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. The adsorption capacity was found to be significantly influenced by pH, with the maximum removal observed at the natural pH of the solution (approximately pH 6.2). 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 = 0.858), which shows single-layer adsorption with a maximum capacity of 45.48 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. These findings underscore the promise of Fe₃O₄@MPA as an effective and magnetically recoverable adsorbent for CR removal under optimum experimental conditions.