Adsorption Isotherms and Kinetics Studies on Adsorption of Malachite Green onto Activated Charcoal from Aqueous Solution

Abstract

The article presents low-cost activated charcoal as an adsorbent in the adsorption process for the removal of malachite green from aqueous solution by batch process. To find the optimum condition of the process, contact time, shaking rate, concentration of malachite green, and concentration of activated charcoal were examined. The malachite green was removed up to 98.9%. The adsorption isotherms were studied to check the performance of the adsorbent. Langmuir, Freundlich, Temkin, Hill De Boer, and Dubinin-Radushkevich adsorption isotherms were studied and compared to which one was suitable in the process. The adsorption process with the activated charcoal adsorbent followed suitably with the order of the Dubinin-Radushkevich > Langmuir > Hill De Boer> Temkin > Freundlich models. According to a kinetic study, the adsorption process was second order. In thermodynamic studies, we obtained negative values of ΔG, ΔS, and ΔH. The negative ΔH and ΔS values suggest that enthalpy contributes more than entropy in producing negative ΔG values. The negative ΔG values of malachite green adsorptions indicate that is a favorable and spontaneous process. The negative value of ΔH ensures the adsorption process is characterized as chemical adsorption and exothermic. The negative ΔS value indicates that randomness decreases at the solid–solution interface during the adsorption of MG by activated charcoal. The surface morphology of the Activated charcoal ensured the adsorption process. The results indicate that the adsorption process is exothermic, spontaneous, and favorable. So, activated charcoal might be useful for removing the malachite green dye from the aqueous solution.