A novel hierarchical porous polyHIPE/Fe₃O₄ nanocomposite foam functionalized by 1-vinylimidazole for Fe²⁺ removal from aqueous solutions

Highly open porous poly(styrene-co-divinylbenzene) polyHIPE foam was successfully synthesized and then functionalized by different percentages of 1-vinylimidazole co-monomer. Fe₃O₄ nanoparticles were synthesized and incorporated in the functionalized polyHIPE foams to enhance Fe²⁺ removal efficiency from aqueous solutions. The co-monomer in the functionalized and functionalized/Fe₃O₄ nanocomposite foams is well-suited to enhance Fe²⁺ removal efficiency. The adsorption efficiency of the 1-vinylimidazole-functionalized polyHIPE foams increased with increasing 1-vinylimidazole percentage. The kinetic studies showed a pseudo-second-order adsorption kinetics at different co-monomer concentrations. The nanocomposite foam containing 10, 20, 30 wt% Fe₃O₄ removed 79.01, 84.03, and 72.56% of Fe²⁺ ions, respectively. The 1-vinylimidazole@PolyHIPE/20 wt% Fe₃O₄ nanocomposite with the highest Fe²⁺ removal capacity was selected for further adsorption studies. The Fe²⁺ removal efficiency by this nanocomposite foam was investigated at different pHs, adsorbent dosages, and initial Fe²⁺ concentrations using the response surface method (RSM) experimental design. In addition to aqueous solutions containing only Fe²⁺ ions, the Fe²⁺ removal efficiency was evaluated in the presence of Ni²⁺, Cr³⁺, Cr⁶⁺, Zn²⁺, and Pb²⁺ for comparison purposes. These competing metal ions in the solution decreased the Fe²⁺ removal efficiency from 84.03 to 77.20%. The adsorption isotherms were best fitted to the Langmuir equation, indicating the adsorption of a monolayer of Fe²⁺ ions on the polyHIPE walls.