Equilibrium and kinetic studies on acid dye Acid Red 88 adsorption by magnetic ZnFe 2 O 4 spinel ferrite nanoparticles Wojciech Konicki a,⇑ , Daniel Sibera b , Ewa Mijowska b , Zofia Lendzion-Bielun ´ b , Urszula Narkiewicz b a Department of Integrated Transport Technology and Environmental Protection, Maritime University of Szczecin, H. Pobo _ znego St. 11, 70-507 Szczecin, Poland b Institute of Chemical and Environment Engineering, West Pomeranian University of Technology, Pułaskiego St. 10, 70 322 Szczecin, Poland article info Article history: Received 24 October 2012 Accepted 8 February 2013 Available online 22 February 2013 Keywords: Adsorption Acid dye Magnetic nanoparticles Kinetics Thermodynamics abstract A magnetic ZnFe 2 O 4 (MNZnFe) was synthesized by microwave assisted hydrothermal method and was used as an adsorbent for the removal of acid dye Acid Red 88 (AR88) from aqueous solution. The effects of various parameters such as initial AR88 concentration (10–56 mg L 1 ), pH solution (3.2–10.7), and temperature (20–60 °C) were investigated. Prepared magnetic ZnFe 2 O 4 was characterized by XRD, SEM, HRTEM, ICP-AES, BET, FTIR, and measurements of the magnetic susceptibility. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Langmuir model. Pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffu- sion model were used to examine the adsorption kinetic data. The adsorption kinetics was found to fol- low the pseudo-second-order kinetic model. Thermodynamics parameters, DG°, DH° and DS°, indicate that the adsorption of AR88 onto MNZnFe was spontaneous and exothermic in nature. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Synthetic dyes are extensively used in various branches of the textile industry, paper printing, color photography, pharmaceuti- cal, leather, cosmetics, plastic, and other industries. The discharges of industrial wastewater containing dyes cause serious environ- mental problems because of its high toxicity and possible accumu- lation in the environment. Synthetic dyes are a group of most dangerous pollutants in water. The presence of even very low con- centrations of dyes in water reduces light penetration through the water surface, precluding photosynthesis of the aqueous flora. Many of these dyes are carcinogenic, mutagenic, and teratogenic and also toxic to human beings, microorganisms, and fish species. Hence, their removal from aquatic wastewater becomes environ- mentally important. Many treatment methods, such as membrane filtration, chemi- cal oxidation, photocatalytic degradation and adsorption, have been examined to remove dyes from aqueous solutions. Of these methods, adsorption has been found to be an efficient and eco- nomic process to remove dyes, pigments, and other colorants and also to control the bio-chemical oxygen demand [1]. Various adsor- bents, such as chitosan [2], cotton [3], orange peel [4], palm fruit bunch [5], and shale oil ash [6], have been investigated for removal of dyes from aqueous solution. In recent years, adsorption process combined with magnetic separation technology has been widely used for dyes removal from wastewaters. Nanosized magnetic materials can be used to pro- duce magnetically-active carbon composites and as magnetic nano-adsorbents. Ai and Jiang have synthesized an activated car- bon/ferrospinel composite as the magnetic adsorbent for fast re- moval of organic dyes from aqueous solutions [7]. Yang et al. have prepared magnetic Fe 3 O 4 -activated carbon nanocomposite particles for removal of methylene blue from aqueous solution [8]. Ai et al. have synthesized an activated carbon/CoFe 2 O 4 com- posite as adsorbent for removal of malachite green dye from water [9]. Zhang et al. have developed magnetic CuFe 2 O 4 /activated car- bon composite for removal of acid orange II [10]. Several works have been devoted to the adsorption of dyes onto magnetic-mod- ified MWCNTs and graphene [11–14]. Qadri et al. have studied a separation of a cationic dye acridine orange, by use of magnetic nanoparticles c-Fe 2 O 3 [15]. Zargar et al. have studied the adsorp- tion and removal of amaranth from an aqueous solution by iron oxide nanoparticles coated with cetyltrimethylammonium bro- mide [16]. Wang et al. have prepared different MFe 2 O 4 (M = Mn, Fe, Co, Ni) ferrite nanocrystals for the removal of Congo Red [17]. Hou et al. have synthesized by a simple sol–gel method porous spi- nel ferrites Mn 1x Zn x Fe 2 O 4 (0 6 x 6 0.8) as adsorbent for the re- moval of methylene blue [18]. Ai et al. have prepared montmorillonite/CoFe 2 O 4 composite for removal of methylene blue [19] and prepared Ag–Fe 3 O 4 composite as a magnetically recyclable catalyst for reduction of Rhodamine B [20]. Iram et al. have prepared Fe 3 O 4 hollow nanospheres for application as an 0021-9797/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2013.02.021 ⇑ Corresponding author. Fax: +48 91 48 09 643. E-mail address: w.konicki@am.szczecin.pl (W. Konicki). Journal of Colloid and Interface Science 398 (2013) 152–160 Contents lists available at SciVerse ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis