Kinetic, isotherm, and thermodynamic studies on the adsorption of malachite green dye using untreated biosorbent derived from geranium plant waste

This study evaluates the potential of an untreated biosorbent derived from Geranium plant waste (GPW-U) for the removal of Malachite Green (MG) dye from aqueous solutions. Batch adsorption experiments were conducted to investigate the effects of biosorbent dose, contact time, initial dye concentration, pH, and temperature. The maximum dye removal was achieved at pH 6 and a contact time of 80 minutes. Adsorption isotherms were analyzed using Langmuir, Freundlich, Temkin, Jovanovic, and Harkin–Jura models, with the Freundlich model providing the best fit (R² = 0.9998). Kinetic analysis indicated that the adsorption followed a pseudo-second-order model (R² = 0.9903). Thermodynamic parameters, including Gibbs free energy (–0.0695 kJ/mol), enthalpy (31.60 kJ/mol), and entropy (0.1122 kJ/mol·K), suggested that the process is feasible, spontaneous, and endothermic. The surface area of the biosorbent was determined using BET analysis. Structural and morphological characterization of the biosorbent before and after dye adsorption was performed using FTIR, SEM, and XRD. The findings highlight the potential of GPW-U as an effective, low-cost biosorbent for dye removal from wastewater.