1603 † To whom correspondence should be addressed. E-mail: ahmahvi@yahoo.com Korean J. Chem. Eng., 30(8), 1603-1608 (2013) DOI: 10.1007/s11814-013-0080-1 INVITED REVIEW PAPER The adsorption of malachite green (MG) as a cationic dye onto functionalized multi walled carbon nanotubes Mohammad Shirmardi* , **, Amir Hossein Mahvi*** , **** ,† , Bayram Hashemzadeh*****, Abolfazl Naeimabadi******, Ghasem Hassani*, and Mehdi Vosoughi Niri* *Department of Environmental Health Engineering, School of Public Health, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran **Member of Student Research Committee of Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran ***School of Public Health and Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran ****National Institute of Health Research, Tehran University of Medical Sciences, Tehran, Iran *****Department of Environmental Health, Khoy School of Nursing and Public Health, Urmia University of Medical Sciences, Urmia, Iran ******Department of Environmental Health, School of Public Health, North Khorasan University of Medical Sciences, Bojnourd, Iran (Received 25 February 2013 • accepted 6 May 2013) Abstract-Synthetic dyes are widely used by several industries to color their products. The discharge of colored waste- water into the hydrosphere causes serious environmental problems. We used functionalized multi wall carbon nanotubes as an adsorbent for the adsorption of cationic dye, malachite green, from aqueous solution. Based on information pro- vided by the Iranian Research Institute of Petroleum Industry, carbon nanotubes are produced using a chemical vapor deposition (CVD) technique. These as-received MWCNTs were functionalized by acid treatment. The remaining dye concentration was read by UV-visible absorption spectroscopy at maximum adsorption wavelength. The effect of dif- ferent operational parameters such as contact time, pH of solution, adsorbent dose and initial dye concentration were studied. The results showed that by increasing of contact time, pH and adsorbent dose the removal of dye increased, but by increasing initial dye concentration, the removal efficiency decreased. Adsorption isotherms and kinetics behavior of f-MWCNTs for removal of malachite green was analyzed, and fitted to various existing models. The experimental data were well correlated with the Langmuir isotherm with a maximum adsorption capacity (q m ) and regression co- efficient (R 2 ) of 142.85 mg/g and 0.997, respectively. The results of this study indicate that functionalized multi wall carbon nanotubes can be used as an effective adsorbent for the removal of dyes. Key words: Adsorption, Carbon Nanotube, Dye, Isotherm, Kinetic Study INTRODUCTION Synthetic dyes are widely used by several industries, such as textile companies, food-processing companies, dye manufacturers, paper and pulp mills, and electroplating factories, to color their products [18]. The discharge of colored wastewater into the hydrosphere not only causes serious environmental problems because of its high toxic- ity and possible accumulation in the environment, but also to human beings, by producing carcinogenic and mutagenic effects [27,38]. To minimize the risk of pollution and adverse health effects gener- ated by such effluent, this effluent must be treated carefully before discharging into the environment [18]. Malachite green (MG) is a popular cationic dye and is used extensively. This dye is widely used for the dyeing of cotton, jute, silk, wool and leather products. It also finds applications in the fish farming industry, aquaculture and ani- mal husbandry as fungicide, ectoparasiticide and disinfectant. It has been shown recently that MG is linked to an increased risk of cancer, acts as a liver tumor-enhancing agent and many other diseases. Mala- chite green is an important water-soluble dye belonging to the triphe- nyl methane family. It may enter into the food chain, and due to its mutagenic and carcinogenic characteristics can cause severe effects on nervous system, reproductive system, liver, brain and kidney [7,33]. There are many processes available for dye removal such as co- agulation, advanced oxidation, combined chemical and biochemi- cal process, aerobic and anaerobic digestion, adsorption and mem- brane treatment; each of these has different removal efficiency, ad- vantage, disadvantage, capital costs and operating rates. Adsorption is one of the cheapest and most effective techniques for wastewater treatment in terms of initial cost, simplicity of design, ease of opera- tion and insensitivity to toxic substances. In addition, this technique can produce high-quality effluent without the formation of harmful substance like ozone and free radicals [1,14,15,24,31,35]. Numer- ous adsorbents and bioadsorbents such as neem sawdust [16], hen feathers [28], cyclodextrin-based [3], oil palm trunk fiber (OPTF) [9], bentonite clay [36], bagasse fly ash [25], bottom ash [8], de- oiled soya [29], Cosmarium sp. [4], Pithophora sp. [17] have been used for removal of malachite green from aqueous solution. More recently, Long and Yang [21] reported that MWCNTs could be more efficient than activated carbon for the removal of dioxin, so carbon nanotubes (CNTs) have attracted the attention of many researchers