- Title
- Symmetry and asymmetry in electrocatalysis: enhancing the electrocatalytic activity of phthalocyanines through synergy with doped graphene quantum dots
- Creator
- Nkhahle, Reitumetse Precious
- ThesisAdvisor
- Nyokong, T
- Subject
- Phthalocyanines
- Subject
- Quantum dots
- Subject
- Graphene
- Date
- 2020
- Type
- text
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10962/117585
- Identifier
- vital:34529
- Description
- An exploration on the enhancement of the electrocatalytic activity of phthalocyanines (Pcs) through coupling with a series of graphene quantum dots (GQDs) is undertaken. The preliminary studies using symmetrical Pcs, a cobalt and an iron chloride tetra substituted diethylaminophenoxy Pc (complexes 1 and 2), for the electro-oxidation of nitrite revealed through the various sequential modifications that doped GQDs fare better than their pristine counterparts with respect to improving the electrocatalytic behaviour of Pcs, in particular, the nitrogen-doped GQDs (NGQDs). Following up on this, a series of asymmetric Pc complexes; 2,9,16-tris-(4-tert-butylphenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (3), 2,9,16-tris-(4-tert-butylphenoxy) mono aminophenoxy phthalocyanato cobalt (II) (4), 2,9,16-tris-(3-diethylamino)phenoxy) mono carboxyphenoxy phthalocyanato cobalt (II) (5) and 2,9,16-tris-(3-diethylamino)phenoxy) mono aminophenoxy phthalocyanato cobalt (II) (6) was prepared in which push-pull systems were compared to other asymmetric complexes that lack this effect towards the electrocatalytic sensing of hydrazine. All asymmetric complexes (3-6) were π-stacked to the NGQDs while those with an NH2 group (4 and 6), were also covalently linked to the NGQDs. These complexes and their corresponding conjugates were characterized accordingly and applied as electrocatalysts in the oxidation of hydrazine. The electrochemical studies revealed that π π stacking yields better responses (higher sensitivities and lower limits of detection) than covalent linking because there are less forces acting on the graphene network. Covalent linking introduces both tensile and compressive forces which in turn results in an increase in the ID/IG ratio and that is unfavourable for electrocatalysis. In comparing the electrodes composed of the π-stacked conjugates to those altered through sequential modifications, despite the conditions not being the same, it can be inferred that the magnitude of the electrostatic forces between the Pcs and the GQDs also plays a significant role in electrocatalysis. The π-stacked conjugates, owing to the manner in which they were prepared, have stronger electrostatic forces acting between the Pc and GQDs hence they were able to elicit a better electrochemical response than the sequentially modified electrodes. In addition to that, it appears that asymmetric Pcs are better electrocatalysts in comparison to the symmetric Pcs.
- Format
- 118 pages, pdf
- Publisher
- Rhodes University, Faculty of Science, Chemistry
- Language
- English
- Rights
- Nkhahle, Reitumetse Precious
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | NKHAHLE-MSc-TR20-49.pdf | 6 MB | Adobe Acrobat PDF | View Details Download |