Removal of toxic metal ions with magnetic hydrogels

Abstract

Hydrogels, based on 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) were synthesized via photopolymerization technique and used for the preparation of magnetic responsive composite hydrogels. These composite hydrogels with magnetic properties were further utilized for the removal of toxic metal ions such as Cd(II), Co(II), Fe(II), Pb(II), Ni(II), Cu(II) and Cr(III) from aqueous environments. It was revealed that hydrogel networks with magnetic properties can effectively be utilized in the removal of pollutants. The results verified that magnetic iron particle containing p(AMPS) hydrogel networks provide advantageous over conventional techniques. Langmuir and Freundlich adsorption isotherms were applied for toxic metal removal and both isotherms were fit reasonably well for the metal ion absorptions.

Introduction

Due to the scientific and technological progress, toxic metal contamination is a serious problem (Jang et al., 2008, Zhou et al., 2009a, Zhou et al., 2009b) threatening human health. Heavy metal ions such as Pb(II), Cd(II), Hg(II), and Ni(II) are toxic and carcinogetic at even relatively low concentrations (Liu et al., 2008). They are not biodegradable and can accumulate in living organisms (Iemma et al., 2008). Therefore, these heavy metals can be considered as one of the most important pollutants for waters and waste waters (Liu et al., 2009). Heavy metals are generally discharged to the environments via automobile emissions, mining activities, battery industry, fossil fuels (Guilherme et al., 2007), metal plating and electronic industries with diverse routes (Denizli et al., 2005). In order to remove heavy metal ions from various environments, the techniques such as precipitation, adsorption, ion exchange (Zhao and Mitomo, 2008), reverse osmosis, electrochemical treatments (Jang et al., 2008), hyperfiltration (Chen et al., 2009), membrane separation, evaporation, coagulation, flotation (Akkaya and Ulusoy, 2008), oxidation and biosorption processes (Yan and Bai, 2005, Liu et al., 2006) are widely used.

Recently, adsorbents with magnetic properties gained much attention due to the readily removal ability with the applied magnetic field upon absorption of pollutants from aqueous environments (Liu et al., 2009, Zhou et al., 2009a, Zhou et al., 2009b). Additionally, magnetic particles have many supplementary usages in biomedical (Wang et al., 2008) as controlled drug releasing agents, in medicine, electric–electronic (Fuhrer et al., 2009), pharmacology, sensors and various other fields including nanorobots (Satarkar and Hilt, 2008a, Satarkar and Hilt, 2008b).

Hydrogels are water-swollen crosslinked network of hydrophilic polymers (Taleb et al., 2007; Chauhan et al., 2006). Due to the hydrophilic groups in their backbone, hydrogels can imbibe large quantities of water and swell. The degree of hydrogel swelling is related to the degree of crosslinker, ionic strength of the solution, temperature, pH (Hernandez and Mijangos, 2009) and the presence and the extent of hydrophilic groups such as –OH, –COOH, –NH₂, –CONH₂, SO₃H (Chern et al., 2004). These functional groups in the hydrogel networks can be utilized for the toxic metal ion removal (Sahiner, 2009; Çavuş and Gürdağ, 2008). Hydrogels can also be modified with new functionalities (Pekel et al., 2001) or prepared as composites with clays and with other materials to increase the metal ion absorption capacities (Kaşgöz et al., 2008).

In this investigation, we prepared an anionic hydrogels from AMPS via photopolymerization method and utilized them for in situ iron magnetic particle synthesis to induce magnetic field responsiveness. The swelling characteristic of the prepared hydrogels was investigated in distilled, tap and sea waters. Various toxic metal ion absorption properties such as Cd(II), Co(II), Fe(II), Pb(II), Ni(II), Cu(II) and Cr(III) by bare and composite hydrogel were studied. The adsorption characteristic demonstrated good compatibility with both Langmuir and Freundlich models.