Investigation of the electrochemical behaviour of thermally prepared Pt-IrO2 electrodes

Different IrO2 electrodes in which the molar percentage of platinum (Pt) varies from 0 %mol Pt to 100 %mol Pt were prepared on titanium (Ti) substrate by thermal decomposition techniques. The electrodes were characterized physically (SEM, XPS) and electrochemically and then applied to methanol oxidation. The SEM micrographs indicated that the electrodes present different morphologies depending on the amount of platinum in the deposit and the cracks observed on the 0 %mol Pt electrode diminish in size tending to a compact and rough surface for 70 %mol Pt electrode. XPS results indicate good quality of the coating layer deposited on the titanium substrate. The voltammetric investigations in the supporting electrolyte indicate that the electrodes with low amount of platinum (less than 10 %mol Pt) behave as pure IrO2. But in the case of electrodes containing more than 40 %mol Pt, the voltammograms are like that of platinum. Electrocatalytic activity towards methanol oxidation was observed with the electrodes containing high amount of platinum. Its oxidation begins at a potential of about 210 mV lower on such electrodes than the pure platinum electrode (100 %mol Pt). But for electrode containing low quantity of Pt, the surface of the coating is essentially composed of IrO2 and methanol oxidation occurs in the domain of water decomposition solely. The increase of the electrocatalytic behaviour of the electrodes containing high amount of Pt towards methanol oxidation is due to the bifunctional behaviour of the electrodes. KEY WORDS: Iridium dioxide, Platinum, Methanol oxidation, Electrocatalytic activity  Bull. Chem. Soc. Ethiop. 2008, 22(1), 125-134

Metal Pollution and Ecological Risk Assessment in Sediment of Artificial Estuary: Case of Vridi Channel, Côte d’Ivoire

This study focused on a yearly monitoring of sediment pollution in Cd, Co, Cu, Fe, Mg, Mn, Ni, Pb, Zn and the ecological incurred risks in Vridi channel. The results, expressed per dry weight, showed that the annual mean were 0.96 (± 0.16) mg/Kg for Cd, 22.36 (± 2.41) mg/kg for Co, 33.98 (± 4.61) for Cu, 31760.5 (± 5652.7) mg/kg for Fe, 981.2 ± (377.5) mg/kg for Mg, 302.9 (± 415.4) mg/kg for Mn, 42.53 (± 9.79) mg/kg for Ni, 83.37 (± 6.66) mg/kg for Pb and 27.11 (± 11.72) mg/kg for Zn. The measured oligo-elements (Fe, Mn, Mg, Zn) originated from naturals sources and were away from accumulation, except from Fe which moderately accumulated. That hence the low sediment contamination by these metals. As for toxic trace metal (not essential) to living organisms (Co, Cu, Pb, Cd, Ni), they resulted from anthropogenic origin. These sediments were moderately contaminated in Co, Cu and Ni, significantly in Pb and strongly in Cd. All the studied trace metals were mainly from continental origin, except Cd which showed a marine origin. This estuary displayed a steady state of progressive deterioration and presented a very high ecological risk.Keywords: Abidjan, Atlantic Ocean, Ebrié System, pollution indicators, trace metal

Mild steel corrosion inhibition by 7-(ethylthiobenzimidazolyl) theophylline

The corrosion inhibition of mild steel by 7-(ethylthiobenzimidazolyl) theophylline (7-ETBT) in 1 M HCl medium was investigated through weight loss and Tafel polarization techniques within a temperature range of 298 to 318 K. The inhibition efficiency depends on the concen-tration of 7-ETBT and reaction system temperature. The maximum inhibition efficiency values of 90.73 and 87.06 %, respectively, were estimated using both weight loss and Tafel polarization techniques at 298 K. The results suggest spontaneous and predominant physical adsorption of 7-ETBT on the metal surface which obeys Langmuir isotherm model. Furthermore, Tafel polarization method revealed that 7-ETBT is a mixed-type inhibitor. Po-tentiodynamic polarization results are in accordance with weight loss data to a good extent

Experimental and DFT Studies on the Behavior of Caffeine as Effective Corrosion Inhibitor of Copper in 1M HNO3

Caffeine was tested as copper corrosion inhibitor in 1M HNO3 using mass loss technique at 308-328K and theoretical studies based on quantum chemistry. The inhibition efficiency is concentration and temperature dependent: Caffeine showed an inhibition efficiency of 78% at 5mM for T =328K. The thermodynamic adsorption parameters ( were determined and analyzed. They revealed a spontaneous adsorption process and a strong interaction between Caffeine and the metal surface. Adsorption isotherms including Langmuir, Temkin and El-Awady were tested. It was found that Caffeine adsorbs on copper according to the modified Langmuir adsorption isotherm. The Dubinin Raduskevitch model was used to distinguish between chemisorption and physisorption. Activation parameters ( were also determined and discussed. Furthermore, the quantum chemical properties/descriptors most relevant to the potential action of the molecule as corrosion inhibitor such as highest occupied molecular energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), energy gap(∆E), dipole moment ( and charges on heteroatoms were calculated using DFT at B3LYP level with 6-31+G (d) and LanL2DZ basis sets. Fukui indices were also determined and discussed. The theoretical results are consistent with the experimental data reported. DOI: http://dx.doi.org/10.17807/orbital.v8i2.80

Characterization of Thermal Prepared Platinized Tin Dioxide Electrodes: Application to Methanol Electro-Oxidation

Different platinized tin dioxide electrodes were prepared by the thermal decomposition procedure on titanium substrate. They were characterized physically and electrochemically. The platinum modified tin dioxide electrodes developed in this work present rough surface with small cracks. Amorphous SnO2 and polycrystalline Pt were identified by X-Ray pattern analysis. The platinum particles size vary from 6,6 to 8,9nm indicated their nanostructure. XPS analysis indicates that pure deposits are prepared and their surface is composed of Pt, O, Sn. Deconvolution of the Pt, O and Sn signals revealed that the deposit is composed of SnO2, zero-valence and oxidised form of Pt. The electrochemical investigation with ferriferrocyanide redox couple showed a quasireversible behaviour on the electrodes. Their electrocatalytic activity increases to reach a maximum for a composition between 40%mol Pt and 70%mol Pt in the deposit. Then after, this activity decreases to reach that of pure platinum. That was related to the distribution of platinum and its size in the deposit. The electrochemical oxidation of methanol on the platinum modified tin dioxide electrodes led to a decrease of its oxidation overpotential in comparison to that of pure platinum. This oxidation begins at potential of about 220mV lower than the pure platinum. The decrease of the overpotential of methanol oxidation is due to the involvement of platinum and tin dioxide in the oxidation process. A mechanism of methanol oxidation has been proposed

Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems, A Case Study, Ebrié Lagoon-Côte d’Ivoire

In aquatic ecosystems, trace metals (TMs) are widely studied due to their harmful effects on living organisms and humans. The aim of the present study was to use different pollution indices to characterize the sediments contamination with six TMs (As, Cd, Fe, Hg, Mn and Pb). Sediments samples were collected in April 2006 with a Van Veen grab at five stations located in the Ebrie Lagoon (Côte d’Ivoire). TMs concentrations were determined using an ICP-MS Instrument for the calculation of the contamination index (CI), contamination factor (CF), pollution load index (PLI), enrichment factor (EF) and Muller’s index of geoaccumulation (Igeo). The CI revealed the sediments contamination in As, Cd and Pb, while CF highlighted their contamination in Hg, As, Fe and Cd. Regarding the PLI, the sediments were uncontaminated with TMs. The EF showed the sediments enrichment with Hg, Pb and As, while the Igeo revealed their pollution with As, Fe, Pb and Cd. In conclusion, the PLI is a useful tool for different locations characterization, while the others (CI, CF, EF, and Igeo) allow individual characterization regarding each TM. Due to high contents in As, Cd and Pb, the studied area need a particular attention

Lead concentrations in sediments and mollusc gastropod from Vridi Canal, Côte d’Ivoire

Lead (Pb) is one of the most frequent and toxic contaminant in the environment. It can be bioaccumulated by marine organisms through contaminated sediments as well as their food chains. The current study aimed at investigating Pb occurrence in the sediments and gastropod P. haemastostoma from Vridi Canal. Sediment samples were taken using a Van Veen steel grab of 0.02 m2 area, sealed in plastic bags and transported to the laboratory at 4 °C. Gastropod P. haemastostoma species were collected manually using gloves, and then placed in polyethylene plastic bags. The different concentrations were determined using atomic absorption spectrometer Varian AA 20. The results showed seasonal variability of Pb concentrations in sediments and P. haemastostoma. In the both matrices, Pb exhibited the same trend in the distribution between the seasons. This study also mentioned that sediments were highly  contaminated by Pb (54.27-134.71 mg/kg). Vridi Canal was found to be one of the most contaminated seaport area. Pb levels  (49.55-104.19 mg/kg) in P. haemastostoma exceeding the maximum permitted levels according to the United Nations Food and Agriculture Organization (FAO). This research demonstrated that sediments having lower ecological risk may be resulting in lower tissue Pb of P. haemastostoma. Keywords: Metal Pb, sediment, P. haemastostoma, seasonal variatio

Removal of Black Remazol in aqueous solution with activated carbons from corncobs based on the design of experiments methodology

This study falls not only into the theme of water depollution but also and above all into the recovery of waste (logic of the 3 R: Reduce, Reuse and Recycle). There was talk of recovering corncobs, which are considered as “agricultural waste” in developing countries such as Côte d’Ivoire. They were used as activated carbon to adsorb Black Remazol in a synthetic aqueous solution. This activated carbon obtained has a specific surface of 673.33 m²/g, a mass loss of 61.44 %, an iodine value of 168.31 mg.g-1 and a zero charge potential of 2.05. The design of experiments methodology was used on the one hand to detect the influential factors and on the other hand to optimize the elimination of this dye. Thus, in a first approach six factors (pH of the solution, mass of activated carbon, temperature, and concentration of the solution, stirring time and stirring speed) were used when using the Hadamard matrix. This showed that only three parameters, the mass of adsorbent, the concentration of the solution and the stirring time actually have an influence on the response. The results of the full two-level factorial design showed that the maximum removal rate of Black Remazol is 96.67 % under the conditions of stirring a solution with a concentration of 10 mg/L of this dye with a mass of adsorbent of 0.3 g for 20 minutes

Validation of HPLC-UV Patulin Determination Method in Traditional Juices From Côte d’Ivoire

Object: The need to reduce dietary mycotoxins exposure, requires development of efficient analytical methods to assess mycotoxins level in food. The purpose of this study was to validate HPLC-UV method for patulin determination in traditional juices made of dry Guinea sorrel flowers or ginger rhizomes. Material and Methods: Patulin was extracted with ethyl acetate and purified with sodium bicarbonate solution (14 g/L). Elution of patulin was realised in isocratic mode with mobile phase consisting of acetonitrile-water (10/90 : v/v). Patulin was detected at 276 nm (UV). An amount of patulin was added to neutral portions of juices and the recovery rates were estimated after extraction. Results: The retention time was 5.03 min and the coefficient of determination of the calibration range (100 - 1500 μg/L) was 0.9994. Detection and quantification limits were respectively 1.4 μg/L and 4.6 μg/L for the two matrices. The recovery rates were 75.09 ± 0.27% and 75.27 ± 0.64% respectively for ginger and Guinea sorrel juices. Patulin was detected in 55% of ginger juice and 70% of Guinea sorrel juice. Patulin contents of 15% of ginger juice and 40% of Guinea sorrel juice were above the maximum level of patulin (50 μg/L) allowed in juices. Conclusion: This method may be used for patulin detection in these traditional juices because its recovery rates were acceptable and limit of quantification (4.6 μg/L) was largely bellow the maximum level of patulin (50 μg/L) allowed in juices. &nbsp

Aldicarbe et crimidine dans les eaux et les sédiments aux alentours de la décharge municipale d’Akouédo (Abidjan, Côte d’Ivoire): niveaux et fréquences de contamination

En Afrique, plusieurs familles de pesticides, susceptibles de nuire à la santé de l’homme et de l’environnement, sont utilisées contre les pestes et autres nuisibles. Cependant, la plupart des études menées se sont focalisées sur les organochlorés. La fréquence de détection et les concentrations des pesticides aldicarbe et crimidine ont été examinées dans les eaux et les sédiments autour de la décharge municipale d’Akouédo (Côte d’Ivoire). Les analyses ont été effectuées de juin 2013 à janvier 2014 par chromatographie liquide à haute performance couplée à la méthode de détection par fluorescence, après une extraction liquide/liquide des eaux, et une extraction au soxhlet des sédiments. Les résultats ont montré une contamination significative des sédiments par l’aldicarbe et la crimidine à des fréquences de détection très élevées, contrairement aux eaux lagunaires et souterraines. Les concentrations ont été significativement plus élevées pendant la saison des crues dans les eaux et pendant la saison des pluies dans les sédiments. Ces résultats suggèrent que la crimidine est utilisée ou rejetée de façon illégale dans la zone d’étude, et que les niveaux de concentration de la crimidine et de l’aldicarbe dans la baie de M’Badon peuvent causer des risques de santé pour certains organismes aquatiques et les populations.© 2016 International Formulae Group. All rights reserved.Mots clés: Pesticides; lixiviat, estuaire, lagune Ebrié, Côte d’IvoireEnglish Title: Aldicarb and crimidine in waters and sediments in the vicinity of the Akouédo municipal dumping site (Abidjan, Cote d’Ivoire): concentrations and detection frequenciesEnglish AbstractThe impact of pesticides on environmental quality is of great concern in many developing countries. However, data on pesticide contamination levels in African estuaries has mainly focused on organochlorine compounds, although some among other pesticide families are able to persist in water for several days and pose toxicological risks to humans and wildlife. This study assessed the detection frequency and concentration levels of aldicarb and crimidine residues in waters and sediments (from leachate, pits, and M’Badon Bay) around the municipal dumping site of Akouédo (Abidjan, Ivory Coast). Samples were analyzed by the HPLCfluorescence detector method after liquid/liquid and soxhlet extractions of waters and sediments, respectively, from June 2013 to January 2014. The results showed significant contamination of sediments by the aldicarb and the crimidine, with detection frequencies up to 100% during the wet season. The highest pesticide concentrations in waters and sediments were observed during the flooding season and the wet season, respectively. The aldicarb and crimidine concentrations were significantly higher in sediments than waters, although they are highly soluble in water. The results suggest that the crimidine is illegally used or disposed of in Abidjan area, and that aldicarbe and crimidine concentration levels could pose health risks to biota.© 2016 International Formulae Group. All rights reserved.Keywords: Pesticides; leachate, estuary, Ebrié Lagoon, Ivory Coas