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The adsorption of C. I. Reactive Red 120 (RR120) on activated oil palm ash (AOPA) was studied in a batch system. The adsorption studies were carried out at different initial dye concentrations (50–600 mg L–1), solution pH (2–12) and temperature (30, 40 and 508C). The experimental data were analyzed by the Langmuir and Freundlich isotherms. The Freundlich model agreed very well with the experimental data. The maximum monolayer adsorption capacities obtained from the Langmuir model was 200.12, 334.78 and 376.41 mg g–1 at 30, 40 and 508C, respectively. The pseudo-first-order and pseudo-second-order were used to describe the kinetics data. The adsorption kinetics of RR120 onto AOPA was described by the pseudo-second-order kinetic equation. The activation energy, change of Gibbs free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of RR120 onto AOPA.

Activated oil palm ash adsorbent was found to be suitable for the removal of reactive dye form aqueous solution. The Freundlich isotherm model was well described the adsorption of RR120 onto AOPA. The adsorption capacities of RR120 dye on AOPA adsorbent were found 200.12, 334.78 and 376.41 mg g–1 at 308C, 408C and 508C, respectively. The pseudo-second-order kinetic model fits very well with the kinetic data. The activation energy of adsorption of RR120 dye onto AOPA adsorbent was found to be 12.42 kJ mol–1. The positive values of DH8, DS8 and negative values of DG8 for the RR120 dye adsorption obtained indicated that the adsorption process is endothermic, spontaneous and random, respectively. Acknowledgment The authors acknowledge the research grant provided by Universiti Sains Malaysia, Penang that has resulted in this article.