Reusable Nanosorbents Based on Polyethylenimine-Functionalized Magnetite for Removal of Metal Ions from Contaminated Water

Abstract

Environmental contamination and human exposure to heavy metals have dramatically increased with growing use in industrial process and products. Some heavy metals are essential to maintain the metabolism of the human body. However, they are serious threats to public health and ecosystem even at low doses due to bioaccumulation. Thus, considerable attention is paid to remove the heavy metal ions efficiently and regenerate the adsorbents from contaminated water. In this study, we developed the reusable adsorbents for removal of the heavy metal ions such as Cu(II), Pb(II) and As(V) by introduction of b-PEI to magnetite particles. Branched polyethylenimine (b-PEI) is known as a good chelating polymer of the heavy metals. Its amine-rich structures chelate cationic metal ions through electrostatic interaction and are regenerated efficiently with repulsion between protonated amine groups and adsorbed metal. Quaternary ammonium b-PEI also combines with anionic metal ions by ionic-bond interaction and releases the adsorbed anions by ion exchanging. Effectiveness of the magnetite that it is efficiently separated from water in external magnetic field can apply in water treatment process. For removal of Cu(II) and Pb(II), b-PEI functionalized magnetite (P-MG) was synthesized by covalent assembly of b-PEI to surface of amine-functionalized magnetite (AMG) using a cyanuric chloride as a liking agent. Next, quaternary ammonium polyethylenimine-functionalized magnetite (QP-MG) was prepared by modification of P-MG by glycidyltrimethylammonium chloride (GTA) for removal of anionic metal ions (As(V), Cr(VI)). The chemical compositions and degree of modification by b-PEI and GTA were investigated using FT-IR spectroscopy, XPS and TGA. It was revealed that b-PEI and quaternary ammonium b-PEI was successfully incorporated in the magnetite. The structure and morphology of adsorbents were characterized by WXRD, FE-SEM and HR-TEM, respectively. It was observed that surface of the adsorbents was covered with organic material such as a polymer. However, all of the adsorbents were maintained the magnetite spheres with spinel structure, so modification using b-PEI and GTA did not affect their morphology and structure. The saturation magnetization of P-MG and QP-MG measured by VSM was similar to that of the AMG, which indicates that the adsorbents have sufficient magnetization (above 60 emu/g) and could be enough to be used for the repeated magnetic separation from water. To optimization of adsorption and recovery property toward Cu(II), Pb(II), As(V) and Cr(VI), adsorption-desorption experiments were carried out at various pH conditions. As a result, maximum adsorption efficiencies of the P-MG for Cu(II) and Pb(II) were 96% and 97%. Moreover, it shown high recovery efficiency of more than 94% toward Cu(II) and Pb(II), after 4 recycling test. Especially, adsorption and recovery property of QP-MG were affected with pH conditions because anionic heavy metals have different formation at various pH value in aqueous solution. As a result, maximum recovery efficiency of QP-MG was presented at pH 4.5 toward As(V) and Cr(VI). In the equilibrium isotherm, maximum adsorption capacities of the adsorbents for Cu(II), Pb(II), As(V) and Cr(VI) were estimated 158.7 mg/g, 163.9 mg/g, 20.9 mg/g and 23.5 mg/g by Langmuir model. In additions, adsorption efficiency of the adsorbents was well maintained during the repeated regeneration. The overall results of our studies suggest that P-MG and QP-MG could be used as separable and reusable adsorbents with high efficiency for adsorption of Cu(II), Pb(II), As(V) and Cr(VI) in contaminated water. Consequently, adsorbents based on b-PEI-functionalized magnetite were successfully prepared and demonstrated to be promising candidates as reusable materials for efficient removal of heavy metal ions in contaminated water.