Manel Bergaoui, Asma Nakhli, Yacine Benguerba, Mohamed Khalfaoui, Alessandro Erto, Felycia Edi Soetaredjo, Suryadi Ismadji, Barbara Ernst
The aim of this study is to investigate the suitability of raw and organo-bentonite for the selective adsorption of methylene blue (MB) from an aqueous solution at three temperatures. SEM characterization confirms the adsorption of MB since there is change in the morphology of the sample after adsorption process. The organo-bentonite allows a higher MB removal than raw-bentonite with a maximum adsorption capacity equal to 321 mg/g at 60 °C. This may be attributed to the carbonyl groups deriving from the rarasaponin used for the preparation of organo-bentonite. The adsorption process of MB is better described by monolayer model coupled to real gas (MMRG) rather than Langmuir and Freundlich models. It was found that the statistical physics approach covers the above-mentioned models. The organo-bentonite showed the highest adsorption energies (2.40; 2.73 and 21.3 kJ/mol) compared to the raw-bentonite (1.22; 2.44 and 15.2 kJ/mol) at 30°C, 45°C and 60°C, confirming the effect of carbonyl group from rarasaponin. MMRG model also allows the calculation of the Isosteric heat of adsorption. According to the retrieved Gibbs free energy values, the adsorption process was noticed spontaneous in nature. Molecular dynamics simulation is conducted to reinforce the results obtained from statistical physics approach. Starting from attraction energy results, it can be concluded that adsorption of MB is located on the bentonite part of the adsorbent, as well as on the rarasaponin part. The interactions that occurred during MB adsorption are identified by MD simulations as Van der Waals forces, which are repulsive for rarasaponin/MB with a stronger electrostatic interaction and attractive for bentonite/MB with zero electrostatic forces. Hydrogen bonding is found to be equal to zero for both systems. © 2018 Elsevier B.V.
Laboratory of Physical Chemistry of Materials, Department of Physics, Faculty of Sciences, University of Monastir, Monastir, 5000, Tunisia; Research Group in Materials Science, Microelectronics and Nanotechnologies, Department of Technology, Higher Institute of Computer Sciences and Mathematics of Monastir, University of Monastir, Monastir, 5000, Tunisia; Department of Process Engineering, Laboratoire de Génie des Procédés Chimiques, Université Ferhat Abbas, Sétif–1, Sétif, 19000, Algeria; Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università di Napoli Federico II, P. leTecchio, 80, Napoli, 80125, Italy; Department of Chemical Engineering, Widya Mandala Catholic University Surabaya, Surabaya, 601-14, Indonesia; Université de Strasbourg, CNRS, IPHC UMR 7178, Laboratoire de Reconnaissance et Procédés de Séparation Moléculaire (RePSeM), ECPM 25 rue Becquerel, Strasbourg, F-67000, France