Materials Science and Engineering C 30 (2010) 304–310

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Materials Science and Engineering C

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Preparation of chitosan/magnetite composite beads and their application for removalof Pb(II) and Ni(II) from aqueous solution

Hoang Vinh Tran a, Lam Dai Tran b,⁎, Thinh Ngoc Nguyen a

a Faculty of Chemical Technology, Hanoi University of Technology, 1, Dai Co Viet Road Hanoi, Vietnamb Institute of Materials Science, Vietnamese Academy of Science and Technology, 18, Hoang Quoc Viet Road, Hanoi, Vietnam

⁎ Corresponding author. Tel.: +84 4 37564129; fax: +E-mail address: tdlam@vast.ac.vn (L.D. Tran).

0928-4931/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.msec.2009.11.008

a b s t r a c t

a r t i c l e i n f o

Article history:Received 7 September 2009Received in revised form 15 October 2009Accepted 12 November 2009Available online 20 November 2009

Keywords:Fe3O4 nanoparticlesChitosan/magnetite composite beadsAdsorption isothermPb and Ni(II)

A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads withsaturation magnetization value as high as uncoated Fe3O4 nanoparticles (ca. 54 emu/g). The reason was thatthe coating chitosan layer was so thin that it did not affect magnetic properties of these composite beads.Especially, chitosan on the surface of the magnetic Fe3O4 nanoparticles is available for coordinating withheavy metal ions, making those ions removed with the assistance of external magnets. Maximum adsorptioncapacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and52.55 mg/g respectively, according to Langmuir isotherm model. These results permitted to conclude thatchitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for Pb(II) and Ni(II)(pH=4–6) but also for other heavy metal ions in wastewater treatment technology.

84 438360705.

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© 2009 Elsevier B.V. All rights reserved.

1. Introduction

Along with the technological progresses, toxic metal contamina-tion becomes a serious problem threatening human health. Heavymetal ions such as Pb(II), Cd(II), Hg(II), and Ni(II) are toxic andcarcinogenic at relatively low concentrations. They are not self-degradable and can accumulate in living organisms, causing severedisorders and diseases. In order to remove heavy metal ions fromvarious environments, the techniques such as precipitation, adsorp-tion, ion exchange, reverse osmosis, electrochemical treatments,membrane separation, evaporation, coagulation, flotation, oxidationand biosorption processes are widely used [1–10]. These conventionaltechniques are costly and have significant disadvantages such asgeneration of metal bearing sludge or wastes, incomplete metalremoval, and the disposal of secondary wastes. For these reasons,there is a need for developing economic and eco-friendly methods forwastewater treatments. Adsorption is an attractive process, in view ofits efficiency and the ability to treat wastewater containing heavymetals. Over the last few decades adsorption has gained importanceas an effective purification and separation technique used inwastewater treatment and low cost adsorbents are becoming thefocus of many investigations on the removal of heavy metals fromaqueous solutions [11–15].

Chitosan has excellent properties for the adsorption of metal ions,principally due to the presence of amino groups (–NH2) in thepolymer matrix, which can interact with metal ions in solution by ion

exchange and complexation reactions [11]. The high content of aminogroups also makes possible many chemical modifications in polymerwith the purpose of improving selectivity and adsorption capacity.

In this paper, chitosan/magnetite nanocomposite beads wereprepared, characterized and used for removal of toxic metal ionssuch as Pb(II), Ni(II) in the pH range from 4 to 6. Langmuir isothermswere used to analyze the equilibrium data at different pH. Thesenanocomposite beads can be removed easily fromwater with the helpof an external magnet thanks to their exceptional magneticproperties.

2. Experimental

2.1. Chemicals

All reagents were analytical grade and used as received withoutfurther purification. FeSO4·7H2O, FeCl3·6H2O, Pb(CH3COO)2 orNiSO4·7H2O, 4-(2-pyridylazo)rezocxin and Ni(II)-dimetyl glyoximwere purchased from Merck. NH4OH 25 wt.%, NaOH, CH3COOH andBr2 were purchased from Duc Giang Chemical Company (Vietnam).Chitosan (MW=400,000, DA=70%) was purchased from Nha TrangAquatic Institute (Vietnam) and re-characterized by viscometry andIR measurements at our laboratory [16].

2.2. Synthesis of chitosan/magnetite composite beads

Chitosan/magnetite composite beads were prepared by chemicalco-precipitation of Fe2+ and Fe3+ ions by NaOH in the presence ofchitosan followed by hydrothermal treatment [17]. Briefly, thesolution of chitosan, prepared with 0.5 g of chitosan was dissolved

Fig. 1. a. Digital camera picture of chitosan/magnetite composite beads. b. SEM image ofchitosan/magnetite composite beads (CS/Fe3O4=4/1).

Fig. 2. XRD pattern of Fe3O4 and composite beads (CS/Fe3O4=1/2; 4/1).

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into 5 ml of CH3COOH (99.5 wt.%, d=1.05 g/ml) and 45 ml of distilledwater (pH=2–3), FeCl2 and FeCl3 were dissolved in 1:2 molar ratioand then the resulting solutionwas dropped slowly into NaOH30 wt.%solution to obtain chitosan/magnetite beadswith differentmass ratiosof chitosan/magnetite: 0/1 (pure Fe3O4); 1/2 and 4/1. The suspensionwas kept at room temperature for 24 h without stirring and separatedby washing several times in water to remove alkaline. The particleswere finally dried in vacuum at 70 °C for 24 h to obtain chitosan/magnetite composite beads as adsorbent.

2.3. Characterization methods

X-ray Diffraction (XRD) patterns were obtained at room temper-ature byD8Advance, Bruker ASX, using CuKα radiation (λ=1.5406 Å)in the range of 2θ=10°–60°, and a scanning rate of 0.02 s−1. Infra red(IR) spectra were recorded with Nicolet 6700 FTIR Spectrometer,using KBr pellets, in the region of 400–4000 cm−1, with resolution of4 cm−1. Morphology of composites was analyzed by Field EmissionHitachi S-4500 Scanning Electron Microscope (FE-SEM) and Trans-mission Electron Microscope (TEM, JEOL, Voltage: 100 kV, magnifi-cation: ×200,000). Absorbance measurements were carried out onUV–vis Agilent 8453 spectrophotometer in the range of 400–800 nm.The magnetic properties were measured with homemade vibratingsample magnetometer (VSM) and evaluated in terms of saturationmagnetization and coercivity. Chemical composition of samples wasdetermined by JEOL Scanning Electron Microscope and EnergyDispersive X-ray (SEM/EDS) JSM-5410 Spectrometer.

2.4. Adsorption studies

Chitosan/magnetite nanocomposite beads were used as magneticadsorbents for the adsorption of Ni(II) and Pb(II). The adsorptionbehaviors of Pb(II) and Ni(II) ions were investigated in aqueoussolutions at pH 4–6 and at room temperature as follows: 0.01 gchitosan/magnetite composite beads were added to 100 ml of Pb(CH3COO)2 or NiSO4 solution respectively with initial concentrations(C0) varied from 50 to 80 mg/l for 120 min (contact time). Theconcentration of Pb(II) and Ni(II) ions was determined by spectro-photometric assay and the procedure is as follows: 1 ml of samplesolution was mixed with 4-(2-pyridylazo)rezocxin (PAR), sodiumacetate, NH3 at pH=10. After the formation of the Pb(II)-4-(2-pyridylazo)rezocxin complex, the concentration of Pb(II) ions wasdetermined from the absorbance peak at 530 nm on a UV–visspectrophotometer. To determine concentration Ni(II) ions, 1 ml ofsample solution was mixed with sodium dimetyl glyoxim 1.2 wt.%,sodium hydroxide solution and Br2 solution. After the formation of theNi(II)-dimetyl glyoxim complex, the concentration of Ni(II) ions wasdetermined from the absorbance at 475 nm. The amount of Pb(II) andNi(II) uptake was calculated as % recovery=C0−Ce /C0, where C0 andCe represented initial and equilibrium concentrations of metal ions inaqueous solution respectively.

3. Results and discussion

3.1. Characterization of chitosan/magnetite composite beads

3.1.1. Morphology and particles of chitosan/magnetite composite beadsBalancing between high adsorption capacity (due to chitosan) and

magnetic properties (due to Fe3O4) various molar ratios of chitosan/Fe3O4 were investigated. In our study, mass ratio of CS/Fe3O4 of 4/1seems to be an appropriate value (see Section 3.1.4 (Magneticproperties) and Section 3.2.1 (Isotherm adsorption study)). Fig. 1aand b shows the digital camera picture and SEM image respectively ofchitosan/magnetite composite beads with CS/Fe3O4 ratio of 4/1. Beingspherical in form, solid in structure and quite big in size, CS/Fe3O4

beads (microspheres) are more applicable for removal of heavy

metals ion in solution with external magnets, and easily recyclablethan CS-free, separated Fe3O4 particles.

3.1.2. XRD analysisFig. 2 showed XRD patterns of pure Fe3O4 (i) and chitosan/

magnetite composite beads (lines (ii) and (iii)). Six characteristicpeaks for Fe3O4 corresponding to (220), (311), (400), (422), (511)and (440) were observed in all samples (JCPDS file, PDF No. 65-3107).Quite weak diffraction lines of composite patterns indicated that

Fig. 3. TEM images of uncoated Fe3O4 (a) and chitosan-coated Fe3O4 (b,c).

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Fe3O4 particles have been coated by amorphous chitosan. Further-more, this coating did not result in phase change of Fe3O4. Linebroadening in the pattern can be quantitatively evaluated usingDebye–Scherrer equation d=(kλ /βcos θ), which gives a relationshipbetween peak broadening in XRD and particle size. In this equation dis the thickness of the crystal, k is the Debye–Scherrer constant (0.89),λ is the X-ray wavelength (0.15406 nm) and β is the line broadeningin radian obtained from the full width at half maximum, θ is the Braggangle. According to Debye–Scherrer equation, particle sizes ofuncoated Fe3O4 and chitosan-coated Fe3O4 are estimated to be22 nm and 35 nm respectively. These results are consistent withthose obtained by TEM technique (see below).

3.1.3. TEM image of pure Fe3O4 and chitosan-coated Fe3O4

Typical TEM micrographs for pure Fe3O4 and chitosan-coatedFe3O4 were demonstrated on Fig. 3. It is clear that pure Fe3O4

nanoparticles were quite agglomerated with mean diameter in the

Fig. 4. Magnetic hysteresis curves of Fe3O4 and composite beads (CS/Fe3O4=1/2; 4/1).

range of 15–20 nm, while TEM image of chitosan-coated magnetitenanoparticles was looser, less agglomerated, and bigger in size (25–30 nm). Moreover, TEM images showed different contrasts of CS–Fe3O4 beads: the dark areas represent crystalline Fe3O4 while thebright ones are assigned for amorphous CS (these areas wereindicated on Fig. 3c by the arrows).

3.1.4. Magnetic properties of chitosan/magnetic composite beadsTo test whether the synthesized beads could be used as a magnetic

adsorbent in the magnetic separation processes, magnetic measure-ments were performed on VSM. Typical magnetization loops wererecorded and shown on Fig. 4. From the plot of magnetization (M),magnetic field (H) and its enlargement near the origin, the saturationmagnetization (Ms), remanence magnetization (Mr), coercivity (Hc) andsquareness (Sr=Mr /Ms) could be calculated. Because of no remanenceand coercivity, it can be suggested that the beads are superparamagnetic.Another characteristic supporting this identification is that small enough

Fig. 5. IR spectra of Fe3O4, CS and composite beads (CS/Fe3O4=4/1).

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particle size made thermal fluctuation (∼kT, T is temperature) over-whelmedmagnetic anisotropy (∼kV,V is particle volume). The saturationmagnetization is around 55 emu/g, which is much higher than thosereported in literature for other chitosan based Fe3O4 beads [18,19]. It canbe also observed from this figure that magnetization moment of Fe3O4

nanoparticles decreases very little after chitosan surface coating (Ms

Fig. 6. Schematic formation process of ch

values for the naked Fe3O4 nanoparticles and composite beadswithmassratio of CS/Fe3O4 of 1/2 and 4/1 are almost the same), this result signifiesthat chitosan does not affect magnetic properties of these compositebeads, which can be explained by high coating efficiency by chitosan(high loading of Fe3O4 core, thin layer of chitosan shell) on Fe3O4

particles. Therefore, maintaining such a high saturation magnetization

itosan/magnetite composite beads.

Table 1Langmuir isotherm parameters for the adsorption of Pb(II) and Ni(II) ions on magneticchitosan/adsorbents at room temperature.

pH Pb(II) Ni(II)

KL qmax

(mg/g–1)R2 %

recoveryKL qmax

(mg/g–1)R2 %

recovery

4 0.01845 49.55 0.971 70.79 0.2974 21.19 0.986 30.275 0.02027 54.80 0.999 78.29 0.5939 23.30 0.977 33.296 0.10973 63.33 0.982 90.47 1.3448 52.55 0.977 75.07

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value (Ms) after coating these beads is more advantageous andsusceptible to the external magnetic field for magnetic separation,compared with those beads obtained by other methods.

3.1.5. IR analysisTo confirm the existence of the surface coating, FTIR spectra of the

pure Fe3O4 (a), chitosan (b) and chitosan/magnetite composite beads(c) were examined and shown on Fig. 5. For the pure Fe3O4, the peakat 605 cm−1 is attributed to Fe–O group, the peak around 3420–3422 cm−1 can be related to the –OH group of adsorbed water. IRspectrum of chitosan is characterized by the following absorptionbands: ν(O–H) appeared at 3395 cm−1, ν(C–H) of backbone polymer:2915, 2860 cm−1, ν(C3–O) of primary alcoholic group: 1409 cm−1,ν(C–O), amide I at 1091 and 1031 cm−1, δ(N–H), amide II of primaryamine: 3400, 1638 cm−1. By comparison of IR spectra of a, b, csamples it can be noted that the presence of chitosan did shift IRvibrations of Fe3O4 but did not alter them very much. Especially, theband shift of Fe–O stretching (from 610 to 595 cm−1) and that of N–Hbending vibration from 1638 to 1681 cm−1 is the most significant.These data indicated possible binding of iron ions to NH2 group ofchitosan. Besides, electrostatic interaction between surface negativecharged Fe3O4 and positively protonated chitosan can also contribute

Fig. 7. Langmuir isotherm of the Ni(II) (a) and Pb(II) (b) adsorption on chitosan/magnetic composite beads (CS/Fe3O4=4/1).

to this IR change. It means that Fe3O4 is coated by chitosan and nochemical bonding between chitosan and Fe3O4 was formed.

SEM, TEM and IR results are important because they evidenced thesuccessful coating of Fe3O4 nanoparticles by chitosan and pelletizingthem in magnetic beads with the aid of NaOH. Chitosan on the surfaceof the magnetic nanoparticles is available for coordinating with heavymetal ions, making those ions removedwith the assistance of externalmagnets. The synthetic procedure of composite beads was schemat-ically presented in Fig. 6.

3.2. Application of chitosan/magnetite composite beads for removalNi(II) and Pb(II) in solution

3.2.1. Isotherm adsorption studyAdsorption isotherm is a functional expression that correlates the

amount of solute adsorbed per unit weight of the adsorbent and theconcentration of an adsorbate in bulk solution at a given temperatureunder equilibrium conditions. It is important to establish the appropri-ate relationship for the batch equilibrium data using empirical ortheoretical equations as it may help in modeling, analyzing anddesigning adsorption systems. The adsorption isotherms are one ofthe most useful data to understand the mechanism of the adsorptionand the characteristics of isothermsareneededbefore the interpretationof the kinetics of the adsorption process. Many models have beenproposed to explain adsorption equilibrium, however, no generalmodelhas been found to fit the experimental data accurately under any givencondition. Among various plots employed for analyzing the nature ofadsorbate–adsorbent interaction, adsorption isotherms were the mostsignificant, among which Langmuir and Freundlich isotherms weremost used to describe the equilibrium sorption of metal ions [17,18,20].Namely, Langmuir adsorption equation has the following form:

Ce

qe=

1qm⋅KL

+Ce

qmð1Þ

where Ce is the equilibrium concentration of metal ions (mg/l), qe is theamount of metal ions adsorbed per gram adsorbent (mg/g), qm is themaximum adsorption of metal ions (mg/g), and KL is the Langmuiradsorption equilibrium constant (l/mg). The plot of Ce/q vs. Ce yieldedstraight lines. The values of qm and KL can be calculated from the slope

Table 2Comparison of metals ion adsorption capacities at different adsorbents.

No. Adsorbent Metals pH T(K)

qmax

(mg/g–1)Ref.

1 Chitosan functionalized with 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol

Ni(II) 3 – 9.6 [2]

2 Magnetic Co3O4-containing resin Ni(II) 7.8 – 75.71 [5]3 Tobacco stem Pb(II) 5 299 5.5435 [12]4 Magnetic-poly-2-acrylamido-2-methyl-

1-propansulfonic acid p(AMPS)hydrogels

Ni(II) – – 114.94 [15]Pb(II) – – 140.84

5 Chitosan-coated perlite beads Ni(II) 5 298 56.18 [17]6 Meranti sawdust Ni(II) 303 35.971 [19]

Pb(II) 303 34.246

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and intercept respectively. The results of adsorption studies of Ni(II) andPb(II)with thefitted Langmuir equations at different concentrationsofNi(II) and Pb(II) for pH=4–6 on a fixed amount of adsorbent werepresented on Fig. 7 and summarized on Table 1. pH selection in the rangeof 4–6 was rationalized by the fact that chitosan could be dissolved withpHb3; while pHN7 could result in the formation of metal hydroxideprecipitates.

From Table 1 it can be seen that pH solution was an importantvariable, because it controls the adsorption of the metals on thesolid–water interfaces. The pH affects the availability of Pb, Ni ions insolution and the metal binding sites of the adsorbent. It can be notedthat there was an increase in metal uptake along with an increase inpH up to 6. Pb(II) was more strongly attracted to the adsorbent thanNi(II), with higher removal percentage than Ni(II) at the same pH.Moreover, according to Table 2, adsorption capacity of synthesized

Fig. 8. SEM images of chitosan/magnetite beads (CS/Fe3O4=4/1): before adsor

chitosan/magnetite beads was at least comparable and even higherto that of other chitosan based adsorbents for both Ni(II) and Pb(II),except for hydrogels of 2-acrylamido-2-methyl-1-propansulfonicacid (AMPS) [11,21–25], thanks to hydrogel cross-linking betweenchitosan matrix and magnetic particles of the later, which made ittechnically more attractive for removal of pollutants, but econom-ically less competitive compared to our composite beads. The per-centage of ion recovery (noted as % r recovery) depends on the initialconcentration C0 and decreases with C0. As can be seen from Table 1,maximum adsorption capacities qmax are 63.33 and 52.55 mg/g andpercentages of ion recovery % r are 90.47 and 75.07% for Pb(II) and Ni(II) respectively at a fixed contact time of 120 min and C0=70 mg/l.Also, it should be noted that at pHN7 the hydroxide metal pre-cipitation would be favorable, triggering the increased percentage ofmetal ion recovery.

ption (a, b); after Ni(II) adsorption (c, d) and after Pb(II) adsorption (e, f).

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It should be also remarked that CS–Fe3O4 composite beads are moreresistant at relatively low pH (pH 3.5–4) than Fe3O4-free CS, which canbe explained by more rigid and more stable structure, reinforced bymagnetite particles of beads compared to that of naked CS.

3.2.2. SEM/EDS analyses after metal ion adsorptionSEMmicrographsof chitosan/magnetite composite beads before and

after their exposure to metal ion solutions were shown on Fig. 8. Theseimages illustrated that the surface texture and porosity of chitosan/magnetite composite beads, having holes and small openings on thesurface, thereby increasing the contact area, were responsible for metalion adsorption. The general morphology before adsorption can becharacterized as rough and folded. After adsorption, surfacemorphologywas observed to have much asperity and to be more coarsely grained.Rod-like (Fig. 8d) and plate-like (Pb adsorption, Fig. 8f) morphologies,corresponding toNi andPbposterior adsorptions respectively could be aresult of NiO·H2O or PbO·H2O formation on the surface.

Fig. 9. EDS spectra of chitosan/magnetite composite beads (CS/Fe3O4=4/1) beforeadsorption (a); after Ni(II) adsorption (b) and after Pb(II) adsorption (c).

The EDS spectra of unexposed chitosan/magnetite composites(Fig. 9a) showed the peaks of C, O and Fe, which were three majorconstituents of CS and magnetite.

EDS spectra of chitosan/magnetite composite beads after adsorp-tion of Ni(II) (Fig. 9b) and Pb(II) (Fig. 9c) respectively presented newappearing peaks, corresponding to Ni and Pb elements. The EDSspectra provided an evidence for efficient metal uptake by chitosan/magnetite composite beads: strong peak values at 2.34; 10.5 and13.5 keV were due to uptake of Pb(II); the peaks at 7.46 and 8.30 keVindicated the presence of Ni(II). These results confirmed that Ni(II)and Pb(II) were efficiently adsorbed onto surface of chitosan/magnetite composite beads. Due to the obstructive presence of OHgroup in chitosan, the atomic ratio of Fe and O could not be calculatedand correlated with magnetic VSM and XRD measurements on phasestructure of magnetite.

4. Conclusions

Chitosan/magnetite nanocomposite beads have been proven to bean effective adsorbent for removal of toxic metal ion such as Pb(II), Ni(II). The adsorption parameters demonstrated good compatibilitywith Langmuirmodel and adsorption capacities of chitosan/magnetitecomposite beads reached maxima at pH 6.0 for both Pb(II) and Ni(II).Themetals ion adsorption on surface of chitosan/magnetite compositewas observed via SEM and EDS analyses. Having a high saturationmagnetization value (Ms) after coating with chitosan made thesebeads advantageous for heavy metal ion removal from water with thehelp of an external magnet.

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