Journal of Hazardous Materials 186 (2011) 1696–1703 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat An efficient calix[4]arene based silica sorbent for the removal of endosulfan from water Sibghatullah Memon a,b , Najma Memon b , Shahabuddin Memon b,∗ , Yawar Latif b a Dr. M. A. Kazi Institute of Chemistry, University of Sindh, Jamshoro 76080, Pakistan b National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan article info Article history: Received 22 September 2010 Received in revised form 26 November 2010 Accepted 13 December 2010 Available online 22 December 2010 Keywords: Endosulfan Calixarene Sorption Freundlich and Langmuir isotherms Kinetics abstract The present work explores sorption behavior of calix[4]arene based silica resin to remove  and  endo- sulfan isomers from aqueous solution. The efficiency of resin was checked through both batch and column sorption methods. In both methods, the sorption parameters, i.e. pH, equilibrium time, shaking speed and sorbent dosage were optimized as 2, 60 min, 125 rpm and 50 mg, respectively. Freundlich and Langmuir sorption isotherm models were applied to validate the sorption process. The data obtained in both mod- els reveal that the sorption is favorable. Column sorption data were analyzed through Thomas model to calculate kinetic coefficient k TH and maximum sorption capacity q o of the resin, which were found to be 6.18 and 5.83 cm 3 mg -1 min -1 as well as 1.11 and 1.08 mg g -1 for  and  endosulfan, respectively. Kinetics of sorption shows that it follows pseudo second order rate equation. The optimized method has also been applied to real water samples and the results show that calix[4]arene based silica resin is an effective sorbent to remove endosulfan from waste waters. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Persistent organic pollutants (POPs) are considered as sub- stances which posses strong resistance to photolytic, chemical and biological degradation. They are semi-volatile, highly toxic, per- sistent and travel long distance through air and water. They have low solubility in water but high solubility in fats therefore; they can bio-accumulate in fatty tissues. Semi-volatility of these compounds enables them for long range transport in the atmosphere. This leads to contamination of water, soil and agriculture products [1]. Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro- 6,9-methano-2,4,3-benzo-dioxathiepine-3-oxide) is an organochlorine pesticide. It is used as an insecticide under different trade names like thiodan, thionex, endosan, endosulfan, etc. This pesticide is used for various crops in developing coun- tries like Pakistan, India, Bangladesh, etc., in order to enhance agriculture production. Due to its dangerous effects for human and environment such as accumulation in fatty tissues, long range transport, difficult to degrade, long half life of isomers and its degradation products (greater then 2 months in water and greater then 6 months in soil) [2]. United Nations Environmental Protec- tion Agency (UNEPA) classified endosulfan highly toxic [3] while WHO consider endosulfan as a moderately hazardous [4] pollu- ∗ Corresponding author. Tel.: +92 22 2772065; fax: +92 22 2771560. E-mail address: shahabuddinmemon@yahoo.com (S. Memon). tant. According to Pesticide Action Network (PAN) International endosulfan fulfills the requirement of persistent organic pollu- tants (POPs). Therefore, it is proposed to be listed in Stockholm Convention [5]. Recently, it was observed that endosulfan isomers (Fig. 1) can cause endocrine disruption in both terrestrial and aquatic organisms. Excessive and improper applications can cause physical disorder, mental disturbance and death in farm workers, particularly in developing countries [6]. A global ban on the use and manufacturing of endosulfan is being considered through Stockholm Convention on persistent organic pollutants (POPs) [7]. WHO recommended limit of single pesticide is 0.1 g dm -3 , while for total amount of pesticide it is 0.5 g dm -3 [8]. Various methods have been utilized to remove endosulfan and related environmental pollutants from water such as biodegrada- tion through Aspergillus sydoni [9], bionitrification and sand filter system [10], anaerobic-membrane bioreactor technology [11]. Removal of endosulfan from water using sorption methodology is current area of research due to its simplicity and effectiveness. Various sorbents such as Sal wood char coal [12], natural organic substances [13], wheat straw [14], peach-nut shells [15], and car- bon slurry [16] are reported. However, very few synthetic sorbents are reported in the literature for the removal of pesticides from water such as mesoporous cyclodextrin-silica nanocomposite [17], pore expanded mesoporous silica [18] and chitosin based molecu- larly imprinted polymers [19]. Calixarenes are a class of synthetic cyclo-oligomers possessing cup like shape with defined upper and lower rim and central annu- 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.12.048