Kinetics, equilibrium and thermodynamics studies on the adsorption of methylene blue and crystal violet from aqueous solution using activated carbon prepared from jack fruit seed

Abstract

Dye removal from industrial effluents has become a significant issue in recent years. In this study Jackfruit (Artocarpus heterophyllus) seed activated carbon (JSAC) with zinc chloride (ZnCl2) was used to investigate its potential as an adsorbent for the removal of two cationic dyes, methylene blue (MB) and crystal violet (CV) from aqueous solution. The dried Jackfruit seed powder/ZnCl2 mixture was put on a crucible placed in an electrical furnace for carbonization. The heating rate of carbonization was 25 ºC/min and continues until the final temperature of 550 oC was reached and it was kept at this temperature for 30 min. The absorbance for MB and CV solution was obtained using UV-Vis spectrophotometer. Experimental parameters such as contact time, medium pH, adsorbent dosage, dye concentration and temperature were studied to explore their effects on the adsorption of cationic dyes onto the adsorbent. Thermodynamics, isotherm models and kinetics were applied on the experimental data in order to further understand the adsorption process and mechanism. Kinetic studies of the data showed that the adsorption follows the pseudosecond-order kinetic model. Thermodynamic parameters, enthalpy change (∆H), entropy change (∆S) and Gibbs free energy change (∆G) were also calculated for the uptake of MB and CV. This parameter showed that adsorption on the surface of JSAC was feasible, spontaneous in nature, and endothermic between temperatures of 25 and 45 oC. The equilibrium data better fitted the Freundlich isotherm model for studying the adsorption behavior of MB and CV by JSAC. Maximum adsorption capacity of JSAC was observed to 1.82 mg/g for MB and 2.39 mg/g for CV at 25 oC and 20 mg/L