwo types of surfaces obtained after oxidation (O-BDD) and mechanical polishing (p-BDD). The results were obtained by two voltametric techniques,namely cyclic and differential pulse voltammetry.The studyrevealedthat DA oxidationis a quasi-reversible process,whereas 5-HT oxidizes irreversibly on O-BDD and p-BDD. Nevertheless, for both neurotransmitters their anodic oxidationonboth BDD surfaces is controlledby diffusion. Due to the passivation of the electrode surface by the oxidation products, anodic reactivation(Eact = +2400 mV, t = 30 s) was first testedto regenerate the O-BDD surface during DA and 5-HT measurements. There was no continuous decrease in DA peak currents on O-BDD and the measuredsignals were characterizedby high repeatabilityin all studiedmedia (sr (Ip) 1.1% in PB of pH 7.0, 1.7% in NB of pH 7.34, 0.9% in NB with phenol red of pH 7.48). In the case of 5-HT, the anodic reactivation was...
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Modification of boron doped diamond electrode by poly-L-lysine and its influence on electrochemical behaviour of dopamine and serotonin
Pejzlová, Michaela ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
This bachelor's thesis deals with the redox behavior of two neurotransmitters, dopamine and serotonin, at bare anodically activated (O-terminated) and poly-L-lysine-coated boron doped diamond electrode in two media, namely phosphate buffered saline and Neurobasal (medium commonly used for neuron cultivation experiments). Oxidation of dopamine in tested environments has a quasi-reversible character, while serotonin oxidizes irreversibly on boron doped diamond electrode, both O-terminated and poly-L-lysine-treated. Clearly, poly-L-lysine modification of boron doped diamond electrode leads to a decrease in peak currents and a positive shift in oxidation potentials compared to the O-terminated boron doped diamond electrode; interestingly, serotonin is much more sensitive to polymer coating than dopamine, particularly in Neurobasal medium. During successive measurements, a considerable decrease in recorded signals of both neurotransmitters can be observed. Hence, possibilities how to ensure stable current values were investigated: for dopamine, stirring the solution between the individual scans is sufficient method for obtaining repeatable signals (sr = 1.4-11.9 %, n = 5). However, in case of serotonin it is necessary to reactivate the electrode surface anodically in H2SO4 (Eact = +2400 mV) for 5...
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The influence of the surface pretreatment of boron doped diamond electrodes on electrochemical oxidation of phenol and its derivatives
Hnízdilová, Lucie ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this thesis is the study of electrochemical oxidation of para-substituted phenol derivates using cyclic voltammetry (CV) and ,,direct current" voltammetry (DCV) on boron-doped diamond electrode (BDD) and comparison with some analogous meta-substituted compounds. Among the studied substances were p-cresol, 4-methoxyphenol, 4-hydroxybenzoic acid, 3-(4-hydroxyphenyl)propionic acid, 4-nitrophenol, 4-chlorophenol and 3-(trifluoromethyl)phenol. The oxidation of the analytes was performed in an acidic (pH 2,0) and basic (pH 11,0) Britton-Robinson buffer on mechanically polished, oxidated and hydrogenated surfaces. Another subject of the thesis is to analyze the influence of different substituents, characterized by the Hammett constant, on the oxidation potential of selected phenols. They are oxidized at more positive redox potentials in acidic media, than in basic media, where they are dissociated. The oxidation on the polished and hydrogenated surfaces were similar, whereas were shifted to higher values on the oxidated surface. Further, the signal intensity decreased on the oxidated one, and the oxidation of phenols was not recognizable in basic media. The passivation of the electrode was less significant in pH 2,0 buffer. The best result of Hammett correlation was achieved on a polished and...
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Influence of surface termination of boron-doped diamond electrode on the electrochemical behaviour of phenol and its derivatives
Nedvěd, Michal ; Schwarzová, Karolina (advisor) ; Gabriel, Jiří (referee)
This thesis is devoted to the study of electrochemical oxidation of meta-substituted phenolic substances on a boron-doped diamond electrode. In the first phase, it was studied the effect of pH on their electrochemical oxidation by the methods of classical "direct current" voltammetry (DCV) and differential pulse voltammetry (DPV). The study was performed on three types of boron doped diamond (BDD) surfaces: polished, anodic and cathodically activated. In the second phase, attention was paid to the Hammett correlation to study the effect of the substituent on the potential of electrochemical oxidation of selected phenolic compounds. Among the substituents studied were (-H, -CH3, -OCH3, -(CH2)2COOH, -COOH a -NO2). In general, the oxidation potentials were lower in the basic medium than in the acidic medium on all studied surfaces. An exception was the studied phenolic acids, which could not be detected in an alkaline medium on the O-terminated BDD, probably due to electrostatic repulsion between the partially negative electrode surface and the acid dianion. The highest correlation coefficient for the dependence composed of all studied phenols was obtained for the polished and H-terminated surface at pH 11, ie the dissociated form of phenolic substances. The high electron density leads to easy...
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