Elsevier

Journal of Membrane Science

Volumes 415–416, 1 October 2012, Pages 250-259
Journal of Membrane Science

Novel polyethersulfone nanocomposite membrane prepared by PANI/Fe3O4 nanoparticles with enhanced performance for Cu(II) removal from water

https://doi.org/10.1016/j.memsci.2012.05.007Get rights and content

Abstract

A novel mixed matrix polymeric membrane was prepared from polyethersulfone (PES) and self-produced polyaniline/iron(II, III) oxide (PANI/Fe3O4) nanoparticles by phase inversion method. The core-shell structured PANI/Fe3O4 nanoparticles were verified and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). Three different amounts of nanoparticles were introduced into the casting solutions to obtain the optimum value. According to the performance test, the membrane with 0.1 wt% nanoparticles indicated the highest Cu(II) ion removal but the lowest pure water flux. This is caused by nanoparticles located in the superficial pores of the membrane during preparation i.e., surface pore blockage. Morphological analysis including field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) as well as membrane performance tests revealed that adsorption is the most possible separation mechanism by the membranes. For better investigation of the adsorption mechanism, several isotherm models such as Langmuir, Freundlich and Redlich-Peterson were tested. Based on the isothermal results, the Redlich-Peterson model offered superior fitness indicating relatively complex adsorption mechanism. The reusability of the nanocomposite membrane was confirmed for several sequential adsorption-desorption processes using EDTA as regenerator.

Highlights

▸ A novel nanocomposite membrane was prepared by PES and PANI/Fe3O4 nanoparticles. ▸ 0.1% of nanoparticles was optimized as proper amount for the highest Cu(II) removal. ▸ Redlich-Peterson isotherm showed superior fitness for Cu(II) adsorption mechanism.

Introduction

Copper ion, as a toxic contaminant of potable water resources at unauthorized dosages (more than 2 mg/l), should be eliminated because of its dangerous risks for human being such as headache, depression and learning problems [1], [2], [3], [4], [5]. Heavy metals including copper are also toxic for plants and can affect the root growth [4].

There are several processes such as precipitation, coagulation, adsorption, ion exchange, electro-dialysis, electro-coagulation, and membrane separation processes for removing metal ions from effluents [3], [6], [7], [8]. Membrane processes offer several advantages compared with other separation methods such as high removal efficiency, low energy consumption, high flow rate, small footprint and ease of scale up [9], [10].

Elimination of copper ion by amphoteric polybenzimidazole nanofiltration hollow fiber membrane has been reported [6]. The removal of copper from effluents by Nanomax50 nanofiltration membrane resulted around 35%Cu(II) rejection at 4 bars [5]. Many studies describe preparation of adsorptive membranes by blending the polymers such as cellulose acetate, acrylonitrile butadiene styrene and polyvinyl alcohol with an adsorptive polymer like chitosan to enhance membrane performance for heavy metal elimination from water [11], [12], [13], [14].

Adsorptive removal of copper ions is carried out not only by membrane separation processes but also with various granola adsorbents like silica gel and chitosan beads [15], [16], [17]. Guolin et al. used cross-linked magnetic chitosan beads prepared with a magnetic fluid containing iron salts [15]. Another study has reported the application of chitosan coated polyvinyl chloride beads to eliminate copper and nickel ions from water [16].

Utilizing the nanoparticles in membrane preparation is applied to improve process effectiveness. For example, metal oxide nanoparticles are widely used as an additive for optimizing ceramic membrane performance [18]. Hosseini et al. showed that addition of proper amount of magnetic iron- nickel oxide particles can improve performance of polyvinyl chloride based heterogeneous ion exchange membranes [19]. Influence of iron and aluminum oxide coating layer on ceramic membranes performance for the elimination of natural organic matter has been examined [20]. Application of iron oxide as filler in polyvinyl alcohol nanocomposite pervaporation membrane was developed for dehydration of organic solvents [21]. Compared with other metal oxides, conspicuous impact of iron oxide nanoparticles on membranes performance for arsenic removal is reported [22], [23]. The observed effect is attributed to the great affinity of iron oxides toward heavy metals [22], [23], [24].

In addition to metal oxides, some polymeric materials such as polyaniline can remove toxic metal ions from water [17], [25], [26], [27] due to the existence of nitrogen atom with a lone electron pair as a reactive adsorption site. It has been revealed that saw dust can efficiently adsorb cadmium ions when it is coated with polyaniline [25]. Belaib et al. modified silica gel and some natural solid materials by coating with polyaniline. They obtained significant enhancement in copper loading capacity as well as adsorption kinetics, using this adsorbent [17]. A polyaniline/inorganic cation- exchanger nanocomposite has been fabricated to obtain a high capacity ion-exchanger with increased ion exchange rate [26]. With regard to these studies, polyaniline can be applied as a modifier to achieve higher heavy metal uptake onto adsorptive nanoparticles. The properties of PANI blended membranes and PANI modified nanoparticles in nanocomposite membrane are crucial. These modified membranes represent significant properties. For example, a novel mixed matrix pervaporation membrane was successfully prepared by polyvinylalcohol and polyaniline treated TiO2 nanoparticles [28]. This modification diminished the flux and improved the selectivity in separation of water-isopropanol mixture. Furthermore, polyaniline nanofibers were widely used as a pore former and additive in improving protein retention and antifouling properties of ultrafiltration membrane [29], [30], [31], [32].

In this work, iron oxide/polyaniline nanoparticles (NPs) as a core-shell structured adsorbent was prepared and utilized in PES matrix to obtain a new nanocomposite membrane with enhanced affinity for copper ions. The performance of the prepared membranes was tested for removing low concentrations of Cu(II) ions from water. The mechanism of copper ion elimination by the membranes was investigated by application of adsorption isotherms. The reusability of the membranes was examined using EDTA as eluting agent. FESEM, AFM, TEM, XRD and FTIR were applied for characterization of the prepared membranes and nanoparticles.

Section snippets

Materials

The chemicals used in the current study are presented in Table 1. All reagents were used without further purification except for aniline which was double-distilled to obtain pure aniline monomers.

Preparation and characterization of PANI/Fe3O4 nanoparticles

Briefly, FeCl3·6H2O and FeCl2·4H2O were dissolved in deionized water with 3:1 M ratio and stirred. The dissolved oxygen in the solution was removed by means of a vacuum pump. Then, the ammonium hydroxide solution was added to the orange-colored solution to adjust the pH value at 10 under vigorous

Nanoparticles identification

The X-ray diffraction pattern of the powder sample is shown in Fig. 1. The Bragg reflection peaks at 2θs equal to 30.24, 35.64, 43.38, 53.84, 57.52, 63.02 and 74.53 are attributed to diffraction from the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0) and (5 3 3) planes of cubic inverse spinel Fe3O4, respectively, which are in good agreement with the previously reported data (Magnetite: 01–1111). No additional peak for other possible phases of iron oxide was observed (pure phase). The

Conclusion

Novel nanocomposite polymeric membrane was prepared by PES and PANI/Fe3O4 nanoparticles. Characterization of nanoparticles using XRD and TEM proved that the prepared core-sell structured particles had mean size of 12–28 nm for iron(II,III) oxide core and thickness of about 8 nm for the polyaniline shell. The FTIR result of prepared nanoparticles verified formation of PANI on iron oxide NPs. Copper ion removal was tested and the results revealed that proper amount of nanoparticles in casting

List of symbols

    β

    Peak width of half-maximum

    θ

    Bragg angle

    λ

    X-ray wavelength (0.15 nm)

    ρf

    Fluid density (g/cm3)

    a

    Adsorption capacity (mg/g)

    AFM

    Atomic force microscopy

    APS

    Ammonium persulfate

    B

    Benzenoid ring

    b

    Affinity parameter

    C0

    Initial ion concentration (mg/l)

    Ce

    Equilibrium ion concentration (mg/l)

    Cf

    Ion concentration in feed (mg/l)

    Cp

    Ion concentration in permeate (mg/l)

    D

    Average size of the crystal (nm)

    DMAc

    N,N-dimethylacetamide

    DW

    Distilled water

    EDTA

    Ethylenediaminetetraacetic acid

    FA0.01

    Mixed matrix membrane with 0.01

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