Elsevier

Chemosphere

Volume 150, May 2016, Pages 275-284
Chemosphere

Removal of bisphenol A from aqueous medium using molecularly surface imprinted microbeads

https://doi.org/10.1016/j.chemosphere.2016.02.040Get rights and content

Highlights

  • Bisphenol A (BPA) imprinted beads was prepared via precipitation polymerization.

  • Selectivity of BPA-imprinted beads and its possible recognition mechanism to BPA were evaluated.

  • BPA and structural analogues was detected using LC-MS.

  • The BPA-imprinted beads demonstrated high adsorption, good selectivity and reusability.

Abstract

The aim of this study is to prepare bisphenol A (BPA) imprinted polymers, which can be used for the selective removal of BPA from aqueous medium. The BPA-imprinted (MIP) and non-imprinted (NIP) microbeads were synthesized, and characterized by Zeta-sizer, FTIR, SEM and BET method. Bisphenol A was determined in solutions using liquid chromatography-mass spectroscopy (LC-MS). The effect of initial concentration of BPA, the adsorption rate and the pH of the medium on the capacity of BPA-imprinting polymer were studied. Adsorption capacity of BPA was affected by the amount of the incorporated functional monomer in the polymer network. BPA adsorption capacity of MIP-3 and NIP microbeads from aqueous medium was estimated as 76.7 and 59.9 mg g−1, respectively. The binding efficiencies of BPA-MIP-3 microbeads for different phenolic compounds (i.e., BPA with p-toluidine, 4-aminophenol or 2-naphthol) were explored at binary solutions, and the binding capacities of BPA-imprinted microbeads were found to be 2.79 × 10−1, 2.39 × 10−1, 7.59 × 10−2 and 5.48 × 10−2 mmol g−1 microbeads, respectively. The satisfactory results demonstrated that the obtained BPA-MIP microbeads showed an appreciable binding specificity toward BPA than similar structural compounds in the aqueous medium. Moreover, the reusability of BPA-MIP-3 microbeads was tested for several times and no significant loss in adsorption capacity was observed. Finally, the binary and multi-component systems results show that MIP-3 microbeads have special recognition selectivity and excellent binding affinity for template molecule “BPA”.

Introduction

Molecular imprinting has been known as a useful technique for preparation of molecular recognition materials (Dragan, 2014, Lata and Samadder, 2016). Molecularly imprinted polymers (MIP) are prepared by co-polymerization of a cross-linking agent with a functional polymer which is complex-conjugated with the template molecules. The interactions between template and functional monomer can occur via hydrogen-bonding, electrostatic interaction and hydrophobic interaction (Abkenar et al., 2015, Bayramoglu and Arica, 2011a, Bayramoglu and Arica, 2011b; Gao et al., 2015a, Gao et al., 2015b). After removing the template molecule from the polymer matrices, the binding sites having the size and shape complementary to the template were generated. Compared with traditional chromatographic materials, the remarkable advantages of MIP polymers are their specific use for target molecules, reusability and low cost (Gao et al., 2015a, Gao et al., 2015b, Eslami and Alizadeh, 2015, Soleimani et al., 2012, Jing et al., 2014). BPA is one of a well-known endocrine disrupting chemical that has been widely used in the production of epoxy resins, polysulfones and polycarbonate plastics. BPA easily leaches from polycarbonate containers for food and beverages, and it can interfere with hormone systems of the consumers. Additionally, BPA can cause cardiovascular disease, diabetes, neurological disorders, carcinogenic sensitivity, and reproductive impairment (Zhang et al., 2014, Qiu et al., 2015, Cooper et al., 2011; Staples et al., 1988). The determination of BPA from the sample is often hard due to its low concentration (Cooper et al., 2011; Staples et al., 1988). Therefore, pretreatment and enrichment are crucial steps prior to its analysis. Adsorption is a common technique for pre-concentration of various molecules such as phenolic compounds and heavy metals, so, several adsorbents have been synthesized and researched (Zhang et al., 2014, Wang et al., 2012, Zarejousheghani et al., 2013, Zhou et al., 2013. Lin et al., 2012, Fu et al., 2015, Ling et al., 2016, Zhang et al., 2016). For example, the activated carbon as an adsorbent is very effective for BPA, but it can be easily interfered with other phenolic compounds such as humic acids in the environmental water (Lim et al., 2015). Therefore, molecular imprinting is a powerful technique for the preparation of selective materials that have the ability to recognize a specific molecule (Gao et al., 2015a, Gao et al., 2015b). The small molecules imprinting have been developed using functional monomer with different groups and optimizing the composition and ratio, employing monomers already known to interact relatively strong with target molecules (Park et al., 2014, Monier et al., 2015, Ren et al., 2014, Gao et al., 2016, Hao et al., 2015). For example, Yu et al. (2015) proposed a novel hybrid imprinting strategy using mesoporous silica for the solid-phase extraction of bisphenol A. The imprinted silica also showed high extraction efficiencies for BPA. Lv et al. (2015) prepared molecularly imprinted magnetic adsorbent by layer-by-layer deposition of functional polymer on the surface of the monodispersed magnetic microspheres for selective enrichment of BPA from aqueous medium. Yang et al. (2015) fabricated BPA imprinted polymeric microspheres using Pickering emulsion polymerization, and the molecularly imprinted microspheres were used for selective extraction of BPA from biological samples. As exemplified above, the beaded form of MIP polymers have received much attention. Because of bulk imprinting polymeric adsorbents have some drawback such as undefined morphological structures, mass transfer resistance due to the irregular structure of the crushed polymers and incomplete template removal (Ren et al., 2014, OMahony et al., 2013). To overcome these disadvantages, imprinting technique using the beaded polymers has been proposed as a novel and more feasible alternate. The mono-disperse beaded supports is mostly preferred due to its maximum surface to volume ratio, which can be synthesized by using different polymerization techniques such as suspension, emulsion and precipitation polymerization Karagoz et al., 2011, Bayramoglu and Arica, 2005, Bayramoglu et al., 2012). Among them, precipitation polymerization is unique for obtaining microbeads with uniform size and shape, which can lead to a narrow size distribution, in addition, the preparation medium is free of any added surfactant or stabilizer (Li and Stove, 1993). Additionally, the imprinted polymer in the well defined structure also gives permission to better reactor applications and excellent reusability compared with the bulk imprinted materials (Jiao et al., 2014).

In this study, the BPA-imprinted polymer for specific recognition of bisphenol A was synthesized via precipitation polymerization of 2-methacrylamido-phenylalanine methylester, methylmethacrylate and ethylene glycole dimethacrylate monomers in the presence of an initiator (i.e., α-α′-Azoisobisbutyronitrile). A series of poly(MAP/MMA/EGDMA) microbeads with different MAP/MMA ratios was prepared. The selective binding behavior of the imprinting polymer for BPA was tested in single and binary systems using its structures analogues such as p-toluidine, 4-aminophenol and 2-naphthol. The binding properties of the MIP-3 microbeads were also evaluated using theoretical isotherm models. The retention and molecular-recognition properties of the MIP-3 microbeads for BPA, and its structural analogues were evaluated using Liquid Chromatography-Mass-Spectrometry (LC-MS).

Section snippets

Materials

Methylmethacrylate (MMA), ethylene glycol dimethacrylate (EGDMA), methacrylochloride, phenylalanine methylester (MAP), bisphenol A, p-toluidine, 4-aminophenol and 2-naphthol were obtained from Sigma–Aldrich (Germany). α-α′-azoisobisbutyronitrile (AIBN) was of the analytical grade, and also purified by recrystallization from methanol. The monomers distilled under reduced pressure in the presence of hydroquinone and stored at 4 °C until use. All other chemicals were of analytical grade and

Characterization studies

A two-step process was carried out in the preparation of MAP containing microbeads (Graphical Abstract). In the first step, MAP was synthesized from 2-methacrylochloride and l-phenylalanine methylester. The second step consisted of the ter-polymerization of MAP, MMA and EGDMA monomer via precipitation polymerization in the presence of an initiator (i.e., AIBN). The schematic representation of the imprinting cavity on the poly(MAP/MMA/EGDMA) microbeads is presented in Fig. 1. In order to acquire

Conclusion

The molecular imprinting method is a useful technique for the separation of target molecules from complex mixtures, such as endocrine disturbed chemicals from aqueous solutions. Molecular imprinted adsorbent is a new type of specific adsorbents that can considerably enhance the adsorption capacity and the selectivity of the target molecule. In this study, BPA-imprinted polymer was prepared in the beaded form via precipitation polymerization. The MIP-3 microbeads were used for selective binding

Acknowledgments

The work was studied at the research laboratories of Gazi University and Hacettepe University.

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