Magnetic ion-imprinted and –SH functionalized polymer for selective removal of Pb(II) from aqueous samples
Introduction
The release of heavy metal ions into our environment poses a threat to human health as well as to the ecosystem. Owing to their severe toxic effects on living organisms, it is necessary to find ways for their removal, especially that from aqueous systems [1]. As a pollutant lead (Pb) is released in mining, printing, metal plating, as well as in textiles, ceramics, glasses, explosives, and acid batteries industries [2]. It is known that over exposure to lead and its compounds can result in damage of nerve, kidneys, liver, brain, cardiovascular, and endocrine system; in serious cases it can cause death [3], [4]. Conventional methods such chemical precipitation [5], ion exchange [6], electrolysis [7], membrane separation [8], biological treatment [9], adsorption [10], and biosorption [11] have been adopted for the removal of heavy metals. Among them, adsorption has been considered to be a rapid, simple, effective, economic, and environment-benign. However, most of the adsorption processed are non-specific, showing low selectivity toward a particular heavy metal [12]. Since copresence of a number of metal ions in wastewater is common, it is of great significance to selectively remove or enrich the ions of a particular toxic or precious metal. Therefore, the development of a technique for such a goal is a current research interest.
The ion imprinting technique has shown great potential in the synthesis of materials that are capable of adsorbing heavy metals ions selectively [13], [14]. Ion-imprinted polymers (IIP) show good thermal and chemical stability and can be used in media that are considered to be aggressive [15], [16]. The IIP capable of binding the ions of a particular metal has imprinted cavities with complexing agents arranged to match the charge, coordination number, coordination geometry, and size of the target metal ions [17], [18]. Among the ion-imprinting technologies, surface imprinting is important in terms of adsorption of metal ions due to advantages such as sites are more accessible, fast binding kinetics, and quick mass transfer [19]. Fan et al. prepared cadmium ion-imprinted polymer from amino-functionalized silica through hydrothermal assisted surface imprinting technique, and the prepared ion-imprinted polymer exhibited high selectivity and adsorption capacity toward Cd(II) [20]. Li et al. [21] prepared surface ion-imprinted materials using a surface imprinting technique combined with a hydrothermal-assisted sol–gel process, and the ion-imprinted polymer could be employed as an effective material for the selective removal of template ions from aqueous solutions. Zhang et al. successfully synthesized magnetic molecularly imprinted polymer beads by microwave-assisted surface imprinting technique. The molecularly imprinted polymer beads had been applied to selectively trace triazines analysis in complicated samples with satisfactory results [22]. Yao et al. [23] prepared core–shell ion-imprinted polymer through microwave-assisted heating preparation and the ion-imprinted polymer show an excellent performance in extraction of Cr(III) from urine. Nevertheless, it is not easy to separate the IIP rapidly and effectively from wastewater after treatment.
In the past decade, Fe3O4 nanoparticles have attracted much attention because of their superparamagnetism, low toxicity, high biocompatibility, and easy separation from a liquid system by an external magnetic field [24], [25], [26], [27]. When IIP particles are incorporated with Fe3O4, they can be easily separated by the application of an external magnetic field. In the recognition and adsorption of copper ions, Ren and Zhang used such an approach to collect the spent composite [28]. Recently, the use of magnetic ion-imprinted polymer for selective adsorption of heavy metal ions is rather common [29], [30], [31]. Zhang et al. prepared a core–shell magnetic ion-imprinted polymers for selective extraction of Pb(II) from water samples [29] while Cui et al. used ion-imprinted magnetic microspheres for the monitoring of lead ions at trace level in water [31]. It is known that Pb2+ ions bind strongly with the –SH groups in enzymes or proteins [32]. In view of the strong interaction between Pb2+ and –SH, we design a new kind of Pb(II) ion-imprinted polymer (Fe3O4@SiO2-IIP) that is functionalized with –SH groups. Adopting 3-mercaptopropyl trimethoxysilane (MPTS) as functional monomer, Pb(II) as template, tetraethyl orthosilicate as cross-linker, and Fe3O4@SiO2 as support, we synthesized the functionalized Pb(II) ion-imprinted polymer using the surface imprinting technique. The adsorption capacity and selectivity of the Fe3O4@SiO2-IIP for lead removal were investigated in detail.
Section snippets
Chemicals
Lead nitrate (Pb(NO3)2), tetraethyl orthosilicate (TEOS), isopropanol, and ammonia solution (28%) were supplied by Pure Crystal Shanghai Reagent Co., Ltd. (Shanghai, China) whereas 3-mercaptopropyl trimethoxysilane (MPTS) was purchased from Aladdin Co., Ltd. (Shanghai, China). Ferric chloride (FeCl3·6H2O) and ferrous sulfate (FeSO4·7H2O) were obtained from Shenyang Chemical Industry Corporation (Shenyang, China). Water was purified using a Milli-Q water system (Bedford, USA). All chemicals were
FT-IR results
The FT-IR spectra of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2-NIP and Fe3O4@SiO2-IIP are shown in Fig. 2. The peak at 590 cm−1 corresponding to Fe–O stretching is observed in all samples. The present of adsorbed water is reflected by the –OH vibration signals at 1630 and 3440 cm−1. The absorptions at around 960 and 1080 cm−1 are due to Si–O–H and Si–O–Si stretching vibrations, indicating that SiO2 has been successful immobilized on the Fe3O4 surface. With the grafting of sulfydryl group, a very weak peak at
Conclusions
A new Pb(II)-imprinted thiol-functionalized silica gel sorbent was prepared by surface imprinting technique. With the inclusion of Fe3O4 nanoparticles, the adsorbent is magnetic. The particles of the as-obtained Fe3O4@SiO2-IIP is uniform in size, showing an average diameter of 140 nm. The Fe3O4@SiO2-IIP adsorbent exhibits excellent characteristics such as fast adsorption kinetics, high chemical stability, and relatively high selectivity toward Pb(II). The experimental data fit well into the
Acknowledgments
This work was financially supported by the Natural Science Foundation of China (50978132, 51178213, 51238002, 51272099, 51008149), Program for New Century Excellent Talents in University (NCET-11-1004), Cultivating Program for Young Scientists of Jiangxi Province of China (20112BCB23016) Natural Science Foundation of Jiangxi Province (20122BAB213014, 20114BAB203018) and Department of Education Fund of Jiangxi Province (GJJ13506, Grant GJJ11508).
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