Alkaline-treated cocoa pod husk as adsorbent for removing methylene blue from aqueous solutions Fei ling Pua a , Mohd Shaiful Sajab b , Chin Hua Chia b, *, Sarani Zakaria b , Irman Abdul Rahman b , Mohd Sapuan Salit c a Centre of Advanced Materials, College of Engineering, Universiti Tenaga Nasional, 43000 Kajang, Selangor, Malaysia b School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia c Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Introduction Cocoa (Theobroma cacao) is a tree of 6–8 m height, which can be found in tropical rainforest. Malaysia is one of the top world producers of cocoa with about 1% of total world cocoa production [1]. Cocoa is abundantly planted in Malaysia and it is an important commercial crop next to palm oil and rubber. Cocoa pod husks (CPH) are produced after the removal of cocoa bean from the fruit. Generally, 10 t of CPH will be generated to produce one ton of dry cocoa beans. CPH is a by-product of the cocoa industries and it has been are disposed as waste material which in turn resulted in landfill problems [2]. According to Malaysian Cocoa Board (2012), about 300,000 t of cocoa beans were produced in 2010, which means that approximately 3,000,000 t of CPH was generated in that particular year. Up to now, there is no specific technical used for CPH and this makes CPH an interesting candidate for researchers to convert it into a useful products. Agricultural lignocellulosic based adsorbents have been gaining wide attentions these years, owing to their characteristics, including renewable, biodegradable, environmentally friendly, low cost and abundantly available, etc. Many studies have been carried out to utilize agricultural by-products as adsorbent material in wastewater treatment, for example rice husk and saw dust [3], oil palm fiber [4], hazelnut shell [5], Eucalyptus kraft lignin [6], coconut shell [7], banana and orange peels [8], etc. Dyes have been extensively used in many industries, such as textile, leather tanning, paper production, food technology, coloring, etc. It is estimated that more than 100,000 types of commercially available dyes and more than 7  10 5 t of dyes are produced every year [4,9,10]. Methylene blue (MB) is one of the most commonly used dyes for dying cotton, wood, and silk. It can cause eye burns which might result in permanent injury to the eyes of human and animals. Besides, it can cause breathing difficulties, burning sensation, nausea, etc. [9,11]. There are two main physical processes to remove dye from effluents, i.e., adsorption and membrane separation [2]. Adsorption is considered to be more effective for quickly lowering the concentration of dissolved dye in an effluent, as compared to other methods which are relatively expensive, for example ultrafiltra- tion, reverse osmosis, ozonation, nanofiltration, etc. In this study, we use CPH as adsorbent material for removing MB from aqueous solution. CPH powders were treated with NaOH prior to the adsorption studies. Surface morphology and chemical analyses were carried out on the raw and NaOH-treated CPH powders. The objective of this study is to evaluate the adsorption performance of CPH for MB removal. Effects of different Journal of Environmental Chemical Engineering 1 (2013) 460–465 A R T I C L E I N F O Article history: Received 21 February 2013 Accepted 15 June 2013 Keywords: Adsorption isotherms Cocoa pod husk Kinetic model Methylene blue Natural adsorbents A B S T R A C T In this study, cocoa pod husk (CPH) was used as adsorbent for removing methylene blue (MB) from aqueous solutions. Before the adsorption studies, the CPH was treated using sodium hydroxide (NaOH) to increase its adsorption capacity toward methylene blue (MB). The NaOH-treated CPH was characterized by SEM and FTIR analyses. Lignin was removed after the NaOH treatment, leaving higher accessible surface for adsorption. The adsorption performances of the CPH were investigated in terms of adsorption kinetics and isotherms under different conditions, i.e., pH, initial MB concentration, and temperature. Freundlich isotherm fits the adsorption experiment data better than that of Langmuir and Sips isotherms, suggesting the heterogeneous adsorption behavior of MB on the CPH. The maximum adsorption capacity of the NaOH-treated CPH toward MB is 263.9 mg/g. Pseudo-second order gives the better correlation to predict the kinetic process. The adsorption of MB on the NaOH-treated CPH was found to be endothermic and spontaneous. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +60 3 8921 5473; fax: +60 3 8921 3777. E-mail addresses: chiachinhua@yahoo.com, chia@ukm.my (C.H. Chia). Contents lists available at SciVerse ScienceDirect Journal of Environmental Chemical Engineering jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jec e 2213-3437/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jece.2013.06.012