Adsorption of Orange II dye in aqueous solution onto surfactant-coated zeolite: Characterization, kinetic and thermodynamic studies Xiaoying Jin a,b , Bing Yu a , Zuliang Chen a,c,⇑ , Joselito M. Arocena d,e , Ronald W. Thring d,e a School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian Province, China b Fujian Key Laboratory of Pollution Control & Resource Reuse, Fuzhou 350007, Fujian Province, China c Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia d Environmental Science and Engineering Programs, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada e College of Life and Environmental Sciences, Wenzhou University, Wenzhou, Zhejiang 325035, China article info Article history: Received 12 May 2014 Accepted 6 August 2014 Available online 23 August 2014 Keywords: Adsorption Mechanisms Orange II HDTMA Zeolite abstract Adsorption of anionic dye – Orange II – in aqueous solution onto hexadecyltrimethylammonium bromide (HDTMA)-coated zeolite (HCZ) reached 38.96 mg/g compared with 8.13 mg/g onto natural zeolite. Fou- rier Transform Infrared (FTIR), scanning electronic microscopy (SEM) and X-ray powder diffraction (XRD) data showed that HDTMA-coated zeolite developed surficial positive charges. The adsorption reac- tion fits the Freundlich isotherm (R 2 = 0.93) and the value of 1/n was less than unity (=0.81) and suggest a multi-layer physi-sorption process. The kinetics of the adsorption is a pseudo-second-order model. The activation energy (E a ) of the reaction is +35.70 kJ/mol to further support a physi-sorption process while the DH o (+82.79 kJ/mol) is characteristic for an endothermic reaction. The DG o values of 2.33, 0.98 and 0.37 kJ/mol at 25 °C, 30 °C and 35 °C, respectively implied that the adsorption reaction was feasible and thermodynamically spontaneous. We proposed that both electrostatic interactions and partitioning pro- cess are involved in the adsorption mechanisms of Orange II dye onto HCZ. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Synthetic dyes are extensively used in textile, leather, painting and printing processes because of their uniquely high brilliant shades, and relatively simple, low cost production methods. More than 10–15% of synthetic dyes produced are lost as effluent and pose a major threat to the health of ecosystem [1]. In some cases, the presence of less than 1 ppm dye is clearly visible to impair the visual impacts of rivers and lakes [1,2]. Azo are the most pop- ular and constitute about 70% of all used dyes [3]. These azo com- pounds are resistant to aerobic degradation and under anoxic conditions, generate aromatic amines, most of which are colorless but toxic and potentially carcinogenic [1,3]. Removal of dyes from industrial effluents is persistently a major industrial challenge. Tra- ditionally, dyes are eliminated from effluents through biochemical and physical processes such as sorption, coagulation, chemical degradation, advanced oxidation, photocatalysis and biodegrada- tion [4–6]. Due to the large content of aromatic compounds and the stability of modern dyes, biological treatments are ineffective methods to degrade dyes [1–3]. The recent trend to eliminate dyes in wastewater integrates multiple techniques. Adsorption is one of the most efficient and popular methods in the dye removal processes [1]. The adsorption process typically uses low cost adsorbents such as clay minerals, agricultural solid wastes, industrial by-products, chitosan, biomass and zeolite [7–10]. Natural zeolites are abundant, low cost and contain permanent negative structural charges that can be modi- fied by cationic surfactants [11]. This charge modification of zeo- lites enhances the retention of organic pollutants. For example, organo-zeolites adsorb anionic dyes both by hydrophobic binding and by electrostatic attraction with cationic surfactants [12]. We had previously focused on several surfactants to modify zeolites and applied them to dyes removal in aqueous solution [13]. For example, we had demonstrated the high efficiency of hex- adecyltrimethylammonium bromide (HDTMA)-modified zeolites to remove Orange II in water. However, sorption parameters such as isotherms, kinetics, and thermodynamic parameters for the Orange II adsorption onto HCZ are still unknown. As a cationic sur- factant, HDTMA ions adsorbed onto zeolite surfaces and altered the surface charge from negative to positive. Orange II is an anionic azo dye with high potential to leach into soils and contaminate the http://dx.doi.org/10.1016/j.jcis.2014.08.011 0021-9797/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia. Fax: +61 08 83025057. E-mail address: Zuliang.chen@unisa.edu.au (Z. Chen). Journal of Colloid and Interface Science 435 (2014) 15–20 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis