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 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 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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Studies on the properties of the carbon nanomaterial based electrodes for potential application in alcohol fuel cells
- Authors: Mpeta, Lekhetho Simon
- Date: 2018
- Subjects: Electrocatalysis , Nanostructured materials , Electrodes, Carbon , Fuel cells - Materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/272800 , uj:29053
- Description: M.Sc. (Chemistry) , Abstract: The investigation of the effect of the platform (electrode) for electrocatalyst in the electro-oxidation of methanol for application in alcohol fuel cells (AFCs) was conducted. The three electrodes that were studied are exfoliated graphite (EG), glassy carbon (GC) and basal plane pyrolytic graphite (BPPG) electrode. The new and cheap electrode material named exfoliated graphite (EG) was prepared by intercalating natural graphite flakes with H2SO4 and HNO3 mixture in the ratio of 3:1 (v/v). The intercalated material was then subjected to thermal shock to obtain EG. In the case of GC and BPPG electrodes, the commercial electrodes were used. This study reports the preparation of platinum monometallic (Pt) and platinum based bimetallic electrocatalysts (Pt-Au, Pt-Ru and Pt-Pd) supported on acid treated multi walled carbon nanotubes using polyol method. The physical properties of the prepared electrocatalysts were investigated using several techniques such as TEM, EDX coupled with TEM, XRD and FTIR spectroscopy. The electrochemical behaviour of Pt/fMWCNTs catalyst on three different electrodes namely EG, GC and BPPG were investigated. The BPPG electrode platform gave a better electrocatalytic performance compared to the EG and GC electrodes. Detailed electrochemical studies (involving cyclic voltammetry and chronoamperometry) proved that the electrocatalytic oxidation of methanol at Pt/fMWCNTs electrocatalyst on BPPG electrode platform is more stable and occurs at lower potential. The results further revealed that Pt-Pd/fMWCNTs catalyst on BPPG platform showed better electrocatalytic behaviour for methanol oxidation in acidic medium, with high current response of 18.2 mAcm-2. However, Pt-Au/fMWCNTs electrocatalyst is more tolerant to CO poisoning than Pt-Ru/fMWCNTs and Pt-Pd/fMWCNTs during methanol oxidation in acidic medium...
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- Authors: Mpeta, Lekhetho Simon
- Date: 2018
- Subjects: Electrocatalysis , Nanostructured materials , Electrodes, Carbon , Fuel cells - Materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/272800 , uj:29053
- Description: M.Sc. (Chemistry) , Abstract: The investigation of the effect of the platform (electrode) for electrocatalyst in the electro-oxidation of methanol for application in alcohol fuel cells (AFCs) was conducted. The three electrodes that were studied are exfoliated graphite (EG), glassy carbon (GC) and basal plane pyrolytic graphite (BPPG) electrode. The new and cheap electrode material named exfoliated graphite (EG) was prepared by intercalating natural graphite flakes with H2SO4 and HNO3 mixture in the ratio of 3:1 (v/v). The intercalated material was then subjected to thermal shock to obtain EG. In the case of GC and BPPG electrodes, the commercial electrodes were used. This study reports the preparation of platinum monometallic (Pt) and platinum based bimetallic electrocatalysts (Pt-Au, Pt-Ru and Pt-Pd) supported on acid treated multi walled carbon nanotubes using polyol method. The physical properties of the prepared electrocatalysts were investigated using several techniques such as TEM, EDX coupled with TEM, XRD and FTIR spectroscopy. The electrochemical behaviour of Pt/fMWCNTs catalyst on three different electrodes namely EG, GC and BPPG were investigated. The BPPG electrode platform gave a better electrocatalytic performance compared to the EG and GC electrodes. Detailed electrochemical studies (involving cyclic voltammetry and chronoamperometry) proved that the electrocatalytic oxidation of methanol at Pt/fMWCNTs electrocatalyst on BPPG electrode platform is more stable and occurs at lower potential. The results further revealed that Pt-Pd/fMWCNTs catalyst on BPPG platform showed better electrocatalytic behaviour for methanol oxidation in acidic medium, with high current response of 18.2 mAcm-2. However, Pt-Au/fMWCNTs electrocatalyst is more tolerant to CO poisoning than Pt-Ru/fMWCNTs and Pt-Pd/fMWCNTs during methanol oxidation in acidic medium...
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