Rais Ahmad Rajeev Kumar Environmental Research Laboratory, Department of Applied Chemistry, Aligarh Muslim University, Aligarh, India Research Article Adsorption of Amaranth Dye onto Alumina Reinforced Polystyrene Adsorptive removal of toxic amaranth dye by alumina reinforced polystyrene (ARP) composite was studied as a function of contact time, pH, initial dye concentration, and temperature. The results indicated that adsorption was strongly dependent on pH and temperature of the dye solution. The adsorption was favored at low pH with the maximum removal at pH 2.0. Langmuir, Freundlich, Temkin, and Dubinin– Radushkevich (D–R) models were used for the description of adsorption equilibrium data and the best interpretation for the experimental data was given by the D–R model. The adsorption kinetics was tested using pseudo first order, pseudo second order, Elovich, intraparticle, and film diffusion models and the removal by ARP followed a pseudo second order kinetics. Thermodynamic studies revealed that both adsorption and desorption was spontaneous and endothermic in nature. From the exhausted adsorbent, about 70 and 96% desorption was obtained with (99%) CH 3 OH and 0.1 M NaOH, respectively. Keywords: Adsorption; Amaranth; Desorption; Isotherms; Kinetics Received: April 8, 2010; revised: May 31, 2010; accepted: July 3, 2010 DOI: 10.1002/clen.201000125 1 Introduction Textile industry is a major consumer of synthetic dyestuffs and utilizes large volumes of water in wet processing operations. Dyes in wastewaters affect the nature of water by inhibiting the sunlight penetration into the stream thereby reducing the photosynthesis reaction [1]. Some synthetic dyes such as azo dyes may be carcino- genic or mutagenic and under anaerobic conditions, can be trans- formed into aryl amines which are potentially more toxic than the parent compounds [2, 3]. Amaranth is an azo dye and its toxicity has been reported for some animals for, e.g., carcinogenic to rat fetus. The amaranth dye is degraded by intestinal microorganisms in vivo and is possible that the toxic or carcinogenic effects may be due to their degradation products [4]. Numerous technologies such as adsorption, membrane separ- ation, flocculation–coagulation, and aerobic or anaerobic treatment have been developed and applied worldwide for the scavenging of dyes [5]. Among the dye removal processes, the adsorption is widely applied because of the system flexibility, low cost as well as low energy consumption. A wide variety of porous materials, such as agricultural waste [6], polymers [7–9], carbon materials [10–12], clay minerals [13–16], and other solid materials [5, 17–20] have been investigated as adsorbents for the removal of dyes. In recent years, polymeric composite adsorbents have been increasingly used to remove and recover dyes from waste streams due to their wide variations in porosity, surface chemistry, and higher thermal stability especially regenerability on site [21–23]. The objective of this work was to explore the possible use of alumina reinforced polystyrene (ARP) composite as an adsorbent for the removal of amaranth dye. For optimization, effect of various parameters such as contact time, pH, temperature, and dye concen- tration were investigated. The experimental data were fitted to the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) adsorption isotherms. In order to understand the rate and mechanism of adsorption process by ARP, the adsorption kinetics was also deter- mined. Thermodynamic analysis was used to elucidate the adsorption and desorption mechanism of amaranth dye onto ARP composite. 2 Materials and methods 2.1 Materials Commercial polystyrene beads and alumina were purchased from BDH Ltd. Acetone and cetyltrimethylammonium bromide (CTAB) was purchased from Emerck Ltd. Amaranth dye, molecular formula –C 20 H 11 O 10 S 3 N 2 Na 3 (C.I. Food Red 9), C.I.-16185 was purchased from CDH Ltd, India. The structure of amaranth is shown in Fig. 1. The solution was prepared by dissolving the appropriate amount of dye in double distilled water. 2.2 Preparation of polystyrene–alumina composite A mixture of 5.0 g alumina powder and 5.0 g polystyrene was blended in 50 mL acetone and kept for 5 days. Then, 0.5 g of CTAB was added as a functionalizing agent and placed in ultrasonic bath for 1 h at 408C. The above mixture was stirred until the alumina gets Correspondence: Dr. R. Ahmad, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, India. E-mail: olifiaraju@gmail.com Abbreviations: ARP, alumina reinforced polystyrene; pHz, point of zero charge; SEM, scanning electron microscopy. 74 Clean – Soil, Air, Water 2011, 39 (1), 74–82 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com