Journal of Hazardous Materials 164 (2009) 675–682 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Estimation of chromium(VI) sorption efficiency of novel regenerable p-tert-butylcalix[8]areneoctamide impregnated Amberlite resin Imdadullah Qureshi a , Shahabuddin Memon a,∗ , Mustafa Yilmaz b a National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan b Department of Chemistry, Selc ¸uk University, Konya 42031, Turkey article info Article history: Received 29 May 2008 Received in revised form 12 August 2008 Accepted 16 August 2008 Available online 29 August 2008 Keywords: Calixarene Dichromate Impregnation Sorption Langmuir/Freundlich isotherm Solid-phase extraction abstract The article describes a convenient synthesis and Cr(VI) extraction efficiency of a novel p-tert- butylcalix[8]areneoctamide impregnated Amberlite (XAD-4) resin. Using p-tert-butylcalix[8]arene macrocyclic building block, two strategies have been developed; i.e., derivatization of p-tert- butylcalix[8]arene framework with sophisticated ionophoric groups having efficiency to extract oxoanions from aqueous media and, impregnation of p-tert-butylcalix[8]arene derivative onto the polymeric sup- port. Liquid–liquid and solid–liquid extraction experiments have been performed to evaluate the Cr(VI) extraction efficiency of both p-tert-butylcalix[8]arene derivative and the impregnated resin. From the results, it has been deduced that solid-phase extraction method is more convenient and efficient than liquid–liquid extraction process. The impregnated XAD-4 resin has been found regenerable with better extracting efficiency as compared to the simple p-tert-butylcalix[8]areneoctamide ionophore. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Hexavalent chromium is extensively used by various indus- tries in particular stainless steel welding, chromate production, electroplating, chrome pigment, catalysts, refractory or corrosion- resistant products, leather tanning, textile dyeing, wood preserving, oil drilling, or locations where large tanks have been cleaned with chromium(VI) solutions [1–3]. When chromium(VI) is ingested higher than its permissible level, it causes health disorders; such as vomiting and hemorrhage [4]. It can easily cross the cell wall and exerts its toxic influence on the cell. Therefore, chromium(VI) is known to exhibit carcinogenic properties; attacks liver, kidney and lungs [5]. Due to the extreme toxicity of Cr(VI), its selective determination and removal from the polluted sites is of particular importance. Calixarenes have been proven to be very useful precursors for the synthesis of host molecules. During the last three decades, they have attracted much attention as key receptors in ‘Supramolecular Chemistry’. Immense interest in these compounds was stimulated by their simple large-scale synthesis and the different ways in which they can be selectively functionalized at the narrow or wide rim [6–9]. Moreover, calixarenes have several advantages for ∗ Corresponding author. Tel.: +92 22 2772065; fax: +92 22 2771560. E-mail address: shahabuddinmemon@yahoo.com (S. Memon). their application as extractants for chromium(VI), e.g., their aro- matic core structure is stable against oxidation, and the association of oxoanion with multiple functionalities present onto the aro- matic core. This association may arise due to the hydrogen bonding between substituents on the calixarene moiety and one or more of the oxygen atoms on the periphery of the oxoanion [10]. Generally, two strategies have been adopted to enhance the affinity of calixarenes toward metal ions and anions. Either dif- ferent ionophoric groups including carbonyl, amide, nitrile and other suitable functionalities have been incorporated onto the calix-platform, or the calix[n]arene units have been fixed in a polymeric matrix [11–14]. Thus, calixarenes need to be modified chemically to reduce their solubility characteristics by immobi- lization on polymeric supports. The preparation of such insoluble polymeric calixarenes is made by linking the calixarene units to the polymeric matrix covalently or by connecting a polymerizable spacer group to calixarene unit to give a resin-like substance after polymerization. Amberlite XAD series resins have been extensively used for the solid-phase extraction and often modified for designing chelating resins [15–17]. Amberlite XAD-4 is a cross-linked polymer which has excellent adsorptive properties for neutral small molecules onto its macroreticular structure and higher surface area. These structures provide excellent chemical, physical and thermal stabil- ity. The modification with calixarenes makes them the best choice for the removal of a variety of metal ions [18,19]. In our previous 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.08.076