Faculty of Natural Sciences

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Welcome to the scholarship of the Faculty of Natural Sciences.

The Faculty is developing a reputation as an important centre of research in South Africa. It equips graduates with solid academic and research skills and gives them the ability to succeed in the market place.

Electronic theses and dissertations are available in the Electronic Theses and Dissertations Repository.

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Coordination polymers as heterogeneous catalysts for oxidation reactions
(University of the Western Cape, 2014) Alarbi, Zohra; Titinchi, Salam; Abbo, Hanna
This study describes the synthesis and characterisation of coordination polymers complexes of Cu(II) and VO(IV) with two polymeric ligands N,Nʹ -1,2-phenylene bis(5-methylenesalicylidenamine)(L1) and N,Nʹ -1,4-butylene bis(5 methylenesalicylidenamine) (L2). Ligands L1 and L2 formed by condensation of 5,5ʹ-methylene bis-(salicylaldehyde) with 1,2-phenylenediamine and 1,4-diaminobutane respectively. The ligands and the complexes were characterized by UV/Vis spectroscopy, proton and carbon nuclear magnetic resonance spectroscopy (1H and 13C-NMR), Fourier transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy (SEM) and thermogravimetric Analysis (TGA)
Graphene based materials for carbon capture
(University of Western Cape, 2020) Kelly, Gabrielle Enid; Titinchi, Salam; Abbo, Hanna
The adverse effects of CO2 and greenhouse gas emissions into the atmosphere is believed to be one of the causes of climate change. The seriousness of global warming is encouraging the development of technologies designed to reduce CO2 emissions. Adsorption in the broadest context can be considered to be a promising method to address this due to the energy saving potential and regenerability, compared to other techniques. In this study, graphite was first oxidized to graphene oxide (GO) with concentrated acid. This was followed by formation of the aminosilanes viz. 3- aminopropyl-triethoxysilane (APTES), tris(2-aminoethyl)amine (TRIS) and guanidine being functionalized onto the surface of graphene oxide (GO). A second series involving the ordered mesoporous materials (OMS) was prepared employing cetyltrimethylammonium bromide (CTAB) and P123 triblock copolymer, as the structure directing agents for the organization of polymerizing silica species. Following the self-assembly of OMS onto GO, the so formed GO-OMS compound was modified with polyethylenimine (PEI). Several characterization techniques such as X-ray powder diffraction (XRD), Fourier Transform Infra-Red (FT-IR) spectroscopy, high resolution scanning microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM) and N2 physisoprion employing the Brunauer-Emmett-Teller (BET) analysis to determine specific surface areas of porous solid materials were employed to study the structural, morphological and textural properties of the adsorbents.
Novel Nanostructure Electrocatalysts for Oxygen Reduction and Hydrogen Evolution Reactions
(University of Western Cape, 2020) Lou, Lin; Titinchi, Salam; Abbo, Hanna
widespread use of fossil energy has been most convenient to the world, while they also cause environmental pollution and global warming. Therefore, it is necessary to develop clean and renewable energy sources, among which, hydrogen is considered to be the most ideal choice, which forms the foundation of the hydrogen energy economy, and the research on hydrogen production and fuel cells involved in its production and utilization are naturally a vital research endeavor in the world. Electrocatalysts are one of the key materials for proton exchange member fuel cells (PEMFCs) and water splitting. The use of electrocatalysts can effectively reduce the reaction energy barriers and improve the energy conversion efficiency. This thesis mainly focuses on development novel nanostructure electrocatalysts with low-cost, high activity and good durability used for oxygen reduction reaction (ORR) and hydrogen evolution. (1) Nitrogen-doped PtNiMo ternary alloys were synthesized by impregnation reduction followed by annealing at high temperatures.
Photocatalytic degradation of organic pollutants using Ag-Fe₃O₄/SiO₂/TiO₂ nanocomposite
(University of the Western Cape, 2015) Noganta, Siyasanga; Titinchi, Salam; Abbo, Hanna
The global lack of clean water for human sanitation and other purposes has become an emerging dilemma for human beings. The presence of organic pollutants in wastewater produced by textile industries, leather manufacturing and chemical industries is an alarming matter for a safe environment and human health. For the last decades, conventional methods have been applied for the purification of water but due to industrialization these methods fall short. Advanced oxidation processes and their reliable application in degradation of many contaminants have been reported as a potential method to reduce and/or alleviate this problem. Lately, it has been assumed that incorporation of some metal nanoparticles such as magnetite nanoparticles as photocatalyst for Fenton reaction could improve the degradation efficiency of contaminants. Core/shell nanoparticles, are extensively studied because of their wide applications in the biomedical, drug delivery, electronics fields and water treatment. The current study is centred on the synthesis of silver-doped Fe₃O₄/SiO₂/TiO₂ photocatalyst. Magnetically separable Fe₃O₄/SiO₂/TiO₂ composite with core–shell structure were synthesized by the deposition of uniform anatase TiO₂ NPs on Fe₃O₄/SiO₂ by using titanium butoxide (TBOT) as titanium source. Then, the silver is doped on TiO₂ layer by hydrothermal method. Integration of magnetic nanoparticles was suggested to avoid the post separation difficulties associated with the powder form of the TiO₂ catalyst, increase of the surface area and adsorption properties. Lastly and most importantly magnetic nanoparticles upsurge the production of hydroxyl groups or reduced charge recombination. The a synthesized catalysts were characterized using Transmission Electron Microscopy, X-ray Diffraction; Infra-red Spectroscopy, Scanning Electron Microscope and Energy Dispersive Spectroscopy. Other characterization techniques includeVibrating Sample Magnetometry, Brunauer Emmett Teller analysis and Thermogravimetric analysis. The average size of the particles size is 72 nm. Furthermore the photocatalytic performances of the magnetic catalysts were assessed in comparison with that commercial titanium dioxide for the degradation of methylene blue using photochemical reactor under ultra violet light. The results showed that the photocatalytic activity was enhanced using Fe₃O₄/SiO₂/TiO₂ and Ag-Fe₃O₄/SiO₂/TiO₂ compared with that for Fe₃O₄, commercial titanium dioxide powder.
Polyethylene glycol (peg-400): An efficient one-pot green synthesis and anti-viral activity of novel α-diaminophosphonates
(Taylor & Francis Online, 2019) Abbo, Hanna; Patnala, Harika; Potla, Krishna Murthy
An efficient and eco-friendly protocol has been accomplished for a series of novel a-diaminophosphonates by a one-pot, three-component system via Kabachnik-Fields reaction of 4,40 -methylenedianiline, a variety of aryl/heteroaryl aldehydes and diphenylphosphite employing polyethylene glycol (PEG-400) as a green solvent at 80 C. All products were obtained in good to excellent yields (80–95%).
Synthesis and characterization of new adsorbents for CO2 capturing
(University of the Western Cape, 2014) Piet, Marvin; Titinchi, Salam; Abbo, Hanna
Carbon dioxide emissions have become a major concern as they are one of the contributing factors to the “green-house” effect. Recently, much effort has been put into separating carbon dioxide (CO2) from flue gases linked to the combustion processes at fixed point sources. The development of solid sorbents for adsorption based on CO2 capture has attracted much attention. Ordered Mesoporous Silica (OMS) materials have recently attracted much attention as solid adsorbents for capturing CO2. OMS have been investigated for this purpose owing to their high pore volume, large surface area and ease of functionalizationIn this work we report on the synthesis of OMS viz. MCM-41 and SBA-15 along with amorphous silica as adsorbents for CO2 capture. MCM-41 was prepared with surfactants having different alkyl chain lengths (C14TABr, C16TABr and C18TABr) where TABr is trimethylammonium bromide. SBA-15 was prepared using a Triblock copolymer as a structure directing agent for the organization of polymerizing silica species. Commercial amorphous silica gel was used for comparative purposes. Initial characterization OMS with powder X-Ray diffraction (XRD) and small angle diffraction (SAXS) yielded diffraction patterns which may be associated with well-ordered structures of hexagonal mesoporous material. Ease of preparation for MCM-41 materials allowed for convenient scale- up, obtaining highly ordered mesoporous silica MCM-41 at room temperature. SBA-15 was also found to be scaled up with considerable ease through increasing the volume of the autoclave during hydrothermal treatment. Structural, morphological and textural properties of the adsorbents were characterized by N2 physisorption measurements, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). TEM confirmed the hexagonal structure; SEM showed that C14MCM-41 had spheroidal particle morphology whereas SBA-15 displayed rod-like structures. High surface areas of up to 1302, 1186, 1211 and 1024 m2/g for C14MCM-41, C16MCM-41, C18MCM-41 and SBA-15, respectively were obtained. The pore size of MCM-41 materials was increased from 2.6 nm for C14MCM-41 to 4.4 nm in diameter for C18MCM-41 using surfactants with different alkyl chain lengths. CO2 adsorption characteristics of OMS were studied using CO2-temperature programmed desorption (TPD). The results showed that C14MCM-41, C16MCM- 41, C18MCM-41 and SBA-15 desorbed 0.19, 0.16, 0.11 and 0.26 mmol/g respectively. The synthesized OMS were then further modified by grafting various amine moieties on their surfaces in order to increase their CO2 adsorptive capabilities. 3-(Aminopropyl)triethoxysilane (APS), N-[3-(trimethoxysilyl)propyl]ethylene- diamine (TPED), 3-chloropropyl)-trimethoxysilane (CPS), ethyl 2-bromopropanoate, tris(2-aminoethyl)amine (TREN) and guanidine. Several characterization techniques such as XRD, SAXS, HRTEM, HRSEM, TGA, Fourier Transform Infra-Red (FT-IR) spectroscopy, CO2 isotherms and CO2-TPD were used to analyze amine grafted solid sorbents for CO2 capture. The results revealed that the structural integrity of the amine modified sorbents was not compromised during the grafting process. The structural properties of the supports, such as surface area and pore size, nature of amine and the number of amine groups, affected the loading and CO2 adsorption capacity of chemically grafted sorbents. APS grafted amorphous silica gel adsorbed 0.67 mmol/g CO2, which proved to be the highest compared to C18MCM-41 and SBA-15 grafted with APS and TPED. C18MCM-41, SBA-15 and amorphous silica gel were also grafted with TREN and adsorbed 0.42, 0.51 and 0.27 mmol/g of CO2, respectively. A systematic study of guanidine grafted on C14MCM-41, C16MCM-41 and C18MCM-41 was investigated, for the first time, to the best of our knowledge. Structural properties like variation in pore size, proved to enhance the adsorption capacity of the adsorbent, coupled with the guanidine molecules grafted on MCM-41 materials. C18MCM-41-guanidine showed the highest CO2 uptake of the guanidine grafted MCM-41 materials, adsorbing 0.30 mmol/g. A novel synthetic route to TPED-TREN grafted C18MCM-41 and SBA-15, using ethyl 2-bromopropanoate as a linker, was investigated as a potential adsorbent for CO2 capture, for the first time. C18MCM-41-TPED-TREN and SBA-15-TPED-TREN CO2 adsorption capacity were found to be 0.14 and 0.14 mmol/g, respectively.

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