Application of montmorillonite–Cu(II)ethylenediamine catalyst for the decolorization of Chromotrope 2R with H 2 O 2 in aqueous solution Ibrahim A. Salem ⇑ , Hoda A. El-Ghamry, Marwa A. El-Ghobashy Chemistry Department, Faculty of Science, Tanta University, Tanta 31527, Egypt highlights  [Cu(en) 2 ] 2+ has been immobilized onto the montmorillonite-K10 and montmorillonite-KSF.  The prepared catalyst showed great activities towards the decolorization of Chromotrope 2R.  The reaction kinetics of color removal confirmed the formation of a brown intermediate which interacts with the dye molecules. graphical abstract 0.0 0.2 0.4 0.6 0.8 1.0 [H 2 O 2 ] / M 0 2 4 6 8 10 12 14 16 18 20 10 8 Initial rate / (mol L -1 sec -1 ) catalyst + UV catalyst UV article info Article history: Received 8 September 2014 Received in revised form 6 November 2014 Accepted 20 November 2014 Available online 28 November 2014 Keywords: Montmorillonite Copper(II)-ethylenediamine complex Chromotrope 2R H 2 O 2 Textile dyes Decolorization abstract The kinetics of decolorization of Chromotrope 2R (C2R) was studied spectrophotometrically using the montmorilloniteK10–Cu(II)ethylenediamine composite (MMTK10–Cu(en) 2 ) as catalyst and H 2 O 2 as oxi- dant in aqueous solution. The catalyst was prepared and characterized by SEM, FTIR, XRD and TGA tech- niques. The dependence of reaction rate on H 2 O 2 concentration was examined under UV irradiation in the presence and absence of the catalyst, and in the presence of the catalyst without the UV irradiation. In all these reaction systems, the rate increased up to a maximum value and then decreased. The rate increased with increasing the concentration of the dye reaching a maximum. Also, the rate of decolorization reaction showed a significant increase with increasing the amount of the catalyst and temperature. The addition of NaCl to the reaction medium has accelerated the rate effectively. A similar catalyst, MMTKSF–Cu(en) 2 , has also been employed and was found to be less efficient compared with MMTK10–Cu(en) 2 . Ó 2014 Elsevier B.V. All rights reserved. Introduction During the last decade, several physico-chemical and biological techniques have been developed to remove colors from textile wastewaters. Some of these techniques rely on the presence of a catalyst whether in homogeneous or heterogeneous systems. The montmorillonite lattice is composed of a sheet of octahedrally coordinated gibbsite, [Al 2 (OH) 6 ], sandwiched between two sheets of tetrahedrally coordinated silicate, [SiO 4 ] 4 sheets [1]. They have attracted great interests as catalysts for chemical reactions because of their natural availability, low cost, and ease of use. Montmorillonite-K10 and montmorillonite-KSF are commercially available clays and used as economical and eco- logical catalysts for water treatment [2]. The iron–montmorilloni- teK10/H 2 O 2 and the montmorillonite KSF/H 2 O 2 systems have been http://dx.doi.org/10.1016/j.saa.2014.11.053 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +20 403305978. E-mail address: dr.ibrahimsalem@science.tanta.edu.eg (I.A. Salem). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 130–137 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa