Electrochemical and electrocatalytic properties of carbon nanotubes integrated with selected metal and metal oxide nanoparticles

This work describes metal (M) and metal oxides (MO) films (where M = Ni, Co and Fe) obtained by electrosynthesis and chemical synthesis, and modified with carbon nanotubes (CNTs) on edged plane pyrolytic graphite electrode (EPPGE). The MO nanoparticles investigated are nickel oxide (NiO), cobalt oxide Co3O4) and iron oxide (Fe2O3). Successful modification of the electrodes with the M or MO/CNT nanocomposite was confirmed by field emission scanning electron microscopy (FESEM), high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), x-ray diffraction spectroscopy (XRD), x-ray photoelectron spectroscopy (XPS), electron dispersive x-ray spectroscopy (EDX), fourier transformed infra-red spectroscopy (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. Electron transport (ET) properties of the modified electrodes was explored using cyclic voltammetry (CV) and electrochemical impedance spectroscopic techniques (EIS) with ferricyanide/ferrocyanide ([Fe(CN) 6]3-/4-) as the redox probe. The electron transfer constant (k0) differs in terms of materials, method of synthesis and electrical equivalent circuits used in the fitting or modelling process. Generally, the k0 values are in the 10-3 – 10-2 cms-1 with Ni nanoparticles having the highest k0 or fastest electron transport. The presence of CNTs also enhances the ET compared with electrodes without CNTs. The electrocatalytic properties of the modified electrodes were explored using the following analytical probes: diethylaminoethanethiol (DEAET), hydrazine, nitrite and dopamine. The study showed that the electrocatalytic oxidation of DEAET and hydrazine was favoured on electrode modified with Ni nanoparticles; nitrite and dopamine were best catalysed by the Co and Fe2O3 nanoparticles, respectively. Electroanalysis results (using chronoamperometry, square wave voltammetry and linear sweep voltammetry) indicated some level of adsorption of DEAET, hydrazine and nitrite on the modified electrode, while dopamine electrocatalytic oxidation and detection followed a simple diffusion controlled process. The adsorption process was found to be physically induced and could be eliminated by repetitive cycling of the electrode in the aqueous electrolyte solution. Electrodes modified with chemically-synthesised material (particularly nickel) were less adsorptive towards DEAET and hydrazine detection, and gave sensitivity and limit of detection values that compared with data obtained using electrochemical deposition / synthesis. The chemical stability and reproducibility of the modified electrodes were determined and discussed. Finally, electrochemical properties were studied to help screen these electrode materials in supercapacitors. CNT-NiO nanocomposites exhibit remarkable super capacitive behaviour in neutral and acidic media compared to the other CNT-MO nanocomposites investigated. Interestingly, the capacitive behaviour of the CNT-NiO was more enhanced in H2SO4 solution than in Na2SO4, possibly due to the high conductivity of the former. The CNT-NiO electrode maintained good stability with only about 5% loss of its specific capacitance after 1000 cycle life.Thesis (PhD)--University of Pretoria, 2011.Chemistryunrestricte

Comparative study of physicochemical properties of Tithonia diversifolia and Sunflower seed oils

This study investigates the physico-chemical properties of Tithonia diversifolia seed and oil using standard analytical methods and then compared the results with Sunflower oil. The results showed that Tithonia diversifolia seed contained 5.80% moisture, 18.83% crude protein, 30.40% crude fat, 17.85% crude fibre, 4.30% ash and 22.82% carbohydrate. The content of magnesium, copper, iron, zinc and calcium were 3930, 168, 277, 2091 and 432 mg/kg, respectively. Iodine value for T. diversifolia and Sunflower oils, respectively were 109.00 and 145.67 g iodine/kg; saponification values, 212.61 and 188.63 mg KOH/g; ester values, 184.15 and 206.86 mg KOH/g; peroxide values 4.0 and 5.87 meq peroxide/kg; acid values, 5.76 and 4.48 mg KOH / g; % unsaponifiable matter, 0.83 and 1.22 %; and total phenol content, 118.63 and 108.75 µg/g. Others include, specific gravity, 0.937 and 0.920; surface tension 0.042 and 0.051 N/m; viscosity 42.50 and 30.50 cSt; and smoke point, 215 and 245 0C. The study revealed that Tithonia diversifolia seed oil content and physicochemical parameters are comparable with those of Sunflower oil. Hence the oil could be used as raw materials for industrial processes, biodiesel production and a good source of dietary antioxidant which could complement or replace some conventional oils

Speciation Study of Heavy Metals in Soil within the Vicinity of a Metal Recycling Factory at Ile-Ife, Southwestern Nigeria

A speciation study of Al, Cd, Cu, Mn, Pb and Zn in soil samples from a metal recycling factory in Ile-Ife Osun State, Nigeria, was carried out in order to assess the heavy metal pollution impact of the industrial processes on the immediate environment. Surface soil dust samples collected within the vicinity of the factory were subjected to a five-stage sequential extraction process. Levels of heavy metals in each fraction were determined using Flame Atomic Absorption Spectrophotometer (FAAS). The overall mean values obtained for the metals in the fractions gave the range: Al (0.03 ± 0.01 to 0.20 ± 0.01 µg/g ); Cd (0.03 ± 0.01 to 0.23 ± 0.02 µg/g) ; Cu (2.93 ± 0.02 to 18.30 ± 1.95 µg/g) ; Mn (17.33 ± 0.03 to 91.68 ± 2.90 µg/g); Pb (0.03 ± 0.01 to 0.43 ± 0.02 µg/g)  and Zn (8.20 ± 0.01 to 35.08 ± 0.02 µg/g) . Both the contamination index and enrichment factor results indicated that all the soil samples were contaminated with Cd while a few sites showed Cu contamination. The mobility potential of the metals in the soil sample decreased in the order: Mn > Al > Zn > Cd > Cu > Pb (West) and Cd > Al > Pb > Zn > Mn > Cu (East). The study revealed that the soil around the metal recycling factory is contaminated with heavy metals, and if left unmonitored and controlled could lead to serious environmental risk in the future.Â

Supercapacitive properties of symmetry and the asymmetry two electrode coin type supercapacitor cells made from MWCNTS/nickel oxide nanocomposite

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Electrocatalytic properties of prussian blue nanoparticles supported on poly(m-aminobenzenesulphonic acid)-functionalised single-walled carbon nanotubes towards the detection of dopamine

Edged plane pyrolytic graphite electrode (EPPGE) was modified with and without Prussian blue (PB) nanoparticles and polyaminobenzene sulphonated single-walled carbon nanotubes (SWCNTPABS) using the chemical deposition method. The electrodes were characterised using microscopy, spectroscopy and electrochemical techniques. Results showed that edged plane pyrolytic graphite-single-walled carbon nanotubes-prussian blue (EPPGE-SWCNT-PB) electrode gave the best dopamine (DA) current response, which increases with increasing PB layers. The catalytic rate constant of 1.69 × 105 mol−1 cm3 s−1, Tafel value of 112 mV dec−1, and limit of detection of DA (2.8 nM) were obtained. Dopamine could be simultaneously detected with ascorbic acid. The electrode was found to be electrochemically stable, reusable and can be used for the analysis of DA in real drug samples.The University of Pretoria and the National Research Foundation (NRF, GUN # 2073666).http://www.elsevier.com/locate/colsurfbnf201

Comparative supercapacitive properties of asymmetry two electrode coin type supercapacitor cells made from MWCNTS/cobalt oxide and MWCNTs/iron oxide nanocomposite

Supercapacitive properties of synthesized metal oxide nanoparticles (MO) vis a vis iron oxides (Fe2O3) and cobalt oxide (Co3O4) nanoparticles integrated with multi-walled carbon nanotubes (MWCNT) in a two-electrode coin cell type asymmetry supercapacitor assembly was investigated. The synthesised MO and nanocomposite films were characterised using techniques such as transmission electron microscopy (TEM), scan electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD). The supercapacitance of the asymmetry MWCNT-MO based supercapacitor in 1 M H2SO4 and 1 M Na2SO4 electrolytes was measured using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic constant current charge-discharge (CD) techniques. The asymmetry supercapacitors MWCNT-Fe2O3|MWCNT and MWCNT-Co3O4|MWCNT gave the highest specific capacitance (SC) values of 439.94 mFcm-2 (or 64.74 Fg-1) and 425.83 mFcm-2 (or 45.79 Fg−1) respectively in 1 M H2SO4 using charge-discharge technique. Results obtained from charge-discharge experiment are much higher compared with those obtained using the CV technique since it is the most reliable and accurate method. The values compared favorably and higher compared to those reported in literature using similar technique. MWCNT-Fe2O3|MWCNT cell gave specific power (SP) and specific energy (SE) of 19.31 Wkg-1 and 2.68 WhKg-1 respectively in 1 M H2SO4, while the energy deliverable efficiency (/%) of the cell is 99.6 and 91.3% in 1 M H2SO4 and 1 M Na2SO4 respectively.http://www.electrochemsci.orgam201

Comparative surface electrochemistry of Co and Co3O4 nanoparticles : nitrite as an analytical probe

This study described the decoration of edge plane pyrolytic graphite electrode (EPPGE) with synthesised cobalt and cobalt oxide nanoparticles. The modified electrode was characterised by techniques such as TEM, FESEM, XRD, EDS, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EPPGE-Co demonstrated enhanced electron transport and catalytic efficiency towards nitrite oxidation at pH 7.4 compared with the other electrodes studied. The catalytic rate constant (K) obtained at the EPPGE-Co for nitrite at pH 7.4 is 2.32 x 106 cm3mol-1s-1 while the limits of detection (LoD = 3.3 δ/m) is 7.3 x 10-7 M

Voltammetric and impedimetric properties of nano-scaled y--Fe2O3 catalysts supported on multi-walled carbon nanotubes : catalytic detection of dopamine

The electron transfer and electrocatalytic proiperties of iron oxide nanoparticle (-Fe2O3) catalysts supported on MWCNTs are described. The MWCNT-Fe2O3 and its electrodes were successfully characterised with FESEM, HRTEM, XRD, EDX, cyclic voltammetry and electrochemical impedance spectroscopy. The MWCNT-Fe2O3 based electrodes demonstrated fastest electron transport and current response towards DA compared to other electrodes studied, giving a catalytic rate constant of 16.4 x 105 cm3mol-1s-1, sensitivity of 0.026 AM-1 and limit of detection of 3.3 x 10-7 M. The electrode may be potentially useful for the detection of DA in real drug sample analysis

Probing the electrochemical behaviour of SWCNT–cobalt nanoparticles and their electrocatalytic activities towards the detection of nitrite at acidic and physiological pH conditions

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Determination of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in some personal care products in Nigeria

The study was carried out to determine the presence and concentration of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in some personal care products in Nigeria. Commonly used consumer care products grouped into four classes, namely: plastics, cosmetics, disinfectants and washing products, were purchased from some supermarkets in Ile-Ife, Nigeria. The solid samples were pulverized and the PAHs and OCPs were extracted with n-hexane and dichloromethane, respectively using Soxhlet extraction method, while the liquid samples were extracted using liquid-liquid extraction method. The quantitative and qualitative determinations were carried out using Gas Chromatography coupled with Flame Ionization Detector (GC-FID) for PAHs, and Gas Chromatography coupled with Electron Capture Detector (GC-ECD) for the OCPs. The results for PAHs analysis gave an overall mean concentration of 3259.10 ± 5223.16 μg g−1 for plastics and 8388.00 ± 7106.55 μg g−1 for cosmetics. Comparatively, the concentrations of PAHs in the cosmetic samples were higher than in plastics samples, while both values were greater than the recommended limits of PAHs in consumer care products as stipulated by the World Health Organization. For the OCPs, disinfectant samples had a total mean concentration of 10.65 ± 6.50 μg mL−1, while washing products had a total mean concentration of 35.31 ± 39.31 μg mL−1. The concentrations of OCPs in washing products were higher than their concentrations in disinfectant samples. The results of the OCPs in some samples were greater than Maximum Residual Limit (MRL) recommended by the European Commission. The study concluded that consumer care products used in this study contained PAHs and OCPs at levels that could be risky to human health if the consumer care products are not used with caution. Keywords: Organochlorine pesticides (OCPs), Polycyclic aromatic hydrocarbons (PAHs), Plastics, Cosmetics, Consumer care product