Charles Péguy Nanseu-Njiki

Mercury(II) removal from water by electrocoagulation using aluminium and iron electrodes.

In this work, electrocoagulation was used to evaluate the treatment of synthetic solutions containing mercury(II) of concentration 2 x 10(-5)M. The effects of the distance between the electrodes, current density, charge loading and initial pH on the removal efficiency were investigated, using aluminium and iron electrodes. Analysis of the filtrates resulting from the treatment was made by anodic redissolution in the differential pulse mode. The removal efficiency was above 99.9% when the distance between the electrodes was 3 cm, the current density ranging from 2.5 to 3.125 A dm(-2); for instance, 99.95% of the mercury(II) was eliminated when a charge loading of 9.33 and 15.55 F m(-3) were used for iron and aluminium respectively. In these conditions, by varying the pH of the mercury(II) solutions from 3 to 7, the removal efficiency remained higher than 99%. In addition, some experiments were carried out on a river water contaminated with mercury(II) ions, and the results obtained showed that the presence of organic matter do not influence the efficiency of the treatment. The elimination of mercury(II) ions is best performed with iron, where 15 min of electrolysis was sufficient to reach the highest removal compared to aluminium which required 25 min for the same result.

Study of the removal of paraquat from aqueous solution by biosorption onto Ayous (Triplochiton schleroxylon) sawdust

This study concerns the batch biosorption of paraquat on Ayous (Triplochiton schleroxylon) sawdust; the study centers on the evolution of biosorption parameters during the process. It appears that paraquat forms a monolayer on the sawdust surface as evidenced by the good correlation between the experimental data and the Langmuir model. The biosorption which is rather fast (the equilibrium was reached after ten minutes) follows a pseudo-second-order kinetic model and does not obey to the intra-particle diffusion model. According to the mathematical kinetic modeling, pore and surface mass transfer well describe the phenomenon. NaCl reduces the adsorption capacity of the material but has no significant effect on the kinetics. Alkaline solutions enhance the accumulation of the pollutant, the reverse being observed for acidic media. According to the thermodynamic data, this biosorption is a spontaneous and exothermic process. From these results we concluded that the adsorption of the pollutant is mainly due to cation exchange as indicated by the adsorption energy determined by the Dubinin-Radushkevich model (E=12.0736 kJ mol(-1)); some other interactions resulting from the affinity through organophilic interactions between paraquat and sawdust have also been pointed out. Desorption experiments conducted in HCl and HNO(3) solutions confirmed the proposed mechanism.

Amperometric sensors based on sawdust film modified electrodes: application to the electroanalysis of paraquat.

Natural or sodium hydroxide treated Ayous sawdusts were used to prepare thin film electrodes (denoted respectively as PSTFE and SSTFE). The sensors obtained exhibit good mechanical stability and a wide electrochemical potential range. Their electrochemical characterization revealed that they present a good capacity to accumulate cations, but are not useful for the electroanalysis of anions. In all cases, the signals were more intense and well defined on SSTFE compared to PSTFE. When applied to the electroanalysis of paraquat, a significant improvement of the current intensities was obtained on these electrodes compared to the bare glassy carbon electrode. The diffusion of this compound through the film which is the main process governing the electrochemical reaction at the electrode surface, is 2.2 times more important with SSTFE compared to PSTFE. After the optimization of the detection parameters, calibration curves were obtained in the concentration range 0.1-0.725 μmol L(-1) for PSTFE and 0.05-0.6 μmol L(-1) for SSTFE. The detection limits determined for a signal/noise ratio=3 are 5.49×10(-9) mol L(-1) for PSTFE and 3.02×10(-9) mol L(-1) for SSTFE.

Removal of Cd (II) from synthetic wastewater by alginate–Ayous wood sawdust (Triplochiton scleroxylon) composite material

ABSTRACT The biosorption characteristics of Cd (II) ions from synthetic wastewater using raw Ayous wood sawdust (Triplochiton scleroxylon), r-AS, immobilized by sodium alginate were investigated with respect to pH, biomass quantity, contact time, initial concentration of heavy metal, temperature and stirring rate. The experimental data fitted well with the Langmuir isotherm, suggesting that monolayer adsorption of the cadmium ions onto alginate–Ayous sawdust composite (a-ASC). The obtained monolayer adsorption capacity of a-ASC for Cd (II) was 6.21 mg/g. From the Dubinin–Radushkevich isotherm model, a 5.39 kJ/mol value for the mean free energy was calculated, indicating that Cd (II) biosorption could include an important physisorption stage. Thermodynamic calculations showed that the Cd (II) biosorption process was feasible, endothermic and spontaneous in nature under examined conditions. The results indicated that a-ASC could be an alternative material replacing more costly adsorbents used for the removal of heavy metals.

Amination of pretreated ayous (Triplochiton scleroxylon) sawdust with two organosilanes: characterization, stability, and permselective property

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 13C 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(NH3)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.