International Journal of Biological Macromolecules 80 (2015) 615–626 Contents lists available at ScienceDirect International Journal of Biological Macromolecules j ourna l h o mepa ge: www.elsevier.com/locate/ijbiomac Synergistic behaviour of ionic liquid impregnated sulphate-crosslinked chitosan towards adsorption of Cr(VI) A. Shekhawat a , S. Kahu a , D. Saravanan b , R. Jugade a,∗ a Department of Chemistry, R.T.M. Nagpur University, Nagpur 440033, India b Department of Chemistry, National College, Tiruchirappalli 620001, India a r t i c l e i n f o Article history: Received 19 January 2015 Received in revised form 15 July 2015 Accepted 17 July 2015 Available online 20 July 2015 Keywords: Sulphate-crosslinked chitosan (SCC) Aliquat-336 Synergistic effect Chromium Cr(VI) adsorption a b s t r a c t Aliquat-336 (an ionic liquid) impregnated sulphate-crosslinked chitosan (SCC) was prepared for esca- lating the adsorption of hexavalent chromium through concurrent interaction. The compound obtained was intensively characterized using Fourier transform infra red (FT-IR), X-ray diffraction (XRD), Scan- ning electron microscopic (SEM) and Energy dispersive X-ray (EDX) studies. Various isotherm studies have been carried out to understand the adsorption mechanism. Quantitative adsorption of Cr(VI) was observed at pH 3.0 with adsorption capacity of 250.90 mg g -1 in accordance with Langmuir isotherm. The adsorption of Cr(VI) followed pseudo-second-order kinetics. The adsorption efficiency was found to decrease with increase in temperature due to increased randomness at interaction sites. The adsorption process was found to be exothermic and spontaneous in nature. Column studies were carried out to understand the applicability of the material for higher sample volumes. The adsorbent could be regen- erated using sodium hydroxide treatment and the regenerated adsorbent had same efficiency towards adsorption of Cr(VI) as that of the original. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Chromium compounds are used in mining, electroplating and dyeing industries [1] leading to contamination in soil and ground water. Primarily, chromium occurs in trivalent state (III), which is stable while the hexavalent state (VI) is an oxidizing agent. Triva- lent chromium Cr(III) is essential trace element for insulin and glucose metabolism [2] but the Cr(VI) is toxic in nature. The LD 50 value for Cr(VI) ranges between 50 and 150 mg kg -1 [3]. It can dif- fuse as CrO 4 2- or HCrO 4 - through the cell membranes and after reaching the blood stream, damages the kidneys, the liver and blood cells through oxidation reactions [4]. Genotoxic and car- cinogenic behaviour of Cr(VI) are well established [5]. Products containing chromates can lead to allergic contact dermatitis and irritant dermatitis [6]. World Health Organization recommended maximum allowed concentration in drinking water for chromium (VI) as 0.05 mg L -1 [7]. Environmental cleanup and remediation for the treatment of brownfield lands are required for chromium reduction. Reduction of metal contamination in surface water and indus- trial effluents is performed by an effective technique known as ∗ Corresponding author. E-mail address: ravinj2001@yahoo.co.in (R. Jugade). biosorption. It involves removal of various components from solu- tions by biological materials like wheat residue [8], agricultural biowastes [9], parthenium weeds [10], cellulose [11], lignocellu- loses [12], tea-waste [13], chitosan [14–19], etc. As compared to natural polymers, biocompatibility and biodegradability of syn- thetic materials are more limited. However in reactivity and process ability, naturally abundant materials also exhibit limitation [20,21]. Chitosan is non-toxic and a universally accepted potential polysaccharide [22]. It shows excellent properties like biocom- patibility, biodegradability and good adsorption behaviour. High percentage of nitrogen in chitosan compared to synthetically sub- stituted cellulose makes chitosan a useful chelating agent [23]. Several functional derivatives of chitosan were prepared by chem- ical modifications resulting in better sorption characteristics for Cr(VI) [24]. Two approaches have been precisely used for structural modification of chitosan in order to improve adsorption proper- ties. First and the obvious approach is the chemical modification of the material by impregnation of various moieties. The sec- ond approach is to crosslink the polymer chains using suitable crosslinking agents. One of such chemical modifications reported is the interaction with quaternary ammonium salts including ionic liquids. Aliquat-336 (methyltrioctylammonium chloride) is one of the ionic liquids improving the adsorption properties of chi- tosan towards Cr(VI) [25]. Simpler approach of crosslinking the http://dx.doi.org/10.1016/j.ijbiomac.2015.07.035 0141-8130/© 2015 Elsevier B.V. All rights reserved.