One-Step Carbon Coating and Polyacrylamide Functionalization of Fe₃O₄ Nanoparticles for Enhancing Magnetic Adsorptive-Remediation of Heavy Metals

Magnetic nanoparticles are used in adsorptive removal of heavy metals from polluted wastewater. However, their poor stability in an acidic medium necessitates their protection with a coating layer. Coating magnetic nanoparticles with carbon showed proper protection but the heavy metal removal efficiency was slightly weak. However, to boost the removal efficiencies of surface functionalization, polyacrylamide was applied to carbon-coated Fe₃O₄ nanoparticles. In this paper, to facilitate the synthesis process, one-step carbon coating and polyacrylamide functionalization were conducted using the hydrothermal technique with the aim of enhancing the adsorptive removal capacity of Fe₃O₄ nanoparticles towards some heavy metals such as Cu(II), Ni(II), Co(II), and Cd(II). The results showed that the one-step process succeeded in developing a carbon coating layer and polyacrylamide functionality on Fe₃O₄ nanoparticles. The stability of the magnetic Fe₃O₄ nanoparticles as an adsorbent in an acidic medium was improved due to its resistance to the dissolution that was gained during carbon coating and surface functionalization with polyacrylamide. The adsorptive removal process was investigated in relation to various parameters such as pH, time of contact, metal ion concentrations, adsorbent dose, and temperature. The polyacrylamide functionalized Fe₃O₄ showed an improvement in the adsorption capacity as compared with the unfunctionalized one. The conditions for superior adsorption were obtained at pH 6; time of contact, 90 min; metal solution concentration, 200 mg/L; adsorbent dose, 0.3 g/L. The modeling of the adsorption data was found to be consistent with the pseudo-second-order kinetic model, which suggests a fast adsorption process. However, the equilibrium data modeling was consistent with both the Langmuir and Freundlich isotherms. Furthermore, the thermodynamic parameters of the adsorptive removal process, including ΔG°, ΔH°, and ΔS°, indicated a spontaneous and endothermic sorption process. The developed adsorbent can be utilized further for industrial-based applications.