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 (R2) 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; ΔG°, ΔH° and ΔS° were evaluated as −18.79 kJ/mol at 25 °C, 3917.4 J/mol, 76.21 J/mol K−1 respectively. These showed that the adsorption process was endothermic and spontaneous.