| Summary: | <p>This thesis focuses on the electrochemical studies for two distinct purposes: one is to invent and validate an electrochemical sensor for detecting phosphate in natural aqueous solutions. The other is to develop a more comprehensive understanding of electrocatalysis at ensemble and single entity multiwalled carbon nanotubes (MWCNTs). Chapter 1 introduces essential background knowledge about fundamental electrochemistry and the generic electrochemical techniques used in this thesis and Chapter 2 gives a detailed description about experimental methods and materials characterization.</p>
<p>Chapter 3 and 4 reports a novel amperometric sensor for aqueous phosphate ions in freshwater systems: Chapter 3 reviews previous work related to amperometric methods for phosphate analysis and uses commercial software to predict the speciation of molybdate, phosphate and their complex species both separately and in mixtures in aqueous solution as a function of concentration and pH. Chapter 4 builds on the work in Chapter 3 to realize the electrochemical detection of phosphate at an ammonium molybdate tetrahydrate-chitosan modified glassy carbon macro electrode in aqueous solutions. By employing cyclic voltammetry (CV) and square wave voltammetry (SWV), the electrocatalytic mechanism for quantitative detection of trace phosphate was inferred and this method was optimized and successfully applied for environmental use.</p>
<p>Chapter 5, 6 and 7 focus on the electrocatalytic nano-impacts of single carbon nanotubes. Chapter 5 reports the electro-oxidation of amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH2) under acidic and neutral conditions, making comparison with pure multiwalled carbon nanotubes (MWCNTs) at ensemble and single entity level. By measuring the extent of protonation of amino groups as a function of pH reflected by the oxidative signals in CV and nano-impacts, the pKa of the amino functionality in the MWCNTs was determined. Chapter 6 studies the mechanism of oxygen reduction reaction (ORR) catalysed by MWCNTs at single entity level. It reveals that the surface oxygen functionality on carbon nanotubes facilitated the reduction from oxygen to peroxide in alkaline media. Then based on this inference, we further compared the electrocatalytic performance of ORR at single MWCNT or MWCNTs-NH2 particles in Chapter 7. By comparing the voltammetric behaviour on glassy carbon macro electrode modified with layers of MWCNTs or MWCNTs-NH2 ensemble and impact signal from the collision of a single MWCNTs or MWCNTs-NH2 particle, it was inferred that the promotion of the electrocatalytic reaction of the oxygen reduction is primarily due to the amount of surface oxygen functionality not the nitrogen content. The generic approach discussed in these three chapters gives proof of concept to the use of joint single entity and ensemble measurements for exploring electrocatalysis with scope for application to a wide range of nano-entities.</p>
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