Adsorption of crystal violet dye by coconut husk powder: Isotherm, kinetics and thermodynamics perspectives

Abstract

The success of this research is to develop coconut husk powder (CHP) as an effective potential adsorbent to remove crystal violet (CV) dye from the synthetic wastewater. Adsorption experiments were performed in batch mode, and various operational parameters like initial dye concentration, adsorbent dosage, solution pH, and contact time were studied to optimize the process. The adsorption of dye content is significantly influenced by pH and initial dye concentration of the wastewater. The maximum adsorption was recorded at a pH of 5 and a dye concentration of 200 ppm, considered optimal operational conditions. Different isotherm models such as Langmuir, Freundlich, Temkin, and Dubinnin–Radushkevich were used for adsorption equilibrium study at various temperatures. The monolayer adsorption mechanism was confirmed by fitting the obtained adsorption data to the Langmuir isotherm model, and the highest adsorption capacity of around 454.54 mg/g was obtained. Moreover, the fittings of adsorption kinetic data to different kinetic models like pseudo first order, second order, and intra–particle diffusion types indicate that the adsorption of CV on CHP surface follows suitably the pseudo second order kinetic model. Various thermodynamic parameters, e.g., standard entropy (ΔS°), Gibbs free energy (ΔG°), and enthalpy (ΔH°) were also experimentally evaluated which proved to be an endothermic and spontaneous adsorption process. Finally, the adsorption mechanism of the adsorbent was explained and a regeneration method for repetitive use was studied. It can be concluded that CHP could be a cost–effective and locally available potential adsorbent to remove dyestuffs from industrial wastewater.