Removal of Malachite Green from Aqueous Phase Using Coconut Shell Activated Carbon: Adsorption, Desorption, and Reusability Studies

The use of coconut shell activated carbon (CSAC) as a potential adsorbent for malachite green (MG) dye from aqueous solution was investigated in this study. The effect of various factors, such as initial dye concentration, contact time, pH, and solution temperature were studied. The interaction between dye molecule and CSAC absorbent was strongly influenced by the pH of the solution. Maximum adsorption of MG was obtained at pH 6.5, while, the point of zero charge (pHzpc) of CSAC was obtained at pH 6.1. The Langmuir, Freundlich, and Temkin isotherms were used to describe the adsorption equilibrium of the MG. The maximum monolayer adsorption capacities, Q(m), were increased with increment in temperature. The kinetics of adsorption followed a pseudo-second-order kinetic model. The intraparticle diffusion model was evaluated to determine the mechanism of the adsorption process. Based on the Boyd plots, the adsorption of MG on the CSAC absorbent was mainly governed by film diffusion. Thermodynamic parameters, such as Delta G degrees, Delta H degrees, and Delta S were determined and it was found that MG adsorption on CSAC was spontaneous and endothermic in nature. The conducted reusability test disclosed the decreasing CSAC performance from 98% MG removal down to 89% MG removal after 5 consecutive adsorption/desorption cycles.