Adsorption of Rhodamine B Dye Using Concentrated Extract of Secondary Metabolites from Mango Peel (Mangifera indica L.)

Rhodamine B is a synthetic dye widely used in various industrial applications and poses a serious environmental pollution risk due to its toxicity and resistance to biodegradation. This study aimed to evaluate the adsorption performance of concentrated secondary metabolite extract from mango peel (Mangifera indica L.) as a natural adsorbent for the removal of Rhodamine B from aqueous solutions. The effects of pH, initial dye concentration, and contact time on adsorption capacity were investigated. The residual Rhodamine B concentration was determined using UV-Visible spectrophotometry, while the adsorption behavior was evaluated using Langmuir and Freundlich isotherm models as well as pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. Functional group interactions before and after adsorption were characterized using Fourier Transform Infrared (FTIR) spectroscopy. The optimum adsorption conditions were obtained at pH 3, an initial Rhodamine B concentration of 1400 ppm, and a contact time of 30 min, resulting in an adsorption capacity of 154.30 mg g-1. The adsorption equilibrium was better described by the Langmuir isotherm model (R2 = 0.8843) than by the Freundlich model (R2 = 0.6289), with a maximum adsorption capacity (Qmax) of 161.29 mg g-1 and a separation factor (RL) of 0.062, indicating favorable monolayer adsorption. Kinetic analysis showed that the adsorption process followed the pseudo-second-order model (R2 = 0.9991) rather than the pseudo-first-order model (R2 = 0.0843), suggesting that adsorption predominantly occurred through chemisorption. FTIR analysis further confirmed the involvement of hydroxyl, carbonyl, aromatic, and C-O functional groups in the adsorption process through shifts in characteristic absorption bands after adsorption. These findings demonstrate that concentrated secondary metabolite extract from mango peel is a promising natural adsorbent for Rhodamine B removal and has potential for application in environmentally friendly dye wastewater treatment.