Photocatalytic treatment of organic and inorganic water pollutants using zinc phthalocyanine-cobalt ferrite magnetic nanoparticle conjugates
- Authors: Mapukata, Sivuyisiwe
- Date: 2019
- Subjects: Phthalocyanines , Cobalt ferrite , Zinc , Nanoparticles
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/67603 , vital:29119
- Description: This work explores the synthesis and photophysicochemical properties of zinc phthalocyanines when conjugated to cobalt ferrite magnetic nanoparticles. Phthalocyanines with amine and carboxylic acid functional groups were synthesised so as to covalently link them via amide bonds to cobalt ferrite magnetic nanoparticles with carboxylic acid and amine groups, respectively. Spectroscopic and microscopic studies confirmed the formation and purity of the phthalocyanine-cobalt ferrite magnetic nanoparticle conjugates which exhibited enhanced triplet and singlet quantum yields compared to the phthalocyanines alone. The studies showed that the presence of cobalt ferrite nanoparticles significantly lowered fluorescence quantum yields and lifetimes. The conjugates not only showed much higher singlet oxygen quantum yields compared to the phthalocyanines alone but were also attractive because of their magnetic regeneration and hence reusability properties, making them appealing for photocatalytic applications. The photocatalytic ability of some of the phthalocyanines and their conjugates were then tested based on their photooxidation and photoreduction abilities on Methyl Orange and hexavalent chromium, respectively. For catalyst support, some of the zinc phthalocyanines, cobalt ferrite magnetic nanoparticles and their respective conjugates were successfully incorporated into electrospun polystyrene and polyamide-6 fibers. Spectral characteristics of the functionalized electrospun fibers confirmed the incorporation of the photocatalysts and indicated that the phthalocyanines and their respective conjuagates remained intact with their integrity maintained within the polymeric fiber matrices. The photochemical properties of the complexes were equally maintained within the electrospun fibers hence they were applied in the photooxidation of azo dyes using Orange G and Methyl Orange as model organic compounds.
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- Date Issued: 2019
Development of a low-cost bioprinting system for the fabrication of cell-laden sodium alginate hydrogels
- Authors: Honiball, John Robert
- Date: 2018
- Subjects: Regenerative medicine , Tissue engineering , Alginates , Colloids , Three-dimensional printing
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/59204 , vital:27470
- Description: Bioprinting is a rapidly expanding technology with the ability to fabricate in vitro 3D tissues in a layer-by-layer manner to ultimately produce a living tissue which physiologically resembles native in vivo tissue functionality. Unfortunately, large costs associated with commercially available bioprinters severely limit the amount of people/research groups with access to the technology. Here, we investigated the potential for modifying a commercially available RepRap Prusa iteration 3 (i3) three-dimensional (3D) printer, by replacing the traditional plastic-based print-head with various open-source syringe-housed microextrusion print-head units, such that deposition of composite bioinks consisting of cells, biopolymer scaffolds and/or biomolecules may be achieved at a relatively low cost. Using adipose-derived human mesenchymal stromal stem cells (ad-HMSC) induced for adipogenic differentiation, as well as human umbilical vein endothelial cells (HUVEC), the potential for fabricating vascularised adipose tissue was investigated. The non-toxic, inexpensive algal polysaccharide, sodium alginate, was used to test the printability of the system, as well as for investigating the functionality unmodified sodium alginate has for use as a potential bioink in adipose tissue engineering. Cell viability assays, namely WST-1 and fluorescein diacetate (FDA)/propidium iodide (PI) live/dead cell staining, revealed that ad-HMSC were viable after 7 days of culture. However, viability of HUVEC encapsulated hydrogels revealed significantly lower cell viability. Live/dead cell staining revealed that the modified printing system was able to print ad-HMSC/HUVEC co-cocultures with a large degree of cell viability after 1 day of culture. However, after 7 days of culture, the majority of cells were revealed to be dead. Furthermore, due to the lack of mechanical integrity possessed by alginate in a liquid-like state, printing sodium alginate hydrogels in air consistently resulted in deformation of printed constructs. The newly developed 3D printing technique termed freeform reversible embedding of suspended hydrogels (FRESH) was therefore investigated as a means for achieving 3D spatial control of printed hydrogels using the modified system. Printing cell-free sodium alginate hydrogels within gelatin sacrificial support baths allowed for fabricating constructs in a spatially defined manner. However, overprinting and swelling of alginate hydrogels negatively affected the overall printing accuracy. The present study aimed to pave the way for further system modifications and refinements, such that the ultimate goal of low-cost bioprinting may be achieved. Further optimisation of printing parameters, hydrogel characteristics and sterilisation techniques may allow for fabricating viable, physiologically relevant tissues using the modified system developed.
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- Date Issued: 2018
Towards standardised reef fish monitoring: an assessment of stereo-video techniques to sample shallow and deep reef fish assemblages
- Authors: Halse, Sarah Jane
- Date: 2017
- Subjects: Reef fishes -- South Africa -- Agulhas, Cape (Cape) , Reef fishes -- Ecology -- South Africa -- Agulhas, Cape (Cape) , Marine biodiversity -- South Africa -- Agulhas, Cape (Cape) , Biotic communities -- South Africa -- Agulhas, Cape (Cape) , Sparidae -- South Africa -- Agulhas, Cape (Cape) , Reef fishes -- Size -- South Africa -- Agulhas, Cape (Cape) , Underwater videography in wildlife monitoring -- South Africa -- Tsitsikamma , Baited remote underwater stereo-video systems (stereo-BRUVs)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4635 , vital:20702
- Description: Baited remote underwater stereo-video systems (stereo-BRUVs) were developed to determine fish abundance and size structure in a more unbiased, and relatively non-invasive manner across a broader range of depths and habitats than conventional sampling methods achieve. These characteristics make stereo-BRUVs particularly useful for research inside marine protected areas (MPAs) where researchers are required to minimize disturbance to the protected environment. Although stereo-BRUVs have been widely used around the world, they are novel to South Africa and standardised protocols for their application are required. As such, this study aimed to address i) the effect of different bait types, namely pilchard (Sardinops sagax), squid (Loligo reynaudi) and bivalves (Crassostrea gigas and Perna perna) on the observed reef fish assemblage structure and ii) the effect of artificial illumination (lighting) on the observed reef fish assemblage structure sampled with stereo-BRUVs. One key component of the stereo-BRUVs methodology is the application of bait to attract fish into the field of view. Globally, pilchard is the most often used bait type for stereo- BRUVs, however, its suitability has never been tested comparatively against other bait types for South African conditions. Significant differences in fish abundance and assemblage structure were recorded between stereo-BRUVs deployments when applying the different bait types. The bivalve baits, oyster and mussel, were typically poor when sampling the reef fish assemblages of the region. Pilchard and squid were sampled in similar communities and were able to attract the majority of the reef fish from the region, suggesting they are suitable bait types for stereo-BRUVs in the Agulhas ecoregion. However, a power analysis indicated that roughly twice the amount of samples are required to effectively sample the same abundances of Chrysoblephus laticeps (roman) and Cheilodactylidae (fingerfins) species when sampling with squid as opposed to pilchard. Both bait types can be locally sourced, however, squid is considerably more expensive than pilchard. Considering the difference in cost, together with the fact that twice as much squid bait is required, squid is not a cost-effective option relative to pilchard. As such this study recommends that pilchard is the most appropriate bait for the Agulhas ecoregion of South Africa. Due to low light levels, artificial lighting is required when conducting remote video research in the sub-photic zone. Blue light has a shorter wavelength than other colour lights and attenuates slower through water. In addition, blue lighting has no recorded effect on fish behaviour and has proven to be a successful light colour for underwater sampling. The use of lighting is unavoidable for sub-photic stereo-BRUVs sampling and is recommended for all stereo-BRUVs sampling for comparability of data from environments characterised by different light levels. A study was conducted to test the necessity of artificial lighting when sampling from environments characterised by ambient light levels adequate for stereo- BRUVs sampling, a comparative to measure the effect of light on the fish assemblage structure. Of the more commonly detected fish species (those observed in >50% of the samples), most were seen at similar abundances in samples using lighting and in those without lighting. No significant differences were observed in fish length data between samples collected with and samples collected without lighting. This suggests that standardised stereo-BRUVs sampling across photic zones on the continental shelf of South Africa can be collected without blue lighting when ambient light levels are sufficient to see the survey area.
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- Date Issued: 2017