Removal of methyl orange from aqueous solution via adsorption on cork as a natural and low-coast adsorbent: equilibrium, kinetic and thermodynamic study of removal process

Abstract

In this study, the cork powder was used as adsorbent to remove methyl orange (MO) from aqueous solutions by adsorption. Batch experiments were conducted to study the effect of reaction parameters on the adsorption of the dye such as: contact time, initial concentrations of solution, adsorbent dosage, solution pH, and temperature; consequently, optimum condition of adsorption was obtained. The surface properties and structure of cork were measured by some techniques including: Scanning electron microscope, Fourier transform infrared spectrometry, point of zero charge, and Boehm titration method. Adsorption capacity of cork for MO is 16.66 mg g−1 at 298 K under the optimum condition of pH of 2, cork dosage of 5.00g l−1, particle size of d<0.08 mm, and contact time of 240 min. The kinetic data obtained from different experiments were analyzed using three kinetic models namely pseudo-first-order, pseudo-second-order, and Elovich kinetics models. Among the kinetics models studied, the pseudo-second-order model was the best applicable model to describe the adsorption of MO onto cork. Freundlich and Langmuir models were used to analyze the obtained experimental data. In comparison, Langmuir model was understood to be a better fit for the experimental data than Freundlich model. The value of Gibbs free energy of adsorption (ΔG°) was found to be −14.96 kJ mol−1; the negative value indicated the spontaneity of the adsorption process of MO onto cork. The values of (ΔH°) and (ΔS°) were found to be −11.71 kJ mol−1 and −10.93 J mol−1 K−1, respectively. The thermodynamics parameters indicated that the adsorption of MO onto cork was spontaneous and exothermal.