Polyethyleneimine‐Modified Magnetic Chitosan Composite Microspheres for Adsorption of Direct Dyes in Wastewater

ABSTRACT To tackle dyeing wastewater pollution, polyethyleneimine (PEI)‐modified magnetic chitosan microspheres (PEI/Fe 3 O 4 /CS) were synthesized via reverse phase emulsion and impregnation methods for efficient removal of Direct Pink 12B and Direct Lake Blue 5B dyes from aqueous solutions. The composite exhibited a rough surface with saturation magnetization of 33.1 emu g −1 , and successful integration of amino groups with Fe 3 O 4 nanoparticles, as confirmed by SEM, VSM, and FTIR. PEI modification significantly enhanced adsorption performance, achieving maximum capacities of 87.83 mg g −1 for Direct Pink 12B and 186.15 mg g −1 for Direct Lake Blue 5B. Kinetic analysis revealed distinct adsorption mechanisms: pseudo‐first‐order for Direct Pink 12B ( 0.9959) and pseudo‐second‐order for Direct Lake Blue 5B ( 0.9958). Both dyes aligned with the Freundlich isotherm ( 0.9900), indicating multilayer adsorption. It is revealed that the adsorption process is synergistically driven by electrostatic interactions (via protonated amino groups, NH 3 + ), hydrogen bonding, and π–π stacking. Notably, the composite microspheres retained > 75% removal efficiency after five cycles and enabled rapid magnetic recovery. This study provides a cost‐effective, recyclable adsorbent with high potential for industrial dye wastewater treatment.