Carbohydrate Polymers 86 (2011) 1533–1541 Contents lists available at ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol Adsorption of Crystal Violet from aqueous solution onto NaOH-modified rice husk Sagnik Chakraborty, Shamik Chowdhury ∗ , Papita Das Saha Department of Biotechnology, National Institute of Technology-Durgapur, Mahatma Gandhi Avenue, Durgapur (WB) 713209, India a r t i c l e i n f o Article history: Received 4 March 2011 Received in revised form 10 June 2011 Accepted 21 June 2011 Available online 29 June 2011 Keywords: Adsorption NaOH-modified rice husk Crystal Violet Equilibrium Kinetics Thermodynamics a b s t r a c t In this study, equilibrium, kinetics and thermodynamics of Crystal Violet (CV) adsorption onto NaOH- modified rice husk (NMRH) was investigated. Experiments were carried out as function of contact time, initial solution pH (2–10), adsorbent dose (0.5–5 g) and temperature (293, 303 and 313 K). The adsorp- tion was favoured at higher pHs and lower temperatures. Adsorption data were well described by the Freundlich model, although they could be modelled by the Langmuir model as well. The adsorption pro- cess followed the pseudo-second order kinetic model. The mass transfer model based on intraparticle diffusion was applied to the experimental data to examine the mechanisms of the rate controlling step. It was found that intraparticle diffusion was not the sole rate controlling step. The activation energy (E a ) of the system was calculated as 50.51 kJ mol -1 . Thermodynamic parameters suggest that the adsorption is a typical chemical process, spontaneous, and exothermic in nature. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, environmental contamination by synthetic dyes is a serious problem due to their negative ecotoxicological effects and bioaccumulation in wildlife (Saha, Chowdhury, Gupta, & Kumar, 2010). The contamination of water due to synthetic dye molecules causes damage to the environment and has adverse effects on public health (Akar, Özcan, Akar, Özcan, & Kaynak, 2009; Kiran, Ilhan, Caner, Iscen, & Yildiz, 2009). Besides, dyes are one of the sources of esthetic pollution and eutrophication (Tsai, Chang, Ing, & Chang, 2004). Industries such as textile, leather, paper, paint, acrylic, cosmetics, plastics, pharmaceutical, etc., use dyes in order to colour their products and also consume substan- tial volumes of water. As a result, they generate a considerable amount of coloured wastewater. It is estimated that approxi- mately 12% of synthetic dyes are lost during manufacturing and processing operations and 20% of these lost dyes enter the indus- trial wastewaters (Chowdhury, Mishra, Saha, & Kushwaha, 2011). Techniques such as coagulation, chemical precipitation, mem- brane filtration, solvent extraction, reverse osmosis, photocatalytic degradation, sonochemical degradation, micellar enhanced ultra- filtration, cation exchange membranes, electrochemical degra- dation, integrated chemical–biological degradation, integrated iron(III) photoassisted-biological treatment, solar photo-Fenton ∗ Corresponding author. Tel.: +91 9831387640; fax: +91 3432547375. E-mail address: chowdhuryshamik@gmail.com (S. Chowdhury). and biological processes, and adsorption have been tested and evaluated for the treatment of dye bearing effluents (Rafatullah, Sulaiman, Hashim, & Ahmad, 2010). Among them, adsorption has been recognized as a promising technique due to its ease of opera- tion, simplicity of design, high efficiency and comparable low cost of application in decoloration process (Chowdhury & Saha, 2010; Saha et al., 2010). A number of natural materials or the wastes/by- products of industries, which cost less and can be used as such or after some minor treatment have been tested and used for removal of dyes from aqueous solutions. In this connection, special attention have been given to agricultural wastes like orange peel, banana pith, banana peel, plum kernels, apple pomace, wheat straw, sawdust, coir pith, sugarcane bagasse, tea leaves, bamboo dust, etc. (Gupta & Suhas, 2009). Rice husk, the hard, protective, outer shell of the rice grain is abundantly available as a by-product of the rice milling industries and creates potential environmental problems (Foo & Hameed, 2009; Li et al., 2011). The annual generation of rice husk is estimated to be around 120 million tonnes, accounting about one-fifth of the annual gross rice produc- tion throughout the world (Foo & Hameed, 2009). Any possible usage of that will yield economic as well as environmental dividends. In nature, rice husk is tough, insoluble in water, woody, has chemical stability, high mechanical strength and is characterized by its abrasive inherent resistance behavior and silica–cellulose structural arrangement. It mainly consists of cellulose (32%), hemi- celluloses (21%), lignin (21%), silica (20%) and crude proteins 0144-8617/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.06.058