Adsorption of crystal violet dye from aqueous solution onto chemically treated Artocarpus odoratissimus skin: equilibrium, thermodynamics, and kinetics studies

Abstract

In this study, the feasibility of utilizing Artocarpus odoratissimus skin (“Tarap” skin or TS) as a potential adsorbent for the removal of crystal violet dye was investigated. X-ray fluorescence, Fourier Transform Spectroscopic, and scanning electron microscopic investigation of TS and its NaOH-treated form (NaOH-TS) before and after interaction with crystal violet (CV) cationic dye indicate that the dye shows a strong affinity toward the adsorbent, which is enhanced upon the treatment with a NaOH solution. Decrease in the concentration of metal ions on the TS/NaOH-TS is indicative of the contribution of an ion-exchange mechanism owing to the positive charge of CV molecules. Comparison of experimental adsorption curves with calculated curves point the way toward the agreement with the Langmuir isotherm among the six models tested (Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Redlich–Peterson, and Sips) under optimized conditions with maximum adsorption capacity of 118 mg g−1 for TS which is significantly enhanced to 195 mg g−1 upon treatment with NaOH. Kinetics studies support pseudo-second-order and intra-particle diffusion mechanisms. Based on the thermodynamic parameters such as enthalpy (∆H°), entropy (∆S°), and Gibbs free energy changes (∆G°), the sorption of CV dye onto TS and NaOH-TS is a spontaneous and endothermic process.