Magnetic amine-functionalized polyacrylic acid-nanomagnetite for hexavalent chromium removal from polluted water

Abstract

A novel magnetic amine-functionalized polyacrylic acid-nanomagnetite (Fe₃O₄-PAA-NH₂) adsorbent prepared using a facile surface-initiated polymerization (SIP) method has delivered a great Cr(VI) removal performance compared to as-received Fe₃O₄ nanoparticles. The maximum amine group (–NH₂) concentration grafted onto Fe₃O₄-PAA is determined to be 3.925 mg g⁻¹ based on acid–base titrimetric analysis. The optimal pH value for Cr(VI) adsorption is around 2.0 with a Fe₃O₄-PAA-NH₂ dose of 30 mg and contact time of 10 min at room temperature. A multilayer adsorption for the Freundlich isotherm model is well-fitted and fits better than the monolayer adsorption of the Langmuir isotherm model. The kinetics of Cr(VI) removal by the Fe₃O₄-PAA-NH₂ nanoadsorbent is found to follow pseudo-second-order behavior with a calculated room temperature rate constant of 1.23 g mg⁻¹ min⁻¹ for a solution with an initial Cr(VI) concentration of 7.0 mg L⁻¹ and pH value of 2.5. The competition adsorption tests show that the presence of other metals in polluted water, including Cu(II), Zn(II), Cd(II), K(I), Ca(II), Na(I), and Mg(II), favors the Cr(VI) adsorption by the fabricated Fe₃O₄-PAA-NH₂ nanoadsorbent due to the affinity of the chemical potential and electronegativity of each metallic element. Moreover, the prepared Fe₃O₄-PAA-NH₂ nanoadsorbent exhibits a good reusability and retains around 85% of its Cr(VI) adsorption capacity even after 5 cycles.