Walnut shell for removal by adsorption of methylene blue from aqueous solution
Walnut shells (WS) were used as an agricultural adsorbent material to remove methylene blue (MB) from aqueous solutions and evaluated in a batch process. WS was analyzed by Scanning Electron Microscopy (SEM) and Fourier transform infrared (FTIR). The experiments were carried out depending on the contact time, the dose of adsorbent (0.5 and 0.1 g), the agitation (50 and 100 rpm) and the temperature (293 and 313 K), initial concentration of the adsorbate (50 mg/L). The kinetic data were analyzed using pseudo-first order and pseudo-second order equations. Isotherm data were modeled with the Langmuir and Freundlich equations. The adsorption isotherm data fit well with the Langmuir isotherm and the adsorption capacity of the monolayer was found to be 80.65 mg/g for MB. MB adsorption on WS is confirmed by FTIR and SEM. The thermodynamic study reveals that MB adsorption in WS is carried out by an endothermic reaction (ΔH = 1,097 kJ/mol), feasible and spontaneous (ΔG0 = -21,157.32 kJ/mol a 293 K; -23,363.13 kJ/mol a 303 K; y -17,333.87 kJ/mol a 313 K) and decreases the disorder of the molecules in the adsorption process (ΔS0 = 2.63 kJ/mol K). The efficiency of the WS on MB was related to the arrangement of adsorption sites, as well as the microporous structure of the adsorbent material. The results indicated that walnut shells could be an alternative to the more expensive adsorbents used to remove the dye.
Keywords: Adsorption isotherm, Equilibrium, Kinetics, Methylene blue, Walnut shell.
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