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In this work, activated carbons (ACs) prepared by chemical activation of garcinia cola nut shell impregnated with H 3 PO 4 (CBH 2/1) and KOH (CBK 1/1) were used to study the kinetics, equilibrium and thermodynamics of the adsorption of thymol blue from aqueous solution. The characterization of ACs showed the BET measurements gave surface area and total pore volume respectively of 328.407 m 2 •g −1 and 0.1032 cm 3 •g −1 for CBH 2/1 and 25.962 m 2 •g −1 and 0.03 cm 3 •g −1 for CBK 1/1 ; elemental analysis showed a high percentage of carbon in both ACs. Influence of parameters such as initial pH, contact time, adsorbent mass, initial concentration, ionic strength and the effect of temperature on the removal of thymol blue from aqueous solution were studied in batch mode. The studies showed that equilibrium adsorption was attained after 60 minutes for the two ACs, adsorption capacity increased with increasing concentration of thymol blue, and maximum adsorption capacity was obtained at an acidic environment with pH 2. Avrami's non-linear kinetic expression was the best suited for describing the adsorption kinetics of thymol blue onto ACs, while equilibrium data showed that the three-parameter isotherms better described the adsorption process since R 2 > 0.96, and the error functions were lowest for all of them.

The removal of amaranth red dye from aqueous solution by untreated and treated pineapple peelings and coconut shells with phosphoric acid was studied in batch mode at room temperature. The study highlighted several parameters such as the contact time, the mass of the adsorbent, the pH of the solution, and the initial concentration of the dye. The results showed that the removal of dyes by the bioadsorbents depended on the pH and the initial concentration of the adsorbate. The adsorption capacity increased with increasing amaranth red dye concentration and the mass of the bioadsorbent. It was also established that maximum adsorption took place at pH = 2 for different adsorbents. The treated raw materials have greater surface area than the untreated materials. In order to deduce the adsorption mechanism, four simplified kinetic models were investigated. The kinetic data were well represented by the pseudo second order kinetic model giving high correlation coefficients R² values for all the biosorbents suggesting that chemisorption was the rate determining step. An equilibrium study of the adsorption process also showed that the Langmuir model best described the adsorption on all the biosorbents. The values of energy obtained from the Temkin isothermare also positive, this shows that the adsorption process isexothermic. These results indicate that pineapple peelings and coconut shells have a high potential as adsorbents for removing amaranth red dye from aqueous solution

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Abstract:Cameroon is one of the six countries of Central Africa with more than 20 000 000 residents. To characterize the Cameroon research performance, Cameroonians publications in the Science Citation Index Expanded during the period of 1936-2015, indexed in the Thomson Reuters SCI-EXPANDED database, were studied in this work. All documents of that period with Cameroon in the address field were included in the study. The document type, language, trend and collaborations were analyzed, as well as the output of different subject categories. Performances of countries, institutions and authors, including total, single, collaborative, first author, and corresponding author publications were also analyzed. Articles were analyzed by the scientific output and research performances of individuals, institutions and collaborative countries with Cameroon. Analyses included 8 457 articles (85 % of 10 591 Cameroonian publications). These bibliometric analyses of Cameroonian publications provided interesting insights concerning authors, institutions and collaboration patterns. Results showed that research in Cameroon was highly dependent on foreign collaborations, and the international collaboration was responsible for the increasing number of publications over the years. It was found that the articles with either first authors or corresponding authors from outside Cameroon got more citations than the others, and that the articles without any international collaboration had lower citations. The number of articles indexed by SCI-EXPANDED has seen an increase in terms of Cameroonian articles that is considerably greater that the increase in number of all articles in SCI-EXPANDED. Articles were more frequent than other types of publication and they were mostly in English. The University of Yaoundé I ranked top one in inter-institutionally collaborative articles, the rank of the total inter-institutionally collaborative articles, and the rank of first author articles and corresponding author articles. The University of Yaoundé I also was in an absolute leading position from 1970s to 2015, followed far away by the other institutions. The categories of tropical medicine, plant sciences, environmental and occupational public health, and infectious diseases, represented the largest number of published articles. Even though physics and chemistry dominated the ranking of the top 20 best Cameroonian authors, an independent mathematics article was the most cited, with 60 citations in 2015 to a Cameroonian author. The top three productive researchers were T. C. Kofane, B. T. Ngadjui, P. Woafo, all from University of Yaoundé I. France and the USA dominated the ranking of countries with strong scientific collaboration with Cameroon. Rev. Biol. Trop. 65 (4): 1582-1591. Epub 2017 December 01.

In this study, shea residues (Vitellaria paradoxa) dumped in the wild by the units processing almonds into butter were used in the production of activated carbons. Shea nut shells harvested in the locality of Baktchoro, West Tandjile Division of Chad were used as a precursor for the preparation of activated carbons by chemical activation with phosphoric acid (H 3 PO 4) and sulphuric acid (H 2 SO 4). Central Composite Design (CCD) was used to optimize the preparation conditions, and the factors used were concentration of activating agent (1-5 M), carbonization temperature (400˚C-700˚C) and residence time (30-120 min). The studies showed that at optimal conditions the yield was 51.45% and 42.35%, while the iodine number (IN) was 709.45 and 817.36 mg/g for CAK-P (phosphoric acid activated carbon) and CAK-S (sulphuric acid activated carbon) respectively. These two activated carbons (ACs) which were distinguished by their considerable iodine number, were variously characterized by elementary analysis, pH at the point of zero charge (pHpzc), bulk density, moisture content, Boehm titration, Fourier transform infrared spectroscopy, BET adsorption and scanning electron microscopy. These analyses revealed the acidic and microporous nature of CAK-P and CAK-S carbons, which have a specific microporous surface area of 522.55 and 570.65 m 2 •g −1 respectively.

Biochar and ferromagnetic biochar obtained from the pyrolysis of dried mango seeds and modified using a hydrothermal method were used as catalyst for the heterogeneous degradation of indigo carmine in an aqueous medium. These prepared biochars were characterized using different techniques: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The analyses of the results revealed the presence of iron oxide in the form of magnetite (Fe3O4) in the catalyst. The catalytic tests carried out with this composite material showed a significant degradation of indigo carmine. The maximum degradation of indigo carmine in the aqueous solution was reached after 240 min of agitation. The Fenton degradation process using irradiation with a 100 W electric lamp and hydrogen peroxide (concentration 4 mol/L) showed the best results at pH = 3. From this study, it emerged that the second-order kinetic model better described the degradation process, and it gave lower half-lives compared to those obtained with the first-order kinetic law. The study also showed that ferromagnetic biochar could be prepared from mango seeds and used for the degradation of indigo carmine in an aqueous solution.

Olives stones and cotton cakes have been investigated as a cheap and available precursor used for the production of novel carbon using potassium hydroxide as chemical activating agent with 2:1 impregnation ratio at 1.5 M KOH. Carbonization was performed at 450°C for one hour. The activated carbons NOK and MK3 were characterized by Iodine Number, Fourier Transform Infrared (FTIR) spectroscopy, EDX Analysis, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) Analysis and Proximate Analysis (pH ZCN , pH, volatile matter, fixed carbon). The effects of initial sorbate concentration and contact time on adsorption were evaluated. Errors analysis methods were used to evaluate the experimental data: Correlation coefficient (R 2), chi-square (χ 2), average relative error (ARE), sum of absolute errors (EABS) and root mean square error (RMSE) values were tested to find the best fitting isotherm. Elovich models provide the best fit in the uptake of 2,4-dinitrophenol by activated carbons NOK and MK3. Thus, among the isotherm models studied, it appears that the Dubinin-Radushkevich and Temkin (two parameters), Sips (three parameters) and Baudu (four parameters) models describe better the adsorption data. Error analysis showed that the models with two parameters better described the adsorption of 2,4-diniphenol data compared with the three parameter and fourparameter models.