Adsorption of p–nitrophenol on coconut shell granular activated carbon: Isotherms, kinetics and thermodynamics

Abstract

Adsorption of p-nitrophenol by modified granular activated carbons based on coconut shell from aqueous solutions has been studied under laboratory conditions. Four granular activated carbons GAC383 (native form), GACO383 (its nitric acid oxidised form), GACZC1073 (native form incorporated with Zn²⁺ ions and activated at 1073) and GACOZC1073 (oxidised form impregnated with ZnCl₂) have been used. Batch experiments have been carried out with variants being concentration, time, temperature and equilibrium conditions. Pseudo first, second order kinetic models, intraparticle diffusion models and Elovich kinetic model are applied to study the respective kinetics. Pseudo second order rate equations are found to be best suited for the adsorption systems. Equilibrium isotherm for concentration range (25-3000 mg/L) is analysed by Langmuir (L) and John - SivanandanAchari (J-SA) isotherm models. GACZC1073 has higher adsorption capacity (490.2 mg/g) than GACO383 (224.2 mg/g). The temperature on the adsorption of p- nitrophenol is studied at different temperatures. The thermodynamic parameters such as Gibbs free energy, enthalpy and entropy are calculated using Van’t Hoff equation. It is inferred that, the adsorption of p-nitrophenol on new modified carbons is endothermic and occurs through physisorption. This study reveals that Zn²⁺ ions impregnated activated carbon GACZC1073 has more adsorption efficiency evidenced by a high adsorption of rate α and surface diffusion K_id1 promoted by extra adsorption sites generated during activation.