Adsorptive removal of both cationic and anionic dyes by using sepiolite clay mineral as adsorbent: Experimental and molecular dynamic simulation studies Fadwa Largo a , Redouane Haounati a , Siham Akhouairi a , Hassan Ouachtak b,c, ⁎, Rachid El Haouti d , Anouar El Guerdaoui e , Naima Hafid f , Diogo M.F. Santos g , Feryal Akbal h , Ayşe Kuleyin h , Amane Jada i,j , Abdelaziz Ait Addi a, ⁎⁎ a Team of Physical Chemistry and Environment, Faculty of Science, Ibn Zohr University, Agadir, Morocco b Faculté des Sciences Appliquées, Ait Melloul, Université Ibn Zohr, Agadir, Morocco c Laboratoire de Chimie Appliquée & Environnement, Equipe de chimie Bio-organique Appliquée, Faculté des Sciences, Université Ibn Zohr, Agadir, Morocco d Materials and Environment Laboratory, Ibn Zohr University, Agadir 8000, Morocco e Département de Chimie, Faculté des Sciences, Université Ibn Zohr, Agadir, Morocco f Centre Régional des Métiers de l'Education et de la Formation Souss Massa, Morocco g Center of Physics and Engineering of Advanced Materials (CeFEMA), Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal h Faculty of Engineering, Department of Environmental Engineering, Ondokuz Mayis University, Samsun 55200, Turkey i Institut de Sciences Des Matériaux De Mulhouse (IS2M-CNRS), Université de Haute Alsace (UHA), F-68100 Mulhouse, France j Université de Strasbourg, Strasbourg F-67081, France abstract article info Article history: Received 25 July 2020 Received in revised form 27 August 2020 Accepted 4 September 2020 Available online 11 September 2020 Keywords: Adsorption Textile dyes Sepiolite clay mineral Kinetics Isotherms Molecular dynamic simulations In the present work, sepiolite clay was assessed as an adsorbent for the removal of cationic (Methylene Blue: MB) and anionic (Direct Red-23: DR-23) dyes from aqueous media. Firstly, the sepiolite clay mineral was character- ized using different instrumental techniques viz., XRD, SEM, EDX, FTIR, X-ray Fluorescence, and BET analysis. Thereafter, the adsorption study was examined as a function of the adsorbent amount, the contact time, the aque- ous phase pH, the ionic strength, and the initial dye amount. The data indicate that the adsorption was a function of the pH with high adsorption amounts of MB and DR-23, in basic and acidic, respectively, pH ranges. By com- paring experimental data to the Langmuir predictions, the calculated maximum dye adsorbed amounts were 124.9 and 649.37 mg g -1 , for MB and DR-23, respectively. Further, kinetic adsorption studies have shown that adsorption of MB and DR-23 from aqueous media onto the sepiolite follow, respectively, the pseudo-second order and the pseudo first-order kinetic models. On the other hand, Molecular Dynamic (MD) simulations were performed to shed light on the pH-effect on the adsorptive properties of the sepiolite clay surface and the adsorption behavior of both hazardous MB and DR-23 dyes into the adsorbent surface. The better affinity of the MB molecules toward the sepiolite in the basic media could be related to the dispersion forces and electro- static interactions. On the other hand, the DR-23 molecules show more favorable interaction in the acidic media as a result of the hydrogen bonds formed between the dye molecule and the sepiolite surface oxygen atoms. In addition, the negative values of interaction energies calculated show that the adsorption processes of both haz- ardous MB and DR-23 molecules on the sepiolite surface are spontaneous, which is in good agreement with the results observed experimentally. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Nowadays, the availability of sufficient and good water quality is a worldwide primary concern, and the protection of this scarce resource from pollution is of utmost importance [1]. Dyes are among the major pollutants found in the industrial effluents causing hence significant water pollution. Note that the dyes are the prevalent contaminants widely used in the textile industries. Their extensive uses generate col- ored wastewaters, leading to environmental pollution [2]. Moreover, Journal of Molecular Liquids 318 (2020) 114247 ⁎ Correspondence to: H. Ouachtak, Faculté des Sciences Appliquées, Ait Melloul, Université Ibn Zohr, Agadir, Morocco. ⁎⁎ Corresponding author. E-mail addresses: Ouachtakhassan@gmail.com (H. Ouachtak), aitaddi.abdelaziz@gmail.com (A.A. Addi). https://doi.org/10.1016/j.molliq.2020.114247 0167-7322/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq