[Show abstract][Hide abstract] ABSTRACT: New chalcone derivatives namely (E)-(1-(5-(4-(3-(4-methylphenyl)-3-oxoprop-1-
enyl)phenoxy)pentyl)-1H-1,2,3-triazol-4-yl)methyl acrylate (CH-5), (E)-(1-(5-(4-(3-(4-
methylphenyl)-3-oxoprop-1-enyl)phenoxy)hexyl)-1H-1,2,3-triazol-4-yl)methyl acrylate (CH-6)
methyl acrylate (CH-10) were synthesized and characterized by Fourier transform infrared (FTIR)
and Nuclear magnetic resonance (NMR) spectroscopic techniques. Ultraviolet-visible (UVvis)
spectra of the synthesized compounds confirmed that the chalcones undergo photo-cross linking upon irradiation with UV-light. Potentiodynamic polarization measurements showed that
both the intact and photo-cross-linked chalcones are mixed-type corrosion inhibitors for mild
steel in aqueous hydrochloric acid. The EIS results showed an increase in charge transfer
resistance with increasing concentration of the inhibitors. The chalcone derivatives adsorb
spontaneously on mild steel surface and their adsorption obeyed the Langmuir adsorption
isotherm. The adsorption mode revealed the possibility of competitive physisorption and
chemisorption mechanisms. Scanning electron microscope coupled with energy dispersive X-ray
spectroscopy (SEM-EDX) analyses confirmed that the chalcones formed protective film on mild
steel surface. The overall results showed that the photo-cross-linked chalcones are better
corrosion inhibitors than the intact chalcones. The results of quantum chemical calculations and
Monte Carlo simulation studies are in good agreement with experimental result.
[Show abstract][Hide abstract] ABSTRACT: The corrosion inhibition properties of some organic dyes, namely Sunset Yellow (SS), Amaranth (AM), Allura Red (AR), Tartrazine (TZ) and Fast Green (FG), for mild steel corrosion in 0.5 M HCl solution, were investigated using gravimetric, potentiodynamic polarization techniques and quantum chemical calculations. The results showed that the studied dyes are good corrosion inhibitors with enhanced inhibition efficiencies. The inhibition efficiency of all the studied dyes increases with increase in concentration, and decreases with increase in temperature. The results showed that the inhibition efficiency of the dyes increases in the presence of KI due to synergistic interactions of the dye molecules with iodide (I −) ions. Potentiodynamic polarization results revealed that the studied dyes are mixed-type inhibitors both in the absence and presence of KI. The adsorption of the studied dyes on mild steel surface, with and without KI, obeys the Langmuir adsorption isotherm and involves physical 16005 adsorption mechanism. Quantum chemical calculations revealed that the most likely sites in the dye molecules for interactions with mild steel are the S, O, and N heteroatoms.
[Show abstract][Hide abstract] ABSTRACT: The effects of seven macrocyclic compounds comprising four
phthalocyanines (Pcs) namely 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine
(Pc1), 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (Pc2), 2,9,16,23-tetratert-
butyl-29H,31H-phthalocyanine (Pc3) and 29H,31H-phthalocyanine (Pc4), and three
naphthalocyanines namely 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine (nPc1),
2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (nPc2) and 2,3-naphthalocyanine (nP3)
were investigated on the corrosion of aluminium (Al) in 1 M HCl using a gravimetric method,
potentiodynamic polarization technique, quantum chemical calculations and quantitative
structure activity relationship (QSAR). Synergistic effects of KI on the corrosion inhibition properties of the compounds were also investigated. All the studied compounds showed
appreciable inhibition efficiencies, which decrease with increasing temperature from 30 °C
to 70 °C. At each concentration of the inhibitor, addition of 0.1% KI increased the inhibition
efficiency compared to the absence of KI indicating the occurrence of synergistic interactions
between the studied molecules and I− ions. From the potentiodynamic polarization studies,
the studied Pcs and nPcs are mixed type corrosion inhibitors both without and with addition
of KI. The adsorption of the studied molecules on Al surface obeys the Langmuir adsorption
isotherm, while the thermodynamic and kinetic parameters revealed that the adsorption of the
studied compounds on Al surface is spontaneous and involves competitive physisorption and
chemisorption mechanisms. The experimental results revealed the aggregated interactions
between the inhibitor molecules and the results further indicated that the peripheral groups
on the compounds affect these interactions. The calculated quantum chemical parameters
and the QSAR results revealed the possibility of strong interactions between the studied
inhibitors and metal surface. QSAR analysis on the quantum chemical parameters obtained with
B3LYP/6-31G (d,p) method show that a combination of two quantum chemical parameters to
form a composite index provides the best correlation with the experimental data.
[Show abstract][Hide abstract] ABSTRACT: The inhibition of the corrosion of N80 steel in 3.5 wt. % NaCl solution saturated with CO2 by four porphyrins, namely 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin 15123 (HPTB), 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin (T4PP), 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrakis(benzoic acid) (THP) and 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP) was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM) techniques. The results showed that the inhibition efficiency, η% increases with increasing concentration of the inhibitors. The EIS results revealed that the N80 steel surface with adsorbed porphyrins exhibited non-ideal capacitive behaviour with reduced charge transfer activity. Potentiodynamic polarization measurements indicated that the studied porphyrins acted as mixed type inhibitors. The SECM results confirmed the adsorption of the porphyrins on N80 steel thereby forming a relatively insulated surface. The SEM also confirmed the formation of protective films of the porphyrins on N80 steel surface thereby protecting the surface from direct acid attack. Quantum chemical calculations, quantitative structure activity relationship (QSAR) were also carried out on the studied porphyrins and the results showed that the corrosion inhibition performances of the porphyrins could be related to their EHOMO, ELUMO, ω, and μ values. Monte Carlo simulation studies showed that THP has the highest adsorption energy, while T4PP has the least adsorption energy in agreement with the values of σ from quantum chemical calculations.
[Show abstract][Hide abstract] ABSTRACT: The inhibition of mild steel corrosion in 1 M HCl solution by some imidazolium-based ionic liquids (ILs), namely 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM]+[BF4]-, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM]+[BF4]- and 1-decyl-3-methylimidazolium tetrafluoroborate [C10MIM]+[BF4]- was investigated using experimental and theoretical techniques. All the studied ILs showed appreciable inhibition efficiencies. Polarization measurements showed that the studied compounds are mixed-type inhibitors and the results obeyed Langmuir adsorption isotherm. Spectroscopic studies confirmed chemical interactions between mild steel and the ILs. Scanning electron microscopy images revealed that the inhibitors formed protective film on mild steel surface. The results of quantum chemical calculations and Monte Carlo simulations agree with experimental observations.
[Show abstract][Hide abstract] ABSTRACT: The inhibition of mild steel corrosion in 1 M HCl solution by some ionic liquids (ILs) namely, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate [HMIM][TfO], 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4], 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF6], and 1-hexyl-3-methylimidazolium iodide [HMIM][I] was investigated using electrochemical measurements, spectroscopic analyses and quantum chemical calculations. All the ILs showed appreciably high inhibition efficiency. At 303 K, the results of electrochemical measurements indicated that the studied ILs are mixed-type inhibitors. The adsorption studies showed that all the four ILs adsorb spontaneously on steel surface with [HMIM][TfO], [HMIM][BF4] and [HMIM][I] obeying Langmuir adsorption isotherm, while [HMIM][PF6] conformed better with Temkin adsorption isotherm. Spectroscopic analyses suggested the formation of Fe/ILs complexes. Some quantum chemical parameters were calculated to corroborate experimental results.
[Show abstract][Hide abstract] ABSTRACT: Mild steel is considered a material of choice in diverse industrial and structural applications. It is used to make a wide range of equipment due to its relatively low cost and good mechanical strength . But acid solutions used in many industrial processes such as acid cleaning and oil well acidizing constitute strong corrosion media that enhance the rate of mild steel corrosion. As a result, corrosion of steel has been identified as a common problem that consumes large maintenance costs in many industries. It has been established that organic molecules containing heteroatoms such as nitrogen, oxygen and sulphur usually exhibit good anticorrosion activities . Quinoxaline and its derivatives are among organic compounds that have been reported to be good corrosion inhibitors . Quinoxaline units are parts of many materials including dyes and pharmaceuticals. They are biodegradable and non-toxic. Thus, the purpose of this work is to investigate the corrosion inhibition activities of some quinoxaline derivatives on the corrosion of mild steel in hydrochloric acid medium. To the best of our knowledge, the set of organic compounds selected for this work has not been investigated for the same purpose in any previous work.
In this study, the corrosion inhibition and adsorption characteristics of four quinoxaline derivatives (Me-4-PQPB, Mt-3-PQPB, Mt-4-PQPB and Oxo-1,3-PQPB) on mild steel surface in 1 M HCl were investigated. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques were used in the study. Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopic techniques were used to investigate possible formation of Fe/inhibitor complex and/or adsorption of the inhibitors on steel surface. Quantum chemical calculations were carried out on the molecules to correlate experimental results with quantum molecular parameters. The results showed that the studied molecules inhibit corrosion of mild steel in HCl medium with Me-4-PQPB having the best inhibition property. The inhibitors are mixed-type in their activities. All the inhibitors physisorb and chemisorb spontaneously on mild steel surface and their adsorption behaviour obeyed Langmuir equation. Some quantum chemical parameters support the observed trend of inhibition potencies and suggest that the inhibition effects were attributed to the protonated forms of the quinoxaline derivatives. The graphical surfaces of condensed Fukui indices suggest possible adsorption sites on the inhibitors.
1. De la Fuente D., Diaz I., Simancas J., Chico B., Morcillo M. “Long-term Atmospheric Corrosion of Mild Steel, Corrosion Science (2010), doi:10.1016/j.corsci.2010.10.007.
2. Obi-Egbedi N.O., Obot I.B., El-Khaiary M.I., Umoren S.A., Ebenso E.E. “Computational Simulation and Statistical Analysis on the Relationship between Corrosion Inhibition Efficiency and Molecular Structure of Some Phenanthroline Derivatives on Mild Steel Surface.” Int. J. Electrochem. Sci., 6 (2011): 5649 – 5675.
3. Obi-Egbedi, N.O. and Obot, I.B. Indeno-1-one-[2,3-b]-quinoxaline as an effective inhibitor for the corrosion of mild steel in 0.5M H2SO4 solution. Materials Chemistry and Physics 122 (2010) 325–328.
227th ECS Meeting, Hilton Chicago 720 S. Michigan Ave, USA; 05/2015
[Show abstract][Hide abstract] ABSTRACT: Abstract: The corrosion inhibition activity of a newly synthesized Schiff base (SB) from 3-acetyl-4-hydroxy-6-methyl-(2H)-pyran-2-one and 2,2'-(ethylenedioxy)diethylamine was investigated on the corrosion of mild steel in 1 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopic techniques. Ultraviolet-visible (UV-vis) and Raman spectroscopic techniques were used to study the chemical interactions between SB and mild steel surface. SB was found to be a relatively good inhibitor of mild steel corrosion in 1 M HCl. The inhibition efficiency increases with increase in concentration of SB. The inhibition activity of SB was ascribed to its adsorption onto mild steel surface, through physisorption and chemisorption, and described by the Langmuir adsorption model. Quantum chemical calculations indicated the presence of atomic sites with potential nucleophilic and electrophilic characteristics with which SB can establish electronic interactions with the charged mild steel surface.
Keywords: Schiff base; electrochemical techniques; mild steel; adsorption; quantum chemical calculations
[Show abstract][Hide abstract] ABSTRACT: In this study, electrocatalytic behaviour of graphene oxide (GO), iron (III) oxide (Fe2O3) and Prussian blue (PB) nanoparticles and their nanocomposite towards Nitrite (NO2-) and nitric oxide (NO) oxidation in neutral and acidic media respectively was carried out on platinum (Pt) modified electrode. Successful synthesis of these nano materials was confirmed using techniques such as transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, Raman spectroscopy and x-ray diffraction spectroscopy (XRD). Successful modification of electrode was confirmed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Results showed that the Pt-GO-Fe2O3 and Pt-GO-PB nanocomposite modified electrodes gave faster electron transfer process in both 5 mM Ferri/Ferro ([Fe(CN)6]3−/4−) redox probe and 0.1 M phosphate buffer solution (PBS). Pt-GO-Fe2O3 and Pt-GO-PB electrodes also gave enhanced NO2- and NO oxidation current compared with bare Pt and other electrodes studied. Electrocatalytic oxidation of the analyte occurred through a simple diffusion process but characterised with some level of adsorption. Tafel slope b of 468.4, 305.2 mVdec-1 (NO2-, NO); and 311.5, 277.2 mVdec-1 (NO2-, NO) were obtained for the analyte at Pt-GO-Fe2O3 and Pt-GO-PB electrode respectively. Pt-GO-Fe2O3 limit of detection and sensitivity in NO2- and NO are 6.60 M (0.0084 A/M) and 13.04 M (0.0160 A/M) respectively, while that of Pt-GO-PB electrode are 16.58 M (0.0093 A/M) and 16.50 M (0.0091 A/M). The LoD compared favourably with literature reported values. Pt-GO-Fe2O3 gave better performance to NO2- and NO electrooxidation, good resistance to electrode fouling, higher catalytic rate constant and lower limit of detection. The adsorption equilibrium constant β and the standard free energy change ΔG0 due to adsorption are 10.29 x 103 M-1 (-22.89 kJmol-1) and 3.26 x 103 M-1 (-20.04 kJmol-1) for nitrite and nitric oxide respectively at Pt-GO-Fe2O3 electrode. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of nitrite and nitric oxide in food, water, biological and environmental samples.
[Show abstract][Hide abstract] ABSTRACT: 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 (Η/%) of the cell is 99.6 and 91.3% in 1 M H2SO4 and 1 M Na2SO4 respectively.
International journal of electrochemical science 01/2015; 10(4):3414-3430. · 1.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work assessed levels of heavy metals exposure from silver coatings of mobile phones recharge cards of three major companies (designated as A, B and C) with price denominations 100, 200 and 400 from companies A, B and C respectively, which were carefully scratched using a plastic scraper into a glass tube. The coatings were acid digested for total metal concentration, while speciation experiment for Mn, Cu, Cd and Pb was carried out. Total metals and speciation analysis were done using AAS and XRF techniques. The total metal concentration from XRF analysis was in the range: Ca (70-2140 μg/g), K (20–4930 μg/g), Sc (80–270 μg/g), Ti (1530–12580 μg/g), Fe (50–6660 μg/g), Ni (20–2040 μg/g), Cu (20 - 850 μg/g) and Zn (40–460 μg/g). Cr had the lowest concentration (10 μg/g) in A ( 400) while Ti had the highest concentration (12580 μg/g) in C ( 500) for all the coatings analyzed. AAS and XRF results agreed closely except for Fe with higher concentration. A ( 100) contained high concentration of the metals compared with others. Speciation study identified Mn as the most mobile element when present in the environment.
[Show abstract][Hide abstract] ABSTRACT: Bread loaves randomly sampled from nine outlets and bakeries within Ile-Ife wereanalysed to determine their safety levels for human consumption with respect to bromate and trace metal contents. Bromate determinationwas carried out via spectrophotometric method while trace metals in the digested bread samples were profiledusing Flame Atomic Absorption Spectrophotometer. Bromate levels in the analyzed bread samples ranged from 2.051 ± 0.011 μg/g to 66.224 ± 0.014 μg/g while the tracemetal levels were of the order: 0.03-0.10 μg/g Co = 0.03-0.10 μg/g Pb< 0.23-0.46 μg/gCu <2.23-6.63 μg/g Zn < 25.83-75.53 μg/g Mn.This study revealed that many bread bakers around Ile-Ife had not fully complied with the bromate-free rule stipulated by NAFDAC contrary to the “bromate free” inscribed on the labels of the bread. The bread samples containedboth essential and toxic trace metals to levels that could threaten the health of consumers over prolonged regular consumption.
[Show abstract][Hide abstract] ABSTRACT: The determination of heavy metals in consumer products is crucial for the safety appraisal and sources classification of human and environmental exposures. These products contain various undisclosed chemical constituents with no or little known health safety information. The public is generally unaware of these types of everyday exposure from chemical constituents of consumer products and their health consequences. In this study, we recorded a body of proof demonstrating potential harm of consumer goods, by determining concentrations of total cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), iron (Fe), lead (Pb) and nikel (Ni contents in a variety of personal care products (n = 82) commonly used in Nigeria, using flame atomic absorption spectrometer after dry and wet digestion methods. The results of the analysis indicated that the range of Cd was 0.035 ± 0.023–0.467 ± 0.167 ppm, Cr 0.015 ± 0.009–0.435 ± 0.232 ppm, Cu 0.230 ± 0.08–0.603 ± 0.025 ppm, Zn 0.003 ± 0.005–0.743 ± 0.066 ppm, Fe 0.233 ± 0.219–1.401 ± 1.878 ppm, Pb 0.02 ± 0.007–0.2050.129 ppm and Ni 0.035 ± 0.015–0.093 ± 0.06 ppm. The values of Cd and Cr are a cause for alarm because the elements are not allowed in any amount in cosmetics. Despite the fact that zinc is essential in the body, the values obtained in this study deserves safety concerns due to cumulative effect, arising from incessant exposure.
International IJC 12/2013; 38(1). DOI:10.1111/ijcs.12061 · 0.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effects of various degumming agents on the trace metal concentrations of five nonconventional oils extracted from the seeds of Terminalia catappa, Irvingia gabonensis, Persea americana, Dacryodes edulis and fleshy mesocarp of D. edulis fruit and one conventional oil extracted from Glycine max were studied. The degumming of these oils was done using distilled water, NaCl solution and Ca–Mg salt solution at various concentrations as degumming agents. The findings showed that the degumming ability of the various degumming agents varied from one oil to another, with the degumming efficiency of 100–300 µg/mL NaCl solutions higher than that of 50–250 µg/mL Mg–Ca solutions. For the developing countries, the degumming process outlined in this study is a viable and an affordable alternative to the hi-tech procedures available in the developed countries.
Irvingia gabonensis, Terminalia catappa, Dacryodes edulis and Persea americana are local plants cultivated across Nigeria. Their seeds and fruits have found applications in both human and animal feeding because of their high oil and protein content. However, these nonconventional oil seed sources are prone to chemical rancidity and poor shelf life because of lack of adequate technology in handling and preserving their fruits, seeds and oils. The main application of this study is to come up with cheap technology and efficient process of removing some of the chemical components of the oils responsible for their low shelf life. This could assist the food industries in the developing countries to solve the problems of the high cost of and unavailable technology from the developed nations, and hence, tackle the problem of oil spoilage or rancidity using the findings of this research.
Journal of Food Processing and Preservation 10/2013; 37(5). DOI:10.1111/j.1745-4549.2012.00670.x · 1.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H2SO4) and sodium sulphate (Na2SO4) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF cm−2 (ca 2,119 F g−1) in H2SO4. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.
Journal of Solid State Electrochemistry 05/2013; 17(5). DOI:10.1007/s10008-012-1978-y · 2.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 × 10(5)mol(-1)cm(3)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.
[Show abstract][Hide abstract] ABSTRACT: Reported in this work is a novel electrochemical ethanol sensor that is simple to prepare, cost effective, stable and resistant to intermediates poisoning by using platinum (Pt) electrode modified with multi-walled carbon nanotubes (MWCNT)/NiO nanoparticles. The modified electrode (Pt-MWCNT-NiO) was characterized using field emission transmission electron microscopy (FETEM), x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The electrode showed the highest ethanol oxidation current compared with the other electrodes studied. Ethanol oxidation current increased with increasing MWCNT-NiO loading on the Pt-MWCNT-NiO electrode. Chronoamperometry analysis gave the lowest limit of detection (LoD) of 1.63 ppm and a sensitivity of 0.01 μAmM -1. The catalytic rate constant K cat and the diffusion coefficient of ethanol on the electrode are 1.94 × 10 3 cm 3 mol -1 s -1 and 5.2 × 10 -8 cm 2s -1 respectively. The high Tafel value of 1227 mVdec -1 obtained suggests the involvement of reaction intermediates. However, the repetitive scanning analyses indicates the electrode to be of very high stability (ca 98%), with capacity to withstand poisoning effects of ethanol oxidation products. The analytical data obtained in this study compared well with other studies reported in literature. The lowest LoD (38.8 μM or 1.63 ppm) obtained for chronoamperometry suggest the high sensitivity of this technique over other techniques studied and as such should be considered when constructing the Pt-MWCNT-NiO ethanol sensor for commercial applications.
International journal of electrochemical science 03/2012; 7(3). · 1.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work describes the modification of platinum electrode with and without functionalised multi-walled carbon nanotubes (MWCNT-SO 3 2-) and prussian blue nanoparticles (PB) for the detection of iodate, periodate and sulphite ions. The modified electrodes were characterised using techniques such as transmission electron microscopy (TEM), electron dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CVs) and electrochemical impedance spectroscopy (EIS). The Pt-MWCNT-PB electrode exhibited enhanced electron transport and catalytic efficiency towards the electrocatalysis of iodate (IO 3 -), periodate (IO 4 -) and sulphite (SO 3 2-) compared to the other electrodes studied. The electrode was characterised by some level of adsorption due to adsorbed intermediates. The degree of adsorption was quantified as indicated by the Tafel values of 211.0, 176.2, and 129.2 mVdec -1 for iodate, periodate and sulphite respectively. The analytes were detected at micromolar level. The limit of detection and the catalytic rate constant were 8.30 µM (1.37x10 6 cm 3 mol -1 s -1), 8.06 µM (0.34x10 6 cm 3 mol -1 s -1) and 4.70 µM (5.24 x 10 7 cm 3 mol -1 s -1) for iodate, periodate and sulphite. The electrode detects iodate in the presence of the interfering effect from other oxo-anions. This electrode can be reliably used to assay iodate in real or commercial salt composition.
International journal of electrochemical science 01/2012; 7(9). · 1.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the synthesis of a nano cobalt complex potassium nitratopentacyanocobaltate (III) (K 3 [Co(CN) 5 NO 3 ]) made by a simple green chemistry method. The synthesized complex was characterized using FTIR, UV-Vis, XRD, EDX, HRSEM and TEM techniques. Electron transfer behaviour of the [Co(CN) 5 NO 3 ] 3-complex on an electrode support was investigated in a ferrocyanide/ferricyanide (Fe(CN) 6 ] 4-/ [Fe(CN) 6 ] 3-) redox probe using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS study in Fe(CN) 6 ] 4-/ [Fe(CN) 6 ] 3-redox probe showed that nano cobalt complex modified edge plane pyrolytic graphite electrode (EPPGE-Co) exhibit faster electron transfer with a charge transfer resistance of R ct = 0.52 Ωcm 2 which was 12 times greater than that of the bare EPPGE (R ct = 6.42 Ωcm 2). The equivalent circuit used demonstrated the pseudocapacitive and the lower capacitance of the EPPGE-Co electrode compared to the EPPGE. The EPPGE-Co showed an enhanced catalytic current (3 and 7 folds higher) in nitrite (NO 2 -) and nitric oxide (NO) respectively, than the current at the bare EPPGE electrode. The nano cobalt complex was simple to prepare, environmental friendly and should be a potential catalyst for sensors, semiconductors and energy storage devices applications.
International journal of electrochemical science 01/2012; 7(4). · 1.50 Impact Factor