Congo Red Removal from Aqueous Solution Using 2-Mercaptopropionic Acid Functionalized Fe₃O₄ Magnetic Nanoparticles

In this study, magnetic Fe₃O₄ nanoparticles were synthesized and were modified with 2-mercaptopropionic acid (MPA). This was done to enhance their adsorption performance toward Congo Red (CR) in aqueous solution. FTIR spectroscopy was used to characterize the resulting MPA-functionalized nanomaterial (Fe₃O₄@MPA), confirming the successful attachment of -SH and -COOH functional groups. To investigate the effects of pH, initial dye concentration, contact period and temperature, the batch adsorption technique was conducted. Since the adsorption capacity was not significantly affected by pH, pH adjustment was continued for minimal chemical and time savings. This finding indicates that the surface charge and functional groups of Fe₃O₄@MPA interact most favorably with CR molecules under near-neutral conditions. The adsorption data were fitted to isotherm models, and the optimal model was found to be the Langmuir model (R² = 0.9901), which shows single-layer adsorption with a maximum capacity of 120.48 mg/g. Analysis of the kinetic data revealed a correlation with the pseudo-second-order kinetic model, confirming the chemical adsorption mechanism with a determination coefficient (R²) greater than 0.99. Thermodynamic parameters further confirmed the process to be spontaneous and endothermic, with negative ΔG°, positive ΔH° (6.92 kJ/mol), and positive ΔS° (0.029 kJ/mol·K). More than 60% removal was achieved in real sample applications. This work presents a new approach using MPA-functionalized Fe₃O₄ nanoparticles, which both increases adsorption efficiency and magnetic recoverability, providing a sustainable and pH-independent method for Congo Red purification from real matrices.