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Synthesis and characterization of mesoporous silica/titania nanocomposites : potential additives for dye sensitized solar cells (DSSCs)

  • Authors: Akawa, Mpingana Ndilimeke
  • Date: 2017
  • Subjects: Dye-sensitized solar cells , Nanostructured materials , Mesoporous materials , Silica , Titanium
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/235628 , uj:24100
  • Description: M.Sc. (Nanoscience) , Abstract: The photoanode is an important part of the DSSCs as it is the medium for dye adsorption, electron transport and electrolyte diffusion. The composition and morphology of the photoanode therefore directly influences the performance of the cell. Optimising the morphology of the photoanode is therefore one of the key factors in improving the performance of the DSSCs. This work entailed the synthesis of titania supported on silica nanocomposites for use as light scattering materials in the photoanode with the motivation of optimising the morphology of the photoanode and further enhance the energy conversion efficiency of the DSSCs. The silica support materials, specifically mesoporous silica, SBA-15 and non-mesoporous SiO2 were synthesized through the soft-template acid catalyzed sol-gel method and base catalyzed sol-gel method respectively. Two SBA-15 nanomaterials were synthesized by varying the hydrolysis and aging times which resulted in materials of different textural and morphological properties. These silica support materials (SiO2, SBA-15 A1 and SBA-15 A2) were used as support materials for the synthesis of TiO2 supported on silica nanocomposites. Also, TiO2 nanoparticles of size 19.32 ±3.70 nm (n = 193) were synthesized for use as active site of the photoanode. The physical, chemical and optical properties of the nanoparticles and nanocomposites were studied using FTIR, TEM, Nitrogen Sorption, SEM-EDS, XRD, and diffuse reflectance Ultraviolet-Visible (DR-UV-VIS) spectroscopy. The nitrogen desorption results of the 10 wt% TiO2 / SBA-15 nanocomposites just like the parent SBA-15 support, revealed the Type IV isotherms with H1 hysteresis loops which indicated that the support materials did not lose their mesoporosity and uniform pore size arrangement upon incorporation of TiO2 nanocrystals. This finding was supported by the TEM results. The energy band gaps of TiO2 supported on the mesoporous silica (SBA-15) (3.60 eV) were blue shifted relative to the unsupported TiO2 (3.44 eV) and TiO2 supported on the non-mesoporous SiO2 (3.55 eV). These results confirmed the XRD results which indicated smaller TiO2 crystallite sizes for TiO2 crystals supported on the SBA-15 support materials which were 10.60 nm as compared to the unsupported TiO2 and TiO2 supported on the non-mesoporous SiO2 (15.89 nm). The band gap increased as the crystallite sizes decreased...
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The evaluation of dendrimer encapsulated ruthenium nanoparticles, immobilised on silica, as catalysts in various catalytic reactions and the effect of ionic liquids on the catalytic activity

  • Authors: Antonels, Nathan Charles
  • Date: 2015-04-22
  • Subjects: Dendrimers , Catalysis , Nanostructured materials , Nanoparticles
  • Type: Thesis
  • Identifier: uj:13555 , http://hdl.handle.net/10210/13696
  • Description: Ph.D. (Chemistry) , This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5) and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1-2.2 nm. The RuDENs were used as nanoparticle solutions in catalytic reactions or immobilised on amorphous silica 60 and silica 100 and subsequently referred to as RuSil catalysts. These catalysts were evaluated in the reduction of 4-nitrophenol, toluene hydrogenation, citral hydrogenation, cinnamaldehyde hydrogenation and styrene oxidation...
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Green synthesis of silver and platinum nanostructures using water hyacinth plant leave extract

  • Authors: Anyik, John Leo
  • Date: 2017
  • Subjects: Nanostructured materials , Green chemistry , Metathesis (Chemistry) , Water-soluble organometallic compounds
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/244024 , uj:25231
  • Description: M.Sc. (Chemistry) , Abstract: An eco-friendly synthesis of silver (Ag) and platinum (Pt) nanoparticles (NPs) using aqueous extracts from both fresh and dried leaves of water hyacinth plant as efficient reducing and stabilizing agents is presented. The optical properties of the as-synthesised material from both extracts were studied at different pH and reaction time and were characterized using UV-visible, transmission electron microscopy (TEM), Fourier Transform infra-red spectroscopy (FTIR), Dynamic light scattering (DLS), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The colour changes from light yellow to brown with the presence of the silver surface plasmon resonance (SPR) band indicated the formation of Ag-NPs while the disappearance of the peak intensity at 260 nm confirmed the formation of Pt-NPs. TEM analysis showed that the as-synthesised materials from both extracts were of different sizes and spherical in shape while DLS analysis revealed their hydrodynamic sizes in the hydrated state. FTIR indicated that, the presence of polyphenols, alkaloids and polysaccharides groups present in both water hyacinth leaf extract were responsible for the reduction and capping of Ag-NPs and Pt-NPs. The presence of elemental silver as well as platinum and the purity of the as-synthesised sample were confirmed by EDS analysis. This study demonstrates the feasibility of using water hyacinth leaf extract from fresh and dried leaves for the synthesis of Ag-NPs and Pt-NPs. However, fresh leaves extract was more preferred than dried leaves extract as it retains most of the phytochemicals that could influence the formations of the nanoparticles. The as-synthesised materials were further used for colorimetric sensing of heavy metals in aqueous solution (Hg2+, Ca2+, Cr3+, Ba2+ Li+, K+, Ni2+, Co2+, Pb2+, Mn2+) and only Ag-NPs shows a sensitive response towards these metal ions as indicated by the shift in the position of the surface plasmon resonance (SPR) band with a more selective response to Hg2+. Pt-NPs on the other hand show no response towards these metal ions and hence cannot act as a colorimetric probe...
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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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Bimetallic nanoparticles on carbon nanotubes and nanofibers copolymerized with ß-cyclodextrin for water treatment

Synthesis and characterization of carbon nanospheres and carbon nanotubes conjugated bisphosphonates as potential drugs for the treatment of secondary bone cancer

Modeling and simulation of nanostructured copper oxides solar cells for photovoltaic application

  • Authors: Enebe, George Chukwuebuka
  • Date: 2019
  • Subjects: Photovoltaic power generation , Nanostructured materials
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/424718 , uj:36333
  • Description: Abstract: The increasing global population and demand for clean and sustainable energy has led to increased research on affordable and efficient energy materials. Solar energy materials are one of those promising options. There is increased research on nanostructured metal oxide solar cell as an option for inexpensive, clean and efficient solar cells material. Copper oxide based solar cells are among those attracting interest although the efficiency is still low. This study investigates the numerical modeling and simulation of nanostructured copper oxide (cuprous and cupric oxide) heterojunction solar cells for photovoltaic applications. This is with a view to providing an optimized cell efficiency to aid experimentation and the development of high-efficiency metal oxide solar cells. The inspiration for this investigation is to give premise for experimental design for affordable, non-harmful and efficient alternative material for silicon-based solar cells. This was performed using Solar cells capacitance simulator (SCAPS). The optimization was performed by varying the effect of film thickness and by varying the effect of annealing temperature on properties of the copper oxide solar cells using SCAPS for the numerical analysis. The simulation and optimization was modeled firstly by varying the thickness of both the absorber layer and the buffer layers of Cu2O/TiO2 and CuO/TiO2 pn nanostructured heterojunction solar cells. The input parameter for SCAPS, obtained from literatures includes; temperature of 300K for the film thickness, input power of 1000W/m2 using illumination of AM1.5 lamp, under varying thickness of 0.5 μm to 10.0 μm for the absorber layers (Cu2O and CuO) and 0.05 μm to 6.0 μm for the buffer layer (TiO2) respectively. The simulated solar cell displayed a short-circuit current (Jsc) of 24.0764 A and 26.0516 A, open-circuit voltage (Voc) of 1.0486 V and 0.0435 V, fill factor (FF) of 63.20 % and 71 % with an efficiency (η) of 1.6 % and 8.05 % respectively, at an absorber layer thickness of 500 nm and buffer layer thickness of 50nm. Furthermore, the defect density was obtained for each solar cell. Secondly, the Cu2O/TiO2 and CuO/TiO2 pn nanostructured heterojunction solar cells was numerically analysed under varied annealing condition. Three annealing conditions were considered i.e. the as-deposited (300K), air and nitrogen annealed (423.15 K). Other working conditions include; an illumination of AM 1.5G with a 500 W Xenon lamp representing the sunlight. For this simulation, silver was used as the electrode/contact. The absorber layer thickness was 2000 nm and buffer layer thickness was 200 nm. The simulation report showed that nitrogen... , M.Ing. (Mechanical Engineering Science)
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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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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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Materials for alkaline direct alcohol fuel cells (ADAFC) and Perovskite solar cells (PSC) : synthesis, characterisation and application

  • Authors: Gwebu, Sandile Surprise
  • Date: 2021
  • Subjects: Fuel cells - Materials , Perovskite solar cells - Materials , Nanostructured materials
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/483993 , uj:43944
  • Description: Abstract: In pursuit of effective and less toxic materials for energy conversion, this study explored various materials for potential application in alkaline direct alcohol fuel cells (ADAFC) and perovskite solar cells (PSC). Alcohol electrooxidation on selected palladium-based electrocatalysts was investigated in alkaline media using various electrochemical techniques. For the first time, carbon nanodots (CNDs) were synthesised by pulverising multi-walled carbon nanotubes (MWCNTs) and functionalised using aqueous sodium hydroxide. Palladium-based nanocatalysts supported on functionalised carbon nanodots (fCNDs) blended with metal oxides promoters were prepared by sonochemical-assisted borohydride reduction method. Zirconium dioxide (ZrO2) and tungsten (VI) oxide (WO3) were selected as promoters while nickel (Ni) and cobalt (Co) were used as cocatalysts to prepare four electrocatalysts denoted by Pd/fCNDs-ZrO2, Pd/fCNDs-WO3, PdNi/fCNDs-WO3 and PdCo/fCNDs-WO3. The ratio of metal oxide to fCNDs was fixed at 1:4 to maintain good electrical conductivity of the support material. Physicochemical properties of the synthesised materials were studied by various microscopic and spectroscopic techniques such as transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS). Alcohol fuel oxidation on the prepared electrocatalysts was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques in KOH electrolyte. Synthesised Pd/fCNDs (8.23 wt. % Pd) and commercial Pd/C (10 wt. % Pd) electrocatalysts were used as benchmark standards... , Ph.D. (Chemistry)
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The effects of succussion on nanoparticles in ferrum metallicum 30C

  • Authors: Hobson, Deborah Dawn
  • Date: 2019
  • Subjects: Homeopathic pharmacy , Nanoparticles , Nanostructured materials , Nanomedicine , Homeopathy
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/399657 , uj:33319
  • Description: Abstract : Nanoparticles are microscopic materials which range in length from 1-100 nanometres (nm). Nanoparticles have unique properties due to their size and shape, which include an increase in surface area, surface reactivity, thermal energy and diffusion rate. Nanomedicine refers to the application of nanoparticles in medicine, particularly in diagnostic techniques and as drug delivery systems. Nanoparticles are ideal for this as they provide greater bioavailability, are more easily absorbed by the body and produce a therapeutic effect with fewer side effects. Laboratory techniques to create nanoparticles include the top-down and bottom-up methods. Within these two methods are various synthesis techniques for creating nanoparticles, including solid phase synthesis, liquid phase synthesis, gas phase synthesis and green synthesis. Homoeopathy uses the top-down method by physically breaking down the starting substance via the process of potentization. Homoeopathy is a branch of complementary medicine (CM) founded by Dr Samuel Hahnemann in the late 1700’s. It is based on the principle similia similibus curantur, which translates to ‘like cures like’. Homoeopathic remedies are highly diluted substances which retain minute particles of the starting substance in the form of nanoparticles. The method used to make homoeopathic remedies is referred to as ‘potentization’ and includes trituration (grinding and serial dilution) of solid substances and succussion (violent shaking) of liquid substances. However, while homoeopathy has set guidelines for the trituration part of potentization, it lacks standardisation regarding the number of succussions which should be used. Iron (Fe) is a highly reactive silvery-white metal that easily forms compounds and alloys with other metals and has unique ferromagnetic properties which are stronger at lower temperatures. Ferrum metallicum, the homoeopathic remedy made from iron, can be used for a wide range of conditions when prepared in homoeopathic form. The aim of this study was to investigate the effect of succussion on the presence, size and distribution of nanoparticles in Ferrum metallicum 30C, when prepared with 0, 10 or 100 succussions, using transmission electron microscopy (TEM). iv This was a quantitative, experimental study performed at the Department of Chemistry, at the University of Johannesburg. Three batches of Ferrum metallicum 30C, with 0, 10 and 100 succussions respectively, and three controls of 43% ethanol with 0, 10 and 100 succussions respectively, were manufactured by the researcher. This was done at the laboratory of a registered manufacturer of homoeopathic medicines in Johannesburg. The researcher underwent training on the use of each of the laboratory analysis techniques. The sample preparation, experimental design and analysis of the samples was conducted by the researcher, under supervision and help of the laboratory technicians. Transmission Electron Microscopy (TEM) was conducted on two batches of samples. The first batch of samples showed contamination of the ethanol used to manufacture the test and control samples. The test samples were therefore manufactured a second time and TEM analysis conducted again. Additional analysis techniques were used to determine whether the first batch of test and control samples were contaminated and how the contamination had occurred. These analysis techniques included Energy Dispersive Spectroscopy (EDS), Inductively Couples Plasma Emission Spectroscopy (ICP-OES), Dynamic Light Scattering (DLS). An analysis for zeta potential of the samples and controls was conducted to explain the agglomeration of particles. TEM photographs were analysed by the researcher, under guidance of the co-supervisor, using the computer programme ImageJ. The results for EDS, ICP-OES, DLS and Zeta Potential were generated by the built-in software of the analysis machines, either as graphs or as numerical values. These were then analysed by the researcher under the guidance of the laboratory technicians. A total of five experimental procedures were conducted. The results of the experiments showed that the first batch of test and control samples was contaminated as the ethanol used to manufacture the samples contained traces of iron and unidentified particles. The additional analysis techniques helped confirm the contamination, and it was discovered that purified water, which was used to manufacture the ethanol used in the study, is not completely free of particles. The second batch of test and control samples, manufactured with distilled water, which is almost completely particle-free, showed positive results. The presence of spherically-shaped iron nanoparticles was confirmed for the test samples. Batch 1, Samples 1 and 2 (Ferrum v metallicum 30C with 0 and 10 succussions respectively), contained nanoparticles which were evenly distributed and unagglomerated. Batch 1, Sample 3 (Ferrum metallicum 30C with 100 succussions) had nanoparticles which were smaller in size, greater in number and agglomerated. Batch 2, Samples 1-2 (Ferrum metallicum 30C with 0 and 10 succussions respectively) contained nanoparticles which were more defined in shape, with similar numbers and sizes, and existed mainly as well-distributed, unagglomerated nanoparticles. Batch 2, Sample 3 (Ferrum metallicum 30C with 100 succussions) had nanoparticles which were slightly less in number and smaller, according to the automatic analysis by ImageJ, and which appeared to be distributed unevenly in smaller clusters. The first batch of control samples contained a large number of unidentified particles. The second batch of control samples also contained particles, although significantly less than the first batch of controls. Overall, the experiments showed that the number of succussions given does affect the number, size and distribution of nanoparticles in a homoeopathic remedy. The results of this experiment help to support the current research on nanoparticles in homoeopathic remedies and help to explain the effect of succussion on the nanoparticles within the remedies. , M.Tech. (Homoeopathy)
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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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Synthesis, characterization and application of carbon nanotube and graphene based nanocomposite platforms in the electrochemical sensing of arsenic and mercury in water

  • Authors: Jimana, Amandla
  • Date: 2017
  • Subjects: Electrochemical analysis , Nanostructured materials , Carbon nanotubes , Heavy metals - Analysis , Water - Analysis
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://ujcontent.uj.ac.za8080/10210/376448 , http://hdl.handle.net/10210/244112 , uj:25242
  • Description: M.Tech. (Chemistry) , Abstract: This study developed carbon nanocomposite modified on exfoliated graphite electrodes that are sensitive and selective for the electrochemical detection of mercury and arsenic. This research explores the new material called exfoliated graphite for the detection of heavy metals in water. The material is relatively cheap and is a promising material for the detection of heavy metals. The exfoliated graphite was prepared by intercalation of natural graphite flakes with a particle size of 300 μm by soaking them in a mixture of concentrated acids, sulphuric acid and nitric acid in the ratio 3:1 respectively. After the intercalation the resulting material was exfoliated. The exfoliation was achieved by subjecting the intercalated graphite to high temperatures of 800 ºC in a furnace for about 30 seconds. The puffed up material was named exfoliated graphite (EG). The EG was compressed into pellets of 5mm using high pressure hydraulic press. The mercury nanocomposite sensor was designed by incorporation of carbon nanotube/polyaniline (CNT/PANI) composite followed by electrodeposition of gold nanoparticles onto the EG electrode. This electrode was named CNT/PANI/AuNPs-EG. The dispersion of carbon nanotubes onto the polymer was obtained via the in situ polymerization method. This electrode was name CNT/PANI/EG. The electrodeposition of gold nanoparticles was achieved by preparing 5 mM of HAuCl4 solution and cycling the potential from -200 mV to 1100 mV for 10 cycles at a scan rate of 50 mV/s. this electrode was used for the detection of mercury in water. The detection limit was calculated to be 0.046 ppb (0.229 nM) and the limit of quantification was 0.152 ppb with a correlation coefficient of 0.9984. Another electrode was prepared for the detection of arsenic. Reduced graphene oxide/cobalt nanoparticles modified on EG electrode. A good detection limit and limit of quantification were found to be 0.31 ppb and 1.01 ppb respectively. The linear regression equation was 𝑦=6.64608×10−4 𝑥+1.96169×10−5 with a high correlation coefficient of 0.9984.
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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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The advances in biomedical applications of carbon nanotubes based on drug delivery system by using MD and DFT modeling

  • Authors: Karimzadeh, Sina
  • Date: 2020
  • Subjects: Carbon nanotubes , Nanostructured materials , Drug delivery systems , Density functionals , Molecular dynamics - Simulation methods , Doxorubicin , Cancer - Chemotherapy
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/480174 , uj:43458
  • Description: Abstract: In this work, interaction and bond properties of anticancer drug doxorubicin (DOX), (6,6) armchair single-walled carbon nanotube (SWCNT), and hydroxyl- and carboxyl-functionalized SWCNT (ƒ-SWCNT) have been investigated based on DFT theory to design, improve and expand carbon nanotube (CNT) drug carriers for any biomedical system. Geometrical, structural, electrical, bonding and thermodynamic properties as well as equilibrium distances, adsorption energies, quantum molecular descriptors and frontier molecular orbitals or different drug arrangements on CNT at the highest equilibrium at WB97XD/6-31+G (d, p) level of theory at aqueous and gas phases were explored. Our calculations showed that hydrogen bonds between active sites of the spontaneous adsorption of doxorubicin (DOX) molecule and hydroxyl- and carboxyl-functionalized CNTs played a more important role than those with pristine CNTs in the adsorption and fixation of the studied complexes. Using quantum theory of atoms in molecules (QTAIMs) method, intermolecular interactions and corresponding descriptors at critical bonding points in aqueous and gas phases were also investigated. Evaluation of the results obtained from the natural bond orbital (NBO) analysis showed that the direction of electron movement was generally from drug molecule to CNT... , M.Ing. (Mechanical Engineering)
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WO3-SnO2 nanostructures supported on carbon nanomaterials for electrochemical energy storage

  • Authors: Kganyago, Peter
  • Date: 2020
  • Subjects: Energy storage , Nanostructured materials , Storage batteries , Supercapacitors
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/458469 , uj:40723
  • Description: Abstract: Electrochemical energy storage devices such as ion batteries or super-capacitors have been developed as energy carriers for new portable technologies. The electrochemical performance of an electrochemical device depends on the physico-chemical properties of the electrode materials. In supercapacitors, the design and composition of the electrode widely influence its performance. Great efforts have been undertaken to fabricate electrode materials of supercapacitors in a quest to improve the electrochemical performance of the electrode. In this project we focus on fabrication of TMOs on carbon nanomaterials. Carbon nanomaterials and transition metal oxides offers an interesting synergistic relationship which can be utilised in electrochemical energy storage devices. The types of metal oxide incorporated into the carbon nanomaterial as well as the nano-architecture of the materials affects the electrochemical properties and thus the performance of supercapacitors. Thus, this project is focused on the development of SnO2 nanostructures supported on carbonaceous 2D materials for electrochemical energy storage devices. The physico-chemical attributes of the nanocomposite were investigated using P-XRD, FTIR, TEM, SEM, TGA and BET. The electrochemical performance of the electrodes was tested using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) in 2M KOH electrolyte in a three-electrode configuration. The hybrid electrodes of NGs/WO3, NGs/SnO2 and NGs/WO3/SnO2 exhibits a maximum specific capacitance of 14 F/g ,30 F/g and 11.2 F/g respectively... , 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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Synthesis and characterization of nano-engineered chalcogen materials for environmental and biomedical applications

  • Authors: Kumar, Neeraj
  • Date: 2017
  • Subjects: Nanostructured materials , Polymers , Inorganic cyclic compounds , Chalcogens
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/243095 , uj:25092
  • Description: Ph.D. (Chemistry) , Abstract: Nano-engineered chalcogen materials have garnered importance among the researchers across all scientific disciplines because of their interesting properties as well the possibility to tailor their electric, optical, thermal and mechanical properties via controlling shape and size. Various chalcogen based nanostructured materials such as Co3O4, MoO3, MoS2, NiS, WS2, WSe2, MoSe2, Bi2Te3, Ag2Te etc have found improved applications in energy conversion and storage devices, electronics, catalysis, sensors, solid lubricants and topological insulators etc. Still, these nanostructured materials have not been much explored for environmental and biomedical aspects although they have immense potential. The expensive and complicated fabrication techniques and perplexity of surface modification are the critical reasons which limit their utility in desired applications. Most of the previously reported synthesis techniques have also no control over issues such as structural composition, variant size and morphologies. However, different shapes and size dependent properties of nano-engineered chalcogen materials are yet to be explored. Thereby, this study addressed the facile strategies to design and develop new materials and structures with controlled morphologies, size, and composition of nano-engineered chalcogen materials via the wet chemical route. The evolved physiochemical properties based on their structural dimensions were also investigated. The effect of various reaction parameters such as the ratio of precursors, precursor concentrations, the role of stabilising/capping agent and new precursors on the composition and morphological evolution of the chalcogen based nanomaterials have been systematically explored. The developed liquid phase synthesis methodologies of nano-engineered chalcogen materials were facile, economical, energy efficient and eco-friendly. The structural, compositional and morphological features of fabricated chalcogen based nanomaterials were studied using various analytical instruments such as SEM/EDX, HRTEM, XRD, TGA, XPS, UV-Vis, FT-IR and Raman. Furthermore, this research also focused on harnessing the full potential of these synthesised nanomaterials in environmental and biomedical applications based on the information of physiochemical properties. Some applications that are covered in the environmental field are adsorption, photocatalysis and nanophosphors, whereas the biomedical field includes mainly cytotoxic behaviour of nanomaterials. The highlights of results obtained from the PhD study are summarised as follows. Part I presents a study of the anions ratio effect of acetate and nitrate ions on the formation of the different morphology of ZnO crystals in presence of NaOH and HMTA. The...
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Fabrication and electrochemical characterization of highly efficient hierarchically assembled hybrid two-dimensional nanointerfaces for electrochemical biosensing and bioelectronics

  • Authors: Kumari, Renu
  • Date: 2018
  • Subjects: Biosensors , Nanostructured materials , Bioelectrochemistry
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/401096 , uj:33504
  • Description: Abstract : Two dimensional (2D) materials have provided a new era to biosensors research. Biosensors are functional biodevices which include the integration of biology with electronics. The integration of 2D materials with other nanomaterials has transformed the understanding of the biological and electronics world and has paved a way for the design and fabrication of novel 2D nanointerfaces. The use of 2D nanointerfaces has given great success to biosensors and bioelectronics field which ultimately impacts on biomedical diagnosis and sensing applications. The superior properties of 2D materials such as large surface area, ease of hybridization, good biocompatibility, and high electron transfer properties make them ideal interface materials for the design and fabrication of bioelectronic devices including biosensors. The thesis focused on the fabrication of 2D nanointerfaces by combining two 2D hybrid materials and then nanostructuring with metal nanoparticles for better electron transfer within the interface which is followed by immobilization of enzyme as a bio-recognition element for biosensing purposes. The conjugation of the 2D hybrid nanointerface materials was achieved through the self-assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used in the study for characterization of the 2D hybrid nanointerface structures and chronoamperometry studies were employed to investigate the electrobiocatalytic properties of the 2D hybrid nanointerfaces structures. Structural characterization was done by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques for morphological details of 2D hybrid nanointerfaces structures. The fabrication of bioelectrodes was achieved by using the conjugated 2D hybrid nanointerface materials. ix There are three different segments in this research study. All of these different segments involved the use of 2D materials for bioelectronics purposes. The first phase involved the fabrication of smart hierarchically self-assembled 2D electrobiocatalytic interface system based on the combination of gold nanoparticles (AuNPs) doped graphene oxide (GO)-molybdenum disulfide (MoS2) layered nanohybrid, conjugated with poly (N-isopropylacrylamide, PNIPAAm) resulting in GO/AuNPs/MoS2/PNIPAAm interface. The introduction of PNIPAAm improved the stability of the self-assembled GO/AuNPs/MoS2 interface structure. Horseradish peroxidase (HRP) was subsequently immobilized on the GO/AuNPs/MoS2/PNIPAAm interface through electrostatic interactions giving GO/AuNPs/MoS2/PNIPAAm/Peroxidase electrobiocatalytic interface system as a platform for electrobiocatalysis reactions for biosensing applications. Morphological characterization of GO/AuNPs/MoS2/PNIPAAm indicates that this 2D nanointerface structure has a wide surface area for enzyme immobilization due to their flake-like structure. CV showed diffusion-controlled electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using hydrogen peroxide (H2O2) as a model analyte. The fabricated bioelectrode exhibits a wide linear response to the detection of H2O2 from 1.57 to 11.33 mM, with a detection limit of 3.34 mM (S/N=3) and a capacitance of 8.6 F/cm2. The second phase of the study involved the fabrication of hybrid dual 2D-nanohybrid structure through self-assembly combination AuNPs with hybrid 2D materials consisting of boron nitride (BN) and tungsten disulphide (WS2) as a nanointerface system for electrochemical biosensing. HRP was immobilized on the hybrid dual 2Dnanoparticle systems to form a biointerface. Structural characterization showed high crystallinity in the fabricated structure, while morphological characterization confirmed x the high surface to volume area of the hybrid material and the presence of welldispersed AuNPs. Electrochemical characterization also confirmed that the fabricated HRP/BN/WS2/AuNPs/GC bioelectrode exhibited excellent electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using H2O2 as a model analyte. The fabricated bioelectrode exhibited a wide linear range from 0.15 mM to 15.01 mM towards detection of H2O2 with a limit of detection of 3.0 mM (S/N = 3) and a sensitivity of 19.16 μA/mM/cm2. Theoretical studies of the BN/Au/WS2(001) nanohybrid structure was carried out using density functional theory (DFT) calculation for confirming the charge transport mobility and conductivity of the fabricated material. DFT calculations combined with the experimental studies showed that the self-assembled combination of the BN/Au/WS2(001) nanocomposite enhances the performance of the fabricated biosensor due to an introduced new electronic state emanating from the N 2p orbital. The third phase of the study involved the synthesis of acetylene sourced graphene (Gr) by chemical vapour deposition (CVD) method. Self-assembly method was used to prepare the 2D nanohybrid interfaces, which consist of Gr, WS2, AuNPs and HRP for fabricating electrochemical biosensor for detection of H2O2. The XRD results revealed that Gr/WS2/AuNPs nanohybrid structure has good crystalline nature. CV and electrochemical impedance spectroscopy results showed that due to the incorporation of AuNPs, the redox properties of Gr/WS2/AuNPs/HRP conjugate 2D hybrid structure improved in comparison to Gr/WS2/HRP. The same trend was observed in the chronoamperometric results. The Gr/WS2/AuNPs/HRP/GCE modified bioelectrode exhibited a good electrobiocatalytic performance towards the detection of H2O2 over a relatively wider linear range (0.40 mM to 23 mM), with a higher xi sensitivity (11.07 μA/mM/cm2) than that of Gr/WS2/HRP/GCE modified bioelectrode (9.23 μA/mM/cm2). The results have shown that electrobiocatalytic reactions can be controlled by modifying the nanohybrid interfaces. , D.Phil. (Chemistry
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Utilization of coal-based sorbents and their fabrication into carbon nanomaterials for the removal of organics from wastewater

  • Authors: Langwenya, Siphiwe P.
  • Date: 2011-05-16T06:58:03Z
  • Subjects: Sorbents , Nanostructured materials , Carbon , Water purification , Coal absorption and adsorption , Organic compounds removal
  • Type: Thesis
  • Identifier: uj:7068 , http://hdl.handle.net/10210/3630
  • Description: M.Sc. , With increasing industrial activities in South Africa, many of its waters are contaminated with both organic and inorganic pollutants. This is also a worldwide challenge which has resulted in an escalation in research efforts to combat it. Organic pollutants, for example, can be harmful to human health and the environment. Even when present at low concentrations, they tend to bio-accumulate and interact with endocrine systems. Therefore it is necessary that these pollutants are removed from effluents before they are integrated with water systems such as rivers and lakes. In an effort to utilize economic and efficient removal techniques, low cost and locally available materials have been used as potential adsorbents for the removal of these organic pollutants from synthetic wastewater. These coal-based materials were further fabricated into nanoporous sorbents through activation processes to improve their adsorption properties. The project reported in this dissertation was thus undertaken to explore, specifically, the efficacy of coal and coal-based sorbents (acid treated coal, activated carbon and activated fly ash) in their ability to remove phenolic compounds from wastewater.
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