Aqueous Phase Adsorption of Dyes onto Activated Carbon Prepared from Vitellaria Paradoxa (Shea Butter) Leaves: Kinetic and Thermodynamic Studies

Abstract

The present study explains the preparation and application of Vitellaria paradoxa activated carbon (VPAC) as a potential low-cost adsorbent in the  removal of Methylene Blue (MB) and Rhodamine B (RhB) dyes from aqueous solution, Scanning electron Microscope (SEM) showed surface morphology  with depositions of adsorbed dyes in smooth regular formation on the surface. The effects of operating parameters such as contact time, adsorbent  dose, pH, temperature, and particle size were investigated for the removal of MB and RhB dyes using VPAC. The adsorption process follows pseudo-  second order kinetic model as the calculated and experimental values of the adsorption capacities are in close agreement, Q_exp = 49.092mg/g, Q_cal =  49.505mg/g for MB while Q_exp = 49.508mg/g, Q_cal = 49.011mg/g for RhB respectively, with R² = 0.999 in each case. The adsorption mechanism results  showed that the adsorption process was controlled by both the internal and external diffusion of the dyes. The values for free energy change (ΔG), and  enthalpy change (ΔH) for MB and RhB were found to be; -2.3314 kJmol^-1 and -7.2125 kJmol^-1 ; and -3.4302 kJmol^-1 and -2.1340 kJmol^-1 respectively, which  indicated the spontaneous, feasible, and exothermic nature of the adsorption process.