Cationic and anionic modifications of oil palm empty fruit bunch fibers for the removal of dyes from aqueous solutions Mohd Shaiful Sajab a , Chin Hua Chia a,⇑ , Sarani Zakaria a , Poi Sim Khiew b a School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia b Faculty of Engineering, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor, Malaysia highlights " Oil palm empty fruit bunch (EFB) fibers were using as adsorbent for dye removal. " Modifications were carried out using citric acid (CA) and polyethylenimine (PEI). " CA-EFB adsorbed methylene blue up to 130 mg/g. " PEI-EFB adsorbed phenol red up to 171 mg/g. " Both EFBs can be reused up to seven cycles of adsorption/desorption processes. graphical abstract article info Article history: Received 15 July 2012 Received in revised form 29 September 2012 Accepted 2 November 2012 Available online 10 November 2012 Keywords: Adsorption Methylene blue Isotherms Natural adsorbent Phenol red abstract Oil palm empty fruit bunch (EFB) fibers were employed to remove dyes from aqueous solutions via adsorption approaches. The EFB fibers were modified using citric acid (CA) and polyethylenimine (PEI) to produce anionic and cationic adsorbents, respectively. The CA modified EFB fibers (CA-EFB) and PEI-modified EFB fibers (PEI-EFB) were used to study the efficiency in removing cationic methylene blue (MB) and anionic phenol red (PR) from aqueous solutions, respectively, at different pHs, temperatures and initial dye concentrations. The adsorption data for MB on the CA-EFB fitted the Langmuir isotherm, while the adsorption of PR on the PEI-EFB fitted the Freundlich isotherm, suggesting a monolayer and heterogeneous adsorption behavior of the adsorption processes, respectively. Both modified fibers can be regenerated up to seven adsorption/desorption cycles while still providing as least 70% of the initial adsorption capacity. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Water pollutants from dyes industries, including textile, leather, paper, printing, and cosmetic, have caused environmental prob- lems in water ecosystem. Release of dye compounds into water system without proper treatment will harm aquatic life due to tox- icity, interrupt aquatic food chains, prevent sunlight into water ecosystem, and reduce photosynthesis (Almeida et al., 2009). Synthetic dyes usually possess complex molecular structure and are stable in water. Dyes can be classified according to their chemical structure and application, for example, anionic (direct, acid, and reactive dyes), cationic (basic dyes), disperse, solvent, sul- fur, vat, etc. (Gupta and Suhas, 2009; Srinivasan and Viraraghavan, 2010). There are many physical and chemical techniques for removing dyes from industrial effluent, including chemical coagulation/floc- culation, ozonation, cloud point extraction, oxidation, nano-filtra- tion, chemical precipitation, ion-exchange, reverse osmosis, adsorption, and ultra-filtration; however, these techniques possess several limitations such as high cost, requirement of activating 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.11.010 ⇑ Corresponding author. Tel.: +603 8921 5473; fax: +603 8921 3777. E-mail address: chia@ukm.my (C.H. Chia). Bioresource Technology 128 (2013) 571–577 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech