Browsing by Author "Jahed, Nazeem"
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Item Complexation-based detection of nickel(ii) at a graphene-chelate probe in the presence of cobalt and zinc by adsorptive stripping voltammetry(MDPI, 2017) Pokpas, Keagan; Jahed, Nazeem; Baker, Priscilla G.The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films.Item Determination of heavy metals at the electrochemically reduced graphene oxide mercury film electrode (ERGO-HgF-PGE) using adsorptive stripping voltammetry(University of Western Cape, 2020) Sanga, Nelia Abraham; Jahed, Nazeem; Iwuoha, Emmanuel. I.; Pokpas, KeaganThis work reports the use of a pencil graphite electrode (PGE) as inexpensive and sensitive electrochemical sensing platform fabricated by using electrochemically reduced graphene oxide (ERGO) in conjunction with an in-situ plated thin mercury film. For the first time the ERGOHgF-PGE sensor is proposed for simultaneous detection of cadmium (Cd2+), copper (Cu2+), lead (Pb2+) and zinc (Zn2+) using N-Nitroso-N-phenylhydroxylamine (cupferron) as complexing agent by square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV). The technique is based on the adsorption of cupferron- metal ion complexes onto the surface of the ERGO-HgFPGE at 0.1 V for 60 s carried out in 0.1 M acetate buffer solution (pH 4.6). The synthesized graphene oxide (GO) and graphene nanosheets (GNs) were characterized using different analytical techniques such as FT-IR which confirms the presence of oxygen moieties embedded in the graphitic structure and further demonstrated by UV-Vis, validating the synthesis of GOItem Determination of paracetamol at the electrochemically reduced graphene oxide-metal nanocomposite modified pencil graphite (ERGO-MC-PGE) electrode using adsorptive stripping differential pulse voltammetry(University of Western Cape, 2020) Leve, Zandile Dennis; Jahed, Nazeem; Iwuoha, EmmanuelThis project focuses on the development of simple, highly sensitive, accurate, and low cost electrochemical sensors based on the modification of pencil graphite electrodes by the electrochemical reduction of graphene oxide-metal salts as nanocomposites (ERGO-MC-PGE; MC = Sb or Au nanocomposite). The electrochemical sensors ERGO-Sb-PGE and ERGO-Au-PGE were used in the determination of paracetamol (PC) in pharmaceutical formulations using adsorptive stripping differential pulse voltammetry. The GO was prepared from graphite via a modified Hummers’ method and characterized by FTIR and Raman spectroscopy to confirm the presence of oxygen functional groups in the conjugated carbon-based structure whilst, changes in crystalline structure was observed after XRD analysis of graphite and GO.Item Determination of paracetamol on electrochemically reduced graphene oxide–antimony nanocomposite modified pencil graphite electrode using adsorptive stripping differential pulse voltammetry(MDPI, 2022) Leve, Zandile D.; Jahed, Nazeem; Sanga, Nelia A.A simple, highly sensitive, accurate, and low-cost electrochemical sensor was developed for the determination of over-the-counter painkiller, paracetamol (PC). The enhanced sensing capabilities of the developed sensor were fabricated by the single-step modification of disposable pencil graphite electrodes (PGEs) with the simultaneous electrochemical reduction in graphene oxide and antimony (II) salts. For this purpose, an electrochemically reduced graphene oxide–antimony nanoparticle (ERGO-SbNP) nanocomposite material was prepared by trapping metallic nanoparticles between individual graphene sheets in the modification of PGEs.Item Electrochemical deposition of Graphene Oxide- metal nano-composite on Pencil-Graphite Electrode for the high sensitivity detection of Bisphenol A by Adsorptive Stripping Differential Pulse Voltammetry(University of the Western Cape, 2018) Ghaffari, Nastaran; Iwuoha, Emmanuel; Jahed, NazeemElectrochemical platforms were developed based on pencil graphite electrodes (PGEs) modified electrochemically with reduced graphene oxide metal nanoparticles (ERGO–metalNPs) composite and used for the high-sensitivity determination of Bisphenol A (BPA) in water samples. Synergistic effects of both reduced Graphene Oxide sheets and metal nanoparticles on the performance of the pencil graphite electrode (PGE) were demonstrated in the oxidation of BPA by differential pulse voltammetry (DPV). A solution of graphene oxide (GO) 1 mg mL-1 and 15 ppm of metal stock solutions (1,000 mg L-1, atomic absorption standard solution) (Antimony or Gold) was prepared and after sonication deposited onto pencil graphite electrodes by cyclic voltammetry reduction. Different characterization techniques such as FT-IR, HR-SEM, XRD and Raman spectroscopy were used to characterize the GO and ERGO–metalNPs. Parameters that influence the electroanalytical response of the ERGO–SbNPs and ERGO–AuNPs such as, pH, deposition time, deposition potential, purging time were investigated and optimized. Well-defined, reproducible peaks with detection limits of 0.0125 μM and 0.062 μM were obtained for BPA using ERGO–SbNPs and ERGO–AuNPs respectively. The rGO-metalNPs–PGE was used for the quantification of BPA in tap water sample and proved to be suitable for the detection of BPA below USEPA prescribed drinking water standards of 0.087 μM.Item An electrochemical DNA biosensor developed on a nanocomposite platform of gold and poly(propyleneimine) dendrimer(MDPI, 2008) Arotiba, Omotayo A.; Owino, Joseph; Songa, Everlyne; Hendricks, Nicolette; Waryo, Tesfaye T.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.An electrochemical DNA nanobiosensor was prepared by immobilization of a 20mer thiolated probe DNA on electro-deposited generation 4 (G4) poly(propyleneimine) dendrimer (PPI) doped with gold nanoparticles (AuNP) as platform, on a glassy carbon electrode (GCE). Field emission scanning electron microscopy results confirmed the codeposition of PPI (which was linked to the carbon electrode surface by C-N covalent bonds) and AuNP ca 60 nm. Voltammetric interrogations showed that the platform (GCE/PPI-AuNP) was conducting and exhibited reversible electrochemistry (E°′ = 235 mV) in pH 7.2 phosphate buffer saline solution (PBS) due to the PPI component. The redox chemistry of PPI was pH dependent and involves a two electron, one proton process, as interpreted from a 28 mV/pH value obtained from pH studies. The charge transfer resistance (Rct) from the electrochemical impedance spectroscopy (EIS) profiles of GCE/PPI-AuNP monitored with ferro/ferricyanide (Fe(CN)6 3-/4-) redox probe, decreased by 81% compared to bare GCE. The conductivity (in PBS) and reduced Rct (in Fe(CN)6 3-/4-) values confirmed PPI-AuNP as a suitable electron transfer mediator platform for voltammetric and impedimetric DNA biosensor. The DNA probe was effectively wired onto the GCE/PPI-AuNP via Au-S linkage and electrostatic interactions. The nanobiosensor responses to target DNA which gave a dynamic linear range of 0.01 - 5 nM in PBS was based on the changes in Rct values using Fe(CN)6 3-/4- redox probe.Item Electrochemical immunosensor based on polythionine/gold nanoparticles for the determination of Aflatoxin B1(MDPI, 2008) Owino, Joseph H.O.; Arotiba, Omotayo A.; Hendricks, Nicolette; Songa, Everlyne; Jahed, Nazeem; Waryo, Tesfaye T.; Ngece, Rachel F.; Baker, Priscilla; Iwuoha, Emmanuel I.An aflatoxin B1 (AFB1) electrochemical immunosensor was developed by the immobilisation of aflatoxin B1-bovine serum albumin (AFB1-BSA) conjugate on a polythionine (PTH)/gold nanoparticles (AuNP)-modified glassy carbon electrode (GCE). The surface of the AFB1-BSA conjugate was covered with horseradish peroxidase (HRP), in order to prevent non-specific binding of the immunosensors with ions in the test solution. The AFB1 immunosensor exhibited a quasi-reversible electrochemistry as indicated by a cyclic voltammetric (CV) peak separation (ΔEp) value of 62 mV. The experimental procedure for the detection of AFB1 involved the setting up of a competition between free AFB1 and the immobilised AFB1-BSA conjugate for the binding sites of free anti-aflatoxin B1 (anti-AFB1) antibody. The immunosensor’s differential pulse voltammetry (DPV) responses (peak currents) decreased as the concentration of free AFB1 increased within a dynamic linear range (DLR) of 0.6 - 2.4 ng/mL AFB1 and a limit of detection (LOD) of 0.07 ng/mL AFB1. This immunosensing procedure eliminates the need for enzyme-labeled secondary antibodies normally used in conventional ELISA–based immunosensors.Item Electrochemical ochratoxin a immunosensors based on polyaniline nanocomposites templated with amine- and sulphate-functionalised polystyrene latex beads(University of the Western Cape, 2010) Muchindu, Munkombwe; Iwuoha, Emmanuel; Jahed, Nazeem; Faculty of SciencePolyaniline nanocomposites doped with poly(vinylsulphonate) (PV-SO3) and nanostructured polystyrene (PSNP) latex beads functionalized with amine (PSNP-NH2) and sulphate ((PSNP-OSO3) were prepared and characterised for use as nitrite electro-catalytic chemosensors and ochratoxin A immunosensors. The resultant polyaniline electrocatalytic chemosensors (PANI, PANI|PSNP-NH2 or PANI|PSNP-OSO3 −) were characterized by cyclic voltammetry (CV), ultraviolet-visible (UV-Vis) spectroscopy and scanning electron microscopy (SEM). Brown-Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations in the order of 10−8 mol/cm. UV-vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid p-p* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that were <100 nm in diameter. When applied as electrochemical nitrite sensors, sensitivity values of 60, 40 and 30 μA/mM with corresponding limits of detection of 7.4, 9.2 and 38.2 μM NO2 −, were obtained for electrodes, PANI|PSNP-NH2, PANI and PANI|PSNP-SO3 −; respectively. Immobilisation of ochratoxin A antibody onto PANI|PSNP-NH2, PANI and PANI|PSNPSO3 - resulted in the fabrication of immunosensors.Item Electrochemically reduced graphene oxide pencil-graphite in situ plated bismuth-film electrode for the determination of trace metals by anodic stripping voltammetry(ESG, 2014) Pokpas, Keagan; Zbeda, Salma; Jahed, Nazeem; Mohamed, Nuralli; Baker, Priscilla; Iwuoha, Emmanuel I.An electrochemical platform was developed based on a pencil-graphite electrode (PGE) modified with electrochemically reduced graphene oxide (ERGO) sheets and in conjunction with an in situ plated bismuth-film (ERGO-PG-BiE). The ERGO-PG-BiE was used as a sensing platform for determining Zn2+, Cd2+ and Pb2+ by square wave anodic stripping voltammetry (SWASV). ERGO sheets were deposited on to pencil-graphite electrodes by cyclic voltammetric reduction from a graphene oxide (GO) solution. The GO, with flake thicknesses varying between 1.78 to 2.10 nm (2 sheets) was characterized using FT-IR, HR-SEM, HR-TEM, AFM, XRD and Raman spectroscopy. Parameters influencing the electroanalytical response of the ERGO-PG-BiE such as, bismuth-film concentration, deposition potential, deposition time and rotation speed were investigated and optimized. The ERGO-PG-BiE gave well-defined, reproducible peaks with detection limits of 0.19 μg L-1, 0.09 μg L-1 and 0.12 μg L-1 for Zn2+, Cd2+ and Pb2+ respectively, at a deposition time of 120 seconds. For real sample analysis, the enhanced voltammetric sensor proved to be suitable for the detection and quantitation of heavy metals below the US EPA prescribed drinking water standards of 5 mg L-1, 5 μg L-1 and 15 μg L-1 for Zn2+, Cd2+ and Pb2+ respectively.Item Few-layer binder free graphene modified mercury film electrode for trace metal analysis by square wave anodic stripping voltammetry(ESG, 2013) Zbeda, Salma; Pokpas, Keagan; Titinchi, Salam J.J.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.;A binding agent free graphene modified glassy carbon electrode in combination with an in situ plated mercury film electrode (Gr-GC-HgFE) was used as a highly sensitive electrochemical platform for the determination of Zn2+, Cd2+ and Pb2+ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Instrumental parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Gr-GC-HgFE sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. Two linear calibration curves ranging from 0 –10 μg L−1 and 0 – 60 μg L−1 were identified yielding detection limits of 0.08 μg L−1, 0.05 μg L−1 and 0.14 μg L−1 for Zn2+, Cd2+ and Pb2+, respectively, for simultaneous analysis and 0.04 μg L−1, 0.11 μg L−1 and 0.14 μg L−1 for Zn2+, Cd2+ and Pb2+, respectively, for individual analysis when using a deposition time of 120 s. For practical applications recovery studies using tap water samples spiked with target metal ions gave recoveries within 10% of the spiked amount. Much better recoveries were obtained for the individual analysis in comparison with simultaneous analysis.Item Graphenated electrode protocol for electrochemical nanosensing of 17β- estradiol as an environmental estrogeneous endocrine disruptor(University of the Western Cape, 2016) Mohamed, Nuralli; Iwuoha, Emmanuel I.; Jahed, Nazeem17β-Estradiol can be defined as an endocrine disruptor chemical with estrogenic activity, which can bind to the estrogen receptor in the body and potentially alter the normal physiological function of the endocrine systems. Estradiol has come into veterinary use both to cure and to prevent animal infections. But owing to its anabolic properties it is also illegally used in livestock production for growth promotion purposes. The presence of low concentrations of estrogens in the environment can cause abnormal sexual development of animals and decrease the average number of human spermatozoa. Therefore, we must monitor the concentration of estradiol in aquatic environment to protect the health of humans and animals. Generally, the detection of estradiol includes the use of high performance liquid chromatography (HPLC), surface plasma resonance (SPR), gas chromatography (GC), liquid chromatography (LC) and electrochemical enzymelinked immunosorbent assay (ELISA). Although these techniques are useful, many of them are expensive and time consuming.Item Graphene-modified pencil graphite mercury-film electrodes for the determination of trace metals by cathodic adsorptive stripping voltammetry(University of the Western Cape, 2018) Tekenya, Ronald; Jahed, NazeemThis project focuses on the simple, fast and highly sensitive adsorptive stripping voltammetry detection of Nickel and Cobalt complexed with DMG and Nioxime respectively at a Reduced Graphene Oxide modified pencil graphite electrode in water samples. This research as well demonstrates a novel electrochemically reduced graphene oxide (ERGO)/mercury film (MF) nanocomposite modified PGE, prepared through successive electrochemical reduction of graphene oxide (GO) sheets and in-situ plated mercury film. The GO and graphene were characterized using FT-IR, HR-SEM, HR-TEM, XRD and Raman spectroscopy. The FT-IR results supported by Xray diffraction analysis confirmed the inclusion of oxygen moieties within the graphitic structure during the chemical oxidation step. Microscopic and spectroscopic analysis was used to confirm the stackings of graphene on the pencil electrode. The ERGO-PG-MFE, in combination with a complexing agents of [dimethylglyoxime (DMG) and Nioxime] and square-wave cathodic stripping voltammetry (SW-CSV), was evaluated towards the individual determination of Ni2+ and Co2+ respectively and simultaneous determination of both metals from the combination of DMG and Nioxime mixture. A single-step electrode pre-concentration approach was employed for the in-situ Hg-film electroplating, metal-chelate complex formation and its non-electrolytic adsorption at – 0.7 V for the individual analysis of Ni2+ and Co2+. The current response due to metal-ligand(s) complex reduction were studied as a function of experimental variables; deposition/accumulation potential, deposition/accumulation time, rotation speed, frequency and amplitude and carefully optimized for the individual determination of Ni2+and Co2+ and simultaneous determination of Ni2+ and Co2+ at low concentration levels (μg L-1) in 0.1 M NH3- NH4Cl buffer solution (pH 9.4) solution. The recorded limit of detection for the individual analysis of Ni2+and Co2+ was found to be 0.120 μg L-1 and 0.220 μg L-1 respectively, at an accumulation time of 120 s for both metals. The recorded limit of detection of the simultaneous analysis of Ni2+ and Co2+ was found to be 6.1 μg L-1 and 1.8 μg L-1 respectively. The ERGO-PG-MFE further demonstrated a highly selective stripping response toward all trace metal analysis. The testing of the applicability of graphene-based sensor and method in laboratory tap water samples was evaluated. This electrode was found to be sensitive enough to detect metal ions in the tap water samples at the 0.2 μg L-1 level for individual analysis and 0.001 μg L-1 for simultaneous, well below WHO standards.Item Metallo-graphene nanocomposite electrocatalytic platform for the determination of toxic metal ions(MDPI, 2011) Willemse, Chandre M.; Tlhomelang, Khotso; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.A Nafion-Graphene (Nafion-G) nanocomposite solution in combination with an in situ plated mercury film electrode was used as a highly sensitive electrochemical platform for the determination of Zn2+, Cd2+, Pb2+ and Cu2+ in 0.1 M acetate buffer (pH 4.6) by square-wave anodic stripping voltammetry (SWASV). Various operational parameters such as deposition potential, deposition time and electrode rotation speed were optimized. The Nafion-G nanocomposite sensing platform exhibited improved sensitivity for metal ion detection, in addition to well defined, reproducible and sharp stripping signals. The linear calibration curves ranged from 1 µg L−1 to 7 µg L−1 for individual analysis. The detection limits (3σ blank/slope) obtained were 0.07 µg L−1 for Pb2+, Zn2+ and Cu2+ and 0.08 µg L−1 for Cd2+ at a deposition time of 120 s. For practical applications recovery studies was done by spiking test samples with known concentrations and comparing the results with inductively coupled plasma mass spectrometry (ICP-MS) analyses. This was followed by real sample analysis.Item Microfluidic graphenised-paper electroanalytical devices (μGPED) for adsorptive cathodic stripping voltammetric detection of metal contaminants(University of the Western Cape, 2017) Pokpas, Keagan William; Jahed, Nazeem; Iwuoha, Emmanuel I.The need for clean, non-toxic drinking water supplies, free of pollutants and metal contamination is vital in impoverished areas and the developing world alike. With this in mind, the development of accurate, inexpensive, portable and simple devices for remote sensing applications is therefore pivotal for early detection and the prevention of illnesses. Over the last two decades, adsorptive stripping voltammetry (AdSV) has emerged as a superior detection method over common analytical techniques due to its low-cost instrumentation, unskilled labour and ability to detect a wide range of analytes.Item Multilayer graphene modified metal film electrodes for the determination of trace metals by anodic stripping voltammetry(2013) Zbeda, Salma Gumaa Amar; Jahed, NazeemIn this study multilayer graphene nanosheets was synthesize by oxidizing graphite to graphene oxide using H2SO4 and KMnO4 followed by reduction of graphene oxide to graphene using NaBH4. The graphene nanosheets were characterized by Fourier Transform Infrared (FTIR) and Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM) and X-ray diffraction (XRD). HRTEM images showed that the multilayer graphene were obtained. The graphene was immobilized directly onto a glassy carbon electrode using the drop coating technique followed by the in situ deposition of mercury, bismuth or antimony thin films to afford graphene modified glassy carbon metal film electrodes (Gr-GC-MEs). The experimental parameters (deposition potential, deposition time, rotation speed, frequency and amplitude) were optimized, and the applicability of the modified electrode was investigated towards the individual and simultaneous determination of Zn2+, Cd2+ and Pb2+ at the low concentration levels (μg L-1) in 0.1 M acetate buffer (pH 4.6) using square wave anodic stripping voltammetry (SWASV). The detection limits values for the Gr-GC-HgE was 0.08, 0.05 and 0.14 μg L-1 for Zn2+, Cd2+ and Pb2+, respectively. The Gr-GC-BiE the detection limits for was 0.12, 0.22 and 0.28 μg L-1 for Zn2+, Cd2+ and Pb2+ while the detection limits for the Gr-GC-SbE was 0.1, 0.3 and 0.3 μg L-1 for Zn2+, Cd2+ and Pb2+, respectively. A Gr-GCE prepared without any binding agents or metal film had detection limits for Zn2+, Cd2+ and Pb2+ of 3.9, 0.8 and 0.2 μg L-1 for Zn2+, Cd2+ and Pb2+. Real sample analysis of which was laboratory tap water was performed using the Gr-GCMEs. Only Gr-GC-HgE was sensitive enough to detect metal ions in the tap water samples at the 3ppb level whereas, the GC-BiE and GC-SbE detected the metal ions at the 10 μg L-1 to 30 μg L-1 level.Item Nanocomposite-graphene based platform for heavy metal detection(University of the Western Cape, 2010) Willemse, Chandre Monique; Jahed, Nazeem; Iwuoha, Emmanuel; Faculty of ScienceThis study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3σblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses.Item Nickel contamination analysis at cost-effective silver printed paper-based electrodes based on carbon black dimethylglyoxime ink as electrode modifier(International Association of Physical Chemists, 2022) Pokpas, Keagan; Jahed, Nazeem; Bezuidenhout, PetroneElectrochemical detection of metal cations at paper-based sensors has been suggested as an attractive alternative to current spectroscopic and chromatographic detection techniques due to the ease of fabrication, disposable nature, and low cost. Herein, a novel carbon black (CB), dimethylglyoxime (DMG) ink is designed as an electrode modifier in conjunction with 3-electrode inkjet-printed paper substrates for use in the adsorptive stripping voltammetric electroanalysis of nickel cations in water samples. Thedeveloped method provides a novel, low-cost, rapid, and portable adsorptive stripping detection approach towards metal analysis in the absence of the commonly used toxic metallic films. The study demonstrated a novel approach to nickel detection at paper-based sensors and builds on previous work in the field of paper-based metal analysis by limiting the use of toxic metal films.Item Polyacrylic acid and polyvinylpyrrolidone stabilised ternary nanoalloys of platinum group metals for the electrochemical production of hydrogen from ammonia(University of the Western Cape, 2016) Molefe, Lerato Yvonne; Iwuoha, Emmanuel; Jahed, Nazeem; Antunes, EdithThe electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.Item Polyester sulphonic acid interstitial nanocomposite platform for peroxide biosensor(MDPI, 2009) Al-Ahmed, Amir; Ndangili, Peter M.; Jahed, Nazeem; Baker, Priscilla; Iwuoha, Emmanuel I.A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (~90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C.Item The synthesis and electrochemical studies of chalcones and flavanones: an investigation of their antioxidant activity(University of Western Cape, 2013) Baugaard, Carlo; Green, Ivan; Jahed, NazeemFlavonoids, one of the biggest classes of secondary metabolites, are found abundantly in nature in a broad range of fruits, vegetables and beverages such as tea, coffee, beer, wine and fruit drinks. Flavonoids have been reported to exert multiple biological functions as well as tremendous pharmacological activity, including anticancer activity, protection, antioxidant activity, cardiovascular protection, antibacterial, antifungal and antiviral activity. The antioxidant activity of flavones is reported to be associated with those bearing hydroxyl functions. In the present study, several reaction steps have been carried out to synthesize three sub classes of flavonoids namely; chalcones, dihydrochalcones and flavanones with various substituents attached. The first step involved protection of hydroxyl groups of acetophenone and benaldehyde as starting materials. Thereafter the Clasien Schmidt condensation reaction, under basic conditions, was performed to afford chalcone intermediates. Treatment of these chalcones with sodium acetate, under reflux, afforded flavanones as a single product in high yields. Thereafter all protecting groups where removed to yield the final products. All products and intermediates where purified by column chromatography and were characterized by Nuclear Magnetic Resonance Spectroscopy (NMR) (1H NMR and 13C NMR). An electrochemical analysis on all flavonoid compounds was performed by Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV) to give information on the accessible redox couples identified by their oxidation potentials. Oxidation potentials, which gave valuable information about reducing ability and hence the antioxidant activity, where used to compare all compounds. The antioxidant activity was observed to increase with the addition of hydroxyl groups on the B-ring. Compounds with a combination of hydroxyl groups on the A-ring and methoxy groups on the B-ring showed increased antioxidant activity when compared to those with only hydroxyl groups on the base structure. 2, 5, 4’-trihydroxy dihydrochalcone showed moderate antioxidant ability. However the 2, 5, 4’-trihydroxychalcone, containing the α, β unsaturated double bond, proved to have the greatest antioxidant ability.