Journal of Hazardous Materials 166 (2009) 904–910 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Rapid decolorization of azo dye methyl orange in aqueous solution by nanoscale zerovalent iron particles Jing Fan a,∗ , Yanhui Guo a , Jianji Wang a , Maohong Fan b a School of Chemical and Environmental Sciences, Henan Key Laboratory for Environmental Pollution Control, Key Laboratory for Yellow and Huai River Water Environmental and Pollution Control, Ministry of Education, Henan Normal University, Xinxiang, Henan 453007, PR China b School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA article info Article history: Received 14 August 2008 Received in revised form 8 November 2008 Accepted 26 November 2008 Available online 3 December 2008 Keywords: Nanoscale zerovalent iron Azo dye Decolorization Methyl orange abstract Azo dyes are recalcitrant and refractory pollutants that constitute a significant burden on the environment. The report here is focused on the decolorization treatment of water soluble azo dye methyl orange (MO) by chemically synthesized nanoscale zerovalent iron (NZVI) particles. Experimental variables such as initial dye concentration, iron dosage, solution pH and temperature were studied systematically. Batch experiments suggest that the decolorization efficiency was enhanced with the increase of NZVI dosage and reaction temperature, but decreased with increasing initial dye concentration and initial solution pH. Further studies indicated that existence of inorganic salt (Na 2 SO 4 ) could inhibit the decolorization of MO. Kinetic analyses based on the experimental data elucidated that the decolorization process followed a first order exponential decay kinetics model. The activation energy was determined to be 35.9kJ/mol. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Modern dyes have a multiple variety and they are often intended to be produced to resist the breakdown of long-term exposure to sunlight, water, and other atrocious conditions, thus making the treatment of dye wastewater more difficult. Within the overall cat- egory of synthetic textile dyestuffs, azo dyes constitute about a half of global production (700,000 ton per year), and during dye- ing operation processes, about 15% of them ends up in wastewaters [1]. Decolorization treatment of azo dye effluents has therefore received increasing attention. Traditional physical and/or chemi- cal methods such as flocculation and adsorption, simply transfer the pollutants to another phase rather than destroying them [2]. Some advanced oxidation processes (AOPs) have been used to min- eralize dye molecules on the basis of the generation of hydroxyl radicals ( • OH) in water. They are technically viable clean-up pro- cesses for dyes, but have some limits. For example, homogeneous Fenton and photo-assisted Fenton reaction process have tight work- ing pH range (pH 2–4) and they may generate large volumes of iron sludge for further disposal [3]. Heterogeneous photo-catalytic degradation using titanium dioxide has been widely studied in laboratory. However, it is not desirable for a practical remedia- tion technology due to the serious problems like low quantum ∗ Corresponding author. Tel.: +86 373 3325971; fax: +86 373 3326445. E-mail address: fanjing@henannu.edu.cn (J. Fan). yields caused by hole-electron recombination and the requirement of UV light [4,5]. Moreover, all these methods are insufficient to treat azo dye wastewater with high concentration and high chroma [6]. Because azo dyes are especially resistant in the natural envi- ronment, their biological degradation has serious obstacles [7]. Therefore, the preferred techniques for the treatment of azo dye wastewater should be based on the combination of pre-treatment and biological methods, and an effective pre-treatment process can enhance significantly the biodegradability of the azo dyes. Zerova- lent iron (ZVI), an environmentally friendly reducing agent, can reduce the azo bond, cleaving dye molecules into products that are more amenable to mineralization in biological treatment processes [8]. Much attention has been paid on the treatment of azo dyes by ZVI in recent years [9–12]. The advantages of the ZVI decoloriza- tion process include the ease in use as a pre-treatment process, easy recycling of the spent iron powder by magnetism as well as low iron concentration remaining and no necessity for further treatment of the effluents [11]. However, traditional ZVI methods to date almost used commercial grade zerovalent iron which has relatively low reactivity, and needs prolonged reaction time and low pH condition for adequate treatment. These disadvantages can be overcome by increasing the activity of Fe 0 particles through decreasing their sizes to nanoscale. Due to the smaller particle size, larger specific surface area, higher density of reactive surface sites and greater intrinsic reactivity of surface sites [13], nanoscale zerovalent iron (NZVI) has gained prominence for environmental remediation, especially for the remediation of contaminants that are susceptible to reductive transformation such as halogenated 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.11.091