One-step synthesis of Fe3O4/carboxylate-rich carbon composite and its application for Cu(ii) removal

Abstract

Fe₃O₄/carboxylate-rich carbon composites (Fe₃O₄/CRC) have been synthesized via a facile one-step low temperature carbonization method from simple precursors, the single iron source FeSO₄·7H₂O, and sodium gluconate. Carboxylate groups from sodium gluconate can coordinate with Fe(II) and form ferricarboxylate complexes. During the low temperature carbonization process, Fe₃O₄ can be obtained through the thermal decomposition of ferricarboxylate complexes. In addition, sodium gluconate can serve as the source of the carboxylate functional group for Fe₃O₄/CRC. Due to the lower temperature of this carbonization process (300 °C), abundant carboxylate groups can remain in the amorphous carbon and serve as the metal-binding functional group to enhance adsorption affinity between Fe₃O₄/CRC and Cu(II). Fe₃O₄/CRC was found to be an ideal adsorbent for Cu(II) removal with a high adsorption capacity. We investigated how the contact time, temperature, pH, and initial concentration of Cu(II) can affect the adsorption of Cu(II) on Fe₃O₄/CRC. In addition, we also did some theoretical simulations on the Cu(II) adsorption model. Among the various kinetics models, the pseudo-second-order model gives the most suitable kinetics model for adsorption of Cu(II) onto Fe₃O₄/CRC. Adsorption of the heavy metals to Fe₃O₄/CRC reached equilibrium in less than 5 min, and agreed well to the Langmuir adsorption model with a maximum adsorption capacity of 66.67 mg g⁻¹ at 25 °C. The adsorption–desorption studies indicated that Fe₃O₄/CRC possesses good stability and good reusability.