Batch adsorption of 4-nitrophenol by acid activated jute stick char: Equilibrium, kinetic and thermodynamic studies

The article describes the performance of acid activated jute stick char (AAJSC) for the adsorption of 4-nitrophenol (4-NP) from aqueous solution in batch mode. Jute stick, a bulk volume agricultural waste, was utilized for adsorption. The char of jute stick prepared at 773 K was activated with phosphoric acid and adsorption experiments were carried out at 298, 308 and 318 K. Equilibrium adsorption data were analyzed using two-parameter models-Langmuir, Freundlich, Temkin. Dubunin-Radushkevich and three-parameter-Redlich-Peterson model. The goodness of the fit was measured using linear regression coefficient (R-2) value and five different error functions. The adsorption data was found to be well described by Langmuir model. The equilibrium time for adsorption was achieved within 4 h. Studies showed that adsorption decreases with the increasing temperature. pH studies were also performed to obtain the equilibrium pH for adsorption. The pseudo-first-order, pseudo-second-order and Elovich kinetic models were applied to test the kinetic data, and were found to closely follow the pseudo-second-order kinetic model. The thermodynamic constants of the adsorption process; Delta G, Delta H and Delta S were evaluated as -18.79 kJ/mol at 25 degrees C, 3917.4 J/mol, 76.21 J/mol K-1 respectively. These showed that the adsorption process was endothermic and spontaneous. (C) 2009 Elsevier B.V. All rights reserved.