Methylene Blue Adsorption from Aqueous Solution by Functionalized Perlites: an Experimental and Computational Chemistry Study

Desalination and Water Treatment 217 (2021) 391–410 www.deswater.com March

doi: 10.5004/dwt.2021.26752

Methylene blue adsorption from aqueous solution by functionalized perlites: an experimental and computational chemistry study

Eda Gökırmak Söğüta,*, Erdem Ergana, Necla Çalışkan Kılıçb, Hakan Dönmezb, Esvet Akbaşb aVan Security Vocational School, Van Yüzüncü Yıl University, 65080 Van, Turkey, emails: [email protected] (E. Gökırmak Söğüt), [email protected] (E. Ergan) bDepartment of Chemistry, Van Yüzüncü Yıl University, 65080 Van, Turkey, Tel. +904322251024; emails: [email protected] (N. Çalışkan Kılıç), [email protected] (H. Dönmez), [email protected] (E. Akbaş)

Received 18 April 2020; Accepted 1 November 2020

abstract In this study, 3-aminopropyltrimethoxy-silane (3-APTMS) and 3-mercaptopropyltrimethoxy-silane (3-MPTMS) were used to functionalize perlite in order to increase the adsorption capacity of methylene blue (MB). These materials were characterized by X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal (thermogravimetry/ differential thermal analysis) analyzes. The performance of perlite and functionalized derivatives was tested by adsorption of MB in a batch system under a variable pH (2–11) and initial MB con- centration (10–60 mg L–1). Nonlinear and linear Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Sips adsorption equations were applied to define equilibrium isotherms. The maxi-

mum dye sorption was found to be at a pH of 11.0 (96.44% for PA, 96.51% for PAPTMS, and 96.73% –1 for PMPTMS). The adsorption capacity for the dye was found to be 4.9445, 5.2014, and 5.3112 mg g for PA, PAPTMS, and PMPTMS, respectively, at 298 K. The adsorption kinetics was best described by the pseudo-second-order model. The obtained results confirm that amino and mercapto functional groups have positive effects on the adsorption of methylene blue by the adsorbents used in this work. Quantum chemical analysis supported better adsorption of methylene blue dye on amine and mercapto-functionalized perlite surfaces than the unmodified surface and the most suitable site for MB adsorption was suggested by Fukui function analysis. Keywords: 3-aminopropyltrimethoxy-silane; 3-mercaptopropyltrimethoxy-silane; Perlite; Methylene blue; Adsorption characteristics

* Corresponding author.