Development of TiO2 nanostructures with a modified energy band gap for hydrogen extraction
- Authors: Mutubuki, Arnold
- Date: 2024-04
- Subjects: Nanostructures , Nanoscience , Nanochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64226 , vital:73666
- Description: A rise in fossil fuel depletion has motivated the research towards alternative, cost effective and clean processes for energy production through renewable sources. The scientific community is currently engaged in extensive research to exploit viable, sustainable methods for generating green hydrogen. Titania (TiO2) is historically the most studied photoactive semiconductor material with great potential in photoelectrochemical water splitting (PECWS), following the discovery by Fujishima and Honda in 1972. TiO2 possesses superior physicochemical characteristics and band gap edges, which enables the semiconductor to effectively facilitate the PECWS process. Efforts are still ongoing to explore alternatives for narrowing the optical band gap energy of TiO2, for an efficient photoelectrode. In this research work, open-ended and well-ordered TiO2 nanotubular arrays were synthesised by a three-step anodization process. The third anodization was crucial to detach the TiO2 thin film from an opaque Ti metal substrate. The free-standing thin films were transferred and pasted onto conductive FTO-coated glass substrates transparent to visible light and annealed at 400 ℃ for crystallisation. The multi-step anodization has shown an improved top tube morphology by eliminating an initiation TiO2 mesh formed when a conventional single-step anodization process is used under similar conditions. To widen the absorption range of the samples, CuO nanosheets were deposited onto nanotubular TiO2/FTO films through successive ionic layer adsorption (SILAR), a wet chemical method. The formation of a CuO/TiO2 nanostructure enhances the transfer of photogenerated carriers, suppressing charge recombination. This research focused on investigating the influence of selected SILAR parameters on the formation of CuO nanostructures. The first was the effect of precursor concentration on the structural, morphological and optical properties of the CuO/TiO2/FTO nanostructured photoelectrode. The effect of the precursor concentration on the structure and morphology was evident in the X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) micrographs. Crystallite sizes of deposited CuO increased from 10.6 nm to 15.7 nm when precursor concentration was varied from 0.02 M to 0.10 M. The UV-visible absorbance results show that an increase in precursor concentration leads to a red shift of both the peak absorbance and edge wavelength of the CuO/TiO2/FTO absorbance spectra. This phenomenon is believed to be caused by the presence of CuO, which exhibits active absorption in the visible spectrum. As evidenced by the study, the continued increase in precursor concentration does not result in a further widening of the absorption band. This is demonstrated by the example of a CuO/TiO2/FTO sample decorated with a 0.2 M precursor. The second was the effect of SILAR immersion cycles on the properties of the CuO/TiO2/FTO nanostructure developed. The increase in the number of immersion cycles led to a notable progression in the adsorption cupric oxide on the TiO2/FTO samples. A redshift in the absorbance peak and edge wavelength is observed in the UV-visible spectra of CuO/TiO2/FTO photoelectrode. The efficacy of the SILAR technique in modifying the absorption band of nanotubular TiO2 thin films has been conclusively demonstrated through comprehensive analysis and correlation of the relationships between the structure and optical properties, as evidenced by the XRD patterns, Raman spectra, SEM, TEM micrographs, and UV-visible absorbance spectra. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Mutubuki, Arnold
- Date: 2024-04
- Subjects: Nanostructures , Nanoscience , Nanochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64226 , vital:73666
- Description: A rise in fossil fuel depletion has motivated the research towards alternative, cost effective and clean processes for energy production through renewable sources. The scientific community is currently engaged in extensive research to exploit viable, sustainable methods for generating green hydrogen. Titania (TiO2) is historically the most studied photoactive semiconductor material with great potential in photoelectrochemical water splitting (PECWS), following the discovery by Fujishima and Honda in 1972. TiO2 possesses superior physicochemical characteristics and band gap edges, which enables the semiconductor to effectively facilitate the PECWS process. Efforts are still ongoing to explore alternatives for narrowing the optical band gap energy of TiO2, for an efficient photoelectrode. In this research work, open-ended and well-ordered TiO2 nanotubular arrays were synthesised by a three-step anodization process. The third anodization was crucial to detach the TiO2 thin film from an opaque Ti metal substrate. The free-standing thin films were transferred and pasted onto conductive FTO-coated glass substrates transparent to visible light and annealed at 400 ℃ for crystallisation. The multi-step anodization has shown an improved top tube morphology by eliminating an initiation TiO2 mesh formed when a conventional single-step anodization process is used under similar conditions. To widen the absorption range of the samples, CuO nanosheets were deposited onto nanotubular TiO2/FTO films through successive ionic layer adsorption (SILAR), a wet chemical method. The formation of a CuO/TiO2 nanostructure enhances the transfer of photogenerated carriers, suppressing charge recombination. This research focused on investigating the influence of selected SILAR parameters on the formation of CuO nanostructures. The first was the effect of precursor concentration on the structural, morphological and optical properties of the CuO/TiO2/FTO nanostructured photoelectrode. The effect of the precursor concentration on the structure and morphology was evident in the X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) micrographs. Crystallite sizes of deposited CuO increased from 10.6 nm to 15.7 nm when precursor concentration was varied from 0.02 M to 0.10 M. The UV-visible absorbance results show that an increase in precursor concentration leads to a red shift of both the peak absorbance and edge wavelength of the CuO/TiO2/FTO absorbance spectra. This phenomenon is believed to be caused by the presence of CuO, which exhibits active absorption in the visible spectrum. As evidenced by the study, the continued increase in precursor concentration does not result in a further widening of the absorption band. This is demonstrated by the example of a CuO/TiO2/FTO sample decorated with a 0.2 M precursor. The second was the effect of SILAR immersion cycles on the properties of the CuO/TiO2/FTO nanostructure developed. The increase in the number of immersion cycles led to a notable progression in the adsorption cupric oxide on the TiO2/FTO samples. A redshift in the absorbance peak and edge wavelength is observed in the UV-visible spectra of CuO/TiO2/FTO photoelectrode. The efficacy of the SILAR technique in modifying the absorption band of nanotubular TiO2 thin films has been conclusively demonstrated through comprehensive analysis and correlation of the relationships between the structure and optical properties, as evidenced by the XRD patterns, Raman spectra, SEM, TEM micrographs, and UV-visible absorbance spectra. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Synthesis, characterization and in vitro biological studies of cholesterol-based carriers as potential therapeutic agents
- Authors: Ruwizhi, Ngonidzashe
- Date: 2021-03
- Subjects: Drug delivery systems , Cholesterol
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20708 , vital:46443
- Description: Malaria, cancer and bacterial infections are numbered among the highest causes of fatalities. Most of the drugs used to combat these diseases suffer from resistance, poor absorption and bioavailability and high toxicity. Therefore, delivering a drug requires an excellent drug delivery system that must provide the medication at the site of action in the minimum time possible. Cholesterol is a sterol that is abundantly found in the human body and forms a part in the structure and organization of cell membranes. Many researchers have used cholesterol, especially in organic synthesis, because of its ready availability, low cost and functional groups that can be readily derivatized. In this research, different therapeutic agents (anticancer, antimalarial and antibacterial) were conjugated to cholesterol, and the synthesized compounds were characterized using FTIR, 1H and 13C NMR, Mass Spectroscopy, 2D 1H-13C, HSQC NMR and tested for in vitro biological activity. Thirteen compounds were successfully synthesized. CHS-Cur was the most effective against all Gram-positive bacterial strains, while CHS-Cur, CHS-ZD and C-CAC-ZD were effective against all the bacterial strains. C-CAC-Pyr showed good antiplasmodial activity with 97.75 and 97.83% inhibition at 20 and 10 μg/ml concentrations, respectively. The biological activity of some of the compounds was increased by the conjugation of cholesterol, while others displayed reduced biological activity. In vitro cytotoxicity of the synthesized compounds on HeLa (cervical cancer) cells showed that compounds 2 (7.559 μg/mL), 3 (5.840 μg/mL), 5 (1.44 mg/mL), 7 (4.308 μg/mL) and 11 (3.295 μg/mL) exhibited some good anticancer activity with IC50 values of less than 10 μg/mL. Treating T3T fibroblast cells with compounds 2, 4, 5, 6, and 10 did not reveal a cytotoxic effect on the normal cells when compared to the control, cisplatin. , Thesis (MSc) (Chemistry) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-03
- Authors: Ruwizhi, Ngonidzashe
- Date: 2021-03
- Subjects: Drug delivery systems , Cholesterol
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20708 , vital:46443
- Description: Malaria, cancer and bacterial infections are numbered among the highest causes of fatalities. Most of the drugs used to combat these diseases suffer from resistance, poor absorption and bioavailability and high toxicity. Therefore, delivering a drug requires an excellent drug delivery system that must provide the medication at the site of action in the minimum time possible. Cholesterol is a sterol that is abundantly found in the human body and forms a part in the structure and organization of cell membranes. Many researchers have used cholesterol, especially in organic synthesis, because of its ready availability, low cost and functional groups that can be readily derivatized. In this research, different therapeutic agents (anticancer, antimalarial and antibacterial) were conjugated to cholesterol, and the synthesized compounds were characterized using FTIR, 1H and 13C NMR, Mass Spectroscopy, 2D 1H-13C, HSQC NMR and tested for in vitro biological activity. Thirteen compounds were successfully synthesized. CHS-Cur was the most effective against all Gram-positive bacterial strains, while CHS-Cur, CHS-ZD and C-CAC-ZD were effective against all the bacterial strains. C-CAC-Pyr showed good antiplasmodial activity with 97.75 and 97.83% inhibition at 20 and 10 μg/ml concentrations, respectively. The biological activity of some of the compounds was increased by the conjugation of cholesterol, while others displayed reduced biological activity. In vitro cytotoxicity of the synthesized compounds on HeLa (cervical cancer) cells showed that compounds 2 (7.559 μg/mL), 3 (5.840 μg/mL), 5 (1.44 mg/mL), 7 (4.308 μg/mL) and 11 (3.295 μg/mL) exhibited some good anticancer activity with IC50 values of less than 10 μg/mL. Treating T3T fibroblast cells with compounds 2, 4, 5, 6, and 10 did not reveal a cytotoxic effect on the normal cells when compared to the control, cisplatin. , Thesis (MSc) (Chemistry) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-03
Composition portfolio
- Authors: Moss, Keith
- Date: 2007
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/193724 , vital:45390
- Description: Whitacre's music is primarily diatonic with subtle modulations, where the new key is always preserved diatonicaliy as well. I refer to this style as expanded diatonicism. Examples in my work of expanded diatonicism within this portfolio are to be found in navem ad somnium, Wynken, Blynken and Nod, as well as Hymn for Brass. My applications of expanded diatonic practices within each of these works are discussed in a separate appendix within the body of this portfolio. That these works are vocal or have a vocal inspiration (Hymn for Brass) reveals the extent of my initial reaction to Whitacre's music during a choral rehearsal. Furthermore, in my vocal compositions especially I chose texts which frequently gravitate towards ideas related to water, the ocean and ships. Whilst water has a soothing and inspiring influence upon me, presumably evidenced in my expanded diatonicism, it also represents my journey and investigation into the sound work of Whitacre in particular. It may be noticed that many of my works in this portfolio have religious orientated themes. I am a Christian, and belong to a Berean 2 Congregational Church. Whilst I am not Catholic or Anglican, I nonetheless have made use of texts from the liturgy of these denominations, as they emphasise the basis of my Christian faith. Why I chose Hymn for Brass as a title could possibly be construed as a religious reference, however it was named after the piece was written, and had no theological connotations in its inception save for the hymnody style of the orchestration. Providence and The Eventide both have a Christian philosophical foundation which is explored in depth in the accompanying appendix. The latter work explores an extension of my expanded diatonic style through incorporating aspects of chromaticism. The rationale for this is dealt with in my discussion of this work. This portfolio represents an overview of my compositional activities to date and displays my growing confidence with the technical aspects of composition as well as my yearning for experimentation with new ideas and manners of expression. , Thesis (MMus) -- Faculty of Humanities, Music and Musicology, 2007
- Full Text:
- Date Issued: 2007
- Authors: Moss, Keith
- Date: 2007
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/193724 , vital:45390
- Description: Whitacre's music is primarily diatonic with subtle modulations, where the new key is always preserved diatonicaliy as well. I refer to this style as expanded diatonicism. Examples in my work of expanded diatonicism within this portfolio are to be found in navem ad somnium, Wynken, Blynken and Nod, as well as Hymn for Brass. My applications of expanded diatonic practices within each of these works are discussed in a separate appendix within the body of this portfolio. That these works are vocal or have a vocal inspiration (Hymn for Brass) reveals the extent of my initial reaction to Whitacre's music during a choral rehearsal. Furthermore, in my vocal compositions especially I chose texts which frequently gravitate towards ideas related to water, the ocean and ships. Whilst water has a soothing and inspiring influence upon me, presumably evidenced in my expanded diatonicism, it also represents my journey and investigation into the sound work of Whitacre in particular. It may be noticed that many of my works in this portfolio have religious orientated themes. I am a Christian, and belong to a Berean 2 Congregational Church. Whilst I am not Catholic or Anglican, I nonetheless have made use of texts from the liturgy of these denominations, as they emphasise the basis of my Christian faith. Why I chose Hymn for Brass as a title could possibly be construed as a religious reference, however it was named after the piece was written, and had no theological connotations in its inception save for the hymnody style of the orchestration. Providence and The Eventide both have a Christian philosophical foundation which is explored in depth in the accompanying appendix. The latter work explores an extension of my expanded diatonic style through incorporating aspects of chromaticism. The rationale for this is dealt with in my discussion of this work. This portfolio represents an overview of my compositional activities to date and displays my growing confidence with the technical aspects of composition as well as my yearning for experimentation with new ideas and manners of expression. , Thesis (MMus) -- Faculty of Humanities, Music and Musicology, 2007
- Full Text:
- Date Issued: 2007
"Burnout" in children's home houseparents
- Authors: Bath, Peter John
- Date: 1983
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/193118 , vital:45300
- Description: Aimed at replicating the results of an American study into "Burnout" in Group Home houseparents, this research had the following aims: 1) To ascertain the validity and reliability of the instrument used in the original study and presented as a "useful measure of burnout”. 2) To establish whether this line of research, within a highly problematic research field, can at present offer any guidelines in the resolution of the current staffing crisis faced by South African children's homes. 3} To describe more closely the burnout syndrome. 4) To study possible etiological factors within a local context. Sixty three houseparents completed questionaires and three independent measures of burnout were obtained. The results were regarded as having failed to replicate those of the original study. The reason for this was found to be the low validity of the original instrument. The main conclusion drawn was that the line of research adopted in the original study can offer only very tentative guidelines towards the resolution of the staffing crisis faced until such time as valid and reliable instruments to measure burnout have been developed. Many of the suggested relationships between situational variables and ones of personal characteristics were confirmed for the local population of houseparents. , Thesis (MSocSci) -- Faculty of Humanities, Psychology, 1983
- Full Text:
- Date Issued: 1983
- Authors: Bath, Peter John
- Date: 1983
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/193118 , vital:45300
- Description: Aimed at replicating the results of an American study into "Burnout" in Group Home houseparents, this research had the following aims: 1) To ascertain the validity and reliability of the instrument used in the original study and presented as a "useful measure of burnout”. 2) To establish whether this line of research, within a highly problematic research field, can at present offer any guidelines in the resolution of the current staffing crisis faced by South African children's homes. 3} To describe more closely the burnout syndrome. 4) To study possible etiological factors within a local context. Sixty three houseparents completed questionaires and three independent measures of burnout were obtained. The results were regarded as having failed to replicate those of the original study. The reason for this was found to be the low validity of the original instrument. The main conclusion drawn was that the line of research adopted in the original study can offer only very tentative guidelines towards the resolution of the staffing crisis faced until such time as valid and reliable instruments to measure burnout have been developed. Many of the suggested relationships between situational variables and ones of personal characteristics were confirmed for the local population of houseparents. , Thesis (MSocSci) -- Faculty of Humanities, Psychology, 1983
- Full Text:
- Date Issued: 1983
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