A South African case study of corrosion management
- Authors: Njomane, Linda
- Date: 2017
- Subjects: Corrosion and anti-corrosives , Electrolytic corrosion , Electrochemical analysis , Gas industry - Equipment and supplies - Corrosion
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269786 , uj:28664
- Description: M.Phil. (Engineering Management) , Abstract: Corrosion is an undesirable electrochemical reaction that affects materials negatively. Electrons flow from a metal of high potential to a metal of low potential. Structures that are built with materials prone to corrosion can fail and lead to incidents, financial loss and reputational damage. Most of the major incidents and maintenance costs that occur in oil and gas industry are attributed to corrosion related failures. Globally; the direct cost of corrosion is estimated at $2.2 trillion per annum. Analysis of availability of tanks and pipelines in Company X shows that the available storage capacity is below 50% due to asset outages. Unavailability of assets are caused by breakdowns and extensive repairs attributed to corrosion related failures. The business disruption cost for 2016 only amounted to $1.1 million while the maintenance costs from 2013 to 2016 are estimated to $4.5mil. Literature review reveals that corrosion is a problem in the oil and gas industry however it can be managed and controlled through design, installation of corrosion control techniques. Cathodic protection is effective in protecting buried and submerged structures while protective coating is effective for atmospheric corrosion. The case study used a mixed research approach, predominantly using quantitative data from the historical reports and qualitative research to gain clarity on the historical reports. A gap analysis to determine the maturity of corrosion management is performed and the preliminary result showed that only one aspect of corrosion management is fully complied to. When the tanks are inspected, most of the measurements for wall thickness especially on the tank floor are below the design limits. Most of the tank breakdowns are caused by the failures on the higher tank shell courses. Some failures on the shell are picked up post inspection when the tank shell is being prepared for external protective coating. The corrosion rate picked on tank floors of the all the uncoated tanks and one coated tank in Mossel Bay is higher than the minimum expected rate on the carbon steel in the marine environment. Jet A1 tanks where the coating is applied with stringent quality controls had the lowest corrosion rate. Inspectors prescribed repairs if wall losses are between 40 - 100% if the tank is to be operated for the next 10 years. Use of generic corrosion rate of 0.05mm per year gives inaccurate remaining life. The remaining life calculations using actual corrosion rates found that even the wall losses between 20 – 39% are not giving life beyond 10 years in Port Elizabeth in some tanks. The implication of the...
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- Authors: Njomane, Linda
- Date: 2017
- Subjects: Corrosion and anti-corrosives , Electrolytic corrosion , Electrochemical analysis , Gas industry - Equipment and supplies - Corrosion
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269786 , uj:28664
- Description: M.Phil. (Engineering Management) , Abstract: Corrosion is an undesirable electrochemical reaction that affects materials negatively. Electrons flow from a metal of high potential to a metal of low potential. Structures that are built with materials prone to corrosion can fail and lead to incidents, financial loss and reputational damage. Most of the major incidents and maintenance costs that occur in oil and gas industry are attributed to corrosion related failures. Globally; the direct cost of corrosion is estimated at $2.2 trillion per annum. Analysis of availability of tanks and pipelines in Company X shows that the available storage capacity is below 50% due to asset outages. Unavailability of assets are caused by breakdowns and extensive repairs attributed to corrosion related failures. The business disruption cost for 2016 only amounted to $1.1 million while the maintenance costs from 2013 to 2016 are estimated to $4.5mil. Literature review reveals that corrosion is a problem in the oil and gas industry however it can be managed and controlled through design, installation of corrosion control techniques. Cathodic protection is effective in protecting buried and submerged structures while protective coating is effective for atmospheric corrosion. The case study used a mixed research approach, predominantly using quantitative data from the historical reports and qualitative research to gain clarity on the historical reports. A gap analysis to determine the maturity of corrosion management is performed and the preliminary result showed that only one aspect of corrosion management is fully complied to. When the tanks are inspected, most of the measurements for wall thickness especially on the tank floor are below the design limits. Most of the tank breakdowns are caused by the failures on the higher tank shell courses. Some failures on the shell are picked up post inspection when the tank shell is being prepared for external protective coating. The corrosion rate picked on tank floors of the all the uncoated tanks and one coated tank in Mossel Bay is higher than the minimum expected rate on the carbon steel in the marine environment. Jet A1 tanks where the coating is applied with stringent quality controls had the lowest corrosion rate. Inspectors prescribed repairs if wall losses are between 40 - 100% if the tank is to be operated for the next 10 years. Use of generic corrosion rate of 0.05mm per year gives inaccurate remaining life. The remaining life calculations using actual corrosion rates found that even the wall losses between 20 – 39% are not giving life beyond 10 years in Port Elizabeth in some tanks. The implication of the...
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Application of “noble metals” for the electrocatalytic detection of monoamine group containing neurotransmitters
- Authors: Meenakshi, K.M.
- Date: 2016
- Subjects: Nanostructured materials , Electrochemical sensors , Nanoscience , Electrocatalysis , Electrochemical analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/124877 , uj:20969
- Description: Abstract: Electrochemical biosensors have provided a new route to biomedical diagnosis and testing. Research to constantly improve biosensor performance and develop new protocols in biosensor design is ongoing. This work contributes to the field of biosensor development by exploring the applicabilities of conductive polymer (CP) and metal nanoparticles (MNPs) based nanocomposites as tools in electrochemical biosensor fabrication. In general, voltammetric and pulsed technique were employed to model the electrochemical reactivities of the CPs- MNPs on working glassy carbon electrodes; while the transmission electron microscopy (TEM), Scanning elelctron microscopy (SEM), UV-vis spectrophotometer (UV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) instrumental techniques were used for further characterisation.This thesis focuses on both the integration of functional nanomaterials to improve electrical interfacing between biological system and electronics. Metal nanoparticles based nanocomposite was prepared by using in situ polymerization and composite formation (IPCF) technique and used in the development of an electrochemical sensor for neurotransmitters (NTs) detection with simultaneous reduction of dyes. The MNPs-CPs composite was deposited on the glassy carbon electrode (GCE) by using the drop and dry method. The integration of various nanomaterials is described, in order to understand the effect of different surface modifications and morphologies of various materials for electrochemical sensing of biological analytes. IPCF approach are promising technique to provide key building blocks of nanocomposites for future practical systems, as well as model systems for fundamental research. A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of IPCF. The formation mechanism of the composite has been supported by a model hydrogen atom (H∙≡H+ + e-) transfer (HAT) type of reaction which belongs to the... , Ph.D. (Chemistry)
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- Authors: Meenakshi, K.M.
- Date: 2016
- Subjects: Nanostructured materials , Electrochemical sensors , Nanoscience , Electrocatalysis , Electrochemical analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/124877 , uj:20969
- Description: Abstract: Electrochemical biosensors have provided a new route to biomedical diagnosis and testing. Research to constantly improve biosensor performance and develop new protocols in biosensor design is ongoing. This work contributes to the field of biosensor development by exploring the applicabilities of conductive polymer (CP) and metal nanoparticles (MNPs) based nanocomposites as tools in electrochemical biosensor fabrication. In general, voltammetric and pulsed technique were employed to model the electrochemical reactivities of the CPs- MNPs on working glassy carbon electrodes; while the transmission electron microscopy (TEM), Scanning elelctron microscopy (SEM), UV-vis spectrophotometer (UV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) instrumental techniques were used for further characterisation.This thesis focuses on both the integration of functional nanomaterials to improve electrical interfacing between biological system and electronics. Metal nanoparticles based nanocomposite was prepared by using in situ polymerization and composite formation (IPCF) technique and used in the development of an electrochemical sensor for neurotransmitters (NTs) detection with simultaneous reduction of dyes. The MNPs-CPs composite was deposited on the glassy carbon electrode (GCE) by using the drop and dry method. The integration of various nanomaterials is described, in order to understand the effect of different surface modifications and morphologies of various materials for electrochemical sensing of biological analytes. IPCF approach are promising technique to provide key building blocks of nanocomposites for future practical systems, as well as model systems for fundamental research. A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of IPCF. The formation mechanism of the composite has been supported by a model hydrogen atom (H∙≡H+ + e-) transfer (HAT) type of reaction which belongs to the... , Ph.D. (Chemistry)
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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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Development of advanced carbon based composite electrodes for the detection and the degradation of organic pollutants in water via electrochemical/photoelectrochemical processes
- Authors: Ntsendwana, Bulelwa
- Date: 2014-07-15
- Subjects: Carbon composites , Electrodes, Carbon , Organic water pollutants , Electrochemical analysis , Photoelectrochemistry
- Type: Thesis
- Identifier: uj:11656 , http://hdl.handle.net/10210/11379
- Description: Ph.D. (Chemistry) , In this study, carbon based electrode materials such as glassy carbon, graphene, diamond and exfoliated graphite were explored as suitable electrode materials for electrochemical detection, electrochemical and photoelectrochemical degradation of organic water pollutants. Graphene modified glassy carbon electrode sensor was developed for bisphenol A. Cyclic voltammetry was used to study the electrochemical properties of the prepared graphene- modified glassy carbon electrode using potassium ferricyanide as a redox probe. The prepared graphene- modified glassy carbon electrode exhibited more facile electron kinetics and enhanced current of about 75% when compared to the unmodified glassy carbon electrode...
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- Authors: Ntsendwana, Bulelwa
- Date: 2014-07-15
- Subjects: Carbon composites , Electrodes, Carbon , Organic water pollutants , Electrochemical analysis , Photoelectrochemistry
- Type: Thesis
- Identifier: uj:11656 , http://hdl.handle.net/10210/11379
- Description: Ph.D. (Chemistry) , In this study, carbon based electrode materials such as glassy carbon, graphene, diamond and exfoliated graphite were explored as suitable electrode materials for electrochemical detection, electrochemical and photoelectrochemical degradation of organic water pollutants. Graphene modified glassy carbon electrode sensor was developed for bisphenol A. Cyclic voltammetry was used to study the electrochemical properties of the prepared graphene- modified glassy carbon electrode using potassium ferricyanide as a redox probe. The prepared graphene- modified glassy carbon electrode exhibited more facile electron kinetics and enhanced current of about 75% when compared to the unmodified glassy carbon electrode...
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Development of electrochemical nano-biosensors for arsenic detection
- Authors: Mushiana, Talifhani
- Date: 2018
- Subjects: Nanochemistry , Nanotechnology , Electrochemical analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292796 , uj:31825
- Description: Abstract: Arsenic contamination in groundwater is a tenacious issue in various parts of the world. Owing to the toxicity of arsenic, its detection and analysis are important for national/global wellbeing of human and animals. This dissertation reports the development of two electrochemical aptamer biosensor on a nano-platform for selective detection of As(lll) in wastewater. In the process of fabricating the biosensor, different nanomaterials such as carbon nanoparticles (CNPs), gold nanoparticles (AuNPs) and iron oxide magnetic nanoparticles (MNPs) were used to facilitate electron transfer. A glassy carbon electrode was modified with CNPs by drop drying, then AuNPs were electrodeposited on the CNPs layer using cyclic voltammetry at 50 mV/s scan rate and a potential window of -400 mV to 1100 mV. The biosensor was prepared by immobilising a thiolated aptamer onto the nano-platform through the Au-S covalent linkage to form GCE/CNPs/AuNPs/Aptamer (aptasensor). The modified electrode (aptasensor) was characterised by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline, ferrocyanide and ruthenium electrolytes. The performance of the aptasensor was evaluated in different standard solutions of As(lll) and also in real water samples using square wave voltammetry. The aptasensor effectively detected As(lll) to a detection limit of 0.092 ppb. The results obtained were validated with ICP-OES and the analytical T-test showed that the two methods were in agreement. The aptasensor was selective in the detection of As(III) in the presence of other metal ions such as cadmium, copper and mercury.The second biosensor was fabricated by incubating a mixture of the aptamer and MNPs on screen printed carbon electrode (SPCE/MNPs-Aptamer). This aptasensor was characterized in a similar way to the GCE/CNPs/AuNPs/Aptamer. It was found to be selective and detected As(III) to a limit of 0.19 ppb (SWV) and 0.24 ppb (EIS). The detection limits were lower when compared to other previously reported As(III) biosensors. The biosensor showed good stability, hence they can be applied in monitoring As(III) in environmental water. , M.Sc. (Chemistry)
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- Authors: Mushiana, Talifhani
- Date: 2018
- Subjects: Nanochemistry , Nanotechnology , Electrochemical analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292796 , uj:31825
- Description: Abstract: Arsenic contamination in groundwater is a tenacious issue in various parts of the world. Owing to the toxicity of arsenic, its detection and analysis are important for national/global wellbeing of human and animals. This dissertation reports the development of two electrochemical aptamer biosensor on a nano-platform for selective detection of As(lll) in wastewater. In the process of fabricating the biosensor, different nanomaterials such as carbon nanoparticles (CNPs), gold nanoparticles (AuNPs) and iron oxide magnetic nanoparticles (MNPs) were used to facilitate electron transfer. A glassy carbon electrode was modified with CNPs by drop drying, then AuNPs were electrodeposited on the CNPs layer using cyclic voltammetry at 50 mV/s scan rate and a potential window of -400 mV to 1100 mV. The biosensor was prepared by immobilising a thiolated aptamer onto the nano-platform through the Au-S covalent linkage to form GCE/CNPs/AuNPs/Aptamer (aptasensor). The modified electrode (aptasensor) was characterised by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline, ferrocyanide and ruthenium electrolytes. The performance of the aptasensor was evaluated in different standard solutions of As(lll) and also in real water samples using square wave voltammetry. The aptasensor effectively detected As(lll) to a detection limit of 0.092 ppb. The results obtained were validated with ICP-OES and the analytical T-test showed that the two methods were in agreement. The aptasensor was selective in the detection of As(III) in the presence of other metal ions such as cadmium, copper and mercury.The second biosensor was fabricated by incubating a mixture of the aptamer and MNPs on screen printed carbon electrode (SPCE/MNPs-Aptamer). This aptasensor was characterized in a similar way to the GCE/CNPs/AuNPs/Aptamer. It was found to be selective and detected As(III) to a limit of 0.19 ppb (SWV) and 0.24 ppb (EIS). The detection limits were lower when compared to other previously reported As(III) biosensors. The biosensor showed good stability, hence they can be applied in monitoring As(III) in environmental water. , M.Sc. (Chemistry)
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Development of electrochemical sensors based on modified glassy carbon electrodes for simultaneous determination of trace elements in environmental samples
- Authors: Mnyiphika, Siyamthanda Hope
- Date: 2017
- Subjects: Electrochemical analysis , Electrochemical sensors , Trace elements - Analysis , Electrodes, Carbon
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235688 , uj:24107
- Description: M.Tech. (Chemistry) , Abstract: The main aim of this study was to develop electrochemical sensors based on modification of glassy carbon electrode of simultaneous detection for selected trace metals in surface water matrices. Trace metals such as Hg, Tl and Cd are extremely harmful pollutants in different environments due to their toxicity and even in trace amounts they pose a serious risk to human health effects. Therefore, it is important to control and monitor their concentrations in surface water systems as they tend to affect the quality of water. Electrochemical sensors were developed and optimized for determination of Cd, Cu, Hg, Tl and Zn in environmental matrices. For determination of Hg and Tl, rapid, simple and sensitive square wave anodic stripping voltammetric (SWASV) technique based on glassy carbon electrode modified with tin oxide nanoparticles@ multiwalled carbon nanotubes was developed. Under optimized condition, the limit of detection and quantification ranged from 0.9−1.2 ng L−1 and 3.3-4.0 ng L−1, respectively. The inter-day (n=10) and intra-day (n=7) precisions expressed in relative standard deviations at 50 μg L−1 of Hg(II) and Tl(I) ranged from 2.1- 3.5% and 3.0-4.3%, respectively. The GCE/SnO2@MWCNTs was applied for the determination of the target trace elements in thirteen surface water samples. The accuracy of analytical results obtained using the developed electrochemical sensor was comparable to those obtained by the ICP-MS. The second electrochemical sensor was based on the fabrication and application of a glassy carbon electrode with reduced graphene Oxide@MnO2 nanocomposite (rGO@MnO2) for simultaneous quantification of Zn, Cd and Cu ions in surface water. The rGO@MnO2 characterized by transmission electron microscopy (TEM) and dispersive xray spectroscopy (EDS). The electrochemical behaviour of rGO@MnO2/GCE nanocomposite was measured by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The electrochemical studies revealed that the rGO@MnO2/GCE dramatically increased the current response against the Zn, Cd and Cd, due to the synergic effect of MnO2 and rGO. Under optimum conditions, the modified electrode portrayed sensitivity and relatively high precision for simultaneous determination of Zn, Cd and Cu. The limits of detection and quantification were up to 9.3-15.1 ng L−1 and 31-50.3 ng L−1, respectively. The results showed that rGO@MnO2 can be successfully used as electrode modifier for the determination of trace metals in water samples...
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- Authors: Mnyiphika, Siyamthanda Hope
- Date: 2017
- Subjects: Electrochemical analysis , Electrochemical sensors , Trace elements - Analysis , Electrodes, Carbon
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235688 , uj:24107
- Description: M.Tech. (Chemistry) , Abstract: The main aim of this study was to develop electrochemical sensors based on modification of glassy carbon electrode of simultaneous detection for selected trace metals in surface water matrices. Trace metals such as Hg, Tl and Cd are extremely harmful pollutants in different environments due to their toxicity and even in trace amounts they pose a serious risk to human health effects. Therefore, it is important to control and monitor their concentrations in surface water systems as they tend to affect the quality of water. Electrochemical sensors were developed and optimized for determination of Cd, Cu, Hg, Tl and Zn in environmental matrices. For determination of Hg and Tl, rapid, simple and sensitive square wave anodic stripping voltammetric (SWASV) technique based on glassy carbon electrode modified with tin oxide nanoparticles@ multiwalled carbon nanotubes was developed. Under optimized condition, the limit of detection and quantification ranged from 0.9−1.2 ng L−1 and 3.3-4.0 ng L−1, respectively. The inter-day (n=10) and intra-day (n=7) precisions expressed in relative standard deviations at 50 μg L−1 of Hg(II) and Tl(I) ranged from 2.1- 3.5% and 3.0-4.3%, respectively. The GCE/SnO2@MWCNTs was applied for the determination of the target trace elements in thirteen surface water samples. The accuracy of analytical results obtained using the developed electrochemical sensor was comparable to those obtained by the ICP-MS. The second electrochemical sensor was based on the fabrication and application of a glassy carbon electrode with reduced graphene Oxide@MnO2 nanocomposite (rGO@MnO2) for simultaneous quantification of Zn, Cd and Cu ions in surface water. The rGO@MnO2 characterized by transmission electron microscopy (TEM) and dispersive xray spectroscopy (EDS). The electrochemical behaviour of rGO@MnO2/GCE nanocomposite was measured by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The electrochemical studies revealed that the rGO@MnO2/GCE dramatically increased the current response against the Zn, Cd and Cd, due to the synergic effect of MnO2 and rGO. Under optimum conditions, the modified electrode portrayed sensitivity and relatively high precision for simultaneous determination of Zn, Cd and Cu. The limits of detection and quantification were up to 9.3-15.1 ng L−1 and 31-50.3 ng L−1, respectively. The results showed that rGO@MnO2 can be successfully used as electrode modifier for the determination of trace metals in water samples...
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Electrochemical and solar photoelectrocatalytic oxidation of selected organic compounds at carbon-semiconductor based electrodes
- Authors: Peleyeju, Moses Gbenga
- Date: 2017
- Subjects: Photoelectrochemistry , Electrocatalysis , Electrochemistry , Electrochemical analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/261547 , uj:27579
- Description: Ph.D. (Chemistry) , Abstract: This study explored preparation, characterisation and applications of different types of carbon and metal oxide semiconductors-based anodes for the electrochemical/photoelectrocatalytic oxidation of some selected organic contaminants. Exfoliated graphite (EG), a form of carbon, was prepared by acids intercalation of natural graphite flakes and thermal treatment. Expanded graphite – diamond (EG-diamond) composite prepared by solution mixing of EG and diamond powder was fabricated into electrodes and characterised. Raman spectrometry and x-ray diffraction (XRD) patterns revealed peaks that are characteristic of EG and diamond. Scanning electron microscopy (SEM) images showed that the diamond particles were well dispersed within sheets of EG. Cyclic voltammetry (CV) showed that the EG electrode exhibited faster electron transfer while the composite electrode gave enhanced current peak. The electrolysis of acid blue 40 (AB 40) in 0.1 M Na2SO4 electrolyte resulted in ca. 80% dye removal at the EG-Diamond electrode and 66% removal at the pristine EG electrode at a current density of 20 mAcm-2 after 4 h. However, in a chlorine mediated electrolysis (NaCl as supporting electrolyte), the decolourisation of the dye was very rapid with over 98% decolourisation in 25 min. The extent of mineralisation was measured by total organic carbon (TOC). EG-Diamond and EG electrodes yielded TOC removal of 44% and 26% respectively in the electrochemical cell with Na2SO4 supporting electrolyte. While NaCl cell presented faster decoulorisation, the TOC decay was much slower compared to the Na2SO4 cell. The degradation of AB 40 follows pseudo first-order kinetic model with apparent rate constants of 2.34 x 10-3 min-1 and 4.41 x 10-3 min-1 obtained at EG and EG-diamond electrodes respectively. The EG-diamond electrode was further applied in the degradation of orange II dye (OG II) and a mixture of OG II and AB 40 with a TOC removal of 49 % for the dye mixture...
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- Authors: Peleyeju, Moses Gbenga
- Date: 2017
- Subjects: Photoelectrochemistry , Electrocatalysis , Electrochemistry , Electrochemical analysis
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/261547 , uj:27579
- Description: Ph.D. (Chemistry) , Abstract: This study explored preparation, characterisation and applications of different types of carbon and metal oxide semiconductors-based anodes for the electrochemical/photoelectrocatalytic oxidation of some selected organic contaminants. Exfoliated graphite (EG), a form of carbon, was prepared by acids intercalation of natural graphite flakes and thermal treatment. Expanded graphite – diamond (EG-diamond) composite prepared by solution mixing of EG and diamond powder was fabricated into electrodes and characterised. Raman spectrometry and x-ray diffraction (XRD) patterns revealed peaks that are characteristic of EG and diamond. Scanning electron microscopy (SEM) images showed that the diamond particles were well dispersed within sheets of EG. Cyclic voltammetry (CV) showed that the EG electrode exhibited faster electron transfer while the composite electrode gave enhanced current peak. The electrolysis of acid blue 40 (AB 40) in 0.1 M Na2SO4 electrolyte resulted in ca. 80% dye removal at the EG-Diamond electrode and 66% removal at the pristine EG electrode at a current density of 20 mAcm-2 after 4 h. However, in a chlorine mediated electrolysis (NaCl as supporting electrolyte), the decolourisation of the dye was very rapid with over 98% decolourisation in 25 min. The extent of mineralisation was measured by total organic carbon (TOC). EG-Diamond and EG electrodes yielded TOC removal of 44% and 26% respectively in the electrochemical cell with Na2SO4 supporting electrolyte. While NaCl cell presented faster decoulorisation, the TOC decay was much slower compared to the Na2SO4 cell. The degradation of AB 40 follows pseudo first-order kinetic model with apparent rate constants of 2.34 x 10-3 min-1 and 4.41 x 10-3 min-1 obtained at EG and EG-diamond electrodes respectively. The EG-diamond electrode was further applied in the degradation of orange II dye (OG II) and a mixture of OG II and AB 40 with a TOC removal of 49 % for the dye mixture...
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Electrochemical co-detection of arsenic, lead and mercury on exfoliated graphite nanocomposite electrodes
- Authors: Mafa, Potlako John
- Date: 2016
- Subjects: Electrochemical analysis , Nanostructured materials , Graphite , Electrodes , Trace elements - Analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/84607 , uj:19241
- Description: Abstract: Please refer to full text to view abstract , M.Sc. (Chemistry)
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- Authors: Mafa, Potlako John
- Date: 2016
- Subjects: Electrochemical analysis , Nanostructured materials , Graphite , Electrodes , Trace elements - Analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/84607 , uj:19241
- Description: Abstract: Please refer to full text to view abstract , M.Sc. (Chemistry)
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Electrochemical detection of arsenic and selenium on modified carbon based nanocomposite electrodes
- Authors: Idris, Azeez Olayiwola
- Date: 2016
- Subjects: Nanostructured materials , Electrodes, Carbon , Electrochemical analysis , Organic water pollutants , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124946 , uj:20978
- Description: Abstract: This study explores the applications of nanomaterial modified on glassy carbon electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE was modified with gold nanoparticles and reduced graphene oxide. Gold nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs was electrochemically investigated using redox probes which are [Fe (CN) 6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical determination of selenium by square wave anodic stripping voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu and Cd were the only significant interferences observed for the electrochemical detection of selenium. Attempt was also made to sense selenium in tap water, concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The electrochemical method was validated with ICP-OES. Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of arsenic was also optimised at different analytical conditions and a detection limit of 0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the interference effect of copper on arsenic sensing in the bid to remove interference. Graphene oxide was synthesised by using Hummer`s methods and was further reduced to reduced graphene oxide using ascorbic acid. The reduced graphene oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in an increase in the electroactive surface area of the electrode which led to enhance the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as supporting electrolyte, deposition potential of -100 mV and pre-concentration time of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and was not susceptible to many interfering cations except Cu (II) and Cd (II). , M.Sc. (Chemistry)
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- Authors: Idris, Azeez Olayiwola
- Date: 2016
- Subjects: Nanostructured materials , Electrodes, Carbon , Electrochemical analysis , Organic water pollutants , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124946 , uj:20978
- Description: Abstract: This study explores the applications of nanomaterial modified on glassy carbon electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE was modified with gold nanoparticles and reduced graphene oxide. Gold nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs was electrochemically investigated using redox probes which are [Fe (CN) 6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical determination of selenium by square wave anodic stripping voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu and Cd were the only significant interferences observed for the electrochemical detection of selenium. Attempt was also made to sense selenium in tap water, concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The electrochemical method was validated with ICP-OES. Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of arsenic was also optimised at different analytical conditions and a detection limit of 0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the interference effect of copper on arsenic sensing in the bid to remove interference. Graphene oxide was synthesised by using Hummer`s methods and was further reduced to reduced graphene oxide using ascorbic acid. The reduced graphene oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in an increase in the electroactive surface area of the electrode which led to enhance the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as supporting electrolyte, deposition potential of -100 mV and pre-concentration time of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and was not susceptible to many interfering cations except Cu (II) and Cd (II). , M.Sc. (Chemistry)
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Synthesis, characterization and application of carbon nanotube and graphene based nanocomposite platforms in the electrochemical sensing of arsenic and mercury in water
- Authors: Jimana, Amandla
- Date: 2017
- Subjects: Electrochemical analysis , Nanostructured materials , Carbon nanotubes , Heavy metals - Analysis , Water - Analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/376448 , http://hdl.handle.net/10210/244112 , uj:25242
- Description: M.Tech. (Chemistry) , Abstract: This study developed carbon nanocomposite modified on exfoliated graphite electrodes that are sensitive and selective for the electrochemical detection of mercury and arsenic. This research explores the new material called exfoliated graphite for the detection of heavy metals in water. The material is relatively cheap and is a promising material for the detection of heavy metals. The exfoliated graphite was prepared by intercalation of natural graphite flakes with a particle size of 300 μm by soaking them in a mixture of concentrated acids, sulphuric acid and nitric acid in the ratio 3:1 respectively. After the intercalation the resulting material was exfoliated. The exfoliation was achieved by subjecting the intercalated graphite to high temperatures of 800 ºC in a furnace for about 30 seconds. The puffed up material was named exfoliated graphite (EG). The EG was compressed into pellets of 5mm using high pressure hydraulic press. The mercury nanocomposite sensor was designed by incorporation of carbon nanotube/polyaniline (CNT/PANI) composite followed by electrodeposition of gold nanoparticles onto the EG electrode. This electrode was named CNT/PANI/AuNPs-EG. The dispersion of carbon nanotubes onto the polymer was obtained via the in situ polymerization method. This electrode was name CNT/PANI/EG. The electrodeposition of gold nanoparticles was achieved by preparing 5 mM of HAuCl4 solution and cycling the potential from -200 mV to 1100 mV for 10 cycles at a scan rate of 50 mV/s. this electrode was used for the detection of mercury in water. The detection limit was calculated to be 0.046 ppb (0.229 nM) and the limit of quantification was 0.152 ppb with a correlation coefficient of 0.9984. Another electrode was prepared for the detection of arsenic. Reduced graphene oxide/cobalt nanoparticles modified on EG electrode. A good detection limit and limit of quantification were found to be 0.31 ppb and 1.01 ppb respectively. The linear regression equation was 𝑦=6.64608×10−4 𝑥+1.96169×10−5 with a high correlation coefficient of 0.9984.
- Full Text:
- Authors: Jimana, Amandla
- Date: 2017
- Subjects: Electrochemical analysis , Nanostructured materials , Carbon nanotubes , Heavy metals - Analysis , Water - Analysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/376448 , http://hdl.handle.net/10210/244112 , uj:25242
- Description: M.Tech. (Chemistry) , Abstract: This study developed carbon nanocomposite modified on exfoliated graphite electrodes that are sensitive and selective for the electrochemical detection of mercury and arsenic. This research explores the new material called exfoliated graphite for the detection of heavy metals in water. The material is relatively cheap and is a promising material for the detection of heavy metals. The exfoliated graphite was prepared by intercalation of natural graphite flakes with a particle size of 300 μm by soaking them in a mixture of concentrated acids, sulphuric acid and nitric acid in the ratio 3:1 respectively. After the intercalation the resulting material was exfoliated. The exfoliation was achieved by subjecting the intercalated graphite to high temperatures of 800 ºC in a furnace for about 30 seconds. The puffed up material was named exfoliated graphite (EG). The EG was compressed into pellets of 5mm using high pressure hydraulic press. The mercury nanocomposite sensor was designed by incorporation of carbon nanotube/polyaniline (CNT/PANI) composite followed by electrodeposition of gold nanoparticles onto the EG electrode. This electrode was named CNT/PANI/AuNPs-EG. The dispersion of carbon nanotubes onto the polymer was obtained via the in situ polymerization method. This electrode was name CNT/PANI/EG. The electrodeposition of gold nanoparticles was achieved by preparing 5 mM of HAuCl4 solution and cycling the potential from -200 mV to 1100 mV for 10 cycles at a scan rate of 50 mV/s. this electrode was used for the detection of mercury in water. The detection limit was calculated to be 0.046 ppb (0.229 nM) and the limit of quantification was 0.152 ppb with a correlation coefficient of 0.9984. Another electrode was prepared for the detection of arsenic. Reduced graphene oxide/cobalt nanoparticles modified on EG electrode. A good detection limit and limit of quantification were found to be 0.31 ppb and 1.01 ppb respectively. The linear regression equation was 𝑦=6.64608×10−4 𝑥+1.96169×10−5 with a high correlation coefficient of 0.9984.
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The application of anodic-stripping voltammetry to the determination of trace elements in standard reference materials
- Authors: Lee, Arthur Foreman
- Date: 2015-10-22
- Subjects: Voltammetry , Electrochemical analysis , Chemistry, Analytic , Trace elements - Analysis
- Type: Thesis
- Identifier: uj:14439 , http://hdl.handle.net/10210/14920
- Description: Ph.D. (Chemistry) , Materials that are to be used as reference samples are frequently analysed using costly and sophisticated instrumentation, itself calibrated with similar certified standards. Analytical programmes using such instrumentation are only as accurate as the initial calibrations, and their poor results have led to the adoption by the United States National Bureau of Standards of definitive methods of analysis for the determination cf trace elements ...
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- Authors: Lee, Arthur Foreman
- Date: 2015-10-22
- Subjects: Voltammetry , Electrochemical analysis , Chemistry, Analytic , Trace elements - Analysis
- Type: Thesis
- Identifier: uj:14439 , http://hdl.handle.net/10210/14920
- Description: Ph.D. (Chemistry) , Materials that are to be used as reference samples are frequently analysed using costly and sophisticated instrumentation, itself calibrated with similar certified standards. Analytical programmes using such instrumentation are only as accurate as the initial calibrations, and their poor results have led to the adoption by the United States National Bureau of Standards of definitive methods of analysis for the determination cf trace elements ...
- Full Text:
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