Published: June 29, 2011 r2011 American Chemical Society 3227 dx.doi.org/10.1021/je200331u | J. Chem. Eng. Data 2011, 56, 3227–3235 ARTICLE pubs.acs.org/jced Comparison of Activated Carbon and Multiwalled Carbon Nanotubes for Efficient Removal of Eriochrome Cyanine R (ECR): Kinetic, Isotherm, and Thermodynamic Study of the Removal Process M. Ghaedi,* ,† A. Shokrollahi, † H. Hossainian, † and S. Nasiri Kokhdan ‡ † Chemistry Department, Yasouj University, Yasouj 75918-74831, Iran ‡ Young Researchers Club, Yasooj Branch, Islamic Azad University, Yasooj, Iran ABSTRACT: The objective of this study was to assess the suitability and efficiency of activated carbon (AC) and multiwalled carbon nanotube (MWCNT) for the removal of Eriochrome Cyanine R (ECR) molecules from aqueous solutions. The effect of different variables in the batch method as a function of solution pH, contact time, initial dye concentration, AC and MWCNT amount, temperature, electrolyte, and so forth by the optimization method has been investigated. ECR contents were determined using a UVvis spectrophotometer before and after ECR adsorption on the AC and MWCNT, and the removal percentage was calculated using the difference in absorbance. The sorption processes followed the pseudosecond order in addition to intraparticle diffusion kinetics models with a good correlation coefficient with the overall entire adsorption of ECR on both adsorbents. Equilibrium data fit well with the Langmuir and Tempkin models with a maximum adsorption capacity based on the Langmuir equation of (40.6 and 95.2) mg 3 g 1 for AC and MWCNT, respectively. Thermodynamic parameters such as change in enthalpy (ΔH°) and entropy (ΔS°), activation energy (E a ), sticking probability (S*), and Gibbs free energy changes (ΔG°) were also calculated. Judgment based on the obtained results of thermodynamic values shows the spontaneous and endothermic nature adsorption processes on both adsorbents. 1. INTRODUCTION Most dye compounds with a complex aromatic structure, especially azo-containing ones, have a high resistance to biode- gradability and are nonoxidizable by conventional biological and physical treatment. Eriochrome Cyanine R (ECR) (Figure 1) generally is completely dissolved at neutral pH in water, and the formed ionic charge species can behave as a bidentate (N, O) univalent ligand for the chelation of several metal ions. Colored wastes present in industrial effluent are harmful to aquatic lives and environment such as rivers, lakes, and sea waters; 1,2 there- fore, such wastewater prior to delivery to the environment with high efficiency must be treated. Adsorption is superior to other dye removal processes such as coagulation, oxidation, ozonation, and ultra-filtration because of its low cost, simplicity of design, and ease of operation. 3 In this study, efficient dye removal technique species are efficiently and quantitatively transferred from the water effluent to a solid phase, and subsequently the adsorbent can be regenerated or kept in a dry place without direct contact in the environment. 4 Most of the work is based on the adsorption behavior of activated carbon (AC) 5 and multiwalled carbon nanotubes (MWCNT) 6 due to their high adsorption capacity, which emerged from their high surface area and porous structure. Depending on the layers involved CNTs have been referred to single-walled (SWCNTs) or MWCNTs; MWCNTs are one of the most commonly used building blocks of nanotechnology. 7 Due to their high surface area and large micropore volume CNTs are also considered to be extremely good adsorbents. Because of the unique advantage and properties of MWCNTs, they have been widely utilized for the sorption, extraction, and removal of a large number of different organic compounds. 8,9 CNT chemical characteristics play a vital role and influence on its sorptive properties. 9,10 Therefore, the aim of the present research is based on the application of AC and MWCNT for the efficient removal of ECR, and their removal properties were compared with each other. 2. EXPERIMENTAL SECTION 2.1. Materials. All chemicals include NaOH, HCl, KCl, AC, MWCNT, and Eriochrome Cyanine R (Figure 1) with the highest purity available are purchased from Merck (Darmstadt, Germany). An accurately weighted amount of ECR was dissolved in deionized water to prepare 800 mg 3 L 1 as stock solution, while the working solution was prepared by daily diluting this solution. The ECR concentration evaluation was carried out using Jusco UVvisible spectrophotometer model V-570 at a wavelength of 510 nm, while the pH/ion meter model-686, thermometer Metrohm, was used for pH adjustment measurements. 2.2. Batch Adsorption Experiments. The influence of vari- ables including pH, adsorbent dosage, contact time, initial dye concentration, KCl concentrations, and temperature on the adsorptive removal of ECR was investigated by batch experi- ments. In each experimental run onto AC and MWCNT, (100.0 and 10.0) mL of contact time of (0 to 60) min for AC and (0 to 35) min for MWCNT. ECR in (250.0 and 50.0) mL Erlenmeyer flasks was agitated with a stirrer at 350.0 rpm at a fixed control temperature. The obtained experimental data at various times, temperatures, and concentrations were fit to different models to Received: April 4, 2011 Accepted: June 6, 2011