- Title
- Development of TiO2 nanostructures with a modified energy band gap for hydrogen extraction
- Creator
- Mutubuki, Arnold
- Subject
- Nanostructures
- Subject
- Nanoscience
- Subject
- Nanochemistry
- Date Issued
- 2024-04
- Date
- 2024-04
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/64226
- Identifier
- 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.
- Description
- Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (151 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Mutubuki, A.pdf | 5 MB | Adobe Acrobat PDF | View Details Download |