Investigation of Adsorption Kinetics, Thermodynamics, and Regeneration Efficiency of Activated Carbon Derived from Fruit Seed Waste for Dye Removal

Abstract

Disposal of artificial dyes into water sources creates many environmental issues due to the characteristics of stability, retention of color, and the non-degradable nature of such dyes. In this research, the use of activated carbon prepared from waste seeds of mangoes for the elimination of methylene blue dye has been investigated with a focus on kinetic, thermodynamic and recyclability aspects of the adsorbent. Waste mango seeds were converted to porous activated carbon by the process of carbonization along with chemical activation with potassium hydroxide. The adsorbent was studied using BET analysis, scanning electron microscopy (SEM), and FTIR spectroscopy. Several factors such as pH of the solution, dosage of adsorbent, concentration of the dye, contact time, and temperature have been considered in determining the adsorption behavior of the adsorbent. The specific surface area, average pore size, and pore volume of activated carbon were determined to be 842.60 m²/g, 2.48 nm, and 0.52 cm³/g, respectively. Process kinetics have shown that the pseudo-second-order model describes the process better. Thermodynamic analysis has revealed the endothermic nature of the adsorption process, with enthalpy and entropy changes of +18.60 kJ/mol and +0.086 kJ/mol·K, respectively. Results from the regeneration studies have shown that the adsorption capacity decreases from 47.55 mg/g to 36.80 mg/g, thus showing 77.39% capacity retention in five cycles. Desorption efficiency reduces to 84% from 92%. From the above results, it can be concluded that the activated carbon derived from mango seeds shows good adsorption behavior and retains good dye adsorption capacity even after several regenerations.