CI
Chargé de Cours
Activité scientifique
Profil chercheur
Enseignant-chercheur à l’Université de Yaoundé I. Grade : Chargé de Cours.
Publications scientifiques
Cyrille Djoko Mbiagaing, Gaëlle Ngnie, Gustave Kenne Dedzo, Emmanuel Ngameni
Applied Catalysis A General
Anselme Junior Tagne, Līva Dzene, Laure Michelin, Ludovic Josien, Séverinne Rigolet, Gustave Kenne Dedzo et 1 autre(s)
Electroanalysis
Considering the environmental and health issues caused by glyphosate, a controversial nonselective herbicide widely used, the development of reliable quantification methods to monitor the concentration of this compound in natural environments is of critical importance. In this work, a carbon paste electrode modified by functionalized saponite clay mineral was applied for the first time for the direct quantification of glyphosate. The grafting of the organophilic cationic silane (dimethyloctadecyl[3‐(trimethoxysilyl)propyl]ammonium chloride) was promoted by the highly charged synthetic saponite layers. The characterizations of the organohybrid saponite by Fourier transformed IR (FTIR) and solid state 29 Si NMR spectroscopies confirmed the grafting of the silane while X‐ray diffraction (XRD) analysis revealed the non‐intercalation of the silane in the interlayer space. This surface functionalization resulted in minor modification of the morphology of the saponite particles as observed on the scanning electron microscope (SEM) images. When the functionalized saponite was used as the electrode modifier, the presence of silane increased the glyphosate signal intensity while decreasing the peak potential, certainly through favorable organophilic and electrostatic interactions between the functionalized clay mineral and the negatively charged pesticide. Under optimal experimental conditions (7 %wt in carbon paste and pH of the solution of 8) and for glyphosate concentrations in the range 5 to 60 µM, a detection limit of 0.12 µM was obtained. Excepted for Cu 2+ , which strongly interferes with the glyphosate signal, the other chemical species investigated (Al 3+ , Ca 2+ , Mg 2+ , and paraquat) poorly affect the pesticide detection. Furthermore, this sensor was successfully applied for the quantification of glyphosate in well water, with a recovery higher than 95%.
Ruth Valerie Ngnokam Nkouonga, Gaëlle Ngnie, Hervé L. Tcheumi, Jordan Jeazet Fouelefack, Cyrille Djoko Mbiagaing, Gustave Kenne Dedzo et 1 autre(s)
New Journal of Chemistry
The recycling of bio-sourced materials derived from forest exploitation and agriculture, in several applications including bioenergy production with less environmental footprint is an actual concern. In the present work, a...
Claudia Mafopa Lontchi, Hervé L. Tcheumi, Gustave Kenne Dedzo, Emmanuel Ngameni
Electroanalysis
Environmental pollution by heavy metals such as Cu(II) and Pb(II) is recognized as a major public health issue. Considering that these two heavy metals are generally present simultaneously in the same polluted environments, the development of fast, robust, and cost‐effective analytical tools for their simultaneous quantification is of considerable importance. In this study, a composite material (MgAl‐RB5) obtained by the modification of a MgAl‐layered double hydroxide (LDH) by an anionic dye (Reactive Black 5 (RB5)) was synthesized and used as a glassy carbon electrode modifier, applied for the simultaneous electrochemical detection of Pb(II) and Cu(II). The presence of the dye adsorbed onto the LDH (0.23 mmol g −1 ) and the affinity of the hybrid material for cationic compounds were highlighted by physicochemical (FTIR, TGA, BET‐specific surface area, and SEM) and electrochemical characterizations. The electrochemical signals of Cu(II) and Pb(II) at the glassy carbon electrode were improved in the presence of MgAl‐RB5 at the electrode surface due to the accumulation of these metal cations through complexation with the immobilized dye molecules. After optimization of some key experimental parameters (pH of the accumulation solution, deposition potential, nature of electrolytic solution, and accumulation times), limits of detection of 5.2 nM (1.08 µg L −1 ) and 8.1 nM (0.51 µg L −1 ) were obtained for Pb(II) and Cu(II), respectively, in the concentration range 0.1–8 μM. The sensor displayed good efficiency in several tested environmental samples, confirming tested and confirmed its potential use for the simultaneous detection of Cu(II) and Pb(II) in environmental pollution monitoring.
Sarrah Sonita Poungoue Hanga, Arlette Danelle Djitieu Deutchoua, Morel Brinda Medonjeu Ntanhaning, Gustave Kenne Dedzo, Emmanuel Ngameni
Electroanalysis
Considering the importance of antioxidants in food and medical industries, the accurate evaluation of their reactivity is of capital importance. In this work, a new electrochemical approach based on the cupric reducing antioxidant capacity (CUPRAC) is proposed for the accurate evaluation of antioxidant properties. The electrochemical behavior of the complex ([Cu(Nc) 2 ] 2+ ) obtained from the reaction between copper(II) and neocuproine (Nc) used in the CUPRAC method was studied to identify the ideal Cu/Nc molar ratio. The Cu/Nc ratio of 4/3, usually used in the CUPRAC method, was not suitable because of the partial reaction of Nc with Cu(II). A more appropriate Cu/Nc molar ratio of 1/7 was experimentally determined by voltammetry at a stationary or rotating electrode. With this molar ratio, [Cu(Nc) 2 ] 2+ presents a fast and monoelectronic system controlled by diffusion. This allowed antioxidant properties determination by chronoamperometry, by following the [Cu(Nc) 2 ] 2+ reduction current as a function of the tested antioxidant. Ascorbic acid and Trolox used in this study as model antioxidants showed inhibition concentrations values (IC 50 ) very close to the expected theoretical values. These results are proof that the developed electrochemical method is accurate and allows a fast and efficient evaluation of antioxidant properties while minimizing interferences encountered using spectrophotometric methods.
Raïssa Siegnin, Cyrille Djoko Mbiagaing, Līva Dzene, Loı̈c Vidal, Gustave Kenne Dedzo, Emmanuel Ngameni
Applied Clay Science
Gaëlle Ngnie, Rock Ambela Atangana, Grace Ingrid Tomou-Mbahim, Lionel Magellan Sambang, Gustave Kenne Dedzo, Hervé Kouamo Tchakouté et 2 autre(s)
RSC Applied Interfaces
Favorable interactions between alkaline treated sawdust and metakaolin/sodium waterglass geopolymer matrix, with substantial improvement of compressive strength and cations adsorption.
Baudelaire Matangouo, Gustave Kenne Dedzo, Līva Dzene, Ludovic Josien, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Journal of Physics and Chemistry of Solids
Yannick Ngueumaleu, Arlette Danelle Djitieu Deutchoua, Sarrah Sonita Poungoue Hanga, Rossel Wendji Liendji, Gustave Kenne Dedzo, Emmanuel Ngameni
Physical Chemistry Chemical Physics
in acetonitrile, the disproportionation was much slower. These preliminary results are proof that many chemical species are likely to react with DPPH and indirectly induce sources of bias during its application, especially when evaluating antioxidant properties.
Cyrille Djoko Mbiagaing, Anselme Junior Tagne, Gaëlle Ngnie, Gustave Kenne Dedzo, Emmanuel Ngameni
New Journal of Chemistry
Successful chemical and electrochemical catalytic reduction of 4-chloro-2-nitroaniline onto palladium nanoparticle supported organo-kaolinite.
Bruno Boniface Nguelo, Urtrich Sandjon Nganji, Yvana Rusca Kamgue Yami, Gustave Kenne Dedzo, Emmanuel Ngameni
Clays and Clay Minerals
Abstract Methoxykaolinite is a very popular organo-modified kaolinite. Even though it has a number of interesting properties, this nanohybrid material is still underused in terms of practical applications. In the present study, methoxykaolinite was synthesized and used for the first time as an electrode modifier for Pb(II) determination in various aqueous media. X-ray powder diffractometry (XRD), 13 C nuclear magnetic resonance (NMR), and Fourier-transform infrared (FTIR) spectroscopy were used as characterization tools to confirm the presence of grafted methoxy groups in the interlayer space of kaolinite. The electrochemical characterization of methoxykaolinite using the cationic probe Ru(NH 3 ) 6 3+ showed that the modified clay presents favorable interactions with cationic compounds. A methoxykaolinite-modified electrode was applied successfully to the quantification of Pb(II) in aqueous solution. At optimized experimental conditions, the calibration curve in the concentration range 0.025–0.3 μM showed excellent linearity (R 2 > 0.99), a sensitivity of 3.36 μA μM –1 , and a detection limit of 5.6 nM. This detection limit was 10 times lower than the minimum concentration of Pb(II) authorized in drinking water. The sensor was used also for the determination of Pb(II) in tap, river, and well water samples with only minor loss of sensitivity and recoveries (90±5% to 110±4%). Thanks to the excellent biocompatibility of kaolinite, the sensor was applied for Pb(II) detection in human urine. Recovery in the range 98±8% to 103±6% was obtained when three freshly collected urine samples were spiked with known amounts of Pb(II). These results showed the interesting potential of methoxykaolinite as an electrode modifier for trace-level detection of cations, even in biological samples.
Baudelaire Matangouo, Gustave Kenne Dedzo, Līva Dzene, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Applied Clay Science
Gustave Kenne Dedzo, Séverinne Rigolet, Ludovic Josien, Emmanuel Ngameni, Līva Dzene
Applied Surface Science
Gaëlle Ngnie, Gustave Kenne Dedzo
Applied Clay Science
Bruno Boniface Nguelo, Mérimée Fotio Fomat, Gustave Kenne Dedzo, Emmanuel Ngameni
Electroanalysis
Abstract A gold electrode modified by a thin film of cationic kaolinite was used for the electrochemical detection of iodide in aqueous solution in the presence of thiosulfate. At gold electrode, iodide showed two electrochemical systems in the potential range explored (0.10 V to 0.85 V). The pH‐independent system was assigned to the redox couple I 2 /I − and the pH‐dependent one assigned to the redox couple HIO/ . For increased amount of thiosulfate the oxidation peak intensity of the first system increases sharply followed by the gradual decrease of the reduction peak, due to the chemical reaction between thiosulfate and oxidized iodide. The calibration curve in the presence of excess thiosulfate resulted in an increase of the sensitivity by a factor of 7. To improve this sensitivity, the bare gold electrode was coated by a thin film of an anionic exchanger kaolinite, obtained by grafting the ionic liquid (1‐(2‐hydroxyethyl)‐4‐(tert‐butyl) pyridinium chloride). Accumulation‐detection method yielded a spectacular increase of the oxidation peak current of iodide in the presence of thiosulfate ions. At optimized experimental conditions, a sensitivity of 2.45 μA.μM −1 and a detection limit of 65 nM were obtained. The method was successfully applied for total iodine determination in povidone−iodine formulation.
Beaufils Ngatchou Ngana, Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Electroanalysis
Abstract Because of its chemical properties, sawdust displays poor anionic exchange capacity. Here we demonstrate that sawdust modification with methylene blue (MB) dye represents an interesting and facile alternative to render this natural biomaterial capable to accumulate anionic species. MB adsorption onto sawdust was monitored by cyclic voltammetry and experimental parameters carefully optimized. Under the ideal experimental conditions (composition of accumulation and desorption solution, accumulation and desorption time and the nature of the electrolytic solution), the adsorbed MB showed poor mobility, which results in the absence of the characteristic electrochemical signal of MB. The ability of the material to accumulate anionic species was thus evaluated using Fe(CN) 6 3− as a model anions. The slow Fe(CN) 6 3−/4− system recorded onto the electrode modified by pristine sawdust (P/SFE) become fast and reversible after immobilization of MB onto P/SFE (MB/SFE). Electrochemical impedance spectroscopy confirms this result through the spectacular decrease of charge transfer resistance after MB adsorption (from 83 kΩ on P/SFE to 637 Ω on MB/SFE). MB/SFE was applied to the electroanalysis of nitrites and a sensitivity of 7.4 μA mM −1 was obtained. Although this sensitivity was less important compared to that obtained on glassy carbon electrode (9.4 μA mM −1 ), the dye modified electrode displays by far the best reproducibility even at higher nitrite concentration.
Mateus R. Lage, Gustave Kenne Dedzo, Stanislav R. Stoyanov, WenJuan Huang, Sergey Gusarov, José Walkimar de M. Carneiro et 2 autre(s)
The Journal of Physical Chemistry C
Nonaqueous extraction is an attractive alternative to the currently employed warm water process for extraction of bitumen from oil sands, as it could use less energy and water. Hydroxylated cosolvents, such as alcohols, that compete for the adsorptive clay surfaces and help release bitumen components could help improve bitumen recovery. The water naturally present in oil sand also affects oil–mineral interactions. Electronic structure methods and the statistical-mechanical 3D-RISM-KH molecular theory of solvation as well as experimental desorption measurements are employed to study the effects of water and aliphatic alcohol cosolvents in toluene solvent on the desorption of fused pyridinic heterocycles (ArN) from kaolinite. The geometries of phenanthridine and acridine (representative of pyridinic heterocycles of petroleum asphaltenes) adsorbed on the kaolinite clay surface are optimized in periodic boundary conditions using density functional theory. The 3D-RISM-KH method is employed to calculate the solvation free energy and potential of mean force for adsorption of the heterocycles on kaolinite in pure and alcohol-containing toluene. The potentials of mean force show that the adsorption of the fused pyridines on kaolinite is stronger in pure toluene than in toluene mixed with aliphatic alcohol. Analysis of the mechanism of desorption of phenanthridine and acridine from kaolinite in toluene containing alcohol reveals that the alcohol stabilizes both the pyridinic moiety and kaolinite platelet by hydrogen bonding, thus disrupting the ArN···HO–Al(kaolinite) hydrogen bond. A mechanism for retention of toluene on kaolinite is also highlighted. Experimental studies of the desorption of fused pyridines from an ArN–kaolinite aggregate show that in water-saturated toluene the rate of desorption of the phenanthridine from kaolinite is twice as high as that in dry toluene. The experimental and computational results show that water and aliphatic alcohols in toluene help desorb pyridinic heterocycles from kaolinite, a clay mineral abundant in the oil sands. The presented insights are valuable for understanding the molecule-clay interactions in solution and relevant to improving the nonaqueous extraction of bitumen from oil sand.
Gustave Kenne Dedzo, Christian Detellier
Materials
Functionalization of the kaolinite (K) interlayer space is challenging. In this work, a new kaolinite-based nanohybridmaterial (K-NI) was successfully synthesized by grafting on the interlayer aluminol surfaces the ionic liquid, 1-(1-methylnaphthyl)-3-(2-hydroxyethyl) imidazolium chloride (NI), using a guest displacement strategy. A substantial increase of the basal spacing (10.8 Å) was obtained. This is a grafted derivative of kaolinite possessing one of the largest d-values. Washing in water for several days and other vigorous treatments such as sonication showed a minor effect on the integrity of the material. FTIR and 13C NMR confirmed the conservation of the structure of the ionic liquid after the grafting. Thermal analysis confirmed the presence of grafted material and was used to estimate the abundance of the grafted ionic liquid (0.44 mole per mole of kaolinite structural formula, (Al2Si2O5(OH)4)). By using cyclic voltammetry, the permeability of a film of K-NI for the bulky ferricyanide ions was demonstrated. The accumulation of nitrophenolate anions was effective (maximum capacity of 190 μmol/g), but was less important than what was expected due to the steric hindrance of the bulky grafted NI. Although the presence of chloride anions reduced the adsorption capacity, the affinity of the modified kaolinite interlayer space for the nitrophenolate anions was demonstrated.
Gustave Kenne Dedzo, Christian Detellier
Advanced Functional Materials
Abstract Clay minerals, whose world resources are extremely large, have the potential to be more exploited as the basis for functional materials. Of interest are their interactions with ionic liquids (ILs). These compounds have found a large number of applications in the last few decades due to unique properties, such as low vapor pressure, high thermal stability, and remarkable solvation abilities. In the case of the swelling smectites, the organic cation of ILs can replace interlayer cations and find applications in the preparation of nanocomposites. This feature article is mainly focused on kaolinite, a nonswelling 1:1 phyllosilicate, whose layers are essentially neutral. Consequently, the intercalation of ILs involves both cation and anion. The organic cations can be designed to bear hydroxyl groups that will react with the aluminol internal surface of kaolinite, resulting in ionic liquids not only intercalated but also grafted. The resulting nanohybrid materials are characterized by a fixed, rigid, constrained 2D structure, whose dimension can be tuned by the size of the organic cation, whereas the anion is exchangeable. These materials are used for sensing applications such as the specific detection of anions as well as their quantitative analysis. They are also used as catalyst support for nanoparticles.
Gustave Kenne Dedzo, Christian Detellier
Applied Clay Science
Gustave Kenne Dedzo, Gaëlle Ngnie, Christian Detellier
ACS Applied Materials & Interfaces
The synthesis of selectively deposited palladium nanoparticles (PdNPs) inside tubular halloysite lumens is reported. This specific localization was directed by the selective modification of the aluminol surfaces of the clay mineral through stable Al-O-C bonds. An ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium) was grafted onto halloysite following the guest displacement method (generally used for kaolinite) using halloysite-DMSO preintercalate. The characterization of this clay nanohybrid material (XRD, NMR, TGA) showed characteristics reminiscent of similar materials synthesized from kaolinite. The grafting on halloysite lumens was also effective without using the DMSO preintercalate. The presence of these new functionalities in halloysite directs the synthesis of uniform PdNPs with size ranging between 3 and 6 nm located exclusively in the lumens. This results from the selective adsorption of PdNPs precursors in functionalized lumens through an anion exchange mechanism followed by in situ reduction. In contrast, the unmodified clay mineral displayed nanoparticles both inside and outside the tubes. These catalysts showed significant catalytic activity for the reduction of 4-nitrophenol (4-NP). The most efficient catalysts were recycled up to three times without reducing significantly the catalytic activities.
Gustave Kenne Dedzo, Christian Detellier
Apple Academic Press eBooks
The concept of chemical reaction involves direct contact between chemical species to promote the formation of new chemical bonds and new chemical compounds. Therefore, this implies a surface contact as large as possible to obtain optimum yields. When the reactor size is reduced at the nanolevel, molecules are in contact in a restricted space. This substantially increases the probability of contact between them. In some cases these nanoreactors provide specific environments in which chemical reactions could take place selectively. These environments can also promote chemical reactions otherwise unfavoured (Shchukin and Sviridov, 2006). Such devices minimize the energy consumption if one considers the increase of yields and the significant reduction of external inputs to facilitate chemical reactions. Such environments created by microemulsions (using block copolymers and other amphiphilic chemical compounds) are used classically (Jang and Ha, 2002), but they are limited by their lower stability. Mesoporous silica and zeolites are also used. These are characterized by pores of well-defined sizes whose internal surfaces may in some cases be functionalized (especially mesoporous silicas), or modified by metal nanoparticles in order to perform specific reactions (Salavati-Niasari, 2009; Fang et al., 2012). Unlike microemulsions or micelles, materials allow reactions in extreme environments due to their better physicochemical stabilities.
Charles Baudouin Njine-Bememba, Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Holzforschung
Abstract Sawdust samples of ayous wood ( Triplochiton scleroxylon ) have been submitted to a warm pretreatment with NaOH and functionalized in dimethylformamide (DMF) by grafting with two amino organosilanes. The reagents were chosen for their ability to bind hydronium ions in acidic medium: 3-aminopropyltriethoxysilane (APTES) and 3-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS). The resulting materials were characterized by Fourier transform infrared (FTIR) and 13 C nuclear magnetic resonance (NMR) spectroscopies, which revealed the Si-O-C covalent bond and the polymerization of the grafted silanes through siloxane bridges (Si-O-Si) leading to the stabilization of the structure. The cyclic voltammetry analyses were performed on a glassy carbon modified with native or functionalized sawdust films in contact with electrochemical probes ([Fe(CN) 6 ] 3- and [Ru(NH 3 ) 6 ] 3+ ). By means of this method, the permselectivity and accumulation capacity of these functionalized materials could be evaluated. The presence of silanes in the functionalized sawdust leads to a progressive accumulation of anionic species, while the cationic species were repelled when the solution is gradually acidified.
Jonathan Fafard, Olga Lyubimova, Stanislav R. Stoyanov, Gustave Kenne Dedzo, Sergey Gusarov, Andriy Kovalenko et 1 autre(s)
The Journal of Physical Chemistry C
Current oil sand mining operations in the Athabasca basin are predominantly aqueous-based. Extracts containing large amounts of fines lead to the formation of stable organoclay suspensions in froths giving lower yields and greater tailing wastes and making the development of more efficient extraction methods desirable from both economical and environmental perspectives. We examine an indole-kaolinite system as a model for these oil fines and their resistance to washing in nonaqueous solvents. The prepared organoclays show indole loading exclusively on the external surface of the clay. Micron-scaled vermicular structures, similar to natural kaolinite, are observed. Their formation is believed to be driven by strong adsorbate–adsorbate interactions. Indole is the primary adsorbate, as solvent adsorption is shown to be minimal based on both experimental and computational results. Isotherms are constructed and parameters calculated from linear regression analysis fitted to the Brunauer–Emmett–Teller equation. Monolayer quantities calculated match well to the theoretical amount calculated from surface areas measurements. Washing the organoclays with both toluene and isopropanol results in a 50% decrease of loaded organic material, leaving a monolayer equivalent of organic matter. The statistical-mechanical 3D-RISM-KH molecular theory of solvation is employed to perform full sampling of solvent orientations around a kaolinite platelet and gain insights into the preferred orientation and adsorption thermodynamics of indole on kaolinite in toluene and heptane solvents. In its preferred orientation, indole is hydrogen-bonded to one or two O atoms at the aluminum hydroxide surface of kaolinite. The calculated solvation free energy and potential of mean force for adsorption of indole and solvents on kaolinite in solution yield the increasing adsorption strength order of heptane < toluene < indole on the aluminum hydroxide surface. Multilayer adsorption profiles are predicted based on the integrated three-dimensional distribution functions of indole, toluene, and heptane.
Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Talanta
Gustave Kenne Dedzo, Christian Detellier
The Analyst
A nanohybrid kaolinite material with anion exchange properties was obtained by the grafting of an ionic liquid in the interlayer spaces of kaolinite. It was used successfully for the amperometric detection of iodide in aqueous solution and tap water after a pre-concentration step, with a detection limit of 1.5 × 10(-7) M. This electrode has an excellent stability. Its selectivity was tested in the presence of several anions.
Charles Péguy Nanseu‐Njiki, Gustave Kenne Dedzo, Emmanuel Ngameni
Journal of Hazardous Materials
Cyrille Djoko Mbiagaing, Rolland Tchoumene, Arlette Danelle Djitieu Deutchoua, Sarrah Sonita Poungoue Hanga, Gustave Kenne Dedzo, Emmanuel Ngameni
ACS Applied Nano Materials
Encapsulation of chemical compounds in reservoirs to prevent degradation and for controlled release is of capital importance in various domains, such as healthcare and food industry. In this work, kaolinite and tubular halloysite clay minerals functionalized by interlayer grafting of an ionic liquid (1-methylnaphthyl-3-(2-hydroxyethyl) imidazolium chloride) were used for the encapsulation of caffeic acid (CA). As shown by the characterization methods (XRD, solid-state 13 C NMR, FTIR, TGA), the initially neutral layers of these clay minerals turned cationic following the grafting of the organic cation, and the resulting structural charge was compensated by exchangeable chloride anions. The anion exchange capacity of these nanohybrid materials was successfully exploited for the encapsulation of CA in its anionic form. Functionalized halloysite showed CA adsorption capacity (230.9 μmol/g) 2-fold higher than functionalized kaolinite (123.3 μmol/g), certainly due to the accumulation of the phenolic compound both in the interlayer space and inside the halloysite tubes. When studying the release of CA in phosphate buffer medium, a slow release was observed, assigned to the high retention of phenolic compounds within the modified clay minerals through hydrogen-bonding and van der Waals interactions. The study of the effect of the phosphate buffer concentration highlighted the release mechanism following ionic exchange between anionic CA and phosphate anions. Moreover, the antioxidant properties of the encapsulated CA (evaluated by the DPPH assay) were effective. The kinetic curve displayed slow antioxidant properties that can be exploited for the long-term protection of a medium against oxidation.
Charles Baudouin Njine-Bememba, Patrick Marcel Seumo Tchekwagep, Beaufils Ngatchou Ngana, Craig E. Banks, Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki et 1 autre(s)
International Journal of Environmental & Analytical Chemistry
Synthetic dyes, widely used in textile industries, pose serious environmental threats due to their toxicity and persistence in water systems. Addressing this issue with cost-effective, sustainable adsorbents is vital, and Ayous sawdust, an abundant wood waste in Central Africa, presents a promising biosorbent alternative. This study explores the chemical modification of Ayous sawdust (Triplochiton scleroxylon) to enhance its adsorption properties for methylene blue removal and its application in electrochemical sensing. Methylene blue was used as a model compound because of its good adsorption by lignocellulosic matrix and its well-known electrochemical behaviour. The sawdust was subjected to alkaline treatment followed by grafting with mercaptopropyltriethoxysilane (MPTMS) to introduce thiol functional groups. Characterisation by FTIR, NMR spectroscopies, and elemental analysis confirmed successful functionalisation, with a significant increase in sulphur content for the modified material. Adsorption studies showed that alkaline-treated sawdust exhibited a higher removal efficiency (75.14 mg.g−1) than pristine sawdust (66.30 mg.g−1), while thiolated sawdust, despite its strong affinity for methylene blue, displayed lower adsorption capacity (45.56 mg.g−1) due to the reduced accessibility of active sites linked to its high hydrophobicity, which limits its practical application as shown on proposed adsorption mechanisms. Electrochemical application demonstrated that sawdust-modified carbon paste electrodes enhanced electron transfer kinetics, with alkaline-treated sawdust providing the most stable and sensitive detection (LOD = 40.1 pmol.L−1) than the native sawdust (LOD = 47.2 pmol.L−1). The sensors showed good performance in real water samples, with minimal signal degradation in the presence of competing ions. These findings highlight the potential of alkaline-treated sawdust as an efficient and cost-effective adsorbent and electrochemical sensor modifier for methylene blue detection.
D N J Njipnang, Cyrille Djoko Mbiagaing, Anselme Junior Tagne, Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
International Journal of Environmental Science and Technology
Lionel Magellan Sambang, Gustave Kenne Dedzo, Emmanuel Ngameni
Journal of Molecular Liquids
Anselme Junior Tagne, Līva Dzene, Laure Michelin, Ludovic Josien, Séverinne Rigolet, Gustave Kenne Dedzo et 1 autre(s)
Journal of Physics and Chemistry of Solids
Cyrille Djoko Mbiagaing, Gustave Kenne Dedzo, Emmanuel Ngameni
Applied Clay Science
Arlette Danelle Djitieu Deutchoua, Yannick Ngueumaleu, Rossel Wendji Liendji, Sarrah Sonita Poungoue Hanga, Bruno Boniface Nguelo, Gustave Kenne Dedzo et 1 autre(s)
RSC Advances
. The reaction mechanism proposed follows complex steps involving two competing phenomena: a disproportionation which accelerates the reaction and an oxidation process that slows it down through DPPH regeneration.
Lionel Magellan Sambang, Gustave Kenne Dedzo, Séverinne Rigolet, Emmanuel Ngameni
Sustainable Chemistry and Pharmacy
Rolland Tchoumene, Gustave Kenne Dedzo, Emmanuel Ngameni
Journal of Solid State Chemistry
Raïssa Siegnin, Gustave Kenne Dedzo, Emmanuel Ngameni
Applied Clay Science
Jenna Geralde Yanke Mbokana, Gustave Kenne Dedzo, Emmanuel Ngameni
Applied Clay Science
Beaufils Ngatchou Ngana, Patrick Marcel Seumo Tchekwagep, Lionel Magellan Sambang, Gustave Kenne Dedzo, Charles Péguy Nanseu‐Njiki, Emmanuel Ngameni
Journal of environmental chemical engineering
Arlette Danelle Djitieu Deutchoua, Raïssa Siegnin, Glory Koutnaitze Kouteu, Gustave Kenne Dedzo, Emmanuel Ngameni
ChemistrySelect
Abstract The electrochemistry of 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) in acetonitrile was studied in presence of ascorbic acid (AAH 2 ) as model antioxidant. In the presence of AAH 2 , the intensities of the two characteristic systems of DPPH decreases and an intense oxidation peak at 1.07 V assigned to the oxidation of reduced DPPH was observed. The currents associated to these electrochemical processes showed excellent correlation with the amount of AAH 2 added and were used for determining its free radicals scavenger activity. Chronoamperometry was found more suitable for a real time monitoring of the chemical reaction between DPPH and an antioxidant, and thus to evaluate their efficiencies by determining the corresponding half‐maximal inhibitory concentration (IC 50 ) values. Comparison of the reactivity of the antioxidants tested was possible by comparing the times necessary for the stabilization of the residual DPPH reduction currents. The method was subsequently applied to the evaluation of antioxidant properties of lemon and orange samples.
F. Adjie Bah, Gustave Kenne Dedzo, Eric Foto, Charles Péguy Nanseu‐Njiki
International journal of innovation and applied studies
The present work focuses on the electrocoagulation treatment of an Evans blue solution (B.E). Of the four bottom salts (KCl, NaCl, Na2SO4, K2SO4) used for the treatment, it appears that, for an optimum charge density of 2.33 F/m3 and a voltage set at 1.5V, potassium chloride (KCl) provides the best abatement rate (95.5%). The variation of the pH of the solution reveals that the best abatement rates are obtained for the basic pH. pH 9 is optimal for treatment whereas for pH values above 10, inefficiency is noted. The speed of the treatment increases with the density of the applied current, the treatment is efficient and the energy cost is limited for a current density value set at 20 mA/ cm2. For the same set values of charge density and voltage, the abatement rate is inversely proportional to the concentration of B.E, and aluminum is better suited as electrode material, compared to iron.
Arlette Danelle Djitieu Deutchoua, Yannick Ngueumaleu, Gustave Kenne Dedzo, Ignas Kenfack Tonlé, Emmanuel Ngameni
Electroanalysis
Abstract The electrochemical behaviour of 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) incorporated in a carbon paste electrode (CPE/DPPH1 %) was studied. Two electrochemical systems assigned to the free‐radical were perfectly defined, including System I where DPPH acts as reducing agent and System II where it acts as an oxidant. Although System II was reversible and remains stable after several consecutive potential scans, System I shows high peak current ratio (Ipa/Ipc=1.4) and a significant decrease in signal intensity when performing consecutive potentials scans. This phenomenon was due to the chemical reaction of the oxidized DPPH and the hydroxide ions present at the vicinity of the electrode surface. This new compound formed was responsible of a new system (System III). Systems II and III were highly pH‐dependent, in agreement with the proton exchange involved in these electrochemical transformations. When experiments were performed in the presence of ascorbic acid (AAH 2 ), only System I was found to be ideal for monitoring the antioxidant activity of AAH 2 . System I clearly shows a linear dependency between the peak currents of DPPH as a function of AAH 2 concentration. This linear response was used to determine the IC 50 of ascorbic acid (0.56 μM) in the described experimental condition. This effect was confirmed when controlled amount of tea extracts were used instead of AAH 2 , confirming the efficiency of CPE/DPPH1 % for the electrochemical evaluation of antioxidant properties.
Israel Journal of Chemistry
Abstract Since the intercalation of 1‐ethylpyridinium chloride in the interlayer space of kaolinite in 2005, several other ionic liquids (ILs) have been successfully intercalated. Unlike other clay minerals that display charged structural units, kaolinite is almost neutral. ILs intercalation in kaolinite results in both the cation and the anion in the interlayer space. The confinement of ILs in this two‐dimensional polarized space is of numerous interests, with certainly the most important to be discovered. Moreover, kaolinite interlayer space is decorated by a dense network of hydroxyl functions that can be easily functionalized. Recent study demonstrates that it is possible to synthesize ILs from simple organic molecules whose cations can be permanently grafted into the interlayer space of kaolinite. This review presents the results obtained in kaolinite functionalization by ILs, by focusing on the synthesis, applications and potential perspectives offered by these new nanohybrid materials.
Rolland Tchoumene, Gustave Kenne Dedzo, Emmanuel Ngameni
ACS Applied Materials & Interfaces
This work reports the preparation of novel kaolinite nanohybrid material obtained by intercalation of methyl viologen (MV) in the interlayer space of kaolinite, using methoxykaolinite (K-M) as starting material. Characterization of the resulting material (K-MV) confirmed the presence of MV units in the interlayer space of K-M with lateral orientation, associated with a high amount of water molecules due to the hydrophilic nature of MV. The resulting structural formula of this organoclay based on thermogravimetric analysis was Si 2 Al 2 O 5 (OH) 3.72 (OCH 3 ) 0.28 (MV) 0.17 (H 2 O) 0.82 . The release of MV from the K-MV composite was studied in order to evaluate the advantages of using this material for pesticide formulation with MV as active ingredient. The localization of MV in the interlayer space of K-M significantly slows its release in water. However, the interactions that retain MV in the interlayer space remain sufficiently less intense to ensure a complete release of MV in a relatively short time (2 h). On the basis of the interactions that ensure MV intercalation in methoxykaolinite, K-M was used as electrode modifier and applied for the electrochemical determination of MV. The electrochemical signal of MV on the K-M modified electrode was 2 times more intense compared to the pristine kaolinite modified electrode. After optimization of experimental parameters, a sensitivity of 3.91 μA M –1 and a detection limit of 0.14 nM were obtained at the K-M modified electrode. This performance represents one of the most important reported so far in the literature during the electrochemical determination of MV. The sensor was also found very efficient for MV determination in real water systems (well, spring, and tap water) despite the decrease of sensitivity due to the presence of interfering species.
Gaëlle Ngnie, Daniela Baitan, Gustave Kenne Dedzo, Christian Detellier
Fuel
Bruno Boniface Nguelo, Gustave Kenne Dedzo, Ignas Kenfack Tonlé, Christian Detellier, Emmanuel Ngameni
Electroanalysis
Abstract Electrochemical sensors have been developed by modifying a glassy carbon electrode with organo‐kaolinite hybrid materials. These materials were obtained by the grafting of four ionic liquids (1‐(2‐hydroxyethyl)‐4‐benzylpyridinium chloride, 1‐(2‐hydroxyethyl)‐4‐(tert‐butyl)pyridinium chloride, 1‐(2‐hydroxyethyl)‐4‐ethylpyridinium chloride and 1‐(2‐hydroxyethyl)‐4‐methylpyridinium chloride) on the interlayer aluminol surfaces of kaolinite. With the presence of ionic liquids in the interlayer space of kaolinite, the hybrid materials acquired anion exchange properties and were successfully applied as electrode modifier for the electroanalysis of thiocyanate (SCN − ), an anion of medical and environmental concern. A pre‐concentration/detection strategy was used to overcome the interfering effect of the electrolytic solution. After the optimisation of some key experimental parameters (sodium nitrate as electrolyte, 5 min of accumulation time) calibration curves were plotted. Excellent linearity was obtained in the low concentration region (1×10 −6 M to 4×10 −5 M). The lowest detection limit (15 nM) was obtained with the benzylpyridinium functionalized kaolinite and the highest (60 nM) with the methylpyridinium functionalized kaolinite. Interfering anions (NO 3 − , Cl − , SO 4 2− and CH 3 COO − ) present in the pre‐concentration solution were found to interfere with SCN − but the sensors remained stable and produced reproducible signals. The most sensitive sensor was successfully applied for the amperometric determination of SCN − in human saliva samples.
Gustave Kenne Dedzo, Emmanuel Pameté, Melissa Ramel Topet Saheu, Gaëlle Ngnie, Charles Péguy Nanseu‐Njiki, Christian Detellier et 1 autre(s)
Journal of Electroanalytical Chemistry
Honoré Dieudonné Bassala, Gustave Kenne Dedzo, Charles Baudouin Njine Bememba, Patrick Marcel Seumo Tchekwagep, Joël Donkeng Dazie, Charles Péguy Nanseu‐Njiki et 1 autre(s)
Process Safety and Environmental Protection
Gustave Kenne Dedzo, Bruno Boniface Nguelo, I. Tonle Kenfack, Emmanuel Ngameni, Christian Detellier
Applied Clay Science
Jenna Geralde Yanke Mbokana, Gustave Kenne Dedzo, Emmanuel Ngameni
Electroanalysis
Abstract The effect of a non‐swelling (toluene) and a swelling (ethylene glycol (EG)) solvent on the grafting of an organophilic silane (octyltriethoxisilane) onto a smectitic clay was investigated. XRD patterns of the resulting materials reveals that the grafting occurred exclusively on the edges of the clay particles without intercalation, as evidenced by the non‐variability of the d‐value before and after the grafting. FTIR and TGA characterizations show that higher amount of silane was grafted when toluene was used as solvent. With EG, the clay particles were well‐dispersed and the grafting well controlled. These functionalized materials were used as carbon paste electrode modifiers to evaluate their abilities for electrochemical detection of organophilic pollutants at trace level. Carbendazim (cbz), a widely used fungicide was used as model compound. The clay functionalized in EG was the most efficient modifier, due to the combined effect of the characteristics of the pristine clay and the grafted silane. The electroanalysis experimental parameters were carefully optimized (pH 6.8, 15 min of accumulation time and 10 % of the modifier in the carbon paste). By varying cbz concentration, a 0.03 μM detection limit was obtained. The sensor provide very reproducible response but strongly affected by some metal ions interferences. By varying cbz concentration in river water, used as environmental sample model, higher detection limit was obtained (0.2 μM), due to interfering species.
Gaëlle Ngnie, Gustave Kenne Dedzo, Christian Detellier
Dalton Transactions
Palladium nanoparticles (PdNPs) were deposited on the surface of the modified clay mineral, kaolinite. To improve compatibility, abundance and control of the size of the nanoparticles, kaolinite was modified by the grafting of an amino alcohol (triethanolamine (TEA)) and an ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium (ImIL)). Characterization techniques (XRD, TGA, solid state (13)C NMR and FTIR spectroscopy) confirmed the effective grafting of these compounds on the internal surface of kaolinite. After the synthesis of PdNPs onto clay particles, TEM allowed the visualization of abundant PdNPs with sizes ranging from 4 to 6 nm, uniformly distributed onto the platelets of modified kaolinite. Unmodified clay showed low abundance and random distribution of the nanoparticles. The catalysts obtained were effective for the catalytic reduction of 4-nitrophenol (4-NP), the material with TEA being the most effective. These materials have exhibited excellent performance during the Heck and particularly the Suzuki-Miyaura coupling reactions, with reaction yields up to 100%. These catalysts showed a very slight loss in activity for three consecutive catalytic cycles (less than 10% decrease of the activity compared to the first cycle). This was an evidence that the prior grafting modification of kaolinite helps in significantly improving the quality of the synthesized NPs and also promotes their strong attachment onto the clay mineral surface.
Gustave Kenne Dedzo, Christian Detellier
Applied Clay Science
WenJuan Huang, Gustave Kenne Dedzo, Stanislav R. Stoyanov, Olga Lyubimova, Sergey Gusarov, Shashank Singh et 3 autre(s)
The Journal of Physical Chemistry C
Molecular recognition interactions between kaolinite and a series of heterocyclic aromatic compounds (HAC) representative of the N- and S-containing moieties in petroleum asphaltene macromolecules are investigated using the three-dimensional reference interaction site model with the Kovalenko–Hirata closure approximation (3D-RISM-KH) theory of solvation and experimental techniques in toluene solvent. The statistical-mechanical 3D-RISM-KH molecular theory of solvation predicts the adsorption configuration and thermodynamics from the 3D site density distribution functions and total solvation free energy, respectively, for adsorption of HAC and toluene on kaolinite. Spectrophotometric measurements show that, among the HAC studied, only acridine and phenanthridine adsorb quantitatively on kaolinite. For these pyridinic HAC, the adsorption results fitted to the Langmuir isotherm in the monolayer domain suggest a uniform monolayer of HAC molecules. The 3D-RISM-KH studies predict that the aluminum hydroxide surface of kaolinite is preferred for HAC adsorption due to strong hydrogen bonding with the pyridinic N atoms, while the rest of the HAC adsorb weaker. Adsorption on the silicon oxide side is weak and delocalized, as evident from the 3D solvation free energy density. Toluene sites effectively compete with non-hydrogen bonding HAC, such as fused thiophenes, for the kaolinite surface. The adsorption enthalpy and phenanthridine-acridine loading ratio are calculated and correlated with the experimentally determined Langmuir constant and adsorption loading. This combined experimental and computational modeling approach is aimed to provide insight into the specific interactions among clays, bitumen, and solvents so as to help accelerate the development of environmentally friendly and efficient desorption systems for nonaqueous extraction of bitumen from Oil Sands, an important unconventional petroleum reserve.
Gustave Kenne Dedzo, Sadok Letaı̈ef, Christian Detellier
Journal of Materials Chemistry
Functionalized nanohybrid materials based on clay minerals were obtained by grafting ionic liquids (trihydroxyethylmethylammonium iodide (AE1), 1-(2-hydroxyethyl)-3-methylimidazolium chloride (AE2) and 1-benzyl-3-(2-hydroxyethyl) imidazolium chloride (AE3) of different sizes in the interlayer spaces of kaolinite. The grafting was confirmed by several characterization techniques (XRD, 13C CP/MAS NMR and thermal analysis). The interlayer distances of the grafted materials were 4.1 Å, 6.0 Å and 8.7 Å for AE1, AE2 and AE3, respectively. These materials have an anion exchange capacity related to the mobility of the counter anions of grafted cations. In aqueous medium, the anion exchange capacity does not allow a variation of the interlayer distance of kaolinite, as confirmed by XRD measurements. The interlayer distance of the nanohybrid materials is controlled by the grafted cations. These properties of anion exchangers have been used to achieve the voltammperometric detection of some anions with different sizes (thiocyanate, sulphite and ferricyanide ions), using glassy carbon electrodes coated with a thin film of the modified kaolinite. There is a good correlation between the size of the analyzed anion and the basal spacing of the material used for the electrode modification: depending on the system, the presence of the thin film induces an increase of the current intensities when the anion can easily diffuse through the interlayer space or acts as a barrier when the basal spacing does not allow its insertion. This work shows that derivatives of kaolinite can be used for the selective detection of anions in aqueous solution, using their size as a differentiating factor.
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