Emmanuel Ngameni

Treatment of dairy effluents by electrocoagulation using aluminium electrodes

This work sets out to examine the efficiency of an electrolytic treatment: electrocoagulation, applied to dairy effluents. The experiments were carried out using a soluble aluminium anode on artificial wastewater derived from solutions of milk powder. The flocks generated during this treatment were separated by filtration. The analysis of the filtrates showed that the chemical oxygen demand (COD) was reduced by up to 61% while the removal of phosphorus, nitrogen contents, and turbidity were 89, 81 and 100%, respectively. An analogous treatment applied to phosphate and lactose solutions revealed that lactose was not eliminated, a fact that could account for the rather poor lowering of the COD. Compared to the chemical coagulation treatment with aluminium sulphate, the efficiency of the electrocoagulation technique was almost identical. However the wastewaters treated by electrocoagulation differed by the fact that they exhibited a lower conductivity and a neutral pH value (by contrast to the acid nature of the solution treated by the chemical coagulation). This result (low conductivity, neutral pH) tends to show that it may be possible to recycle the treated water for some industrial uses. Moreover, the electrocoagulation process uses fewer reagents: the mass of the aluminium anode dissolved during the treatment is lower compared to the quantity of the aluminium salt used in chemical coagulation. These two observations clearly show that the electrocoagulation technique is more performing.

Nanohybrid materials from the grafting of imidazolium cations on the interlayer surfaces of kaolinite. Application as electrode modifier

This work reports the preparation and characterization of a new nanohybrid material obtained by the grafting of an organic cation, namely 1-(2-Hydroxyethyl)-3-methylimidazolium, on the interlayer surfaces of kaolinite by utilizing a dimethylsulfoxide (DMSO) kaolinite intercalate as starting material. The chemical modification process involved the in-situ displacement of DMSO by the imidazolium salt, followed by the grafting under carefully controlled melt reaction conditions. The structure of the resulting material was characterized by X-ray Diffraction (powder and oriented sample), thermal analysis (TG, DTG and DTA), FTIR, as well as by 29Si and 13C MAS NMR spectroscopy, that demonstrated the covalent binding of imidazolium cations on the kaolinite internal surfaces. Ion-exchange and permeation properties of this new nanohybrid material were tested upon its deposition onto the surface of a glassy carbon electrode (GCE), by means of multisweep cyclic voltammetry towards the preconcentration of thiocyanate species. Upon stabilization, the voltammogram signal of the GCE coated with the imidazolium-grafted kaolinite was increased in comparison to the signal obtained at the bare GCE for a thiocyanate solution. This was attributed to the accumulation of thiocyanate anions by the positively charged organoclay material due to favourable electrostatic interactions. No electrochemical signal was observed at the GCE coated with unmodified kaolinite. When hexacyanoferrate was used as probe, in strong contrast to what was obtained in the case of thiocyanate, the peak currents obtained at the clay modified electrode were essentially similar to those recorded at the bare GC electrode, showing that this functional two-dimensional material has selective anionic recognition properties.

Organoclay-modified electrodes: preparation, characterization and recent electroanalytical applications

Amperometric sensors dedicated to the determination of pollutants and other compounds of interest face daily a great challenge: the development of sensitive, reproducible and low-cost devices allowing fast analyses. This review deals with the beneficial role and application of organoclays exploited as sensing materials in various fields of electroanalysis, for the past 15xa0years (period 2000–2014). After a description of different preparation methods leading to clay minerals chemically modified by organic compounds, the common methods used for their characterization are exposed; then, their application as electrode modifiers is described, covering several approaches that were developed to enhance either the sensitivity or the selectivity of the indexed organoclay-based sensors. Finally, a brief description of voltammetric methods frequently used for electroanalytical purposes is given, followed by an update of recent and salient results achieved for the detection of inorganic and organic electroactive compounds or ions.

Voltammetry Study of 2‐Hydroxy‐3‐isopropenyl‐1,4‐naphthoquinone Using a Carbon Paste Electrode

The electrochemical behavior of 2-hydroxy-3-isopropenyl-1,4-naphthoquinone also named lapachol, a potent antimalarial agent that also displays activity against various other diseases including some types of cancer, sleeping sickness etc., has been examined. This was achieved by the use of a carbon paste electrode, chemically modified with lapachol. The various parameters that can influence the electrochemical signal (the scan rate of the electrode, the composition of the paste, the pH of the electrolyte) have been scrutinized. The ability of this quinonic compound to serve as a proton donor for the determination of the acidity level of concentrated acids was also investigated: this was achieved by considering the Strehlows acidity function: Ro(H) which involves the ferricinium/ferrocene couple as a comparison system.

Square wave voltammetric detection by direct electroreduction of paranitrophenol (PNP) using an organosmectite film-modified glassy carbon electrode.

This work describes the development of a low-cost and reliable adsorptive stripping voltammetric method for the detection of PNP in water. Organoclays were prepared by intercalation in various loading amounts of cetyltrimethylammonium ions (CTA(+)) in the interlayer space of a smectite-type clay mineral. Their structural characterization was achieved using several techniques including X-ray diffraction (XRD), N2 adsorption-desorption (BET method) and Fourier Transform Infrared spectroscopy (FTIR) that confirmed the intercalation process and the presence of the surfactant ions within the clay mineral layers. Using [Fe(CN)6](3-) and [Ru(NH3)6](3+) as redox probes, the surface charge and the permeability of the starting clay mineral and its modified counterparts were assessed by multisweep cyclic voltammetry, when these materials were coated on the surface of a glassy carbon electrode (GCE). In comparison with the bare GCE, the organoclay modified electrodes exhibited more sensitive response towards the reduction of paranitrophenol (PNP). Under optimized conditions, a calibration curve was obtained in the concentration range from 0.2 to 5.2µmolL(-1); leading to a detection limit of 3.75×10(-8)molL(-1) (S/N=3). After the study of some interfering species on the electrochemical response of PNP, the developed sensor was successfully applied to the electroanalytical quantification of the same pollutant in spring water.