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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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Optimization of anodic and cathodic pre-treatments of boron doped diamond electrode surfaces for electroanalysis
Baudisová, Kateřina ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
This bachelor thesis deals with the optimization of anodic and cathodic pretreatment of BDD electrodes and subsequent comprehensive characterization and comparison of electrochemical parameters of unmodified, O-terminated and H-terminated BDD electrodes. The study was carried out using cyclic voltammetry of two model inner sphere redox systems [Fe(CN)6]4−/3− and dopamine/dopamine-o-quinone. Boron concentrations in the BDD films ranged from 500 ppm to 8000 ppm. O-termination of the electrode surface was most effectively achieved when an activation potential of Eakt = +3.0 V was inserted for 10 min into 0.5 mol l−1 H2SO4. For the dopamine/dopamine-o-quinone system, the O-terminated BDD electrodes caused deceleration of electron transfer compared to the unmodified BDD electrodes, which was accompanied by an increase in the potential difference with the highest ΔEp at 500 ppm BBD electrode (ΔEp = 711 mV). To achieve the H-terminal surface, single and cumulative reduction was tested by inserting Eakt = −3.0 V. A sufficient single reduction time for the [Fe(CN)6]4−/3− system was determined to be 60 s, whereas in the case of dopamine, the electrochemical parameters did not stabilize at the selected reduction times, but the cathodic and anodic peak signal at the H-terminated 1000 ppm BDD electrode was up...
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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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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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Study of redox reactions and adsorption of 4-nitrophenyl triazole labeled nucleosides and cresols on boron doped diamond electrodes for development of electroanalytical methods
Vosáhlová, Jana ; Schwarzová, Karolina (advisor) ; Havran, Luděk (referee) ; Navrátil, Tomáš (referee)
In this work, the application of boron-doped diamond electrodes with various surface pre- treatment were tested on selected oxidizable and reducible model compounds, specifically para and ortho cresols and 2'-deoxycytidine and 7-deazaadenosine labeled by 4-nitrophenyl triazole. The aim of the study was the investigation of electrochemical and adsorptive processes with respect to the development of electroanalytical methods of detection of the selected compounds, or utilization of boron-doped diamond electrodes as detectors in liquid-flow systems. Cresols were used as the model oxidizable compound. On O-terminated and polished boron- doped diamond electrodes, cresols provide oxidation signal owing to their oxidation to methylphenoxy radical at comparable potentials as on other carbon-based electrodes used as a reference in this work, i.e., glassy carbon electrode, pyrolytic graphite electrode, and carbon paste electrode. These carbon electrode materials show relatively high propensity to adsorption of reaction products, while such adsorption is minimal on boron-doped diamond. In situ anodic activation allows for a rapid regeneration of boron-doped diamond surface prior to each scan. A differential pulse voltammetric method that was developed with a detection limit of 0.61 mol∙l-1 to 2.97 mol∙l-1...
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