Electrode surface modification using iron(II) phthalocyanine immobilized via electrografting and click chemistry and clicked onto azide-functionalized quantum dots: applications in electrocatalysis
- Authors: Nxele, Siphesihle Robin
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3464 , vital:20501
- Description: Tetrakis(5-hexynoxy)Fe(II) phthalocyanine was used alone and in combination with quantum dots (QDs) in order to test the electrocatalytic ability with hydrazine and paraquat as the analytes of interest. This novel phthalocaynine was successfully synthesised and characterized using various characterisation techniques. The QDs used were the well-known core-shell CdSe/ZnS nanostructures. The fabrication of glassy carbon electrodes involved covalent attachment by electrochemical grafting and click chemistry for the first part of the work and the second part involved the conjugation of the synthesised QDs and the phthalocyanine by click chemistry. This approach of conjugating these nanostructures introduced another aspect of novelty to the work reported in this thesis. The immobilisation of this conjugate on a glassy carbon electrode (GCE) was achieved by adsorption. Characterisation techniques such as infrared spectroscopy, x-ray diffractometry, UV/vis spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterise the molecules and conjugates of interest. With respect to the electrocatalytic part of the work, electrode surface characterisation involved scanning electrochemical microscopy and cyclic voltammetry to determine changes in the nature of the surface as well as reactivity of the surface at different modification steps. Detection limits and the sensitivity determined for the electrocatalysts fabricated here proved to be an improvement compared to other reported work involving phthalocyanines and the test analytes chosen for application. With respect to the conjugate, the electrocatalytic ability was improved when the QDs and phthalocyanine were combined using click chemistry compared to using the phthalocyanine alone.
- Full Text:
- Authors: Nxele, Siphesihle Robin
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3464 , vital:20501
- Description: Tetrakis(5-hexynoxy)Fe(II) phthalocyanine was used alone and in combination with quantum dots (QDs) in order to test the electrocatalytic ability with hydrazine and paraquat as the analytes of interest. This novel phthalocaynine was successfully synthesised and characterized using various characterisation techniques. The QDs used were the well-known core-shell CdSe/ZnS nanostructures. The fabrication of glassy carbon electrodes involved covalent attachment by electrochemical grafting and click chemistry for the first part of the work and the second part involved the conjugation of the synthesised QDs and the phthalocyanine by click chemistry. This approach of conjugating these nanostructures introduced another aspect of novelty to the work reported in this thesis. The immobilisation of this conjugate on a glassy carbon electrode (GCE) was achieved by adsorption. Characterisation techniques such as infrared spectroscopy, x-ray diffractometry, UV/vis spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterise the molecules and conjugates of interest. With respect to the electrocatalytic part of the work, electrode surface characterisation involved scanning electrochemical microscopy and cyclic voltammetry to determine changes in the nature of the surface as well as reactivity of the surface at different modification steps. Detection limits and the sensitivity determined for the electrocatalysts fabricated here proved to be an improvement compared to other reported work involving phthalocyanines and the test analytes chosen for application. With respect to the conjugate, the electrocatalytic ability was improved when the QDs and phthalocyanine were combined using click chemistry compared to using the phthalocyanine alone.
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Improved singlet oxygen generation by a novel bodipy dye and a study of upconverison nanoparticles mixed with a functionalized bodipy compound
- Wildervanck, Martijn Johannes
- Authors: Wildervanck, Martijn Johannes
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3718 , vital:20538
- Description: This research explores the use of the versatile 4,4-difluoro-4-boro-3a,4a-diaza-s-indacene (BODIPY) dyes and the modification of their spectroscopic properties. The synthesis of a tetramethyl-BODIPY bearing a sterically hindered meso-phenyl ring with an ethynyl functional group at the para-position was compared to that of its freely rotating counterpart with no methyl substituents on the BODIPY core, with the fluorescence properties in particular proving to be markedly different. These phenyl-ethynyl-substituted BODIPYs were used as the starting materials for the synthesis of novel BODIPY dyes for sensor applications via Sonogashira coupling reactions at the ethynyl position, but this resulted instead in the serendipitous synthesis of a novel BODIPY dimer in which the para-positions of the meso-phenyl rings are linked by a diethynyl bridge. Following iodination at the 2, 6-positions, the dimer was found to have a singlet oxygen quantum yield of 0.88, compared to the value of 0.86 that was obtained for the analogous monomer. Since the εmax values for the main spectral bands of the dimers are significantly higher, the compounds may be of interest for singlet oxygen generation applications. A second study was carried out on the interaction between methyl ester functionalized BODIPY dyes and upconversion nanoparticles (UCNPs) to explore the possible use of BODIPY-UCNP conjugates in biomedical applications. The singlet oxygen generation properties of the BODIPY were tested following iodination at the 2, 6-positions, a singlet oxygen quantum yield value of 0.86 was obtained. Three sets of oleate capped UCNPs were synthesized with different diameters and were rendered water dispersible with the addition of a silica shell. The necessary scaffolding for conjugation to the BODIPY was provided by amine groups following functionalization of this shell. All of the sets of oleate capped and silica coated UCNPs were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD) and their emission properties were studied upon excitation at 978 nm with a diode laser with a Picoquant Fluotime 300 spectrophotometer that enables the measurement of anti-Stokes emission. The potential utility of UCNP-BODIPY conjugates for singlet oxygen applications, such as PDT, was then assessed.
- Full Text:
- Authors: Wildervanck, Martijn Johannes
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3718 , vital:20538
- Description: This research explores the use of the versatile 4,4-difluoro-4-boro-3a,4a-diaza-s-indacene (BODIPY) dyes and the modification of their spectroscopic properties. The synthesis of a tetramethyl-BODIPY bearing a sterically hindered meso-phenyl ring with an ethynyl functional group at the para-position was compared to that of its freely rotating counterpart with no methyl substituents on the BODIPY core, with the fluorescence properties in particular proving to be markedly different. These phenyl-ethynyl-substituted BODIPYs were used as the starting materials for the synthesis of novel BODIPY dyes for sensor applications via Sonogashira coupling reactions at the ethynyl position, but this resulted instead in the serendipitous synthesis of a novel BODIPY dimer in which the para-positions of the meso-phenyl rings are linked by a diethynyl bridge. Following iodination at the 2, 6-positions, the dimer was found to have a singlet oxygen quantum yield of 0.88, compared to the value of 0.86 that was obtained for the analogous monomer. Since the εmax values for the main spectral bands of the dimers are significantly higher, the compounds may be of interest for singlet oxygen generation applications. A second study was carried out on the interaction between methyl ester functionalized BODIPY dyes and upconversion nanoparticles (UCNPs) to explore the possible use of BODIPY-UCNP conjugates in biomedical applications. The singlet oxygen generation properties of the BODIPY were tested following iodination at the 2, 6-positions, a singlet oxygen quantum yield value of 0.86 was obtained. Three sets of oleate capped UCNPs were synthesized with different diameters and were rendered water dispersible with the addition of a silica shell. The necessary scaffolding for conjugation to the BODIPY was provided by amine groups following functionalization of this shell. All of the sets of oleate capped and silica coated UCNPs were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD) and their emission properties were studied upon excitation at 978 nm with a diode laser with a Picoquant Fluotime 300 spectrophotometer that enables the measurement of anti-Stokes emission. The potential utility of UCNP-BODIPY conjugates for singlet oxygen applications, such as PDT, was then assessed.
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Nanocomposites of carbon nanomaterials and metallophthalocyanines : applications towards electrocatalysis
- Authors: Nyoni, Stephen
- Date: 2016
- Subjects: Nanocomposites (Materials) , Nanostructured materials , Electrocatalysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4561 , http://hdl.handle.net/10962/d1020846
- Description: Nanohybrid materials have been prepared and examined for their electrocatalytic activity. The nanocomposites have been prepared from carbon nanomaterials (multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets), cadmium selenide quantum dots and metallophthalocyanines (MPcs). The MPcs used in this work are cobalt tetraamino-phthalocyanine (CoTAPc) and tetra (4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt (II)) (CoPyPc). Their activity has also been explored in different forms; polymeric MPcs, iodine doped MPcs and covalently linked MPcs. The premixed drop-dry, sequential drop-dry and electropolymerisation electrode modification techniques were used to prepare nanocomposite catalysts on the glassy carbon electrode (GCE) surface. The sequential drop dry technique for MPc and MWCNTs gave better catalytic responses in terms of limit of detection, catalytic and electron transfer rate constants relative to the premixed. MWCNTs and CdSe-QDs have been used as intercalating agents to reduce restacking of graphene nanosheets during nanocomposite preparation. Voltammetry, chronoamperometry, scanning electrochemical microscopy and electrochemical impedance spectroscopy methods are used for electrochemical characterization modified GCE. X-ray photoelectron spectroscopy, X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, infra-red spectroscopy, Raman spectroscopy were used to explore surface functionalities, morphology and topography of the nanocomposites. Electrocatalytic activity and possible applications of the modified electrodes were tested using oxygen reduction reaction, l-cysteine oxidation and paraquat reduction. Activity of nanocomposites was found superior over individual nanomaterials in these applications.
- Full Text:
- Authors: Nyoni, Stephen
- Date: 2016
- Subjects: Nanocomposites (Materials) , Nanostructured materials , Electrocatalysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4561 , http://hdl.handle.net/10962/d1020846
- Description: Nanohybrid materials have been prepared and examined for their electrocatalytic activity. The nanocomposites have been prepared from carbon nanomaterials (multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets), cadmium selenide quantum dots and metallophthalocyanines (MPcs). The MPcs used in this work are cobalt tetraamino-phthalocyanine (CoTAPc) and tetra (4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt (II)) (CoPyPc). Their activity has also been explored in different forms; polymeric MPcs, iodine doped MPcs and covalently linked MPcs. The premixed drop-dry, sequential drop-dry and electropolymerisation electrode modification techniques were used to prepare nanocomposite catalysts on the glassy carbon electrode (GCE) surface. The sequential drop dry technique for MPc and MWCNTs gave better catalytic responses in terms of limit of detection, catalytic and electron transfer rate constants relative to the premixed. MWCNTs and CdSe-QDs have been used as intercalating agents to reduce restacking of graphene nanosheets during nanocomposite preparation. Voltammetry, chronoamperometry, scanning electrochemical microscopy and electrochemical impedance spectroscopy methods are used for electrochemical characterization modified GCE. X-ray photoelectron spectroscopy, X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, infra-red spectroscopy, Raman spectroscopy were used to explore surface functionalities, morphology and topography of the nanocomposites. Electrocatalytic activity and possible applications of the modified electrodes were tested using oxygen reduction reaction, l-cysteine oxidation and paraquat reduction. Activity of nanocomposites was found superior over individual nanomaterials in these applications.
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The effect of shaped nanoparticles on the photophysicochemical behaviour of metallophthalocyanines
- Authors: D'Souza, Sarah
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/529 , vital:19967
- Description: The synthesis, spectroscopic characterization and photophysicochemical analysis of novel and known metallophthalocyanines are reported in this thesis. The novel lowsymmetry compounds were extensively studied. Selected phthalocyanines were conjugated to a variety of nanoparticles consisting of silver (AgNPs), gold (AuNPs) and zinc oxide (ZnO NPs) in order to improve their photophysical and photochemical behaviour. As with the phthalocyanines, the nanoparticles and phthalocyaninenanoparticle conjugates were thoroughly investigated. Research on the effect of the solvent used, as well as the influence of nanoparticle composition and shape on the properties of the phthalocyanines, were performed. The findings showed that there was a general increase in triplet quantum yields of the phthalocyanines in the presence of the nanoparticles. It was also noted that the use of different solvents directly affected the photophysicochemical properties. In the case of the nanoparticle conjugates, photophysical and photochemical changes were observed. Of significance were the gold nanostars, which decreased the degree of phthalocyanine aggregation in water, resulting in increased fluorescence lifetimes. The studies also revealed that the effect of the nanoparticle shape on the phthalocyanine properties was highly dependent on the nanoparticle material. The photodynamic antimicrobial activity of selected phthalocyanine-zinc oxide nanoparticle conjugates was investigated against Staphylococcus aureus (S. aureus) in solution. The phthalocyanines alone exhibited remarkable growth inhibition, however the presence of the nanoparticles in the conjugates increased the photoinactivation of S. aureus.
- Full Text:
- Authors: D'Souza, Sarah
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/529 , vital:19967
- Description: The synthesis, spectroscopic characterization and photophysicochemical analysis of novel and known metallophthalocyanines are reported in this thesis. The novel lowsymmetry compounds were extensively studied. Selected phthalocyanines were conjugated to a variety of nanoparticles consisting of silver (AgNPs), gold (AuNPs) and zinc oxide (ZnO NPs) in order to improve their photophysical and photochemical behaviour. As with the phthalocyanines, the nanoparticles and phthalocyaninenanoparticle conjugates were thoroughly investigated. Research on the effect of the solvent used, as well as the influence of nanoparticle composition and shape on the properties of the phthalocyanines, were performed. The findings showed that there was a general increase in triplet quantum yields of the phthalocyanines in the presence of the nanoparticles. It was also noted that the use of different solvents directly affected the photophysicochemical properties. In the case of the nanoparticle conjugates, photophysical and photochemical changes were observed. Of significance were the gold nanostars, which decreased the degree of phthalocyanine aggregation in water, resulting in increased fluorescence lifetimes. The studies also revealed that the effect of the nanoparticle shape on the phthalocyanine properties was highly dependent on the nanoparticle material. The photodynamic antimicrobial activity of selected phthalocyanine-zinc oxide nanoparticle conjugates was investigated against Staphylococcus aureus (S. aureus) in solution. The phthalocyanines alone exhibited remarkable growth inhibition, however the presence of the nanoparticles in the conjugates increased the photoinactivation of S. aureus.
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