Green synthesis and adsorption performance of Fe₃O₄/chitosan/polypyrrole composites for efficient removal of chromium ion

In this study, Fe₃O₄/chitosan/polypyrrole (Fe₃O₄/CS/PPy) magnetic adsorbents were successfully synthesized using the <i>in situ</i> chemical oxidation polymerization method. These adsorbents were characterized by SEM, FT-IR, TGA, and XPS. The results of batch adsorption experiments showed that the Fe₃O₄/CS/PPy composite exhibited a maximum adsorption capacity of 193.23 mg g^-1 in a 100 mg L^-1 Cr(vi) solution at 298 K, with a pH of 2.0. The adsorption behavior of the adsorbent to Cr(vi) was in good agreement with the Langmuir isothermal model and the quasi-second-order kinetic model. Thermodynamic studies indicated that the process of adsorption was spontaneous and endothermic. The mechanism of adsorption may be attributed to electrostatic interactions and chemical reduction. After five cycles, the removal efficiency of the Fe₃O₄/CS/PPy composite for Cr(vi) has consistently remained at 84.32%. Overall, the Fe₃O₄/CS/PPy composite exhibits great potential as an adsorbent for effectively removing Cr(vi) from aqueous solutions.