Adsorption of methyl violet dye onto a prepared bio-adsorbent from date seeds: isotherm, kinetics, and thermodynamic studies

Abstract

Raw date seeds, as prospective natural, broadly obtainable and low-price agricultural waste for adsorbing cationic dyes from aqueous solutions, have been studied. In this work, Iraqi date seeds were prepared and characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) surface area analysis before being used as an efficient bio-adsorbent for methyl violet (MV) dye removal. Adsorption tests were conducted with three investigated parameters, namely, time of contact, first adsorbate concentration and adsorbent dose. Compared with the pseudo first-order model (coefficient of determination = 0.9001), the pseudo second-order model was determined to be the best-fitting model with a coefficient of determination (R2) of 0.9917. The equilibrium isotherms for MV were obtained, and their ultimate capacity of adsorption was (59.5 mg g1). Two isotherm models, Langmuir and Freundlich, were studied to fit the equilibrium data. Compared with the Freundlich isotherm model (R2 = 0.8154), the Langmuir model functioned better as an adsorption isotherm with R2 of 0.9837. In addition, the adsorption process was endothermic and spontaneous. The date seeds acted as active adsorbents to remove MV from the aqueous solutions in the model experiments.