Journal of Hazardous Materials 174 (2010) 592–597 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Removal of direct azo dyes and aromatic amines from aqueous solutions using two -cyclodextrin-based polymers Elif Yilmaz a , Shahabuddin Memon b , Mustafa Yilmaz a,∗ a Selc ¸ uk University, Department of Chemistry, 42031 Konya, Turkey b National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan article info Article history: Received 7 March 2009 Received in revised form 3 June 2009 Accepted 17 September 2009 Available online 23 September 2009 Keywords: -Cyclodextrin Carcinogens Direct azo dye Aromatic amines Sorption Solid-phase extraction abstract Two -cyclodextrin (-CD)-based polymers were synthesized using 4,4 ′ -methylene-bis- phenyldiisocyanate (MDI) or hexamethylenediisocyanate (HMDI) as a cross linking agent in dimethylformamide and used as sorbents for the removal of azo dyes (Evans Blue and Chicago Sky Blue), as well as aromatic amines (benzidine, p-chloroaniline and -naphthalamine) from aqueous solutions. The sorption experiments were carried out by using batch-wise procedure involving the determination of pH effect, sorbate concentration and contact time. Moreover, from the equation isotherms such as Langmuir and Freundlich were successfully applied to model the experimental data. From the results polymer 2 was found to be a better sorbent for both azo dyes and the aromatic amines as compared to polymer 1 as proved by Langmuir isotherm model. The proposed sorption mechanism involved several kinds of interactions: physical adsorption, hydrogen bonding and formation of an inclusion complex due to the -CD molecules through host–guest interactions. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Synthetic dyes are common water pollutants and due to their good solubility they may frequently be found in trace quantities in industrial wastewater. Many of these dyes are also toxic and even carcinogenic and these pose a serious hazard to aquatic living organisms. The formation of a carcinogenic amine from a dye by human skin bacteria and the antifungal activities of diazobenzene dyes have been reported [1–3]. In the textile industry, it is estimated that 10–15% of the dyestuffs are lost during the dyeing process and released with the effluent, which are more difficult to degrade [4–6]. The release of those colored wastewaters in the environment is a consider- able source of non-aesthetic pollution since the presence of small amounts of dyes (below 1 ppm) is clearly visible. Dyes wastes can also generate eutrophication and dangerous by-products through oxidation, hydrolysis or other chemical reactions taking place in the wastewater-phase [7,8]. Due to the large degree of aromat- ics present in dye molecules and the stability of modern dyes, biological treatment is ineffective for their degradation [6,9,10]. Moreover, azo compounds are resistant to aerobic degradation and under anaerobic conditions, the azo linkage is reduced to generate aromatic amines that are colorless but can also be toxic and poten- ∗ Corresponding author. Tel.: +90 332 2232774; fax: +90 332 2410106. E-mail addresses: myilmaz42@yahoo.com, myilmaz@selcuk.edu.tr (M. Yilmaz). tially carcinogenic [11]. Various chemical and physical processes are currently in use for the removal of dyes by conventional treat- ment technologies including biological and chemical oxidation, chemical coagulation, foam flotation, electrolysis, biodegradation, advanced oxidation, photocatalysis and adsorption processes as discussed in the present reports [12–14]. However, among all the techniques solid-phase extraction (SPE) using sorbents is one of the most efficient and popular methods for the removal of organic compounds from wastewater. The sorbents may be of mineral or organic origin; silica beads, activated carbon, zeolites, polyamines beads, polyurethanes resins, gels, calixarenes, chitosan and - cyclodextrin are significant examples [15–19]. -Cyclodextrin (-CD) is a torus-shaped cyclic oligosaccharide made up of seven -1,4-linked d-glucopyranose units with an inter- nal hydrophobic cavity. It is well known that this structure gives rise to a remarkable capacity to form inclusion complexes in solution or in the solid state with organic molecules, especially aromat- ics, through host–guest interactions. Generally, cyclodextrins are water-soluble in their native form, which are often modified to prepare new insoluble derivatives. These materials which form water insoluble cross-linked polymers are obtained using some polyfunctional crosslinking agents such as aldehydes, ketones, iso- cyanates or epoxides. There have been considerable studies of the preparation, properties and applications of insoluble polymers and copolymers containing -CD [20–22]. The utility of these -CD- containing polymers has been recognized in many applications such as; these polymers have been used for synthetic purposes, 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.09.093