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A high-throughput, combinatorial and robotic approach to catalysis

A two-dimensional simulation of atomic layer deposition process on substrate trenches

  • Authors: Olotu, Olufunsho Oladipo
  • Date: 2019
  • Subjects: Atomic layer deposition , Thin films , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/413228 , uj:34805
  • Description: Abstract: In the cause of the increasing need for miniaturisation of devices, a more sophisticated nano-manufacturing technique of component was rummage around for, which has led to the adoption of atomic layer deposition (ALD) technique due to its competency of accomplishing superb uniformity, conformality, pinhole-free and ultra-thinness. In this dissertation, the ALD process within the cavity and surface of substrate trench was studied numerically with the intent to optimise the deposition process while formulating suitable ALD recipe. In the cause of optimising the process of an atomic layer deposition (ALD) for trenched substrate, a numerical model was presented, and two-dimensional simulations of the ALD process of substrate trenches in an arbitrary reactor were performed. Here, the deposition of aluminium oxide (Al2O3) was illustrated with trimethylaluminum (TMA) and ozone (O3) precursors as Aluminum (Al) and oxygen (O2) sources respectively while inert argon was used as purging gas in an arbitrary reactor. The flow is similar to a typical top-to-bottom type ALD reactor. The gases are assumed to enter at an inlet temperature of 150°C while the substrate, reactor walls and outlet temperature of 250°C is used. The TMA and O3 precursors are both pulsed separately, according to the sequence, into the reactor at 0.085 m/s for 0.2 and 1 second, respectively. While inert-purge gas (Ar) is used to purge the reactor domain at 0.17 m/s for 5 seconds between the pulse and exposure times. For this work the ALD sequence follows in a pulse-exposure-purge-exposure-pulse-exposure-purge manner to form a complete ALD cycle. After the reactive and inert-gases have flown and penetrated into the trenched substrate the excess and by-products are then exhausted past the edges of the trenched substrate towards the outlet of the reactor. The reactor flow domain is meshed into 67023 nodes. The ALD process within the arbitrary reactor is investigated by numerical simulating the reactor using computational fluid dynamics (CFD) within commercial software packages ANSYS FLUENT and CHEMKINPRO. This transient process is implemented by the coupled algorithm approach... , M.Ing. (Mechanical Engineering)
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Application of monometallic and bimetallic dendrimer encapsulated nanoparticles (DENs) and their catalytic evaluation on reduction of 4-nitrophenol

  • Authors: Patala, Rapelang
  • Date: 2016
  • Subjects: Dendrimers , Dendrimers - Synthesis , Catalysis , Inorganic compounds - Analysis , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/226086 , uj:22850
  • Description: M.Sc. (Chemistry) , Abstract: The compound 4-nitrophenol found in wastewater streams is mainly the result of industrial and agricultural production. Having adverse health effects associated with it, 4-nitrophenol should be removed from the environment or converted to less hazardous forms as efficiently as possible. Feasible techniques to get rid of this chemical compound are of great research interest. The synthesized nanoparticles encapsulated inside dendrimers (DENs) will be evaluated for catalytic activity against the reaction of 4-nitrophenol reduction. Transition metal nanoparticles find their application in catalysis; this makes them to be of great technological importance. They can be synthesized by evaporation, condensation and chemical or electrochemical reduction of metal salts in the presence of stabilizers. Dendrimers were used as templates for the synthesis of both monometallic and bimetallic nanoparticles which were evaluated as catalysts for the reduction of 4-nitrophenol. We also focused on comprehensive kinetic analysis of 4-nitrophenol reduction using dendrimer encapsulated metal nanoparticles (DENs). The adsorption rates and reaction rates were found and evaluated, and it could be concluded that bimetallic catalysts were more catalytically active than monometallic ones. Different ratios of bimetallic (AuPd) nanoparticles were also supported on different mesoporous metal oxides (MMOs) and their catalytic activity evaluated on reduction of 4-nitrophenol. The results were interpreted in the light of Langmuir Hinshelwood model. The AuPd bimetallic nanoparticles supported on MMOs showed synergistic effect. With the use of power rate law it was shown that 4-nitrophenol reduction follows first order kinetics.
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Application of “noble metals” for the electrocatalytic detection of monoamine group containing neurotransmitters

  • Authors: Meenakshi, K.M.
  • Date: 2016
  • Subjects: Nanostructured materials , Electrochemical sensors , Nanoscience , Electrocatalysis , Electrochemical analysis
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/124877 , uj:20969
  • Description: Abstract: Electrochemical biosensors have provided a new route to biomedical diagnosis and testing. Research to constantly improve biosensor performance and develop new protocols in biosensor design is ongoing. This work contributes to the field of biosensor development by exploring the applicabilities of conductive polymer (CP) and metal nanoparticles (MNPs) based nanocomposites as tools in electrochemical biosensor fabrication. In general, voltammetric and pulsed technique were employed to model the electrochemical reactivities of the CPs- MNPs on working glassy carbon electrodes; while the transmission electron microscopy (TEM), Scanning elelctron microscopy (SEM), UV-vis spectrophotometer (UV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) instrumental techniques were used for further characterisation.This thesis focuses on both the integration of functional nanomaterials to improve electrical interfacing between biological system and electronics. Metal nanoparticles based nanocomposite was prepared by using in situ polymerization and composite formation (IPCF) technique and used in the development of an electrochemical sensor for neurotransmitters (NTs) detection with simultaneous reduction of dyes. The MNPs-CPs composite was deposited on the glassy carbon electrode (GCE) by using the drop and dry method. The integration of various nanomaterials is described, in order to understand the effect of different surface modifications and morphologies of various materials for electrochemical sensing of biological analytes. IPCF approach are promising technique to provide key building blocks of nanocomposites for future practical systems, as well as model systems for fundamental research. A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of IPCF. The formation mechanism of the composite has been supported by a model hydrogen atom (H∙≡H+ + e-) transfer (HAT) type of reaction which belongs to the... , Ph.D. (Chemistry)
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Aqueous synthesis and characterization of CdSe/ZnO and Ag/ZnO core/shell nanomaterials

  • Authors: Rakgalakane, Ben Pesana
  • Date: 2012-07-31
  • Subjects: Nanoparticles , Nanostructured materials , Water-soluble organometallic compounds
  • Type: Thesis
  • Identifier: uj:8856 , http://hdl.handle.net/10210/5323
  • Description: M.Sc. , This dissertation describes the synthesis and characterization of CdSe/ZnO and Ag/ZnO core/shell nanoparticles using water as a solvent. The effects of the concentration of the shell precursor, pH, and stabilizing agents on the properties of the nanoparticles were investigated. In general, the type of capping agents had an influence on the crystallite size of the core nanocrystals. The particle size distributions which were calculated from TEM images show that thioglycolic acid as a capping agent produced larger particle sizes compared to thioglycerol. For example, thioglycolic acid produced on average 5.0 nm CdSe nanoparticles while 4.0 nm average CdSe particle size was obtained when using thioglycerol as stabilizer. This observation was confirmed by UV/Vis absorption results which showed that thioglycerol capped CdSe NCs exhibited excitonic peaks positioned at lower wavelength than thioglycolic capped CdSe NCs. XRD results showed that the capping agents used in the current work had no influence upon crystal structure of the CdSe nanocrystals as the cubic structure was obtained with both stabilizers. The effect of shell precursor concentration at pH 12 showed heterogeneous formation of ZnO nanoparticles at high shell precursor concentrations. Various ZnO morphologies including nanoflowers and nanotriangles were observed on TEM images when 50 mL and 25 mL of zinc nitrate solution were used as shell precursors. UV/Vis absorption results also confirmed the presence of ZnO absorption peaks for samples prepared with 50 mL and 25 mL of zinc nitrate solution as shell precursors. PL results showed an increase in peak intensity as a function of precursor volumes. XRD results showed diffraction patterns due to the wurtzite structure of ZnO. CdSe diffraction patterns in these samples were not detected by the XRD instrument. At low volume of the shell precursor, which was 5 mL of 0.05 M zinc nitrate, TEM results showed that spherical CdSe/ZnO core/shell nanoparticles were obtained at pH 12 with 5 mL of 0.05 M zinc nitrate solution and 0.1 M sodium hydroxide used as shell precursor solutions, and thioglycerol as a stabilizer. XRD analysis of the v sample exhibited ZnO diffraction patterns and the CdSe patterns were not detected owing to their low peak intensities compared to those of the ZnO. Similar results were obtained when thioglycolic acid was used a stabilizing agent. However, TEM images showed the hexagonal shape of the CdSe/ZnO core/shell nanoparticles. The pH level was found to influence the photoluminescence properties of the CdSe/ZnO core/shell nanoparticles. The enhanced PL intensity was obtained with CdSe/ZnO core/shell nanoparticles with pH 9 in comparison with CdSe/ZnO core/shell nanoparticles prepared at pH 12. TEM images showed the presence of a thin ZnO shell on the surface of CdSe cores for CdSe/ZnO prepared at pH 9 which could be attributed to the PL enhancement. Although EDS results confirmed the presence of elements such as Cd, Se, Zn and O for both the CdSe core and ZnO shell, the XRD results confirmed the presence of only CdSe diffraction patterns, which suggested the ZnO shell had low peak intensity or was amorphous. A similar effect of these capping agents was observed for Ag nanoparticles as thioglycerol produced average particle size of 16.0 nm whereas 31.0 nm as the average particle size was obtained with thioglycolic acid as stabilizing agent. The crystal phase of Ag NPs was independent of the type of stabilizer. The Ag NPs precipitated in face centred cubic phase. Core/shell Ag/ZnO nanoparticles were produced with 5 ml of zinc nitrate as shell precursor. Higher volumes (50 ml and 25 ml) of zinc nitrate shell precursor induced heterogeneous precipitation of ZnO nanoparticles. XRD patterns confirmed peaks due to ZnO and Ag for Ag/ZnO core/shell nanoparticles.
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Bimetallic nanoparticles on carbon nanotubes and nanofibers copolymerized with ß-cyclodextrin for water treatment

Biosynthesis, characterization and antibacterial activity of silver and gold nanoparticles from the leaf and bark extracts of Zanthoxylum Capense

  • Authors: Nephawe, Mbavhalelo Jade
  • Date: 2015
  • Subjects: Nanotechnology , Nanoparticles , Nanostructured materials , Gold , Silver
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://ujcontent.uj.ac.za8080/10210/372050 , http://hdl.handle.net/10210/84769 , uj:19260
  • Description: Abstract: The biosynthesis of nanoparticles has many advantages over tedious, expensive and toxic physical and chemical methods of synthesis. Plants are stocked with valuable metabolites that are capable of reducing metal salts to form nanoparticles. In this study, aqueous leaf and bark extracts of Zanthoxylum capense were reacted with AgNO3 and HAuCl4 to determine the plants reducing abilities and hence synthesis of Ag and Au nanoparticles capabilities. The goal was to develop a reliable, eco-friendly and easy process for the synthesis of silver and gold nanoparticles using extracts of medicinal plant Zanthoxylum capense. Characterization of the nanoparticles formed by the aqueous extracts was performed using Ultraviolet visible (UV-vis) spectroscopy, Dynamic light scattering, Fourier transforms infrared spectroscopy (FTIR), Transmission electron microscope (TEM). Nanoparticles were characterised by measuring their relevant physicochemical properties. Among the determined properties are size, shape, zeta potential and surface charge. UV-vis spectrophotometry was used as a confirmatory as well as a characterizing tool. Phytochemical tests revealed that the leaf and bark extracts of the plant contained “alkaloids, sterols, terpenoids, flavonoids, steroids, phlabotannins and reducing sugars” which were linked as potential reducing agents... , M.Sc.
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Cadmium removal from water using nanoparticles embedded on a membrane and detection using anodic stripping voltammetry

  • Authors: Sam, Simanye
  • Date: 2019
  • Subjects: Cadmium , Carbon , Nanostructured materials , Water - Purification
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/401568 , uj:33567
  • Description: Abstract : Water pollution by heavy metals is a serious problem in South Africa due to mining activities, electroplating industries, weathering of minerals and soils and coal combustion. Most river systems have been exposed to heavy metals contamination due to effluent disposal and this directly affects communities that use these sources for domestic purposes. For example, Umtata River which is exposed to Cd(II) is used for various purposes by a large population of the Transkei, most of which is rural - domestic (cooking, drinking and washing), agricultural (that is, livestock watering and irrigation), and recreational purposes (swimming). Water pollution by heavy metals such as, Cd(II) in particular is unavoidable and it causes undesirable health effects, such as hypertension and kidney failure. Thus, it is very important to find new ways to efficiently remove these metals from water. Nanostructured membranes are amongst other water treatment methods that have shown the ability to efficiently remove heavy metals from water. Therefore, this study seeks to provide a facile and effective method to remove heavy metals such as cadmium(II) from synthetic solutions and industrial water effluents. This was achieved by embedding carbon nanodots (CNDs) on a polyethersulfone (PES) membrane as support via phase inversion. The synthesized CNDs and fabricated membranes were characterized using Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscope (SEM), Atomic Force Microscope (AFM), contact angle and pure water flux assessment. TEM analysis confirmed that the synthesized CNDs were well dispersed with uniform shape and size (6.7±2.8 nm). Raman analysis illustrated that the CNDs were embedded on the PES and that after blending the PES with CNDs the ID/IG ratio slightly increased after modification of the membranes with CNDs showing that the membranes maintained good structural integrity. The CNDs/PES membranes showed improved hydrophilicity compared to the pristine PES. vi At constant pressure of 300 kPa the flux of pristine PES, 0.01% CNDs/PES, 0.05% CNDs/PES and CNDs/PES was 60.00 L.m-2.h-1, 96.93 L.m-2.h-1, 142.16 L.m-2.h-1 and 196.62 L.m-2.h-1 respectively. The performance of the membrane was optimised using batch adsorption experiments. The analysis revealed that 95.71, 96.32, 97.69 and 99.78% Cd2+ was removed by PES, 0.01% CNDs/PES, 0.05% CNDs/PES and 0.5% CNDs/PES, respectively at optimum conditions: 30 minutes contact time, at pH 5 and 0.5 ppm Cd(II) solution. The membrane, which contained 0.5% CNDs/PES, showed the highest percentage removal. This was due to the –OH and enhanced -COO- on the membrane composite, which could be attributed to the increase in the presence of CNDs within the membrane. , M.Sc. (Chemistry)
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Carbon footprint analysis in the preparation of the platinum nanophase electro catalyst composite electrode

  • Authors: Mabiza, Junior , Mbohwa, Charles
  • Date: 2013
  • Subjects: Carbon footprint analysis , Platinum group , Nanostructured materials , Life Cycle Inventory Assessment , Electrodes
  • Type: Article
  • Identifier: uj:6161 , http://hdl.handle.net/10210/13765
  • Description: A new approach in the use of PGMs for the highly catalytic activity in the production of hydrogen by water electrolysis, is to reduce PGMs into nanometer size (nanophase), then integrate them into electrodes. Water electrolysis is an environmental friendly process of producing hydrogen. This study was for the cognition of likely impacts to environment with regard to the manufacturing process of the composite electrode. The Life Cycle Inventory Assessment method and the carbon footprint calculation in the preparation of the composite electrode were essentially assisted by the Umberto for carbon footprint software, which helped to build an inventory analysis and provided a useful database of materials with respective carbon footprints. Direct emissions were likely involved when heating, calcinating, drying materials. Palliative recommendations were suggested in accordance with the types of emissions identified.
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Carbon nanotubes and nanospheres: synthesis by nebulised spray pyrolysis and use in catalysis

  • Authors: Cele, Leskey Mduduzi
  • Date: 2009-05-13T08:47:51Z
  • Subjects: Carbon , Nanotubes , Nanostructured materials , Pyrolysis , Organic compounds synthesis , Palladium catalysts , Hydrogenation , Ethylene
  • Type: Thesis
  • Identifier: uj:8370 , http://hdl.handle.net/10210/2536
  • Description: Ph.D. , This work presents a detailed study of the synthesis of carbon nanotubes and nanospheres by nebulised spray pyrolysis. This method has been used by other workers mainly for preparation of sub-micron particles and the deposition of thin films on various substrates. The effect of various synthesis parameters including the temperature, choice of the carbon source and the metal precursor as well as the carrier gas flow rate on the selectivity of the reaction and the properties of the carbon nanotubes produced was investigated. A major part of this work was devoted to a study of the effects of the addition of small quantities of oxygencontaining compounds (alcohols, esters and aldehydes) to the reaction mixture. The products were analysed using various methods including TEM, SEM, Laser- Raman spectroscopy and HRTEM. Furthermore, the possible use of carbon nanotubes and carbon nanospheres as supports for palladium in the hydrogenation of ethylene was investigated. Nebulised spray pyrolysis proved to be a suitable technique for the synthesis of well graphitized carbon nanotubes and carbon nanospheres with uniform diameters and it was demonstrated that good control of the carbon nanotube properties could be achieved by controlling the synthesis parameters. Better graphitization of the carbon nanotubes was observed at higher temperatures. Ferrocene, iron pentacarbonyl, nickelocene and cobaltocene were successfully used in carbon nanotube synthesis with the last two producing carbon nanotubes with diameters close to those on single-walled carbon nanotubes. Toluene (with and without acetylene as a supplementary carbon source), benzene, mesitylene, xylene and nhexane were successfully used to produce carbon nanotubes with a high degree of alignment while no success was achieved with ethanol. The poor yields obtained with ethanol appear to be a consequence of chemical changes in the ethanol induced by exposure to ultrasound irradiation. On the other hand, low concentrations of methyl acetate and ethyl acetate appear to enhance the production of carbon nanotubes. It was demonstrated that carbon nanotubes and nanospheres are suitable for use as supports for palladium in the hydrogenation of ethylene. Pd particles of uniform size were obtained and the conversion rates were slightly higher when the carbon nanotubes were pre-treated with a mixture of sulphuric acid and nitric acid.
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Characterization, in vitro cytotoxicity studies and photoactive effect of gold nanorods on colorectal cancer cells

  • Authors: Kadanyo, Sania
  • Date: 2016
  • Subjects: Nanostructured materials , Rectum - Cancer - Treatment , Cancer - Treatment , Nanomedicine
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/124772 , uj:20958
  • Description: Abstract: Cancer is a disease formed from abnormal growth of cells affecting any part of the body. It is reported that cancer is the third leading cause of death after stroke and heart disease in developed countries. Colorectal cancer (CRC) incidence and mortality rates vary markedly around the world; according to the World Health Organization (WHO) colorectal cancer is the third most commonly diagnosed cancer as well as being the third leading cause of cancer death after lung and gastric cancer worldwide in both sexes. Thus each year over 1 million new patients develop colorectal cancer and over 600,000 patients die from it. The main problem in using most conventional cancer therapies such as anticancer drugs (chemotherapy); as well as radiation is their low selectivity for cancer cells coupled with their often high toxicity to non-targeted cells in the body and they often cause side effects that may be more unbearable than the disease at that particular point in time. In contrast with conventional cancer therapy’s photodynamic therapy (PDT) was developed to try and address the disadvantages caused by conventional therapy’s. Photodynamic therapy is a non-invasive method which yields satisfactory clinical results with fewer adverse side effects accompanied by higher selectivity. Although photodynamic therapy has significantly improved the quality of life and life expectancy of patients with cancer, further advances in therapeutic efficacy are required to overcome numerous side effects for example hydrophobicity and poor selectivity between deceased cells and healthy cells related to conventional PDT. Much attention has been directed to improving photosensitizers. Due to the highly desirable and tunable optical properties of light sensitive nanoparticles they are deemed resourceful in developing phototherapeutic agents for cancer therapy. Gold nanorods (GNRs) showing a surface plasmon resonance (SPR) band at the near infra-red (NIR) region are of great interest for the development of nanomedicine in particular phototherapy of cancer and drug delivery. The main concerns usually encountered when using metal nanoparticles for general bio-applications are their potential toxicity and biological interactions of the nanoparticles with the cells... , M.Sc. (Nanoscience)
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CO2 hydrogenation to synthetic fuel via modified Fischer-Tropsch process using cobalt-based catalysts

  • Authors: Khangale, Phathutshedzo Rodney
  • Date: 2019
  • Subjects: Fischer-Tropsch process , Cobalt catalysts , Catalysts , Carbon dioxide , Nanostructured materials
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/444915 , uj:38904
  • Description: Abstract: The effect of promoting Co/Al2O3 catalyst with potassium on CO2 hydrogenation to longerchain hydrocarbons was investigated. The catalysts used in this study were synthesized using an incipient wetness impregnation of the support with cobalt nitrate solutions. All catalysts were supported on γ-alumina and promoted with potassium (0 – 8 wt.%) and/or 0 – 3 wt.% of either copper, ruthenium or palladium. The synthesized catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), tempetature programmed reduction (TPR) and CO2 temperature programmed desorption (CO2–TPD) analyses. The catalysts were evaluated for CO2 hydrogenation using a fixed-bed tube reactor. The effect of reaction temperature (190 – 345 oC) during CO2 hydrogenation was evaluated at atmospheric pressure to determine the optimum reaction temperature that would favor the formation of longer chain hydrocarbons. Once the optimum temperature was selected, the effect of pressure (1 – 20 bar) was evaluated to determine the optimum operating pressure under the selected optimum temperature... , D.Phil. (Chemical Engineering)
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Corrosion inhibition of mild steel in 1 M Hcl using synthesized eco-friendly polymer composites

  • Authors: ‘Mofu, Ts’oeunyane George
  • Date: 2017
  • Subjects: Corrosion resistant materials , Nanostructured materials , Stainless steel - Corrosion , Corrosion and anti-corrosives
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/269731 , uj:28658
  • Description: M.Tech. (Metallurgy) , Abstract: In this work, two polymer composites namely PBSLP and PBSLH were synthesized and characterized by FTIR, NMR, XRD, SEM, CHNS and TGA. The results revealed that the formed polymer composite were graft polymer composites. The two synthesized polymer composites were investigated as corrosion inhibitors for MS in 1 M HCl. The corrosion inhibition characteristics including, corrosion rate, corrosion inhibition efficiency, and inhibitor adsorption to the metal surface were studied with gravimetric and electrochemical studies. The gravimetric studies revealed that adsorption of the polymer composites to the MS surface were both physisorption and chemisorption although physisorption appeared to be the more dominant process. Moreover, both polymer composites obeyed Langmuir isotherm. Electrochemical studies were also used to characterize that inhibitory mechanism of the said polymer composites. PDP, specifically Tafel plot and VASP with used to determine the corrosion parameters while EIS was employed to determine the charge transfer characteristics during corrosion. The results indicated that PBSLP and PBSLH are both mixed type corrosion inhibitors with cathodic reaction being the most affected reaction. In addition, the charge transfer resistance during corrosion increased with the increase in concentration of inhibitors. SEM was also used to examine the morphology of MS coupons before and after exposure to corrosive, the results revealed that PBSLP and PBSLH reduce corrosion of MS by forming a film on MS surface.
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Cytotoxicity and genotoxicity evaluation of green synthesised glutathione capped CdTe/CdSe/ZnSe core-multishell quantum dots

Determination of Cd(II) in water using aptamer-based electrochemical biosensors

  • Authors: Fakude, Colani Thembinkosi
  • Date: 2020
  • Subjects: Water - Analysis , Cadmium , Electrochemical analysis , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/458431 , uj:40718
  • Description: Abstract: The World Health Organisation has recommended strict permissible limits for cadmium(II) in drinking water owing to the harmful threats it poses to humans and the environment. As a result, strict monitoring of cadmium(II) is a necessity. This dissertation reports on the design of monitoring tools referred to as electrochemical aptamer biosensors (aptasensors) based on nano-platforms for selective detection of Cd(II) in water. Nanomaterials such as carbon black, gold nanoparticles and carbon nanofibres were the smart materials of choice used in the fabrication of electrode supports for enhancement of detection signals. A screen-printed electrode was modified using carbon black following the dropcoating technique and then gold nanoparticles were electrodeposited by cyclic voltammetry (CV) at 50 mVs-1 in a potential window of -400 mV to 1100 mV. A thiolated single stranded DNA aptamer was immobilised on the nano-platform via a Au-S covalent linkage. The aptasensor was characterised using CV and electrochemical impedance spectroscopy ((EIS). The designed electrochemical aptasensor selectively detected Cd(II) using the square wave voltammetry (SWV) technique with a detection limit (LOD) of 0.14 ppb in the presence of interferents like chromium, copper and other ions. The second electrochemical aptasensor was based on the fabrication of a screen-printed electrode using acid treated carbon nanofibres. The characterisation procedure was similar with the first aptasensor and upon application, the aptasensor was found to be selective towards Cd(II) detection. A detection limit of 0.11 ppb was obtained using SWV and the aptasensor. Both the aptasensor findings were validated with inductively coupled plasma optical emission spectroscopy (ICP-OES) which showed an LOD of 1.4 ppb. Both electrochemical aptasensor provide a cost effective approach for the mitigation of interferences during electrochemical detection of Cd(II) and they can be applied in the monitoring of Cd(II) in environmental samples. , M.Sc. (Chemistry)
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Development of an electrochemical cholesterol biosensor based on poly (propylene imine) dendrimer- quantum dots nanocomposite

  • Authors: Mokwebo, Kefilwe Vanessa
  • Date: 2018
  • Subjects: Electrochemical sensors , Biosensors , Quantum dots , Nanostructured materials , Dendrimers in medicine , Cholesterol - Physiological effect
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/279597 , uj:30029
  • Description: M.Sc. (Nanoscience) , Abstract: One of the parameters that cause cardiovascular diseases (CVDs) is high level of cholesterol in the blood. Therefore, monitoring of cholesterol level is of great importance, especially to elderly people and people with high risk of such diseases. This work explores the applicability of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) in developing a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The as-synthesized mercaptopropionic acid (MPA) capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), powdered X-ray diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima red-shifted as the reaction time and shell growth increased. The increase in PL intensities shows proper passivation of the QDs surface with PL quantum yield (PLQY) of 33.8 %, 69.2 % and 57 %, for CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe QDs respectively. The XRD patterns of all the as-synthesized QDs consist of three diffraction peaks corresponding to (111), (220) and (311) cubic zinc blended structures. The estimated particle size of CdTe/CdSe/ZnSe QDs from XRD and TEM are 4.32 and 4.08 nm, respectively while the EDX confirmed the presence of corresponding elements. For biosensor design, PPI dendrimer was electrochemically deposited on glassy carbon electrode (GCE) and characterized using cyclic voltammetry (CV) and impedance spectroscopy (EIS) in both phosphate buffer solution (PBS) and ferricyanide solution ([Fe(CN)6]-3/-4) This was followed by drop-drying the QDs on the electrode to form GCE/PPI/QDs. Finally, cholesterol oxidase (ChOx) was drop-dried on the GCE/PPI/QDs electrode to produce GCE/PPI/QDs/ChOx-based electrochemical cholesterol biosensor. Scanning electron microscopy (SEM) was used to characterize screen printed carbon electrode (SPCE) as it was modified with different materials and was able to capture the nano-globular morphology of PPI dendrimer. The GCE/PPI/QDs/ChOx based cholesterol biosensor was able to detect cholesterol in the range 0.1-10 mM with a...
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Electrocatalytic properties of platinum and platinum-based carbon nanodots nanocomposites as electrocatalysts for direct alcohol fuel cells

  • Authors: Gwebu, Sandile Surprise
  • Date: 2018
  • Subjects: Electrocatalysis , Fuel cells , Solid oxide fuel cells , Nanostructured materials , Platinum
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/271337 , uj:28856
  • Description: M.Tech. (Chemistry) , Abstract: Direct alcohol fuel cells are potential future energy sources for mobile and stationary appliances. They are fascinating more than the hydrogen fuel cells because they utilise a liquid fuel that is easy to store and transport. However, several drawbacks such as the high cost of pure platinum and the instability of carbon electrodes in the fuel cell environment are hindering the commercialisation of the DAFC technology. The platinum electrocatalyst is easily poisoned by the intermediates that are produced during alcohol electro-oxidation reactions, this result in low energy output. This study was devoted in synthesising a carbon support material with high surface area and to prepare platinum-based electrocatalysts with anti-poisoning and anti-corrosion properties. Carbon nanodots (CNDs) with sizes below 10 nm were synthesised by pyrolysing oats grains. The BET surface area of the CNDs was found to be 312.5 m2 g-1. XPS and FTIR results jointly revealed that the CNDs contain oxygen-containing functional groups which facilitate the attachment of metal nanoparticles. The Pt/CNDs electrocatalyst was synthesised using water as a solvent without adding any reducing agent. The Pt/CNDs electrocatalyst was tested against the commercial Pt/C standard to evaluate the performance of the CNDs (support material). Cyclic voltammetry results showed that the Pt/CNDs electrocatalyst prepared by this method exhibit superior performance for methanol and ethanol electro-oxidation at room temperature. The Pt-Sn/CNDs electrocatalyst was synthesised by the alcohol reduction method with the aim to reduce platinum loading and improve electroactivity. XPS results showed that the nanoparticles were present in the form of Pt-Sn metallic alloy with a significant amount of SnO- species. The lattice parameter of Pt in Pt-Sn/CNDs electrocatalyst was calculated to be 0.3926 nm; this value is higher than 0.3921 nm, the lattice parameter of Pt in Pt/CNDs electrocatalyst. XRD results proved that...
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Electrochemical co-detection of arsenic, lead and mercury on exfoliated graphite nanocomposite electrodes

Electrochemical detection of arsenic and selenium on modified carbon based nanocomposite electrodes

  • Authors: Idris, Azeez Olayiwola
  • Date: 2016
  • Subjects: Nanostructured materials , Electrodes, Carbon , Electrochemical analysis , Organic water pollutants , Carbon composites
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/124946 , uj:20978
  • Description: Abstract: This study explores the applications of nanomaterial modified on glassy carbon electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE was modified with gold nanoparticles and reduced graphene oxide. Gold nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs was electrochemically investigated using redox probes which are [Fe (CN) 6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical determination of selenium by square wave anodic stripping voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu and Cd were the only significant interferences observed for the electrochemical detection of selenium. Attempt was also made to sense selenium in tap water, concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The electrochemical method was validated with ICP-OES. Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of arsenic was also optimised at different analytical conditions and a detection limit of 0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the interference effect of copper on arsenic sensing in the bid to remove interference. Graphene oxide was synthesised by using Hummer`s methods and was further reduced to reduced graphene oxide using ascorbic acid. The reduced graphene oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in an increase in the electroactive surface area of the electrode which led to enhance the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as supporting electrolyte, deposition potential of -100 mV and pre-concentration time of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and was not susceptible to many interfering cations except Cu (II) and Cd (II). , M.Sc. (Chemistry)
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Electrochemical/photoelectrochemical studies of nickel(II) dimethylglyoxime and gold nanoparticles and their applications in the detection of phenolic water pollutants

  • Authors: Olorundare, Foluke O. Grace
  • Date: 2017
  • Subjects: Organic water pollutants , Nanostructured materials , Phenols , Mass spectrometry , Phenols - Identification
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/235745 , uj:24114
  • Description: M.Sc. (Chemistry) , Abstract: The electrochemical behaviour and detection of phenols such as o-nitrophenol (o-NP) and p-nitrophenol (p-NP) and also 2-chlorophenol (2-CP) and 3-chlorophenol (3-CP), has been studied on a gold nanoparticle - nickel dimethylglyoxime complex (N(II)DMG) modified glassy carbon electrode (GCE). The electrode was prepared by drop coating nickel dimethylglyoxime complex on a GCE followed by the electrodeposition of gold nanoparticle. Each step in the electrode modification was characterised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and high resolution scanning electron microscopy (HRSEM). There two redox probes hexacyanoferrate (III) - hexacyanoferrate(II) ion ([Fe(CN)6]3−/4− ) and hexaammineruthenium (III) chloride – hexaammineruthenium (II) chloride [Ru(NH3)6 ]2+/3+ were applied to verify the suitability of the modified electrode (i.e. GCE/NiDMG-AuNP) with satisfactory results. The results showed that nickel dimethylglyoxime complex/gold nanoparticles electrode had improved conductivity, reversibility and electron transfer rate in selected redox probe than the unmodified GCE. The GCE/NiDMG-AuNP electrode was used in the determination of o-NP and p-NP in water. Under the optimal conditions, detection limits of 0.58 μM and 0.103 μM were calculated for o-NP and p-NP respectively. The GCE/NiDMG-AuNP electrode was applied to real water sample and the effects of interferences were studied. Photoelectrochemical analysis was done with p-NP with substantial results. The GCE/NiDMG-AuNP electrode was also used to investigate the electrochemical behaviour of 2-CP and 3-CP by Cyclic Voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the GCE/NiDMG-AuNP exhibited remarkable enhancement effects towards 2-CP and 3-CP. Under the optimized conditions, the oxidation peak currents displayed a good linear relationship to concentration in the ranges from 0.5 to 30 μM for 2-CP and 0.5 to 35 μM for 3-CP, with detection limits of 0.097 and 0.093 μM, respectively. This sensor was successfully used in the detection 2-CP and 3-CP of real water samples with good results.
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