Materials for alkaline direct alcohol fuel cells (ADAFC) and Perovskite solar cells (PSC) : synthesis, characterisation and application
- Authors: Gwebu, Sandile Surprise
- Date: 2021
- Subjects: Fuel cells - Materials , Perovskite solar cells - Materials , Nanostructured materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/483993 , uj:43944
- Description: Abstract: In pursuit of effective and less toxic materials for energy conversion, this study explored various materials for potential application in alkaline direct alcohol fuel cells (ADAFC) and perovskite solar cells (PSC). Alcohol electrooxidation on selected palladium-based electrocatalysts was investigated in alkaline media using various electrochemical techniques. For the first time, carbon nanodots (CNDs) were synthesised by pulverising multi-walled carbon nanotubes (MWCNTs) and functionalised using aqueous sodium hydroxide. Palladium-based nanocatalysts supported on functionalised carbon nanodots (fCNDs) blended with metal oxides promoters were prepared by sonochemical-assisted borohydride reduction method. Zirconium dioxide (ZrO2) and tungsten (VI) oxide (WO3) were selected as promoters while nickel (Ni) and cobalt (Co) were used as cocatalysts to prepare four electrocatalysts denoted by Pd/fCNDs-ZrO2, Pd/fCNDs-WO3, PdNi/fCNDs-WO3 and PdCo/fCNDs-WO3. The ratio of metal oxide to fCNDs was fixed at 1:4 to maintain good electrical conductivity of the support material. Physicochemical properties of the synthesised materials were studied by various microscopic and spectroscopic techniques such as transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS). Alcohol fuel oxidation on the prepared electrocatalysts was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques in KOH electrolyte. Synthesised Pd/fCNDs (8.23 wt. % Pd) and commercial Pd/C (10 wt. % Pd) electrocatalysts were used as benchmark standards... , Ph.D. (Chemistry)
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- Authors: Gwebu, Sandile Surprise
- Date: 2021
- Subjects: Fuel cells - Materials , Perovskite solar cells - Materials , Nanostructured materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/483993 , uj:43944
- Description: Abstract: In pursuit of effective and less toxic materials for energy conversion, this study explored various materials for potential application in alkaline direct alcohol fuel cells (ADAFC) and perovskite solar cells (PSC). Alcohol electrooxidation on selected palladium-based electrocatalysts was investigated in alkaline media using various electrochemical techniques. For the first time, carbon nanodots (CNDs) were synthesised by pulverising multi-walled carbon nanotubes (MWCNTs) and functionalised using aqueous sodium hydroxide. Palladium-based nanocatalysts supported on functionalised carbon nanodots (fCNDs) blended with metal oxides promoters were prepared by sonochemical-assisted borohydride reduction method. Zirconium dioxide (ZrO2) and tungsten (VI) oxide (WO3) were selected as promoters while nickel (Ni) and cobalt (Co) were used as cocatalysts to prepare four electrocatalysts denoted by Pd/fCNDs-ZrO2, Pd/fCNDs-WO3, PdNi/fCNDs-WO3 and PdCo/fCNDs-WO3. The ratio of metal oxide to fCNDs was fixed at 1:4 to maintain good electrical conductivity of the support material. Physicochemical properties of the synthesised materials were studied by various microscopic and spectroscopic techniques such as transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS). Alcohol fuel oxidation on the prepared electrocatalysts was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques in KOH electrolyte. Synthesised Pd/fCNDs (8.23 wt. % Pd) and commercial Pd/C (10 wt. % Pd) electrocatalysts were used as benchmark standards... , Ph.D. (Chemistry)
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Nanostructured carbon-based materials as efficient electrocatalysts for application in direct alcohol fuel cells
- Authors: Tlou, Selepe Cyril
- Date: 2021
- Subjects: Nanostructured materials , Electrocatalysis , Fuel cells - Materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/495703 , uj:45165
- Description: Abstract: Given the increasing demands in environmental protection issues, direct alcohol fuel cells (DAFCs) which use alcohol as fuel have emerged as promising renewable power devices. The fabrication of electro-catalyst materials dictates the efficiency, stability, the cost of a stack of fuel cells. Palladium (Pd) and its alloys are known as the best electro-catalysts for alcohol oxidation reaction in alkaline media. The support material has a significant impact on how well electro-catalysts function. For better metal dispersion, suitable support material should have a large surface area. It must also have oxygen-containing functional groups for bonding and interacting with the electro-catalysts. Furthermore, the support material should be corrosion resistant in the severe fuel cell environment. In this study, the effect of carbon nanofibers (CNFs) and carbon nano-onions (CNOs) support materials and composition on the structure, stability, and activity of Pd and palladium tin (PdSn) nanoparticles for electro-oxidation of methanol and ethanol have been discussed. The structures of electro-catalysts were studied using a variety of physicochemical techniques (FTIR, Raman spectroscopy, HR-TEM, XRD, XPS, TGA, and BET analysis). CNFs and CNOs were synthesized via flame pyrolysis and chemical vapor deposition respectively and the Pd-CNFs, Pd-CNOs, Pd-Sn-CNFs, and Pd-Sn-CNOs electro-catalysts were prepared by the alcohol reduction method. Carbon nanofibers and nano-onions were functionalized with carboxylic acid functional groups, which improved the dispersion of Pd and Sn nanoparticles, according to FTIR findings. The synthesized CNFs and CNOs have two Raman peaks, D and G, which correspond to a disordered carbon peak (D) and a graphite peak (G) respectively. The nanoscale nature of the synthesized nanomaterials was verified by TEM images, which showed that the size of the nanomaterials was not uniform. The carbon nanofibers and nano-onions were confirmed to be amorphous by XRD peaks, and Pd (111) was found in the electro-catalysts. In addition, Pd diffraction peaks shifted to lower angles upon the addition of Sn. XPS was used to determine the composition of the prepared samples as well as the oxidation states of Pd and Sn in the electro-catalysts. As compared to the Pd-C electro-catalyst, all the prepared electro-catalysts perform better in both methanol and ethanol oxidation reactions. , M.Sc. (Nanoscience)
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- Authors: Tlou, Selepe Cyril
- Date: 2021
- Subjects: Nanostructured materials , Electrocatalysis , Fuel cells - Materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/495703 , uj:45165
- Description: Abstract: Given the increasing demands in environmental protection issues, direct alcohol fuel cells (DAFCs) which use alcohol as fuel have emerged as promising renewable power devices. The fabrication of electro-catalyst materials dictates the efficiency, stability, the cost of a stack of fuel cells. Palladium (Pd) and its alloys are known as the best electro-catalysts for alcohol oxidation reaction in alkaline media. The support material has a significant impact on how well electro-catalysts function. For better metal dispersion, suitable support material should have a large surface area. It must also have oxygen-containing functional groups for bonding and interacting with the electro-catalysts. Furthermore, the support material should be corrosion resistant in the severe fuel cell environment. In this study, the effect of carbon nanofibers (CNFs) and carbon nano-onions (CNOs) support materials and composition on the structure, stability, and activity of Pd and palladium tin (PdSn) nanoparticles for electro-oxidation of methanol and ethanol have been discussed. The structures of electro-catalysts were studied using a variety of physicochemical techniques (FTIR, Raman spectroscopy, HR-TEM, XRD, XPS, TGA, and BET analysis). CNFs and CNOs were synthesized via flame pyrolysis and chemical vapor deposition respectively and the Pd-CNFs, Pd-CNOs, Pd-Sn-CNFs, and Pd-Sn-CNOs electro-catalysts were prepared by the alcohol reduction method. Carbon nanofibers and nano-onions were functionalized with carboxylic acid functional groups, which improved the dispersion of Pd and Sn nanoparticles, according to FTIR findings. The synthesized CNFs and CNOs have two Raman peaks, D and G, which correspond to a disordered carbon peak (D) and a graphite peak (G) respectively. The nanoscale nature of the synthesized nanomaterials was verified by TEM images, which showed that the size of the nanomaterials was not uniform. The carbon nanofibers and nano-onions were confirmed to be amorphous by XRD peaks, and Pd (111) was found in the electro-catalysts. In addition, Pd diffraction peaks shifted to lower angles upon the addition of Sn. XPS was used to determine the composition of the prepared samples as well as the oxidation states of Pd and Sn in the electro-catalysts. As compared to the Pd-C electro-catalyst, all the prepared electro-catalysts perform better in both methanol and ethanol oxidation reactions. , M.Sc. (Nanoscience)
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Understanding the C and N modifying effect on borophene as a highly selective and sensitive acetone sensor : a DFT study
- Authors: Molefi, Reitumetse Precious
- Date: 2021
- Subjects: Volatile organic compounds , Gas detectors , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/484113 , uj:43959
- Description: Abstract: Detection of volatile organic compounds (VOCs) and flammable gases for health and security purposes using two-dimensional (2D) based materials for gas sensing has fascinated and attracted a great attention owing to their remarkable high surface to volume ratio and unique electronic properties. Furthermore, 2D based materials have attracted a great deal of interests due to their high sensitivity, selectivity as well as fast response. It is well known that for a material to be regarded as a gas sensor, it should have a certain combination of properties, such as high sensitivity, exceptional selectivity, high stability and rapid response time, while operating at normal conditions. Most of these properties are dependent on the surface area to volume ratio, high comparative number of defects and the crystal structure of 2D material sensing sheet. Moreover, the high demand for gas sensors worldwide justifies this work, as the market is estimated to increase to $1,336.2 million by 2027 from $823.1 million in 2019. The World Health Organisation (WHO) has reported that about 5.5 million deaths occur in a year due to air pollution... , M.Sc. (Nanoscience)
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- Authors: Molefi, Reitumetse Precious
- Date: 2021
- Subjects: Volatile organic compounds , Gas detectors , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/484113 , uj:43959
- Description: Abstract: Detection of volatile organic compounds (VOCs) and flammable gases for health and security purposes using two-dimensional (2D) based materials for gas sensing has fascinated and attracted a great attention owing to their remarkable high surface to volume ratio and unique electronic properties. Furthermore, 2D based materials have attracted a great deal of interests due to their high sensitivity, selectivity as well as fast response. It is well known that for a material to be regarded as a gas sensor, it should have a certain combination of properties, such as high sensitivity, exceptional selectivity, high stability and rapid response time, while operating at normal conditions. Most of these properties are dependent on the surface area to volume ratio, high comparative number of defects and the crystal structure of 2D material sensing sheet. Moreover, the high demand for gas sensors worldwide justifies this work, as the market is estimated to increase to $1,336.2 million by 2027 from $823.1 million in 2019. The World Health Organisation (WHO) has reported that about 5.5 million deaths occur in a year due to air pollution... , M.Sc. (Nanoscience)
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A high-throughput, combinatorial and robotic approach to catalysis
- Authors: Potgieter, Kariska
- Date: 2020
- Subjects: Catalysis , Nanostructured materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/477512 , uj:43148
- Description: Abstract: Please refer to full text to view abstract. , D.Phil. (Chemistry)
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- Authors: Potgieter, Kariska
- Date: 2020
- Subjects: Catalysis , Nanostructured materials
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/477512 , uj:43148
- Description: Abstract: Please refer to full text to view abstract. , D.Phil. (Chemistry)
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Determination of Cd(II) in water using aptamer-based electrochemical biosensors
- Authors: Fakude, Colani Thembinkosi
- Date: 2020
- Subjects: Water - Analysis , Cadmium , Electrochemical analysis , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/458431 , uj:40718
- Description: Abstract: The World Health Organisation has recommended strict permissible limits for cadmium(II) in drinking water owing to the harmful threats it poses to humans and the environment. As a result, strict monitoring of cadmium(II) is a necessity. This dissertation reports on the design of monitoring tools referred to as electrochemical aptamer biosensors (aptasensors) based on nano-platforms for selective detection of Cd(II) in water. Nanomaterials such as carbon black, gold nanoparticles and carbon nanofibres were the smart materials of choice used in the fabrication of electrode supports for enhancement of detection signals. A screen-printed electrode was modified using carbon black following the dropcoating technique and then gold nanoparticles were electrodeposited by cyclic voltammetry (CV) at 50 mVs-1 in a potential window of -400 mV to 1100 mV. A thiolated single stranded DNA aptamer was immobilised on the nano-platform via a Au-S covalent linkage. The aptasensor was characterised using CV and electrochemical impedance spectroscopy ((EIS). The designed electrochemical aptasensor selectively detected Cd(II) using the square wave voltammetry (SWV) technique with a detection limit (LOD) of 0.14 ppb in the presence of interferents like chromium, copper and other ions. The second electrochemical aptasensor was based on the fabrication of a screen-printed electrode using acid treated carbon nanofibres. The characterisation procedure was similar with the first aptasensor and upon application, the aptasensor was found to be selective towards Cd(II) detection. A detection limit of 0.11 ppb was obtained using SWV and the aptasensor. Both the aptasensor findings were validated with inductively coupled plasma optical emission spectroscopy (ICP-OES) which showed an LOD of 1.4 ppb. Both electrochemical aptasensor provide a cost effective approach for the mitigation of interferences during electrochemical detection of Cd(II) and they can be applied in the monitoring of Cd(II) in environmental samples. , M.Sc. (Chemistry)
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- 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)
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- 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)
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- 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)
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- 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)
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- 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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Production of polymeric carbon solids (PCS) and their application as adsorbents for potentially toxic elements in water and wastewater
- Authors: Mabu, Dance
- Date: 2020
- Subjects: Water - Purification - Materials , Nanostructured materials , Adsorption
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/477308 , uj:43123
- Description: Abstract: Heavy metals are considered as some of the toxic substances that pollute water globally, as such, they tend to have negative effects on living organisms. Manganese and chromium metals exist in different oxidation states which some are dangerous at their low concentrations and they can cause dementia, anxiety, and ataxia, and nervous system problems. The main aim of this study was to produce PCS, hydrochar, and AC from wood chips and evaluate their potential as adsorbents for toxic inorganic ions from aqueous systems. The hydrochar was successfully produced by hydrothermal carbonization (HTC) of eucalyptus wood chips in the presence of a catalyst, water as a solvent, under the temperature of 240 °C and pressure of 4 bars. The activated carbon (AC) was generated by heating the hydrochar in a tube furnace, this process is called annealing. The hydrochar and AC were used as adsorbents for the removal of Mn(II) and Cr(VI) from aqueous solutions. The hydrochar and AC were characterized by sophisticated analytical instruments such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray powder diffraction (XRD), thermogravimetric analyzer (TGA), energy dispersive x-ray (EDX), Dynamic Light Scattering (DLS), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET)... , M.Sc. (Chemistry)
- Full Text:
- Authors: Mabu, Dance
- Date: 2020
- Subjects: Water - Purification - Materials , Nanostructured materials , Adsorption
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/477308 , uj:43123
- Description: Abstract: Heavy metals are considered as some of the toxic substances that pollute water globally, as such, they tend to have negative effects on living organisms. Manganese and chromium metals exist in different oxidation states which some are dangerous at their low concentrations and they can cause dementia, anxiety, and ataxia, and nervous system problems. The main aim of this study was to produce PCS, hydrochar, and AC from wood chips and evaluate their potential as adsorbents for toxic inorganic ions from aqueous systems. The hydrochar was successfully produced by hydrothermal carbonization (HTC) of eucalyptus wood chips in the presence of a catalyst, water as a solvent, under the temperature of 240 °C and pressure of 4 bars. The activated carbon (AC) was generated by heating the hydrochar in a tube furnace, this process is called annealing. The hydrochar and AC were used as adsorbents for the removal of Mn(II) and Cr(VI) from aqueous solutions. The hydrochar and AC were characterized by sophisticated analytical instruments such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray powder diffraction (XRD), thermogravimetric analyzer (TGA), energy dispersive x-ray (EDX), Dynamic Light Scattering (DLS), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET)... , M.Sc. (Chemistry)
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The advances in biomedical applications of carbon nanotubes based on drug delivery system by using MD and DFT modeling
- Authors: Karimzadeh, Sina
- Date: 2020
- Subjects: Carbon nanotubes , Nanostructured materials , Drug delivery systems , Density functionals , Molecular dynamics - Simulation methods , Doxorubicin , Cancer - Chemotherapy
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/480174 , uj:43458
- Description: Abstract: In this work, interaction and bond properties of anticancer drug doxorubicin (DOX), (6,6) armchair single-walled carbon nanotube (SWCNT), and hydroxyl- and carboxyl-functionalized SWCNT (ƒ-SWCNT) have been investigated based on DFT theory to design, improve and expand carbon nanotube (CNT) drug carriers for any biomedical system. Geometrical, structural, electrical, bonding and thermodynamic properties as well as equilibrium distances, adsorption energies, quantum molecular descriptors and frontier molecular orbitals or different drug arrangements on CNT at the highest equilibrium at WB97XD/6-31+G (d, p) level of theory at aqueous and gas phases were explored. Our calculations showed that hydrogen bonds between active sites of the spontaneous adsorption of doxorubicin (DOX) molecule and hydroxyl- and carboxyl-functionalized CNTs played a more important role than those with pristine CNTs in the adsorption and fixation of the studied complexes. Using quantum theory of atoms in molecules (QTAIMs) method, intermolecular interactions and corresponding descriptors at critical bonding points in aqueous and gas phases were also investigated. Evaluation of the results obtained from the natural bond orbital (NBO) analysis showed that the direction of electron movement was generally from drug molecule to CNT... , M.Ing. (Mechanical Engineering)
- Full Text:
- Authors: Karimzadeh, Sina
- Date: 2020
- Subjects: Carbon nanotubes , Nanostructured materials , Drug delivery systems , Density functionals , Molecular dynamics - Simulation methods , Doxorubicin , Cancer - Chemotherapy
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/480174 , uj:43458
- Description: Abstract: In this work, interaction and bond properties of anticancer drug doxorubicin (DOX), (6,6) armchair single-walled carbon nanotube (SWCNT), and hydroxyl- and carboxyl-functionalized SWCNT (ƒ-SWCNT) have been investigated based on DFT theory to design, improve and expand carbon nanotube (CNT) drug carriers for any biomedical system. Geometrical, structural, electrical, bonding and thermodynamic properties as well as equilibrium distances, adsorption energies, quantum molecular descriptors and frontier molecular orbitals or different drug arrangements on CNT at the highest equilibrium at WB97XD/6-31+G (d, p) level of theory at aqueous and gas phases were explored. Our calculations showed that hydrogen bonds between active sites of the spontaneous adsorption of doxorubicin (DOX) molecule and hydroxyl- and carboxyl-functionalized CNTs played a more important role than those with pristine CNTs in the adsorption and fixation of the studied complexes. Using quantum theory of atoms in molecules (QTAIMs) method, intermolecular interactions and corresponding descriptors at critical bonding points in aqueous and gas phases were also investigated. Evaluation of the results obtained from the natural bond orbital (NBO) analysis showed that the direction of electron movement was generally from drug molecule to CNT... , M.Ing. (Mechanical Engineering)
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WO3-SnO2 nanostructures supported on carbon nanomaterials for electrochemical energy storage
- Authors: Kganyago, Peter
- Date: 2020
- Subjects: Energy storage , Nanostructured materials , Storage batteries , Supercapacitors
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/458469 , uj:40723
- Description: Abstract: Electrochemical energy storage devices such as ion batteries or super-capacitors have been developed as energy carriers for new portable technologies. The electrochemical performance of an electrochemical device depends on the physico-chemical properties of the electrode materials. In supercapacitors, the design and composition of the electrode widely influence its performance. Great efforts have been undertaken to fabricate electrode materials of supercapacitors in a quest to improve the electrochemical performance of the electrode. In this project we focus on fabrication of TMOs on carbon nanomaterials. Carbon nanomaterials and transition metal oxides offers an interesting synergistic relationship which can be utilised in electrochemical energy storage devices. The types of metal oxide incorporated into the carbon nanomaterial as well as the nano-architecture of the materials affects the electrochemical properties and thus the performance of supercapacitors. Thus, this project is focused on the development of SnO2 nanostructures supported on carbonaceous 2D materials for electrochemical energy storage devices. The physico-chemical attributes of the nanocomposite were investigated using P-XRD, FTIR, TEM, SEM, TGA and BET. The electrochemical performance of the electrodes was tested using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) in 2M KOH electrolyte in a three-electrode configuration. The hybrid electrodes of NGs/WO3, NGs/SnO2 and NGs/WO3/SnO2 exhibits a maximum specific capacitance of 14 F/g ,30 F/g and 11.2 F/g respectively... , M.Sc. (Nanoscience)
- 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)
- Full Text:
- 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)
- Full Text:
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)
- Full Text:
- 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)
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- 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)
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- 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)
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- 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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