Effective removal of heavy metal ions Cd2+, Zn2+, Pb2+, Cu2+ from aqueous solution by polymer-modified magnetic nanoparticles

https://doi.org/10.1016/j.jhazmat.2011.12.013Get rights and content

Abstract

We prepared novel Fe3O4 magnetic nanoparticles (MNPs) modified with 3-aminopropyltriethoxysilane (APS) and copolymers of acrylic acid (AA) and crotonic acid (CA). The MNPs were characterized by transmission electron microscopy, X-ray diffraction, infra-red spectra and thermogravimetric analysis. We explored the ability of the MNPs for removing heavy metal ions (Cd2+, Zn2+, Pb2+ and Cu2+) from aqueous solution. We investigated the adsorption capacity of Fe3O4@APS@AA-co-CA at different pH in solution and metal ion uptake capacity as a function of contact time and metal ion concentration. Moreover, adsorption isotherms, kinetics and thermodynamics were studied to understand the mechanism of the synthesized MNPs adsorbing metal ions. In addition, we evaluated the effect of background electrolytes on the adsorption. Furthermore, we explored desorption and reuse of MNPs. Fe3O4@APS@AA-co-CA MNPs are excellent for removal of heavy metal ions such as Cd2+, Zn2+, Pb2+ and Cu2+ from aqueous solution. Furthermore, the MNPs could efficiently remove the metal ions with high maximum adsorption capacity at pH 5.5 and could be used as a reusable adsorbent with convenient conditions.

Introduction

Heavy metals released into the environment from plating plants, mining, metal finishing, welding and alloy manufacturing pose a significant threat to the environment and public health. The major concern with heavy metals is their ability to accumulate in the environment and cause heavy metal poisoning. Unlike some organic pollutants, heavy metals are not biodegradable and cannot be metabolized or decomposed. Heavy metals can easily enter the food chain through a number of pathways and cause progressive toxic effects with gradual accumulation in living organisms over their life span. Although acute heavy metal toxicity is rare, chronic low-grade toxicity may be more damaging in the long-term and result in chronic illness. Therefore, reliable methods are needed to remove and detect heavy metals in environmental and biological samples.

A great deal of effort has been devoted to the effective removal of heavy metal ions. The traditional methods commonly used for removal from aqueous solution include ion-exchange [1], solvent extraction [2], [3], chemical precipitation [4], nano-filtration [5], reverse osmosis [6] and adsorption [7], [8], [9], [10]. The adsorption process is arguably one of the most popular methods for removal and has attracted considerable attention because of its simplicity, convenience and efficiency. Recently, many research groups have explored several nanoparticles for removal because of the ease of modifying their surface functionality and their high surface area-to-volume ratio for increased adsorption capacity and efficiency. In the last decade, magnetic nanoparticle (MNP) adsorption has attracted much interest and is an effective and widely used process because of its simplicity and easy operation [8], [11], [12], [13], [14], [15].

In recent years, much attention has focused on surface functionalized MNPs such as MNP polymers with core–shell nanostructures, because the polymer shell prevents the core part from particle–particle aggregation and improves the dispersion stability of the core–shell nanostructures in suspension medium [16], [17], [18], [19], [20], [21], [22], [23]. Deposition of mesoporous silica layers on MNPs is considered promising for developing magnetic materials for removal of environmental pollutants [24]. Organosilanes are non-poisonous agents widely used in the chemical industry. However, a search of the literature revealed few reports concerning Fe3O4@Organosilane@Polymer core–shell–shell magnetic nanostructures for removal of environmental pollutants [25].

Considering the biocompatibility and low toxicity of organosilanes and high adsorption ability of polymers, here we report on our preparation and characterization of novel Fe3O4 MNPs modified with 3-aminopropyltriethoxysilane (APS) and copolymers of acrylic acid (AA) and crotonic acid (CA). We investigated the adsorption capacity of Fe3O4@APS@AA-co-CA for heavy metal ions Cd2+, Zn2+, Pb2+, Cu2+ in different pH solution and metal ion uptake capacity as a function of contact time and metal ion concentration. We also studied the adsorption isotherms, kinetics and thermodynamics to understand the mechanism of the synthesized MNPs adsorbing metal ions and explored the effect of the background electrolytes, desorption and MNP reuse.

Section snippets

Instrumentation

We used a PHS-3C pH-meter (Shanghai, Tianyou) for pH measurement. The concentrations of the metal ions in the solution were measured by use of a flame atomic absorption instrument (Hewlett-Packard 3510). Transmission electron microscopy (TEM) involved use of a JEM-1011 transmission electron microscope. X-ray diffraction (XRD) measurement involved use of a Bruker D8 Advance X-ray diffraction analyzer (Germany) with Copper K-alpha (Cu Kα) radiation. The operation voltage and current were kept at

Characterization of the adsorbents

TEM revealed the diameters of the MNPs as typically 15–20 nm (Fig. 1), for a generally homogeneous size. The edges show the immobilization of the copolymers (Fig. 1c).

The 3 types of MNPs possessed superparamagnetic properties, which could be seen from the room-temperature magnetization curves (Supplementary Fig. S1). The saturation magnetization of the naked Fe3O4, Fe3O4@APS and Fe3O4@APS@AA-co-CA MNPs was 79, 67 and 52 emu/g, respectively. The significant reduction in saturation magnetization

Conclusions

We describe the preparation and characterization of MNPs modified with APS and AA-co-CA (Fe3O4@APS@AA-co-CA). Fe3O4@APS@AA-co-CA MNPs are excellent for removal of heavy metal ions such as Cd2+, Zn2+, Pb2+ and Cu2+ from aqueous solution. Furthermore, the MNPs could efficiently remove the metal ions with high maximum adsorption capacity at pH 5.5 and could be used as a reusable adsorbent with convenient conditions.

Acknowledgement

This study was supported by 973 Program (2010CB933504).

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