Modeling of competitive ultrasonic assisted removal of the dyes – Methylene blue and Safranin-O using Fe 3 O 4 nanoparticles M. Ghaedi a,⇑ , S. Hajjati a , Z. Mahmudi a , I. Tyagi b , Shilpi Agarwal b , A. Maity c , V.K. Gupta b,d,⇑ a Chemistry Department, Yasouj University, Yasouj 75918-74831, Iran b Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India c National Centre for Nanostructured Materials, CSIR Material Science and Manufacturing, Pretoria 0001, South Africa d King Fahd University of Petroleum and Minerals Dhahran, Saudi Arabia highlights  Ultrasonic power combined Fe 3 O 4 NPs were synthesized and characterized.  CCD was used to study the individual and joint effects of the factors on the responses.  An empirical extension of Langmuir model was proposed to predict the simultaneous adsorption of MB and SO. graphical abstract TEM images of nanospheres. article info Article history: Received 15 October 2014 Received in revised form 22 December 2014 Accepted 24 December 2014 Available online 19 January 2015 Keywords: Adsorption Fe 3 O 4 NPs Binary mixture Methylene blue Safranin-O abstract The study was focused on the simultaneous removal of Methylene blue (MB) and Safranin-O (SO), as most together hazardous dye in wastewater, from aqueous solution by ultra-sonic-assisted adsorption onto the developed adsorbent i.e. Fe 3 O 4 NPs. Fe 3 O 4 NPs were synthesized, by using central composite design (CCD), the effects of variables such as pH, adsorbent dosage, MB concentration, SO concentration and con- tact time on binary dyes removal were examined and optimized values were found to be 6, 0.01 g, 10 and 20 mg/L and 2 min, respectively. The very rapid removal of dyes makes this novel adsorbent as a prom- ising tool for wastewater management applications. Different adsorption isotherm model i.e. Langmuir, Freundlich, non-modified Langmuir, modified competitive Langmuir, modified extended Langmuir, extended Freundlich and sips models are studied out of which extended-Freundlich model proved to be the best fit to equilibrium data because of correlation value (R 2 ) is 0.99 which is very close to 1, addi- tionally it depicts the high adsorption capacity around (89.2–91.9 mg g 1 ). An empirical extension of competitive extended-Freundlich model was proposed to predict the simultaneous adsorption behavior of MB and SO. It was observed that pseudo-second-order equation is suitable to fit the experimental data. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Any water reservoir or aquatic source is an integral part of the ecosystem. It is prejudiced by formation conditions of surface or underground water runoff. Toxic pollutants affecting the aquatic ecosystem are classified depending on the way they approach. http://dx.doi.org/10.1016/j.cej.2014.12.090 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. Abbreviations: MB, Methylene blue; SO, Safranin-O; CCD, central composite design; NPs, nanoparticles; HOD, high oxygen demand. ⇑ Corresponding authors at: Chemistry Department, Yasouj University, Yasouj, Iran. Tel./fax: 00987433223048; Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India. Tel.: +91 1332285801; fax: +91 1332273560 (V.K. Gupta). E-mail addresses: m_ghaedi@mail.yu.ac.ir (M. Ghaedi), vinodfcy@iitr.ac.in, vinodfcy@gmail.com (V.K. Gupta). Chemical Engineering Journal 268 (2015) 28–37 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej