Composition-dependent adsorption performance of magnetic Fe3O4/chitosan nanocomposites for Pb(II) removal from aqueous solutions

Magnetic Fe 3 O 4 /chitosan (Fe 3 O 4 /Cs) nanocomposites with different Fe 3 O 4 -to-Cs ratios were fabricated using a co-precipitation and Cs-coating approach and evaluated for Pb(II) adsorption from aqueous media. The materials were characterized using XRD, FTIR, SEM-EDX, TEM, and VSM. Batch experiments were conducted to examine the adsorption behavior as a function of pH, contact time, adsorbent dosage, initial Pb(II) concentration, and temperature. Pb(II) adsorption increased with increasing pH and reached the highest value at pH 5. Equilibrium was reached after 120 min, indicating the adsorption time required to achieve equilibrium. Among the evaluated composites, Fe 3 O 4 /Cs (1:1) exhibited the highest adsorption capacity while maintaining magnetic recoverability. The PSO model provided the best mathematical fit among the tested kinetic models, describing the overall adsorption kinetics under the investigated conditions. The maximum adsorption capacity of the Fe 3 O 4 /Cs (1:1) reached 44.31 mg/g, and the equilibrium data showed the best agreement with the Langmuir isotherm model among the tested models. The positive ΔH° value of +16.64 kJ/mol indicated an endothermic adsorption process, and the positive ΔS° value indicated increased randomness at the solid–solution interface during adsorption; the negative ΔG° value indicated thermodynamically favorable adsorption. The kinetic and equilibrium results, together with functional groups identified in the unloaded Fe 3 O 4 /Cs composite, suggest that surface functional groups may contribute to Pb(II) adsorption. These results indicate that Fe 3 O 4 /Cs, particularly at a 1:1 composition, has potential as magnetically recoverable adsorbents for Pb(II) removal from controlled aqueous solutions.