Adsorption of Cu(II) from Aqueous Solution on Sonicated Activated Carbon Prepared from Arenga Pinnata Merr Fruit Shell Waste: Isotherm, Kinetic and Thermodynamic Studies

Abstract

Adsorption of Cu(II) from aqueous solution on the activated carbon (AC) prepared from Arenga pinnata Merr fruit shell (APMFS) waste with the assistance of ultrasound was evaluated by conducting batch mode experiments. As a result, KOH activation using 40 kHz of ultrasound restructured active binding sites and produced more pores on the APMFS-AC according to FT-IR and SEM analyses, respectively. Increasing the sonication time from 45 min to 135 min increased the adsorption capacity from 6.535 mg/g to 7.042 mg/g, respectively, at the initial Cu(II) concentration of 257.213 mg/L, 27°C and pH 5. With an increment of the adsorption temperature to 45°C, it increased the adsorption capacity up to 11.765 mg/g. The investigation on the independent variables showed the optimum conditions of adsorption which were 257.213 mg/L of the initial Cu(II) concentration, 60 min of contact time, pH 5 and 45°C using 135 min of sonicated APMFS-AC. The Cu(II) adsorption isotherm was fitted with the Langmuir model at the optimum condition. The Langmuir mono-layer adsorption capacity obtained was 11.765 mg/g with the BET saturation capacity, and the total pore volume values were 13.029 mg/g and 3.987 L/mg, respectively. The Cu(II) adsorption followed the pseudo second-order kinetics model with the adsorption rate 0.473 g/mg.min. Thermodynamic parameters of enthalpy change (∆H⁰, 27.035 kJ/mol), Gibbs free energy (∆G⁰, 7.292 kJ/mol), entropy change (∆S⁰, 0.062 kJ/mol.K), and activation energy (E, 22.637 kJ/mol) were determined. These results confirmed that endothermic, spontaneous and chemical adsorption took place.