Adsorption of Eosin Dye from Aqueous Solution Using Groundnut Hull–Based Activated Carbon: Kinetic, Equilibrium, and Thermodynamic Studies

This article reports the use of activated carbon prepared from groundnut hulls (GHAC) in the adsorption of eosin dye from aqueous solution in batch process. The prepared GHAC was characterized using Brunauer, Emmett and Teller (BET), Fourier transform infrared, and scanning electron microscopy. Operational parameters such as agitation time, initial dye concentration, pH, and effect of temperature were studied. Equilibrium time for the adsorption process was attained in 6 h. Adsorption isotherms used to test the adsorption data were Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherms. Adsorption equilibrium data were best described by these isotherms in the following order: Temkin > Langmuir > Freundlich > D-R. Kinetic data were fit using pseudo-first- and second-order kinetic models. Adsorption of eosin dye onto GHAC was best described by the pseudo-second-order kinetic model. Thermodynamic parameters such as ΔG0, ΔH0, and ΔS0 of the adsorption process were determined; the adsorption process was feasible, endothermic, and spontaneous with increased randomness at the solid–solution interface. The mean energy of adsorption (<8 kJ/mol) obtained from D-R isotherm showed that the reaction followed a physisorption mechanism. Regeneration and reusability of GHAC were assessed for four successive adsorption–desorption cycles and was found to retain its adsorptive capacity as high as 98%. This study has shown that GHAC is a good adsorbent in the treatment of eosin dye from aqueous solution.