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)
- Full Text:
- 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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Exploring and understanding the catalytic potential of phosphabicyclononane ligands in palladium catalysed cross coupling reactions
- Authors: Masanabo, Ntombenhle
- Date: 2020
- Subjects: Nanostructured materials , Nanomedicine , Ligands , Phosphine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/474076 , uj:42719
- Description: Abstract: Electron-rich bulky phosphine forms the most effective Pd catalyst systems for cross coupling reactions as they enhance the rate determining step of the catalytic cycle. The quest for an affordable and efficient ligand, prompted the implementation of tertiary bicylic phosphine ligands (Phoban family) in Pd-catalysed cross coupling reactions. Phoban (isomers mixture phosphabicyclo[3.3.1]nonane and phosphabicyclo[4.2.1]nonane) ligand is derived from cis, cis-1,5-cyclooctadiene and considered to be good electron donors, sterically bulk and have an unsymmetrical geometry to assist with an active catalytic system. Catalytic efficiency of phoban was investigated in Suzuki-Miyaura and Heck- Mizoroki cross coupling reactions, and the outcome of the study after an extensive optimisation study of various reaction parameters showed that palladium catalysts derived from 9-eicosyl-9-phosphabicyclononane (L2) gave superior results. This ligand L2 has also been demonstrated by SASOL R & D to be an excellent ligand in Co-catalysed hydroformylation reactions. The results obtained in this study have illustrated that this ligand L2 can facilitate couplings of a wide range of electronically diverse aryl bromides and chlorides with various coupling partners in Suzuki and Heck reactions. The implementation of 9-eicosyl-9-phosphabicyclononane in Heck and Suzuki reactions, provided the desired coupled products in 30-90% yields. In addition, this novel palladium catalyst derived from phoban was applied in the synthesis of industrial important products. The efficacy of this novel catalyst in Suzuki reaction was demonstrated in the synthesis of Felbinac (an anti-inflammatory drug under the trade name Traxam) and OTBN (an anti-hypertensive drug intermediate). Similarly, the success of the new protocol in Heck reaction was exemplified in the synthesis of octinoxate (trade names: Eusolex 2292 and Uvinul MC80; UV absorbers or filters), raspberry ketone derivatives (4-phenyl-2-butanone and 4-(4-methoxyphenyl)-2-butanone) used as flavourants. These products were successfully synthesised in yields ranging from 51 to 94% (GC). , M.Sc. (Chemistry)
- Full Text:
- Authors: Masanabo, Ntombenhle
- Date: 2020
- Subjects: Nanostructured materials , Nanomedicine , Ligands , Phosphine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/474076 , uj:42719
- Description: Abstract: Electron-rich bulky phosphine forms the most effective Pd catalyst systems for cross coupling reactions as they enhance the rate determining step of the catalytic cycle. The quest for an affordable and efficient ligand, prompted the implementation of tertiary bicylic phosphine ligands (Phoban family) in Pd-catalysed cross coupling reactions. Phoban (isomers mixture phosphabicyclo[3.3.1]nonane and phosphabicyclo[4.2.1]nonane) ligand is derived from cis, cis-1,5-cyclooctadiene and considered to be good electron donors, sterically bulk and have an unsymmetrical geometry to assist with an active catalytic system. Catalytic efficiency of phoban was investigated in Suzuki-Miyaura and Heck- Mizoroki cross coupling reactions, and the outcome of the study after an extensive optimisation study of various reaction parameters showed that palladium catalysts derived from 9-eicosyl-9-phosphabicyclononane (L2) gave superior results. This ligand L2 has also been demonstrated by SASOL R & D to be an excellent ligand in Co-catalysed hydroformylation reactions. The results obtained in this study have illustrated that this ligand L2 can facilitate couplings of a wide range of electronically diverse aryl bromides and chlorides with various coupling partners in Suzuki and Heck reactions. The implementation of 9-eicosyl-9-phosphabicyclononane in Heck and Suzuki reactions, provided the desired coupled products in 30-90% yields. In addition, this novel palladium catalyst derived from phoban was applied in the synthesis of industrial important products. The efficacy of this novel catalyst in Suzuki reaction was demonstrated in the synthesis of Felbinac (an anti-inflammatory drug under the trade name Traxam) and OTBN (an anti-hypertensive drug intermediate). Similarly, the success of the new protocol in Heck reaction was exemplified in the synthesis of octinoxate (trade names: Eusolex 2292 and Uvinul MC80; UV absorbers or filters), raspberry ketone derivatives (4-phenyl-2-butanone and 4-(4-methoxyphenyl)-2-butanone) used as flavourants. These products were successfully synthesised in yields ranging from 51 to 94% (GC). , M.Sc. (Chemistry)
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Exposure assessment of engineered nanomaterials released from commercially available nano-enabled products into water systems
- Authors: Lehutso, Raisibe Florence
- Date: 2020
- Subjects: Nanostructured materials , Nanochemistry
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/473988 , uj:42708
- Description: Abstract: Please refer to full text to view abstract. , Ph.D. (Chemistry)
- Full Text:
- Authors: Lehutso, Raisibe Florence
- Date: 2020
- Subjects: Nanostructured materials , Nanochemistry
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/473988 , uj:42708
- Description: Abstract: Please refer to full text to view abstract. , Ph.D. (Chemistry)
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Heterojunctions cerium oxide nanocomposites for photocatalytic synthesis of bio-based chemicals
- Authors: Mavuso, Mlungisi Arnold
- Date: 2020
- Subjects: Photocatalysis , Heterojunctions , Nanostructured materials , Nanocomposites (Materials)
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/474108 , uj:42723
- Description: Abstract: In the last decade, selective photocatalytic processes have been developed for fabrication of value-added chemicals with promising activities and selectivities. However, to achieve highly selective photocatalytic oxidation is still presenting a formidable challenge because of the generation of non-selective •OH radicals. Also, photocatalysis could be associated with two major problems including: (i) low photocatalytic efficiency (i.e. activity and selectivity) and (ii) unsatisfactory visible-light responsive photocatalytic materials. To develop highly efficient visible-light photocatalytic materials, several photocatalysts modification strategies such as bandgap modification, selective growth of crystal facets and surface treatment have been explored. To achieve this feat, morphology-controlled CeO2 nanostructures (i.e. CeO2-NPs, CeO2-NRs and CeO2-NCs) and heterostructured CeO2 interfaces (i.e. CeO2- MO, MO = SnO2, ZnO, TiO2, Nb2O5, MoO3, CuO, Co3O4, NiO, MnO2 & Fe2O3) were successfully synthesized by solution processes and characterized by the XRD, BET, UV/Vis, PL, XPS, EPR, SEM and TEM analytical techniques. According to the data, CeO2-NRs photocatalyst gave the best pinene conversion amount of 33.6% and pinene oxide selectivity of 54.3% as the major product after 5 h reaction time. The CeO2-NRs photocatalyst was recycled 5 times without any significant loss of its photocatalytic activity. Furthermore, CeO2-NRs photocatalyst was versatile for the photooxidation of HMF under visible light irradiation to afford DFF selectivity of 40.3% as the major product and oxalic acid formation (23% selectivity) at 70% HMF conversion. The heterostructured CeO2-based interfaces showed an increase in the photocatalytic efficiency when compared to pure CeO2 NPs in the selective oxidation of Pinus wood-derived α-pinene to aroma oxygenated derivatives. Particularly, the Fe2O3-CeO2 and NiO-CeO2 photocatalysts afforded good pinene conversions of 71.3% and 53.1%, respectively. The corresponding pinene oxide selectivities of 57.3% and 58.2% for Fe2O3-CeO2 and NiO-CeO2 photocatalysts were obtained after 5 h reaction. Furthermore, the heterojunction MoO3-CeO2 nanocatalyst offered the best pinene oxide selectivity of 63.8% at 65.8% pinene conversion after 5 h visible light irradiation at 25 °C. Also, H2O2 and reaction temperature had a positive influence on the photoactivity but negatively affected the product selectivity. selectivity. Lastly, the heterojunction MoO3-CeO2 nanocatalyst exhibited potential for application for various types of biomass-derived chemicals, including HMF, furfural, vanillyl alcohol, isoeugenol and glycerol. , Ph.D. (Chemistry)
- Full Text:
- Authors: Mavuso, Mlungisi Arnold
- Date: 2020
- Subjects: Photocatalysis , Heterojunctions , Nanostructured materials , Nanocomposites (Materials)
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/474108 , uj:42723
- Description: Abstract: In the last decade, selective photocatalytic processes have been developed for fabrication of value-added chemicals with promising activities and selectivities. However, to achieve highly selective photocatalytic oxidation is still presenting a formidable challenge because of the generation of non-selective •OH radicals. Also, photocatalysis could be associated with two major problems including: (i) low photocatalytic efficiency (i.e. activity and selectivity) and (ii) unsatisfactory visible-light responsive photocatalytic materials. To develop highly efficient visible-light photocatalytic materials, several photocatalysts modification strategies such as bandgap modification, selective growth of crystal facets and surface treatment have been explored. To achieve this feat, morphology-controlled CeO2 nanostructures (i.e. CeO2-NPs, CeO2-NRs and CeO2-NCs) and heterostructured CeO2 interfaces (i.e. CeO2- MO, MO = SnO2, ZnO, TiO2, Nb2O5, MoO3, CuO, Co3O4, NiO, MnO2 & Fe2O3) were successfully synthesized by solution processes and characterized by the XRD, BET, UV/Vis, PL, XPS, EPR, SEM and TEM analytical techniques. According to the data, CeO2-NRs photocatalyst gave the best pinene conversion amount of 33.6% and pinene oxide selectivity of 54.3% as the major product after 5 h reaction time. The CeO2-NRs photocatalyst was recycled 5 times without any significant loss of its photocatalytic activity. Furthermore, CeO2-NRs photocatalyst was versatile for the photooxidation of HMF under visible light irradiation to afford DFF selectivity of 40.3% as the major product and oxalic acid formation (23% selectivity) at 70% HMF conversion. The heterostructured CeO2-based interfaces showed an increase in the photocatalytic efficiency when compared to pure CeO2 NPs in the selective oxidation of Pinus wood-derived α-pinene to aroma oxygenated derivatives. Particularly, the Fe2O3-CeO2 and NiO-CeO2 photocatalysts afforded good pinene conversions of 71.3% and 53.1%, respectively. The corresponding pinene oxide selectivities of 57.3% and 58.2% for Fe2O3-CeO2 and NiO-CeO2 photocatalysts were obtained after 5 h reaction. Furthermore, the heterojunction MoO3-CeO2 nanocatalyst offered the best pinene oxide selectivity of 63.8% at 65.8% pinene conversion after 5 h visible light irradiation at 25 °C. Also, H2O2 and reaction temperature had a positive influence on the photoactivity but negatively affected the product selectivity. selectivity. Lastly, the heterojunction MoO3-CeO2 nanocatalyst exhibited potential for application for various types of biomass-derived chemicals, including HMF, furfural, vanillyl alcohol, isoeugenol and glycerol. , Ph.D. (Chemistry)
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Nanostructured materials as sorbents for sample preparation in trace metal analysis
- Authors: Nyaba, Luthando
- Date: 2020
- Subjects: Nanostructured materials , Inorganic compounds - Synthesis , Trace elements - Analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/458607 , uj:40742
- Description: Abstract: Trace metals pollution of the environment is a global challenge. This is because these may be a health risk to humans, as well as other living organisms. Metals such as As, Co, Cr, Cd, Pb, Tl, Te, Sb, are regarded as toxic inorganic pollutants. These metals normally exist at trace levels in various environmental matrices such as, soil, water and biological samples to name a few. Toxic metals can cause severe health problems that can even lead to fatalities for animals and human beings, this is due to the fact that unlike organic contaminants these trace toxic metal ions are non-biodegradable and have a tendency to accumulate in vital human organs, such as liver, lungs, heart and kidneys. Therefore, the aim of this research was to prepare a nanostructured material and applied as an effective adsorbent for preconcentration of trace from complex matrices. The quantification of the trace metals was achieved using inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The nanocomposites were then characterized using scanning electron microscopy (SEM), Fourier Transform infrared (FTIR) spectroscopy transmission electron microscopy (TEM), and x-ray diffraction (XRD). Several effective experimental parameters controlling the preconcentration of the trace metals were optimized using central composite design. Under optimum conditions they showed good the linearity ranged, correlation of coefficients (R2), limits of detection (LODs) and quantification (LOQs). The prepared adsorbents are Mg/Al-LDH@CNTs nanocomposite, MPC@SiO2@Fe3O4, and Fe3O4@Mg/Al-layered double hydroxide were characterized and used to develop three preconcentration methods which are mainly ultrasound assisted solid phase extraction using magnetic and dispersive ultrasound-assisted cloud point- dispersive μ-solid phase extraction... , Ph.D. (Chemistry)
- Full Text:
- Authors: Nyaba, Luthando
- Date: 2020
- Subjects: Nanostructured materials , Inorganic compounds - Synthesis , Trace elements - Analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/458607 , uj:40742
- Description: Abstract: Trace metals pollution of the environment is a global challenge. This is because these may be a health risk to humans, as well as other living organisms. Metals such as As, Co, Cr, Cd, Pb, Tl, Te, Sb, are regarded as toxic inorganic pollutants. These metals normally exist at trace levels in various environmental matrices such as, soil, water and biological samples to name a few. Toxic metals can cause severe health problems that can even lead to fatalities for animals and human beings, this is due to the fact that unlike organic contaminants these trace toxic metal ions are non-biodegradable and have a tendency to accumulate in vital human organs, such as liver, lungs, heart and kidneys. Therefore, the aim of this research was to prepare a nanostructured material and applied as an effective adsorbent for preconcentration of trace from complex matrices. The quantification of the trace metals was achieved using inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The nanocomposites were then characterized using scanning electron microscopy (SEM), Fourier Transform infrared (FTIR) spectroscopy transmission electron microscopy (TEM), and x-ray diffraction (XRD). Several effective experimental parameters controlling the preconcentration of the trace metals were optimized using central composite design. Under optimum conditions they showed good the linearity ranged, correlation of coefficients (R2), limits of detection (LODs) and quantification (LOQs). The prepared adsorbents are Mg/Al-LDH@CNTs nanocomposite, MPC@SiO2@Fe3O4, and Fe3O4@Mg/Al-layered double hydroxide were characterized and used to develop three preconcentration methods which are mainly ultrasound assisted solid phase extraction using magnetic and dispersive ultrasound-assisted cloud point- dispersive μ-solid phase extraction... , Ph.D. (Chemistry)
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Nanostructured membranes and carbon nanofibers in ionic diode mechanisms : prospects for future desalination
- Authors: Tshwenya, Luthando
- Date: 2020
- Subjects: Polyethylene terephthalate , Nanostructured materials , Composite materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/458701 , uj:40753
- Description: Abstract: In this work, the idea of fabricating ionic diode or rectifier devices using a materials approach was pursued, based on embedding nanostructured ion conducting materials and membranes on insulating poly (ethylene terephthalate) (PET) substrates with laser drilled microholes. The ion conducting membranes provided ion selectivity, whilst the microhole substrate allowed current rectification and ion concentration polarisation phenomena to be possible. Current rectification in ionic diode devices fabricated in this fashion were shown to result in the similar “ion pump” effect reported for cell membranes in living organisms, but with a much higher ionic current flow. If properly understood and optimised, this behaviour may be valuable in sensing and in desalination amongst many other suggested applications. The first part of the doctoral thesis dealt with developing a method for joining two ready made films together; one an ion-exchange membrane with semi-permeability for cations (Fumasep FKS-30), and the other a PET substrate with a microhole, to allow current rectification. Hot-pressing, was chosen as a suitable method to achieve this, offering stable and better-defined ionic diode geometries. Confocal microscopy was used to define symmetric and asymmetric diode geometries, and to measure the thickness of the films after hot-pressing. Cation rectification phenomena are shown to be dependent on microhole diameter, electrolyte concentration, and on the nature of the electrolyte. Significant competition of cation transport with proton transport was observed. In the second milestone, surface oxidised carbon nanofibers were used in ionic diode fabrication. The carbon nanofibers were synthesised using chemical vapour deposition, and hydrogen peroxide as oxidising agent, to induce negative surface charges, which when embedded asymmetrically on a microhole in PET, allow cation selectivity and cationic diode behaviour. The carbon nanofibers were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), elemental analysis, and by zeta potential measurements. And the effects of pH, ionic strength, and nature of electrolyte, on ionic diode behaviour were investigated... , Ph.D. (Chemistry)
- Full Text:
- Authors: Tshwenya, Luthando
- Date: 2020
- Subjects: Polyethylene terephthalate , Nanostructured materials , Composite materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/458701 , uj:40753
- Description: Abstract: In this work, the idea of fabricating ionic diode or rectifier devices using a materials approach was pursued, based on embedding nanostructured ion conducting materials and membranes on insulating poly (ethylene terephthalate) (PET) substrates with laser drilled microholes. The ion conducting membranes provided ion selectivity, whilst the microhole substrate allowed current rectification and ion concentration polarisation phenomena to be possible. Current rectification in ionic diode devices fabricated in this fashion were shown to result in the similar “ion pump” effect reported for cell membranes in living organisms, but with a much higher ionic current flow. If properly understood and optimised, this behaviour may be valuable in sensing and in desalination amongst many other suggested applications. The first part of the doctoral thesis dealt with developing a method for joining two ready made films together; one an ion-exchange membrane with semi-permeability for cations (Fumasep FKS-30), and the other a PET substrate with a microhole, to allow current rectification. Hot-pressing, was chosen as a suitable method to achieve this, offering stable and better-defined ionic diode geometries. Confocal microscopy was used to define symmetric and asymmetric diode geometries, and to measure the thickness of the films after hot-pressing. Cation rectification phenomena are shown to be dependent on microhole diameter, electrolyte concentration, and on the nature of the electrolyte. Significant competition of cation transport with proton transport was observed. In the second milestone, surface oxidised carbon nanofibers were used in ionic diode fabrication. The carbon nanofibers were synthesised using chemical vapour deposition, and hydrogen peroxide as oxidising agent, to induce negative surface charges, which when embedded asymmetrically on a microhole in PET, allow cation selectivity and cationic diode behaviour. The carbon nanofibers were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), elemental analysis, and by zeta potential measurements. And the effects of pH, ionic strength, and nature of electrolyte, on ionic diode behaviour were investigated... , Ph.D. (Chemistry)
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Piperidinylphosphine ligands in palladium-catalyzed cross-coupling reactions
- Authors: Lekgau, R. Denise
- Date: 2020
- Subjects: Nanostructured materials , Nanomedicine , Ligands , Phosphine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/473996 , uj:42709
- Description: Abstract: Please refer to full text to view abstract. , M.Sc. (Chemistry)
- Full Text:
- Authors: Lekgau, R. Denise
- Date: 2020
- Subjects: Nanostructured materials , Nanomedicine , Ligands , Phosphine
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/473996 , uj:42709
- Description: Abstract: Please refer to full text to view abstract. , M.Sc. (Chemistry)
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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)
- Full Text:
- 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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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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- 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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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)
- Full Text:
- 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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CO2 hydrogenation to synthetic fuel via modified Fischer-Tropsch process using cobalt-based catalysts
- Khangale, Phathutshedzo Rodney
- 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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- 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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Fabrication and characterization of nanocomposite membrane of polyethersulfone (PES) embedded with hyperbranched polyethyleneimine (HPEI) and bismuth vanadate (BiVO4) nanoparticles for the photocatalytic degradation of triclosan in solution
- Authors: Shaku, Koketjo Madielane
- Date: 2019
- Subjects: Nanocomposites (Materials) , Polyethylene , Polyethylene - Analysis , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401609 , uj:33572
- Description: Abstract : An increase in the production and usage of pharmaceutical and personal care products in various water bodies has attracted significant attention amongst the public and scientists. Classified as emerging pollutants, these pharmaceutical and personal care products ultimately accumulate and contaminate several water bodies through several pathways. Although reported to be found at very low concentrations, exposure to these emerging organic pollutants has adverse health effects to humans. Conventional methods are reported to partially degrade emerging pollutants. Therefore, it is of importance to explore effective and innovative methods for the complete degradation of these pollutants. In this study, a photocatalytic-membrane consisting of bismuth vanadate (BiVO4) nanoparticles, hyperbranched polyethyleneimine (HPEI) and polyethersulfone (PES) were used in the degradation of triclosan. BiVO4 is an n-type semiconductor with excellent properties such as lower band gap and visible light active. However, it has drawbacks such as agglomeration and having lower surface area. HPEI was used as a dispersing agent for the BiVO4 photocatalyst as this polymer has been found to be an excellent template/host for the production of monodispersed and uniform size particles. HPEI can also induce hydrophilic properties on the membrane thus alleviating fouling. BiVO4 was characterised using X-ray Diffraction (XRD) and Raman depicted that spectroscopy. These analyses revealed that there was successful synthesis of the monoclinic phase of BiVO4, as well as a phase transformation between the monoclinic phase and the tetragonal phase upon addition of HPEI within the nanoparticles. The modified membranes showed improved water flux and hydrophilicity (71°- 56°) as compared to the bare PES (75°) upon addition of HPEI and BiVO4. The modified membranes were effective in the photodegradation of triclosan (upto 86%) and this was accompanied by the generation of Cl- ions. , M.Sc. (Nanoscience)
- Full Text:
- Authors: Shaku, Koketjo Madielane
- Date: 2019
- Subjects: Nanocomposites (Materials) , Polyethylene , Polyethylene - Analysis , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401609 , uj:33572
- Description: Abstract : An increase in the production and usage of pharmaceutical and personal care products in various water bodies has attracted significant attention amongst the public and scientists. Classified as emerging pollutants, these pharmaceutical and personal care products ultimately accumulate and contaminate several water bodies through several pathways. Although reported to be found at very low concentrations, exposure to these emerging organic pollutants has adverse health effects to humans. Conventional methods are reported to partially degrade emerging pollutants. Therefore, it is of importance to explore effective and innovative methods for the complete degradation of these pollutants. In this study, a photocatalytic-membrane consisting of bismuth vanadate (BiVO4) nanoparticles, hyperbranched polyethyleneimine (HPEI) and polyethersulfone (PES) were used in the degradation of triclosan. BiVO4 is an n-type semiconductor with excellent properties such as lower band gap and visible light active. However, it has drawbacks such as agglomeration and having lower surface area. HPEI was used as a dispersing agent for the BiVO4 photocatalyst as this polymer has been found to be an excellent template/host for the production of monodispersed and uniform size particles. HPEI can also induce hydrophilic properties on the membrane thus alleviating fouling. BiVO4 was characterised using X-ray Diffraction (XRD) and Raman depicted that spectroscopy. These analyses revealed that there was successful synthesis of the monoclinic phase of BiVO4, as well as a phase transformation between the monoclinic phase and the tetragonal phase upon addition of HPEI within the nanoparticles. The modified membranes showed improved water flux and hydrophilicity (71°- 56°) as compared to the bare PES (75°) upon addition of HPEI and BiVO4. The modified membranes were effective in the photodegradation of triclosan (upto 86%) and this was accompanied by the generation of Cl- ions. , M.Sc. (Nanoscience)
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Graphene oxide and metal organic frameworks hybrids : synthesis, characterization and assessment in membrane application
- Authors: Masibi, Gaobodiwe Elizabeth
- Date: 2019
- Subjects: Graphene , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401277 , uj:33528
- Description: Abstract : Membrane technology has emerged as a viable means of water purification with advantages such as low cost, energy efficient, high removal efficiency and environmentally friendly production. The membrane that is considered ideal should provide improved stability, higher selectivity, higher flux, and resistance to chlorine and fouling. However fouling, low hydrophilicity and low flux remain challenges facing this technology. In this study Polyethersulfone (PES) membrane was used as a support for thin film composite membrane (TFC) and was adjusted by controlling fabrication processes, which are commonly recognized by adding additives that includes organic and inorganic materials and also by altering controlling fabrication parameters. Zeolitic imidazolate framework-8 @ graphene oxide (ZIF-8@GO) composites at different concentrations (0.1, 0.5, 0.9 and1):1 were synthesized and characterized using SEM, TEM, XRD, BET, TGA, FTIR and Raman instruments before they were embedded on top thin layer of polyamide-thin film composite (PA-TFC) membranes. PA-TFC membranes were prepared successfully using m-Phenylenediamine (MPD) and trimesoyl chloride (TMC) as monomers whereby composites (GO, ZIF-8, ZIF-8@GO) were dispersed into aqueous solution of MPD over PES support layer via interfacial polymerization process. Thereafter the surface morphology, cross section and surface roughness were characterized using SEM and AFM microscopes before reverse osmosis application. The membranes incorporated with composites resulted in lower surface roughness, higher fluxes, higher salt and dye rejection as compared to the pure PES. In addition membranes with lower surface roughness displayed a better fouling propensity than pristine PES and TFC membranes. , M.Sc. (Nanoscience)
- Full Text:
- Authors: Masibi, Gaobodiwe Elizabeth
- Date: 2019
- Subjects: Graphene , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401277 , uj:33528
- Description: Abstract : Membrane technology has emerged as a viable means of water purification with advantages such as low cost, energy efficient, high removal efficiency and environmentally friendly production. The membrane that is considered ideal should provide improved stability, higher selectivity, higher flux, and resistance to chlorine and fouling. However fouling, low hydrophilicity and low flux remain challenges facing this technology. In this study Polyethersulfone (PES) membrane was used as a support for thin film composite membrane (TFC) and was adjusted by controlling fabrication processes, which are commonly recognized by adding additives that includes organic and inorganic materials and also by altering controlling fabrication parameters. Zeolitic imidazolate framework-8 @ graphene oxide (ZIF-8@GO) composites at different concentrations (0.1, 0.5, 0.9 and1):1 were synthesized and characterized using SEM, TEM, XRD, BET, TGA, FTIR and Raman instruments before they were embedded on top thin layer of polyamide-thin film composite (PA-TFC) membranes. PA-TFC membranes were prepared successfully using m-Phenylenediamine (MPD) and trimesoyl chloride (TMC) as monomers whereby composites (GO, ZIF-8, ZIF-8@GO) were dispersed into aqueous solution of MPD over PES support layer via interfacial polymerization process. Thereafter the surface morphology, cross section and surface roughness were characterized using SEM and AFM microscopes before reverse osmosis application. The membranes incorporated with composites resulted in lower surface roughness, higher fluxes, higher salt and dye rejection as compared to the pure PES. In addition membranes with lower surface roughness displayed a better fouling propensity than pristine PES and TFC membranes. , M.Sc. (Nanoscience)
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Incorporation of zwitterion modified graphene oxide onto thin-film composite layer to enhance flix and solute rejection
- Authors: Xabela, Sinethemba Snezz
- Date: 2019
- Subjects: Nanostructured materials , Membrane separation , Graft copolymers , Nanofiltration , Membrane filters
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401694 , uj:33583
- Description: Abstract : In this work, surface Zwitterion functionalization of graphene oxide (GO) was carried out by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface by means of reverse atom transfer radical polymerization (RATRP) approach to generate GO-PSBMA nanoplates. GO-PSBMA was characterized by Fourier transforms infrared spectra (FT-IR), thermal gravimetric analysis (TGA), X-Ray Diffraction (XRD), Raman spectroscopy and Transmission Electron Microscopy (TEM) techniques. The influence of GO-PSBMA was investigated on different membrane polymers by incorporating different amounts of this additive into cellulose acetate (CA) and polyphenylsulfone (PPSU) casting solutions through phase inversion method, initially for the removal of both organic dyes and salts in water. Furthermore, GO-PSBMA was incorporated into the polyamide (PA) selective layer to develop a novel thin-film composite (TFC) membrane for desalination application. The effect of GO-PSBMA on the morphology and surface property of the CA, PPSU and TFC membranes was examined using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and ATR-FTIR. The contact angle (CA), pure water flux (PWF) and antifouling properties of modified membranes were also used to investigate the membranes performance. On cellulose acetate hybrid membranes, it was found that the water flux of the hybrid membrane was greatly enhanced from 100.71 L.m-2.h-1 to 258.39 L.m-2.h-1 when the GO-PSBMA content increased from 0 to 0.5 wt.%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (FRR) (93%) and a low total flux decline ratio (0.01%). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified CA membranes, the hybrid membranes had a higher retention of CR dye (99.01%), MO dye (84%) and MB dye (95%), and a lower rejection of salts at an operational pressure of 900 kPa, rendering the membranes... , M.Sc. (Chemistry)
- Full Text:
- Authors: Xabela, Sinethemba Snezz
- Date: 2019
- Subjects: Nanostructured materials , Membrane separation , Graft copolymers , Nanofiltration , Membrane filters
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401694 , uj:33583
- Description: Abstract : In this work, surface Zwitterion functionalization of graphene oxide (GO) was carried out by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface by means of reverse atom transfer radical polymerization (RATRP) approach to generate GO-PSBMA nanoplates. GO-PSBMA was characterized by Fourier transforms infrared spectra (FT-IR), thermal gravimetric analysis (TGA), X-Ray Diffraction (XRD), Raman spectroscopy and Transmission Electron Microscopy (TEM) techniques. The influence of GO-PSBMA was investigated on different membrane polymers by incorporating different amounts of this additive into cellulose acetate (CA) and polyphenylsulfone (PPSU) casting solutions through phase inversion method, initially for the removal of both organic dyes and salts in water. Furthermore, GO-PSBMA was incorporated into the polyamide (PA) selective layer to develop a novel thin-film composite (TFC) membrane for desalination application. The effect of GO-PSBMA on the morphology and surface property of the CA, PPSU and TFC membranes was examined using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and ATR-FTIR. The contact angle (CA), pure water flux (PWF) and antifouling properties of modified membranes were also used to investigate the membranes performance. On cellulose acetate hybrid membranes, it was found that the water flux of the hybrid membrane was greatly enhanced from 100.71 L.m-2.h-1 to 258.39 L.m-2.h-1 when the GO-PSBMA content increased from 0 to 0.5 wt.%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (FRR) (93%) and a low total flux decline ratio (0.01%). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified CA membranes, the hybrid membranes had a higher retention of CR dye (99.01%), MO dye (84%) and MB dye (95%), and a lower rejection of salts at an operational pressure of 900 kPa, rendering the membranes... , M.Sc. (Chemistry)
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Indium-zinc oxide nanostructure materials based sensors for the detection of volatile organic compounds and carbon monoxide
- Authors: Kortidis, Ioannis
- Date: 2019
- Subjects: Volatile organic compounds , Nanostructured materials , Indium , Zinc oxide , Gas detectors
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/292586 , uj:31798
- Description: Abstract: Detection of poisonous and flammable gases for health and security purpose utilizing semiconductor metal oxides (SMO) based sensors has fascinated ample attention owing to their incomparable advantages, such as a flawless evidence in variation of their sensor resistance when exposed to either reducing or oxidizing gases. Moreover, their rapid response and recovery times as well as their remarkable sensitivity make them appealing. It is well-known that an anticipated gas sensor ought to possess a combination of enhanced sensitivity, excellent selectivity, rapid response-recovery times, long-term stability and low working temperature. These factors are mostly reliant on surface area to volume ratio, higher relative concentration of defects and crystal structure of the SMO sensing layer. Moreover, this work is justified by the demand of gas sensors globally, with the market estimated to reach approximately R38.4-billion by 2020. According to World Health Organization (WHO) and World Bank, about 5.5 million deaths happen annually costing the world economy R70-trillion a year due to air pollution. While in South Africa about 20 000 deaths occur every year, costing the economy nearly R300-million due to air pollution. Recently, WHO has indicated that most of the cities in SA (such as Pretoria, Johannesburg, etc.) exceed the limit of air quality (AQ) with roughly five times the WHO recommendation, while over 90% of the world's population live in areas that exceed WHO limits on air pollution... , Ph.D. (Chemistry)
- Full Text:
- Authors: Kortidis, Ioannis
- Date: 2019
- Subjects: Volatile organic compounds , Nanostructured materials , Indium , Zinc oxide , Gas detectors
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/292586 , uj:31798
- Description: Abstract: Detection of poisonous and flammable gases for health and security purpose utilizing semiconductor metal oxides (SMO) based sensors has fascinated ample attention owing to their incomparable advantages, such as a flawless evidence in variation of their sensor resistance when exposed to either reducing or oxidizing gases. Moreover, their rapid response and recovery times as well as their remarkable sensitivity make them appealing. It is well-known that an anticipated gas sensor ought to possess a combination of enhanced sensitivity, excellent selectivity, rapid response-recovery times, long-term stability and low working temperature. These factors are mostly reliant on surface area to volume ratio, higher relative concentration of defects and crystal structure of the SMO sensing layer. Moreover, this work is justified by the demand of gas sensors globally, with the market estimated to reach approximately R38.4-billion by 2020. According to World Health Organization (WHO) and World Bank, about 5.5 million deaths happen annually costing the world economy R70-trillion a year due to air pollution. While in South Africa about 20 000 deaths occur every year, costing the economy nearly R300-million due to air pollution. Recently, WHO has indicated that most of the cities in SA (such as Pretoria, Johannesburg, etc.) exceed the limit of air quality (AQ) with roughly five times the WHO recommendation, while over 90% of the world's population live in areas that exceed WHO limits on air pollution... , Ph.D. (Chemistry)
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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)
- Full Text:
- 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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Nanostructured TIO₂ based materials for the photocatalytic degradation of emerging organic pollutants from aqueous solution
- Authors: Sambaza, Shepherd Sundayi
- Date: 2019
- Subjects: Nanostructured materials , Titanium dioxide , Photocatalysis , Sewage - Purification
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/401572 , uj:33568
- Description: Abstract : Water is regarded as the most vital of natural resources for the sustainability of life, yet freshwater systems are directly threatened by pollution. Among the many pollutants are organic emerging pollutants such as synthetic chemicals and pharmaceuticals. Bisphenol A (BPA) and ibuprofen are examples of such a synthetic organic compounds. Current wastewater treatment technologies such as membrane technology, chemical treatment and biodegradation are not always efficient in removing toxic emerging organic pollutants. This is because they were not specifically designed to remove these contaminants. Photocatalysis on the other hand, has shown great potential to remove toxic emerging pollutants from the environment. Over the years, TiO2 catalyst has been used widely for water remediation applications. Surface modification of TiO2 is necessary to extend its use in the visible region of the solar spectrum and to reduce the inherent fast recombination rate of charges. Polyaniline (PANI)-wrapped TiO2 nanorods (PANI-TiO2), obtained through the oxidative polymerization of aniline at the surface of hydrothermally pre-synthesized TiO2 nanorods, were evaluated as photocatalysts for the degradation of BPA. Fourier-transform infrared spectroscopy (FTIR) analysis revealed the successful incorporation of PANI into TiO2 by the appearance of peaks at 1577 cm-1 and 1502 cm-1 that are due to the C=C and C=N stretch of the benzoid and quinoid. Brunauer- Emmett-Teller (BET) analysis revealed the presence of mesoporous material in PANI-TiO2. Transmission electron microscopy (TEM) analysis showed that TiO2 nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO2 nanorods. X-ray diffraction (XRD) and Raman spectroscopy revealed that anatase phase TiO2 was synthesized with typical Raman vii vibration peaks at 637 cm-1, 514 cm-1, 396 cm-1, and 195 cm-1. X-ray Photon Spectroscopy (XPS) survey scan of the PANI-TiO2 nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including, pH, contact time, dosage and initial concentration of BPA was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using 0.2 g/L PANI-TiO2 photocatalyst at pH 10. PANI-TiO2 showed a better performance than as-synthesized TiO2 with a rate constant of 4.46 x 10-2 min-1 compared to 2.18 x 10-2 min-1. Nitrate ions increased the rate of degradation of BPA whilst humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1 and 93.1. The PANI-TiO2 nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. PANI capped WO3@TiO2 nanocomposite prepared through a three–stage synthetic route was evaluated for the degradation of ibuprofen under visible light. XRD analysis confirmed the anatase phase of TiO2 and monoclinic and orthorhombic WO3 crystalline structures were formed. The XRD analysis confirmed that the phases were not affected by wrapping in PANI.TEM analysis confirmed that TiO2 nanorods were synthesized with different diameters. TEM analysis showed that a WO3@TiO2 heterojunction was formed. A PANI layer was wrapping the heterojunction was observed. Photoluminescence analysis revealed that pairing TiO2 and WO3 resulted in improved charge separation. The charge separation was further improved by wrapping the heterojunction in a PANI matrix. DRS calculations showed that pairing TiO2 with WO3 extended the band edge to about 420 nm thus facilitating the use of the nanocomposite in the visible region of the solar spectrum. XPS analysis revealed viii the presence of W, C, O, Ti, N, and their corresponding photo electron peaks were found to be W4f, W4d, C1s, O 1s, N1s, and Ti 2p. The degradation of ibuprofen was influenced by pH with maximum degradation observed at pH 9. The degradation conformed to the Langmuir-Hinshelwood kinetic model. The rate constant, K for the degradation of ibuprofen by WO3@TiO2 and PANI/WO3@TiO2 was 2.59 x 10-2 and 3.5 x 10-2 respectively that were significantly higher than that of pristine TiO2, which was 1.92 x10-2... , Ph.D. (Chemistry)
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- Authors: Sambaza, Shepherd Sundayi
- Date: 2019
- Subjects: Nanostructured materials , Titanium dioxide , Photocatalysis , Sewage - Purification
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/401572 , uj:33568
- Description: Abstract : Water is regarded as the most vital of natural resources for the sustainability of life, yet freshwater systems are directly threatened by pollution. Among the many pollutants are organic emerging pollutants such as synthetic chemicals and pharmaceuticals. Bisphenol A (BPA) and ibuprofen are examples of such a synthetic organic compounds. Current wastewater treatment technologies such as membrane technology, chemical treatment and biodegradation are not always efficient in removing toxic emerging organic pollutants. This is because they were not specifically designed to remove these contaminants. Photocatalysis on the other hand, has shown great potential to remove toxic emerging pollutants from the environment. Over the years, TiO2 catalyst has been used widely for water remediation applications. Surface modification of TiO2 is necessary to extend its use in the visible region of the solar spectrum and to reduce the inherent fast recombination rate of charges. Polyaniline (PANI)-wrapped TiO2 nanorods (PANI-TiO2), obtained through the oxidative polymerization of aniline at the surface of hydrothermally pre-synthesized TiO2 nanorods, were evaluated as photocatalysts for the degradation of BPA. Fourier-transform infrared spectroscopy (FTIR) analysis revealed the successful incorporation of PANI into TiO2 by the appearance of peaks at 1577 cm-1 and 1502 cm-1 that are due to the C=C and C=N stretch of the benzoid and quinoid. Brunauer- Emmett-Teller (BET) analysis revealed the presence of mesoporous material in PANI-TiO2. Transmission electron microscopy (TEM) analysis showed that TiO2 nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO2 nanorods. X-ray diffraction (XRD) and Raman spectroscopy revealed that anatase phase TiO2 was synthesized with typical Raman vii vibration peaks at 637 cm-1, 514 cm-1, 396 cm-1, and 195 cm-1. X-ray Photon Spectroscopy (XPS) survey scan of the PANI-TiO2 nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including, pH, contact time, dosage and initial concentration of BPA was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using 0.2 g/L PANI-TiO2 photocatalyst at pH 10. PANI-TiO2 showed a better performance than as-synthesized TiO2 with a rate constant of 4.46 x 10-2 min-1 compared to 2.18 x 10-2 min-1. Nitrate ions increased the rate of degradation of BPA whilst humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1 and 93.1. The PANI-TiO2 nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. PANI capped WO3@TiO2 nanocomposite prepared through a three–stage synthetic route was evaluated for the degradation of ibuprofen under visible light. XRD analysis confirmed the anatase phase of TiO2 and monoclinic and orthorhombic WO3 crystalline structures were formed. The XRD analysis confirmed that the phases were not affected by wrapping in PANI.TEM analysis confirmed that TiO2 nanorods were synthesized with different diameters. TEM analysis showed that a WO3@TiO2 heterojunction was formed. A PANI layer was wrapping the heterojunction was observed. Photoluminescence analysis revealed that pairing TiO2 and WO3 resulted in improved charge separation. The charge separation was further improved by wrapping the heterojunction in a PANI matrix. DRS calculations showed that pairing TiO2 with WO3 extended the band edge to about 420 nm thus facilitating the use of the nanocomposite in the visible region of the solar spectrum. XPS analysis revealed viii the presence of W, C, O, Ti, N, and their corresponding photo electron peaks were found to be W4f, W4d, C1s, O 1s, N1s, and Ti 2p. The degradation of ibuprofen was influenced by pH with maximum degradation observed at pH 9. The degradation conformed to the Langmuir-Hinshelwood kinetic model. The rate constant, K for the degradation of ibuprofen by WO3@TiO2 and PANI/WO3@TiO2 was 2.59 x 10-2 and 3.5 x 10-2 respectively that were significantly higher than that of pristine TiO2, which was 1.92 x10-2... , Ph.D. (Chemistry)
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Photoreduction of chromium (VI) using multi-phase bismuth vanadate (BiVO4) photocatalyst
- Authors: Zwane, Qedile Innocent
- Date: 2019
- Subjects: Water - Purfication , Sewage - Treatment , Nanostructured materials , Photochemistry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401702 , uj:33585
- Description: Abstract : Sustainable development goals emphasise the importance of access to clean drinking water. However, due to industrialisation, a lot of pollutants find their way into water bodies. Heavy metals like chromium and arsenic are some of the most dangerous pollutants that are accumulating in water bodies due to anthropogenic processes. Recent research reported precipitation, coagulation, membrane technology, adsorption and flocculation as some of the possible techniques for the removal of these pollutants. However, all these techniques have serious draw back including that they produce sludge that may require further treatment or have high operational costs which make the impractical to use in real life. The purification of water through photocatalysis using nanoparticles (NPs) has emerged as one of the most promising approach to solving the issue of wastewater treatment. This work presents the use of novel multiphase BiVO4 NPs for the removal of hexavalent chromium from wastewater. Novel Y3+ and Mo6+ dual-doped, multiphase BiVO4 NPs were synthesized using a modified hydrothermal method through a gradient doping method. Yttrium (III) was used as a phase-stabilizing agent for the tetragonal phase while Mo6+ was used to control the volume of the crystals. The NPs were characterized using scan electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), Fourier transform Infrared spectroscopy (FTIR), X-Ray diffraction spectroscopy (XRD) and Braunnauer-Emmett-Teller theory (BET) to determine crystal phase, morphology and surface area. It was found that introduction of the dopants and formation of the phase junction lead to a diminished PL spectra indicative of reduced electron-hole recombination. The 10% (m-m) Y-Mo dual-doped multiphase BiVO4 NPs showed the highest electron-hole separation efficiency. However, 15% (m-m) Y-Mo had the least charge separation and due to the formation of recombination centers at high degrees of metal doping. The multiphase systems also showed a red shift in the UV-Vis absorption spectrum. The Mott-Schottky plot obtained from Electro Impedance Spectroscopy confirmed formation of a phase junction in the multiphase systems which resulted in an improvement of the photocurrent to twice that of the pristine BiVO4 NPs for the 10% Y-Mo BiVO4 NPs... , M.Sc. (Chemistry)
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- Authors: Zwane, Qedile Innocent
- Date: 2019
- Subjects: Water - Purfication , Sewage - Treatment , Nanostructured materials , Photochemistry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/401702 , uj:33585
- Description: Abstract : Sustainable development goals emphasise the importance of access to clean drinking water. However, due to industrialisation, a lot of pollutants find their way into water bodies. Heavy metals like chromium and arsenic are some of the most dangerous pollutants that are accumulating in water bodies due to anthropogenic processes. Recent research reported precipitation, coagulation, membrane technology, adsorption and flocculation as some of the possible techniques for the removal of these pollutants. However, all these techniques have serious draw back including that they produce sludge that may require further treatment or have high operational costs which make the impractical to use in real life. The purification of water through photocatalysis using nanoparticles (NPs) has emerged as one of the most promising approach to solving the issue of wastewater treatment. This work presents the use of novel multiphase BiVO4 NPs for the removal of hexavalent chromium from wastewater. Novel Y3+ and Mo6+ dual-doped, multiphase BiVO4 NPs were synthesized using a modified hydrothermal method through a gradient doping method. Yttrium (III) was used as a phase-stabilizing agent for the tetragonal phase while Mo6+ was used to control the volume of the crystals. The NPs were characterized using scan electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), Fourier transform Infrared spectroscopy (FTIR), X-Ray diffraction spectroscopy (XRD) and Braunnauer-Emmett-Teller theory (BET) to determine crystal phase, morphology and surface area. It was found that introduction of the dopants and formation of the phase junction lead to a diminished PL spectra indicative of reduced electron-hole recombination. The 10% (m-m) Y-Mo dual-doped multiphase BiVO4 NPs showed the highest electron-hole separation efficiency. However, 15% (m-m) Y-Mo had the least charge separation and due to the formation of recombination centers at high degrees of metal doping. The multiphase systems also showed a red shift in the UV-Vis absorption spectrum. The Mott-Schottky plot obtained from Electro Impedance Spectroscopy confirmed formation of a phase junction in the multiphase systems which resulted in an improvement of the photocurrent to twice that of the pristine BiVO4 NPs for the 10% Y-Mo BiVO4 NPs... , M.Sc. (Chemistry)
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Sintering of nanostructured titanium carbonitride from carbonitrothermic reduced ilmenite
- Authors: Mojisola, Tajudeen
- Date: 2019
- Subjects: Sintering , Nanostructured materials , Titanium , Nitrides , Ilmenite
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/418221 , uj:35451
- Description: Abstract: In recent years, there has been concerted effort towards the synthesis of cermet materials from low grade titanium ore. This is because the reserve of high grade titanium containing ore, i.e. natural rutile, is fast depleting and rutile becoming more expensive across the globe. Today, titanium containing hard ceramic powders, e.g. TiC, TiN and their solid solution TiCN powders have become important reinforcement materials due to their suitable properties. Titanium carbonitride, which is a boundary solid solution of titanium carbide and titanium nitride combines the excellent properties of both TiC and TiN in one structure of TiCN. In order to make this special material readily available, various methods have been adopted to synthesize titanium carbonitride powder. Although, the synthesis of titanium carbonitride by carbothermic reduction of titanium dioxide (rutile) with carbon under nitrogen atmosphere has been the most widely used for the commercial production of titanium carbonitride. However, this process requires the extraction and purification of titanium dioxide from its ore e.g. ilmenite, which itself is a costly process, or the use of natural rutile, which is fast depleting and becoming more expensive across the globe. Ilmenite (FeTiO3), which is a mineral source of titanium dioxide, is abundantly found in many parts of the world, most especially in South Africa. South Africa, is a leading producer of ilmenite in the world, accounting for about 37% of 6.2 million metric tons of the global production. Hence sourcing and processing of TiCN powder directly from South African ilmenite will be an added advantage. It is on this premises that the urgency for the processing of South African ilmenite to its final products, e.g. titanium containing hard ceramic products, such as TiC, TiN and/or TiCN powders or composite, and titanium metal, is being hung. Hence, this study develops a mechano-chemical processing route for the synthesis of titanium containing hard ceramic powders from ilmenite concentrate, which could be used for the production of cutting tools made of TiC and TiCN composite materials. The study also determines the possibility of sintering bulk TiCN based cermets with different metal matrices. For the synthesis of titanium carbide and titanium nitride/carbonitride powders, mixtures of ilmenite concentrate and graphite were milled in a planetary ball mill (PM 100) for different time intervals of 0, 30, 60 and 120 min, and carbo(nitro)thermally reduced under argon and nitrogen gas in a high temperature laboratory furnace (Thermal Tech., USA), respectively. These carbo(nitro)thermic reductions of mixtures of ilmenite concentrate and graphite result in the formation of Fe –TiC and Fe – TiCN powder composites in which globules of TiC and TiCN particles are embedded in the iron matrix,.. , Ph.D. (Engineering Metallurgy)
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- Authors: Mojisola, Tajudeen
- Date: 2019
- Subjects: Sintering , Nanostructured materials , Titanium , Nitrides , Ilmenite
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/418221 , uj:35451
- Description: Abstract: In recent years, there has been concerted effort towards the synthesis of cermet materials from low grade titanium ore. This is because the reserve of high grade titanium containing ore, i.e. natural rutile, is fast depleting and rutile becoming more expensive across the globe. Today, titanium containing hard ceramic powders, e.g. TiC, TiN and their solid solution TiCN powders have become important reinforcement materials due to their suitable properties. Titanium carbonitride, which is a boundary solid solution of titanium carbide and titanium nitride combines the excellent properties of both TiC and TiN in one structure of TiCN. In order to make this special material readily available, various methods have been adopted to synthesize titanium carbonitride powder. Although, the synthesis of titanium carbonitride by carbothermic reduction of titanium dioxide (rutile) with carbon under nitrogen atmosphere has been the most widely used for the commercial production of titanium carbonitride. However, this process requires the extraction and purification of titanium dioxide from its ore e.g. ilmenite, which itself is a costly process, or the use of natural rutile, which is fast depleting and becoming more expensive across the globe. Ilmenite (FeTiO3), which is a mineral source of titanium dioxide, is abundantly found in many parts of the world, most especially in South Africa. South Africa, is a leading producer of ilmenite in the world, accounting for about 37% of 6.2 million metric tons of the global production. Hence sourcing and processing of TiCN powder directly from South African ilmenite will be an added advantage. It is on this premises that the urgency for the processing of South African ilmenite to its final products, e.g. titanium containing hard ceramic products, such as TiC, TiN and/or TiCN powders or composite, and titanium metal, is being hung. Hence, this study develops a mechano-chemical processing route for the synthesis of titanium containing hard ceramic powders from ilmenite concentrate, which could be used for the production of cutting tools made of TiC and TiCN composite materials. The study also determines the possibility of sintering bulk TiCN based cermets with different metal matrices. For the synthesis of titanium carbide and titanium nitride/carbonitride powders, mixtures of ilmenite concentrate and graphite were milled in a planetary ball mill (PM 100) for different time intervals of 0, 30, 60 and 120 min, and carbo(nitro)thermally reduced under argon and nitrogen gas in a high temperature laboratory furnace (Thermal Tech., USA), respectively. These carbo(nitro)thermic reductions of mixtures of ilmenite concentrate and graphite result in the formation of Fe –TiC and Fe – TiCN powder composites in which globules of TiC and TiCN particles are embedded in the iron matrix,.. , Ph.D. (Engineering Metallurgy)
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Synthesis and characterization of carbon nanospheres and carbon nanotubes conjugated bisphosphonates as potential drugs for the treatment of secondary bone cancer
- Authors: Dlamini, Njabuliso Lucia
- Date: 2019
- Subjects: Carbon , Carbon nanotubes , Nanostructured materials , Bone - Cancer - Radiotherapy , Bone - Cancer - Chemotherapy , Diphosphonates - Therapeutic use
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/417240 , uj:35327
- Description: Abstract: The statistical proof that most of the different forms of cancer metastasize to bone tissue from other body organs has seen to the development of several treatment regimes. These include surgery, radiotherapy, hormonal therapy and chemotherapy. The latter was established to be an effective form of treatment for secondary bone cancer. This is due to that drugs administered into the body system can reach most areas where the cancerous cells have metastasized... , Ph.D. (Chemistry)
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- Authors: Dlamini, Njabuliso Lucia
- Date: 2019
- Subjects: Carbon , Carbon nanotubes , Nanostructured materials , Bone - Cancer - Radiotherapy , Bone - Cancer - Chemotherapy , Diphosphonates - Therapeutic use
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/417240 , uj:35327
- Description: Abstract: The statistical proof that most of the different forms of cancer metastasize to bone tissue from other body organs has seen to the development of several treatment regimes. These include surgery, radiotherapy, hormonal therapy and chemotherapy. The latter was established to be an effective form of treatment for secondary bone cancer. This is due to that drugs administered into the body system can reach most areas where the cancerous cells have metastasized... , Ph.D. (Chemistry)
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