Activation des fibres lignocellulosiques (cas de la sciure de cortex des cabosses de cacao) par plasma de type « glidarc » en vue de la biosorption des polluants organiques industriels : cas de l’Azur II, du rouge de réactif 2 et du vert de malachite

Abstract

This study is based on the modification of surface properties of Cocoa shell by gliding arc plasma for the removal of textile dyes in aqueous solution. Removal of cationic dye, Azur II, and anionic dye, Reactive Red 2 (RR-2) from aqueous solutions, has been successfully achieved by using a modified agricultural biomaterial waste: cocoa shell husk (Theobroma cacao) treated by gliding arc plasma (CPHP). The biomass in its natural form CPHN and modified form CPHP was characterized by infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), XRD analysis, BET analysis and point of zero charge (pHpzc). Experimental variables such as initial pH, contact time, particle size, sorbent dosage and temperature were optimized for adsorptive characteristics of CPHN and CPHP. The results show that the removal of the Azur II dye was favorable in the basic pH region (pH 10) while the Reactive Red 2 dye was favorable in the acidic pH region (pH 2). The minimum equilibrium time for Azur II and RR-2 dye was obtained after 40 and 240 min, respectively. The adsorption kinetics and isotherm data obtained were best described by a pseudo-second-order kinetic rate model and a combination of Langmuir-Freundlich isotherm models. The thermodynamic parameters of biosorption (ΔH°; ΔS° and ΔG°) were calculated and indicated that the biosorption process for CPHN and CPHP was exothermic and spontaneous in nature. In order to reduce the treatment time and to improve the efficiency of the discoloration process of dyes solutions (RR-2 and Azur II) observed on the previous; the Azur II and RR-2 solutions were treated in three different experimental processes: in-situ treatment by plasma alone, in-situ treatment by plasma coupled with CPHN and in-situ treatment by plasma coupled with CPHP. The combination of the plasma and the biosorbents improved the discoloration efficiency of plasma alone from 18.08% to 79.14% and 18.08% to 91.12% respectively for CPHN and CPHP biosorbents after five minutes exposure time for cationic dye Azur II and from 16.09% to 58.93% and 16.09% to 78.13% after ten minutes exposure time for anionic dye RR-2. Desorption and recycle experiments conducted on the other textile dye, malachite green (MG) demonstrate that cocoa shell as biosorbent can be reuse several times. This work indicates that the plasma-treated raw materials are good alternative multi-purpose sorbents for the removal of many coexisting pollutants from aqueous solutions.