<p>In the present study, adsorption experiments were carried out to investigate the removal of rhodamine B from an aqueous solution using chemically activated carbon from corn cobs, a cheaper adsorbent. The characteristics of carbon were determined using X-ray diffraction, SEM, iodine number, pHpzc, and the Boehm titration method. The results show that the prepared activated carbon is amorphous, microporous, and generally acidic on the surface. The kinetic study of the adsorption of rhodamine B on this carbon was carried out, and the rate of sorption was found to conform to pseudo-second-order kinetics with 80 min as equilibrium time. The equilibrium adsorption revealed that the experimental data fitted better to the Langmuir isotherm model for removing rhodamine B. The interaction rhodamine B-activated carbon is mainly chemisorption type. The optimal conditions of rhodamine B removal onto the carbon of this study are mass of carbon = 0.3 g and pH = 3.15. The maximum monolayer adsorption capacity for rhodamine B removal was found to be 5.92 mg.g<sup>-1</sup>. This study has shown that the prepared activated carbon makes it possible to effectively clean up wastewater contaminated by rhodamine B with a removal efficiency of up to 99.60% for 300 mg of AC in 25 mL of the rhodamine B solution (5 mg.L<sup>-1</sup>).</p>
This study investigated the electrochemical behavior of iohexol in its commercial formulation omnipaque on a boron-doped diamond electrode using cyclic voltammetry and chronoamperometry. The dependence of the anodic peak current density vs. iohexol concentration is linear and can be applied to the determination of the substrate concentration in environmental samples and pharmaceuticals. The iohexol electrooxidation on boron-doped diamond electrode is diffusion-controlled process and proceed via two ways: a direct electron transfers at the surface of boron-doped diamond electrode and an indirect oxidation mediated by in situ oxidative species. The iohexol electrooxidation in pH range from 2 to 6 includes exchange of 4 electrons and 1 proton, at pH superior to 6 it includes an exchanged of 2 electrons and 1 proton. The values of activation energy, anodic transfer coefficient, heterogenous rate constant, diffusion coefficient and the catalytic rate constant were 14.164 kJ mol-1, 0.428, 1.06 s-1, 4.47 cm2 s-1 and 3.61 M-1 s-1 respectively. It appears from those results that, on our electrode, for the high potential scan rates, few actives sites mainly those located at the electrode surface are involved in the iohexol oxidation process. As the potential scan rate decreases, more actives sites are involved in the process.
This study showed that the oxidation of rhodamine B by the Fenton process is a very fast method because the reaction takes place within the first 20 minutes. The mixture of Fe2+ and H2O2 produces hydroxide radicals responsible for the degradation of rhodamine B. The study of pH influence on the rhodamine B oxidation reveals that for maximum oxidation of rhodamine B, the pH must be less than or equal to 2. For pH > 2, there is a decrease in rhodamine B oxidation. This is due to side reactions that occur if the concentration of Fe2+ is high. This reduces the amount of oxidized rhodamine B. We note that the oxidation of rhodamine B is faster for low concentrations than for high concentrations of rhodamine B. According to our results, for a maximum oxidation of 5 mg / L of rhodamine, it takes 8.4.10−4 mg / L of Fe2+, 3.10−3 M of H2O2 and pH = 2. This work also showed that the presence of inorganic ions strongly slows down the rate of degradation of rhodamine in the following order: Cl− ˂ NO3− ˂ SO42− ˂ PO43−.
The platinum anode modified by metal oxides electrodes degrades Abidjan wastewater which contains a high concentration of Cl-. During this degradation process, the organic polluants are oxidized, O2 and Cl2 are produced. The purpose of this study is to contribute to the understanding of these reaction mechanisms by studying the kinetics of O2 and Cl2 evolution at neutral pH on Pt. The study was performed by interpreting the voltammograms and Tafel slopes obtained. The voltammetric measurements were carried out using an Autolab Potentiostat from ECHOCHEMIE (PGSTAT 20) connected by interface to a computer. Pt electrode was prepared on titanium (Ti) substrate by thermal decomposition techniques at 400°C. The characterization of the surface of the prepared electrode by scanning electron microscopy and X-ray photoelectron spectrometry showed the presence of platinum on its surface. The results obtained show that the OH· are adsorbed on the active sites of Pt. Then they react to form PtO. Then by reaction between the surface oxygen and PtO, O2 is produced and the active sites are regenerated. In the presence of low Cl- concentration, there is a competition between the Cl2 and O2 evolution reactions. However, Cl2 only is produced for high Cl- concentrations. The kinetics of the evolution reaction of chlorine increases with the concentration of Cl- and remains constant for concentrations greater than 0.5 M. This study also showed that the chlorine reduction reaction produced in solution is a diffusion-controlled reaction for low scan rates.
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