Structural characterization and adsorption performance of Nd₂O₃ nanoparticles for methylene blue removal from water

Abstract

High efficiency removal of synthetic dyes remains an important challenge in water purification because persistent dye residues can compromise water quality and pose environmental risks. This study investigates the rapid sonochemical synthesis of neodymium oxide nanoparticles (Nd₂O₃ NPs) and evaluates their adsorption performance toward methylene blue (MB) removal from drinking and tap water. The synthesized Nd₂O₃ NPs were characterized by SEM, TEM, EDX, FT-IR, XRD, TGA/DTG, and zeta-potential analysis, confirming the formation of crystalline hexagonal Nd₂O₃ nanoparticles with an average particle size of approximately 10 nm and a chemically active, hydroxylated surface. Batch adsorption experiments showed optimum performance at pH 7, 25 °C, and 25 min contact time. Equilibrium data were best described by the Freundlich isotherm (R² = 0.9923), indicating adsorption on a heterogeneous surface. Kinetic analysis showed that the pseudo-first-order model provided the best fit (R² = 0.9336), while thermodynamic parameters confirmed a spontaneous (ΔG° = −27.05 to −27.83 kJ mol⁻¹) and exothermic (ΔH° = −17.48 kJ mol⁻¹) adsorption process with positive entropy change (ΔS° = +32.32 J mol⁻¹ K⁻¹). Recovery experiments in drinking and tap water yielded satisfactory recoveries of 94–100%, demonstrating good applicability in real-water matrices. These findings indicate that sonochemically synthesized Nd₂O₃ nanoparticles are promising sorbents for efficient removal of methylene blue from aqueous systems.