Efficient adsorbent derived from Argania Spinosa for the adsorption of cationic dye: Kinetics, mechanism, isotherm and thermodynamic study

Abstract In this paper, the wood powder from the shell of Argan nuts was used in raw form, or modified form by Sodium hydroxide, as a new economic and ecologic adsorbent. The effectiveness of these materials was evaluated on Methylene Blue (MB), a cationic dye. Those adsorbents were characterized by using scanning electron microscopy (SEM) and Fourier transformed infrared spectroscopy (FTIR). The effect of contact time (2-180 min), adsorbent dose (0.02- 0.8 g), initial dye concentration (50-500 mg/L), pH (2-10.5), and temperature (24-50°C) on the adsorption capacity was studied in a batch reactor. Result obtained showed that the process of MB adsorption onto both adsorbents is in good agreement with the Langmuir adsorption isotherm (R²=0.99 and qe, exp ≈ qe, cal=14.28 for ASN and 64.62 mg/g for ASNN) and followed the pseudo-second-order kinetic model (R²≈1 and qe, cal ≈ qe, exp). According to the equilibrium study, MB was better adsorbed on the modified powder (Qmax ≈ 70 mg/g) than on the raw powder (Qmax ≈ 14 mg/g). The thermodynamic study gives a negative enthalpy (- 28.70 for ASN and  - 60.45 KJ/mol for ASNN), a negative Gibbs free energy (- 13.0 for ASN and -16.5 KJ/mol for ASNN), and negative entropy (- 53.14 for ASN and - 148.04 J/mol/K for ASNN) That confirms that the adsorption reaction is energetically favorable, exothermic and spontaneous. We propose an adsorption mechanism-based to electrostatic attractions and H- bonding interaction. The modified adsorbent was found to be comparable or better than others already studied materials, because of its high adsorption capacity and in only 10 minutes of agitation and its efficiency even after five utilizations.