In this study, an oil palm empty fruit bunch-based activated carbon was modified using ammonia aqueous solution. The effect of the chemical modification on the adsorption capacity of modified activated carbon (MAC) for 2,4-dichlorophenol (2,4-DCP) adsorption was investigated. The monolayer adsorption capacity of MAC was 285.71 mg/g at 30 degrees C. Adsorption isotherm fitting revealed that Langmuir model was applicable for the MAC. The adsorption kinetics of 2,4-DCP onto MAC was described by the pseudo-second-order kinetic model. The surface modification of the activated carbon using ammonia was shown to be able to increase its adsorption capacity for 2.4-DCP. (C) 2011 Elsevier B.V. All rights reserved.