Comparative adsorption performance of bare and chitosan-coated La-Zn-Fe spinel/perovskite nanocomposites for efficient dye removal

Abstract Effective and affordable treatment of dye-contaminated wastewater remains essential for environmental protection. This study reports the synthesis of La 0.5 Zn 0.5 Fe 2 O 4 (LZNF) nanoparticles via coprecipitation and their in situ polymerization with Chitosan to form LZNF/CS nanocomposites. The materials were characterized using EDX, FT-IR, VSM, XRD, TEM, SEM, and BET analyses. XRD confirmed nanocrystalline cubic spinel La 0.5 Zn 0.5 Fe₂O₄ as the main phase, with orthorhombic perovskite LaFeO₃ as a secondary component. LZNF showed high adsorption efficiency toward the anionic dyes indigo carmine (IC) and Acid Blue 25, achieving removals of 97.7% and 92%, respectively, while LZNF/CS achieved 92% and 69% under acidic conditions. Adsorption of both dyes followed a pseudo-second-order kinetic model and was spontaneous and exothermic. IC and AB 25 adsorption on LZNF fitted the Langmuir model, indicating monolayer adsorption, whereas adsorption on LZNF/CS followed the Freundlich model, suggesting multilayer uptake due to Chitosan modification. Electrostatic interactions dominated the adsorption mechanism, with hydrogen bonding and electrostatic interactions contributing secondarily. Both materials retained strong performance over five regeneration cycles, supporting their potential as efficient adsorbents for wastewater purification.