Enhanced adsorption of congo red from aqueous solutions by chitosan hydrogel beads impregnated with cetyl trimethyl ammonium bromide Sudipta Chatterjee a , Dae S. Lee b , Min W. Lee c , Seung H. Woo a, * a Department of Chemical Engineering, Hanbat National University, San 16-1, Deokmyeong-Dong, Yuseong-Gu, Daejeon 305-719, Republic of Korea b Department of Environmental Engineering, Kyungpook National University, Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea c Department of Chemical Engineering/School of Environmental Science and Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang, Gyeongbuk 790-784, Republic of Korea article info Article history: Received 19 September 2008 Received in revised form 16 December 2008 Accepted 16 December 2008 Available online 8 February 2009 Keywords: Adsorption Chitosan bead Congo red CTAB Surfactant abstract The adsorption of congo red (CR) onto chitosan (CS) beads impregnated by a cationic surfactant (CTAB, cetyl trimethyl ammonium bromide) was investigated. Chitosan beads impregnated at a ratio of 1/20 of CTAB to CS (0.05% of CTAB and 1% of CS) increased the CR adsorption capacity by 2.2 times from 162.3 mg/g (0% CTAB) to 352.5 mg/g (0.05% CTAB). The CR adsorption decreased with an increase in pH of the CR solution from 4.0 to 9.0. The Sips isotherm model showed a good fit with the equilibrium experimental data and the values of the heterogeneity factor (n) indicated heterogeneous adsorption of CR onto CS/CTAB beads, as well as CS beads. The kinetic data showed better fit to the pseudo sec- ond-order rate model than to the pseudo first-order rate model. The impregnation of CS beads by cationic surfactants showed the highest adsorption capacities of CR compared to any other adsorbents and would be a good method to increase adsorption efficiency for the removal of anionic dyes in a wastewater treat- ment process. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Wastewater effluents from different industries such as textiles, rubber, paper and plastics, contain several kinds of synthetic dye- stuffs (Chiou et al., 2004). A very small amount of dye in water is highly visible. Further, discharging even a small amount of dye into water can affect aquatic life and food webs due to the carcinogenic and mutagenic effects of synthetic dyes (Crini, 2006). Congo red [1- naphthalene sulfonic acid, 3,3 0 -(4,4 0 -biphenylenebis (azo)) bis (4- amino-) disodium salt] is a benzidine-based dye. This dye has been known to cause an allergic reaction and to be metabolized to ben- zidine, a human carcinogen. Synthetic dyes such as congo red (CR) are difficult to biodegrade due to their complex aromatic struc- tures, which provide them physico-chemical, thermal and optical stability (Han et al., 2008). Although contaminated waste water may be treated with conventional physical–chemical methods like reverse osmosis, ion exchange, chemical precipitation or lime coagulation, and oxidation, the application of these techniques has been restricted due to high energy consumptions or expensive synthetic resins and chemicals. Moreover, these methods generate large amount of toxic sludge and are ineffective at lower concen- trations of dye (Blackburn, 2004; Chakraborty et al., 2003). There- fore, there is an urgent requirement for development of innovative, but low cost processes, by which dye molecules can be removed. Adsorption technique is quite popular due to simplicity and high efficiency, as well as the availability of a wide range of adsor- bents. It has proved to be an effective method for removal of dye from wastewater (Allen et al., 2004). Activated carbon is the most popular adsorbent for removal of dyestuffs from wastewater (Kadirvelu et al., 2003). However, adsorbent grade carbon is cost- prohibitive and both regeneration and disposal of the used carbon are often very difficult. Therefore, there is a growing need to find locally available, low cost, and effective materials for the removal of dyes. A number of non-conventional, low cost adsorbents such as montmorillonite (Yermiyahu et al., 2003), bentonite (Lian et al., 2009), rice hull ash (Chou et al., 2001), leaf (Bhattacharrya and Sharma, 2004), fly ash (Mall et al., 2005), activated red mud (Tor and Cengeloglu, 2006), rice husk (Han et al., 2008), and fungi (Fu and Viraraghavan, 2002; Binupriya et al., 2008) have been used for the removal of congo red from aqueous solutions. However, some of these adsorbents do not have good adsorption capacities for anionic dyes because most have hydrophobic or anionic sur- faces. Hence, there is a need to search for more effective adsorbents. Chitosan, a linear biopolymer of glucosamine, has exhibited excellent adsorption capacity for anionic dyes and heavy metal ions because chitosan molecules contain a large number of active amine (–NH 2 ) groups. In a recent review paper, chitosan was noted 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.12.035 * Corresponding author. Tel.: +82 42 821 1537; fax: +82 42 821 1593. E-mail address: shwoo@hanbat.ac.kr (S.H. Woo). Bioresource Technology 100 (2009) 2803–2809 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech