- Title
- Enhancing the electrocatalytic activity of phthalocyanines through finding the ideal combination of substituents in push-pull phthalocyanine-based systems
- Creator
- Nkhahle, Reitumetse Precious
- ThesisAdvisor
- Nyokong, Tebello
- Subject
- Phthalocyanines
- Subject
- Electrocatalysis
- Subject
- Hydrazine
- Subject
- Nitrites
- Subject
- Activating group
- Subject
- Deactivating group
- Date
- 2023-10-13
- Type
- Academic theses
- Type
- Doctoral theses
- Type
- text
- Identifier
- http://hdl.handle.net/10962/432578
- Identifier
- vital:72882
- Identifier
- DOI 10.21504/10962/432578
- Description
- Phthalocyanines (Pcs) are a class of synthetic pigments with a similar structure to porphyrins. The work presented in this thesis is centred around these electron-rich macrocycles and their use in electrocatalysis. This body of work provides a more rigorous analysis on asymmetric Pcs, focusing on finding the “ideal” combination of substituents in the synthesis of A3B-type Pcs and how these asymmetric structures compare with their symmetric counterparts (A4) in the electrocatalysis of hydrazine and nitrite. The choice in substituents in the syntheses of the Pcs was such that there is both electron-donating and electron-withdrawing groups to induce a push-pull effect. In the studies involving the electrocatalysis of hydrazine, asymmetric cobalt Pcs (CoPcs) possessing alkyl groups as the primary substituents, with variations in the acid-containing group, along with their symmetric counterparts, probes with potential for further improvement were identified. Using voltammetric and amperometric techniques, the analyte-electrode kinetics, mechanism in which the electrochemical reaction proceeds along with the limits of detection (LoD) were determined. In the general sense, the pentadecylphenoxy-derived CoPcs performed better than those containing the tert-butyl substituent as the dominant substituent with the asymmetric CoPcs producing more favourable results than their symmetric analogues. With respect to the probes designed for nitrite, a multi-dimensional approach was undertaken in that acetaminophen was chosen as the primary substituent whilst multiple changes in the asymmetric component were made. In addition to varying the carboxylic acid-containing substituent, alkyne- and amine-based substituents were also explored in which the alkyne-containing Pc was anchored onto the electrode surface through click chemistry while the amine-bearing Pc was covalently linked (and π-stacked) to nitrogen-doped graphene quantum dots (NGQDs). Another component that was altered was the central metal where CoPcs were compared to manganese Pcs (MnPcs). The most desirable peak oxidation potential for nitrite was observed in the MnPcs as it was the lowest with adsorption sometimes being a better suited method of electrode modification relative to clicking. The inclusion of NGQDs was found to be beneficial when combined with the symmetric CoPc whilst in the presence of an asymmetric Pc complex, less desirable results were observed. Overall, there were variations in the results with the symmetric CoPc sometimes being better than some of the asymmetric CoPcs demonstrating that a blanket-approach in terms of synthesizing and applying asymmetric Pcs is not always viable.
- Description
- Thesis (PhD) -- Faculty of Science, Chemistry, 2023
- Format
- computer, online resource, application/pdf, 1 online resource (253 pages), pdf
- Publisher
- Rhodes University, Faculty of Science, Chemistry
- Language
- English
- Rights
- Nkhahle, Reitumetse Precious
- Rights
- Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-ShareAlike" License (http://creativecommons.org/licenses/by-nc-sa/2.0/)
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details | SOURCE1 | NKHAHLE-PHD-TR23-277.pdf | 7 MB | Adobe Acrobat PDF | View Details |