Carbon is due to its electrochemical properties a favourite material for construction of electrodes suitable for detection in flow system. The two most often used techniques (coulometric and amperometric) will be discussed in this Thesis. Carbon paste electrodes (CPE) represent the amperometric detectors. CPE are unstable in the medium with high content of organic solvents, which might complicate their application in HPLC, where the mobile phase contains organic component. It is interesting, that glassy carbon paste electrodes are more stable under such conditions. The change of surface and response of the electrode caused by the effect of methanol are described in this Thesis along with the possible reason of stability of GCPE. Roughing of the surface exposed to methanol is demonstrated by confocal microscopy. This effect leads to increase of height of the peak, background current and noise and to the shift of peak potential to less positive values. These changes are dependent on the time of exposure and the concentration of methanol. Coulometric detectors work with high conversion effectiveness and sensitivity, but in case of their passivation, reactivation is a relatively complicated problem, often leading to the replacement of electrode material. Answer to this problem can be given by using...

Electrocatalysis is key to both sensitive electrochemical sensing and efficient electrochemical energy conversion. Despite high catalytic activity, traditional metal catalysts have poor stability, low selectivity, and high cost. Metal-free, carbon-based materials are emerging as alternatives to metal-based catalysts because of their attractive features including natural abundance, environmental friendliness, high electrical conductivity, and large surface area. Altering surface functionalities and heteroatom doping are effective ways to promote catalytic performance of carbon-based catalysts. The first chapter of this dissertation focuses on developing electrode modification methods for electrochemical sensing of biomolecules. After electrochemical pretreatment, glassy carbon demonstrates impressive figures-of-merit in detecting small, redox-active biomolecules such as DNA bases and neurotransmitters. The results highlight a simplified surface modification procedure for producing efficient and highly selective electrocatalysts. The next four chapters focus on evaluating nitrogen-doped carbon nano-onions (𝑛-CNOs) as electrocatalysts for oxygen reduction and CO2 reduction. 𝑛-CNOs exhibit excellent electrocatalytic performance toward O2 to H2O reduction, which is a pivotal process in fuel cells. 𝑛-CNOs demonstrate excellent resistance against CO poisoning and long-term stability compared to state-of-the-art Pt/C catalysts. In CO2 electrochemical conversion, 𝑛-CNOs demonstrate significant improvement in catalytic performance toward reduction of CO2 to CO with a low overpotential and high selectivity. The outstanding catalytic performance of 𝑛-CNOs originates from the asymmetric charge distribution and creation of catalytic sites during incorporation of nitrogen atoms. High contents of pyridinic and graphitic N are critical for high catalytic performance. This work suggests that carbon-based materials can be outstanding alternatives to traditional metal-based electrocatalysts when their microstructures and surface chemistries are properly tailored.

<p>This work reports the chemical synthesis, characterisation and electrochemical application of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles in the determination of phthalates. The other part of this work involved electrochemical polymerization of aniline doped with titanium and iron oxide nanoparticles for the sensor platform in the electrolytic determination of phthalates. The TiO2 and Fe2O3 nanoparticles were prepared by sol gel and hydrothermal methods respectively. Particle sizes of 20 nm (TiO2) and 50 nm (Fe2O3) were estimated from transmission electron microscopy (TEM) The other technical methods used in this study for the characterization of the TiO2 and iron oxide Fe2O3 NPs were SEM, XRD and UV- visible spectroscopy. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of the nanoparticles. These electrochemical studies of the nanoparticles were performed with a Fe2O3 or TiO2/nafion/glassy carbon membrane electrode in 0.1 M phosphate buffer (pH 7.0) and 0.1 M lithium perchlorate (pH 6.8) under an aerobic condition.</p>

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

<p>In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species.</p>

This study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3σblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses.

The main objective of this work was to develop simple and sensitive electrochemical sensors for the detection of bisphenol A. To investigate the electrochemical behavior of BPA on a bare glassy carbon electrode. To apply the developed biosensor for the determination BPA by differential pulse voltammetry, electrochemical impedance spectrometry, square wave voltammetry and steady-state amperometry. To characterize the synthesized PDMA-PSS by cyclic voltammetry (CV), UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM).

<p>This work reports the chemical synthesis, characterisation and electrochemical application of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles in the determination of phthalates. The other part of this work involved electrochemical polymerization of aniline doped with titanium and iron oxide nanoparticles for the sensor platform in the electrolytic determination of phthalates. The TiO2 and Fe2O3 nanoparticles were prepared by sol gel and hydrothermal methods respectively. Particle sizes of 20 nm (TiO2) and 50 nm (Fe2O3) were estimated from transmission electron microscopy (TEM) The other technical methods used in this study for the characterization of the TiO2 and iron oxide Fe2O3 NPs were SEM, XRD and UV- visible spectroscopy. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of the nanoparticles. These electrochemical studies of the nanoparticles were performed with a Fe2O3 or TiO2/nafion/glassy carbon membrane electrode in 0.1 M phosphate buffer (pH 7.0) and 0.1 M lithium perchlorate (pH 6.8) under an aerobic condition.</p>

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

<p>In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species.</p>