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

These results permitted to conclude that chitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for PbII and NiII pH = 4–6 but also for other heavy metal io

Preparation of chitosan/magnetite composite beads and their application for removal

of Pb(II) and Ni(II) from aqueous solution

a

Faculty of Chemical Technology, Hanoi University of Technology, 1, Dai Co Viet Road Hanoi, Vietnam

b Institute of Materials Science, Vietnamese Academy of Science and Technology, 18, Hoang Quoc Viet Road, Hanoi, Vietnam

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 7 September 2009

Received in revised form 15 October 2009

Accepted 12 November 2009

Available online 20 November 2009

Keywords:

Fe 3 O 4 nanoparticles

Chitosan/magnetite composite beads

Adsorption isotherm

Pb and Ni(II)

A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads with saturation magnetization value as high as uncoated Fe3O4nanoparticles (ca 54 emu/g) The reason was that the 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 Fe3O4nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets Maximum adsorption capacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and 52.55 mg/g respectively, according to Langmuir isotherm model These results permitted to conclude that chitosan/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

© 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 Heavy

metal ions such as Pb(II), Cd(II), Hg(II), and Ni(II) are toxic and

carcinogenic at relatively low concentrations They are not

self-degradable and can accumulate in living organisms, causing severe

disorders and diseases In order to remove heavy metal ions from

various environments, the techniques such as precipitation,

adsorp-tion, ion exchange, reverse osmosis, electrochemical treatments,

membrane separation, evaporation, coagulation,flotation, oxidation

and biosorption processes are widely used[1–10] These conventional

techniques are costly and have significant disadvantages such as

generation of metal bearing sludge or wastes, incomplete metal

removal, and the disposal of secondary wastes For these reasons,

there is a need for developing economic and eco-friendly methods for

wastewater treatments Adsorption is an attractive process, in view of

its efficiency and the ability to treat wastewater containing heavy

metals Over the last few decades adsorption has gained importance

as an effective purification and separation technique used in

wastewater treatment and low cost adsorbents are becoming the

focus of many investigations on the removal of heavy metals from

aqueous solutions[11–15]

Chitosan has excellent properties for the adsorption of metal ions,

principally due to the presence of amino groups (–NH2) in the

polymer matrix, which can interact with metal ions in solution by ion

exchange and complexation reactions[11] The high content of amino groups also makes possible many chemical modifications in polymer with the purpose of improving selectivity and adsorption capacity

In this paper, chitosan/magnetite nanocomposite beads were prepared, characterized and used for removal of toxic metal ions such as Pb(II), Ni(II) in the pH range from 4 to 6 Langmuir isotherms were used to analyze the equilibrium data at different pH These nanocomposite beads can be removed easily from water with the help

of an external magnet thanks to their exceptional magnetic properties

2 Experimental 2.1 Chemicals All reagents were analytical grade and used as received without further purification FeSO4·7H2O, FeCl3·6H2O, Pb(CH3COO)2 or NiSO4·7H2O, 4-(2-pyridylazo)rezocxin and Ni(II)-dimetyl glyoxim were purchased from Merck NH4OH 25 wt.%, NaOH, CH3COOH and

Br2were purchased from Duc Giang Chemical Company (Vietnam) Chitosan (MW = 400,000, DA = 70%) was purchased from Nha Trang Aquatic Institute (Vietnam) and re-characterized by viscometry and

IR measurements at our laboratory[16] 2.2 Synthesis of chitosan/magnetite composite beads Chitosan/magnetite composite beads were prepared by chemical co-precipitation of Fe2+and Fe3+ions by NaOH in the presence of chitosan followed by hydrothermal treatment [17] Briefly, the solution of chitosan, prepared with 0.5 g of chitosan was dissolved

⁎ Corresponding author Tel.: +84 4 37564129; fax: +84 438360705.

E-mail address: tdlam@vast.ac.vn (L.D Tran).

0928-4931/$ – see front matter © 2009 Elsevier B.V All rights reserved.

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into 5 ml of CH3COOH (99.5 wt.%, d = 1.05 g/ml) and 45 ml of distilled

water (pH = 2–3), FeCl2and FeCl3were dissolved in 1:2 molar ratio

and then the resulting solution was dropped slowly into NaOH 30 wt.%

solution to obtain chitosan/magnetite beads with different mass ratios

of chitosan/magnetite: 0/1 (pure Fe3O4); 1/2 and 4/1 The suspension

was kept at room temperature for 24 h without stirring and separated

by washing several times in water to remove alkaline The particles

were 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 by D8 Advance, 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 of

4 cm− 1 Morphology of composites was analyzed by Field Emission

Hitachi S-4500 Scanning Electron Microscope (FE-SEM) and

Trans-mission Electron Microscope (TEM, JEOL, Voltage: 100 kV, magni

fi-cation: × 200,000) Absorbance measurements were carried out on

UV–vis Agilent 8453 spectrophotometer in the range of 400–800 nm

The magnetic properties were measured with homemade vibrating

sample magnetometer (VSM) and evaluated in terms of saturation

magnetization and coercivity Chemical composition of samples was

determined by JEOL Scanning Electron Microscope and Energy

Dispersive X-ray (SEM/EDS) JSM-5410 Spectrometer

2.4 Adsorption studies

Chitosan/magnetite nanocomposite beads were used as magnetic

adsorbents for the adsorption of Ni(II) and Pb(II) The adsorption

behaviors of Pb(II) and Ni(II) ions were investigated in aqueous

solutions at pH 4–6 and at room temperature as follows: 0.01 g

chitosan/magnetite composite beads were added to 100 ml of Pb

(CH3COO)2or NiSO4solution respectively with initial concentrations

(C0) varied from 50 to 80 mg/l for 120 min (contact time) The

concentration of Pb(II) and Ni(II) ions was determined by

spectro-photometric assay and the procedure is as follows: 1 ml of sample

solution was mixed with 4-(2-pyridylazo)rezocxin (PAR), sodium

acetate, NH3 at pH = 10 After the formation of the

Pb(II)-4-(2-pyridylazo)rezocxin complex, the concentration of Pb(II) ions was

determined from the absorbance peak at 530 nm on a UV–vis

spectrophotometer To determine concentration Ni(II) ions, 1 ml of

sample solution was mixed with sodium dimetyl glyoxim 1.2 wt.%,

sodium hydroxide solution and Br2solution After the formation of the

Ni(II)-dimetyl glyoxim complex, the concentration of Ni(II) ions was

determined from the absorbance at 475 nm The amount of Pb(II) and

Ni(II) uptake was calculated as % recovery = C0−Ce/ C0, where C0and

Cerepresented initial and equilibrium concentrations of metal ions in

aqueous solution respectively

3 Results and discussion

3.1 Characterization of chitosan/magnetite composite beads

3.1.1 Morphology and particles of chitosan/magnetite composite beads

Balancing between high adsorption capacity (due to chitosan) and

magnetic properties (due to Fe3O4) various molar ratios of chitosan/

Fe3O4were investigated In our study, mass ratio of CS/Fe3O4of 4/1

seems to be an appropriate value (see Section 3.1.4 (Magnetic

properties) andSection 3.2.1(Isotherm adsorption study)).Fig 1a

and b shows the digital camera picture and SEM image respectively of

chitosan/magnetite composite beads with CS/Fe3O4ratio of 4/1 Being

spherical 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 recyclable than CS-free, separated Fe3O4particles

3.1.2 XRD analysis

Fig 2 showed XRD patterns of pure Fe3O4 (i) and chitosan/ magnetite composite beads (lines (ii) and (iii)) Six characteristic peaks for Fe3O4corresponding to (220), (311), (400), (422), (511) and (440) were observed in all samples (JCPDSfile, PDF No 65-3107) Quite weak diffraction lines of composite patterns indicated that

Fig 1 a Digital camera picture of chitosan/magnetite composite beads b SEM image of chitosan/magnetite composite beads (CS/Fe 3 O 4 = 4/1).

Fe3O4 particles have been coated by amorphous chitosan

Further-more, this coating did not result in phase change of Fe3O4 Line

broadening in the pattern can be quantitatively evaluated using

Debye–Scherrer equation d=(kλ/βcos θ), which gives a relationship

between peak broadening in XRD and particle size In this equation d

is 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 broadening

in radian obtained from the full width at half maximum,θ is the Bragg

angle According to Debye–Scherrer equation, particle sizes of

uncoated Fe3O4 and chitosan-coated Fe3O4 are estimated to be

22 nm and 35 nm respectively These results are consistent with

those obtained by TEM technique (see below)

3.1.3 TEM image of pure Fe3O4and chitosan-coated Fe3O4

Typical TEM micrographs for pure Fe3O4 and chitosan-coated

Fe3O4 were demonstrated on Fig 3 It is clear that pure Fe3O4

nanoparticles were quite agglomerated with mean diameter in the

range of 15–20 nm, while TEM image of chitosan-coated magnetite nanoparticles 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 the bright ones are assigned for amorphous CS (these areas were indicated onFig 3c by the arrows)

3.1.4 Magnetic properties of chitosan/magnetic composite beads

To 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 were recorded and shown onFig 4 From the plot of magnetization (M), magneticfield (H) and its enlargement near the origin, the saturation magnetization (Ms), remanence magnetization (Mr), coercivity (Hc) and squareness (Sr=Mr/Ms) could be calculated Because of no remanence and coercivity, it can be suggested that the beads are superparamagnetic Another characteristic supporting this identification is that small enough

Fig 3 TEM images of uncoated Fe 3 O 4 (a) and chitosan-coated Fe 3 O 4 (b,c).

particle size made thermalfluctuation (∼kT, T is temperature)

over-whelmed magnetic anisotropy (∼kV, V is particle volume) The saturation

magnetization is around 55 emu/g, which is much higher than those

reported in literature for other chitosan based Fe3O4beads[18,19] It can

be also observed from thisfigure that magnetization moment of Fe3O4

nanoparticles decreases very little after chitosan surface coating (Ms

values for the naked Fe3O4nanoparticles and composite beads with mass ratio of CS/Fe3O4of 1/2 and 4/1 are almost the same), this result signifies that chitosan does not affect magnetic properties of these composite beads, 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

value (Ms) after coating these beads is more advantageous and

susceptible to the external magnetic field for magnetic separation,

compared with those beads obtained by other methods

3.1.5 IR analysis

To 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 onFig 5 For the pure Fe3O4, the peak

at 605 cm− 1is attributed to Fe–O group, the peak around 3420–

3422 cm− 1can be related to the–OH group of adsorbed water IR

spectrum of chitosan is characterized by the following absorption

bands: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 primary

amine: 3400, 1638 cm− 1 By comparison of IR spectra of a, b, c

samples it can be noted that the presence of chitosan did shift IR

vibrations of Fe3O4but did not alter them very much Especially, the

band shift of Fe–O stretching (from 610 to 595 cm− 1) and that of N–H

bending vibration from 1638 to 1681 cm− 1is the most significant

These data indicated possible binding of iron ions to NH2group of

chitosan Besides, electrostatic interaction between surface negative

charged Fe3O4and positively protonated chitosan can also contribute

to this IR change It means that Fe3O4is coated by chitosan and no chemical bonding between chitosan and Fe3O4was formed

SEM, TEM and IR results are important because they evidenced the successful coating of Fe3O4nanoparticles by chitosan and pelletizing them in magnetic beads with the aid of NaOH Chitosan on the surface

of the magnetic nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets The synthetic procedure of composite beads was schemat-ically presented inFig 6

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

3.2.1 Isotherm adsorption study Adsorption isotherm is a functional expression that correlates the amount of solute adsorbed per unit weight of the adsorbent and the concentration of an adsorbate in bulk solution at a given temperature under equilibrium conditions It is important to establish the appropri-ate relationship for the batch equilibrium data using empirical or theoretical equations as it may help in modeling, analyzing and designing adsorption systems The adsorption isotherms are one of the most useful data to understand the mechanism of the adsorption and the characteristics of isotherms are needed before the interpretation

of the kinetics of the adsorption process Many models have been proposed to explain adsorption equilibrium, however, no general model has been found tofit the experimental data accurately under any given condition Among various plots employed for analyzing the nature of adsorbate–adsorbent interaction, adsorption isotherms were the most significant, among which Langmuir and Freundlich isotherms were most used to describe the equilibrium sorption of metal ions[17,18,20] Namely, Langmuir adsorption equation has the following form:

Ce

qe

qm⋅KL

+ Ce

where Ceis the equilibrium concentration of metal ions (mg/l), qeis the amount of metal ions adsorbed per gram adsorbent (mg/g), qmis the maximum adsorption of metal ions (mg/g), and KL is the Langmuir adsorption equilibrium constant (l/mg) The plot of Ce/q vs Ceyielded straight lines The values of qmand KLcan be calculated from the slope

Fig 7 Langmuir isotherm of the Ni(II) (a) and Pb(II) (b) adsorption on chitosan/

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

K L q max

(mg/g–1)

R 2

% recovery

K L q max

(mg/g–1)

R 2

% recovery

4 0.01845 49.55 0.971 70.79 0.2974 21.19 0.986 30.27

5 0.02027 54.80 0.999 78.29 0.5939 23.30 0.977 33.29

6 0.10973 63.33 0.982 90.47 1.3448 52.55 0.977 75.07

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

(K)

q max

(mg/g–1) Ref.

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

2 Magnetic Co 3 O 4 -containing resin Ni(II) 7.8 – 75.71 [5]

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]

Pb(II) 303 34.246

and intercept respectively The results of adsorption studies of Ni(II) and

Pb(II) with thefitted Langmuir equations at different concentrations of Ni

(II) and Pb(II) for pH =4–6 on a fixed amount of adsorbent were

presented onFig 7and summarized onTable 1 pH selection in the range

of 4–6 was rationalized by the fact that chitosan could be dissolved with

pHb3; while pHN7 could result in the formation of metal hydroxide

precipitates

FromTable 1it can be seen that pH solution was an important

variable, because it controls the adsorption of the metals on the

solid–water interfaces The pH affects the availability of Pb, Ni ions in

solution and the metal binding sites of the adsorbent It can be noted

that there was an increase in metal uptake along with an increase in

pH up to 6 Pb(II) was more strongly attracted to the adsorbent than

Ni(II), with higher removal percentage than Ni(II) at the same pH

Moreover, according toTable 2, adsorption capacity of synthesized

chitosan/magnetite beads was at least comparable and even higher

to that of other chitosan based adsorbents for both Ni(II) and Pb(II), except for hydrogels of 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS)[11,21–25], thanks to hydrogel cross-linking between chitosan matrix and magnetic particles of the later, which made it technically 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 initial concentration C0and decreases with C0 As can be seen fromTable 1, maximum adsorption capacities qmaxare 63.33 and 52.55 mg/g and percentages of ion recovery % r are 90.47 and 75.07% for Pb(II) and Ni (II) respectively at afixed 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 of metal ion recovery

It should be also remarked that CS–Fe3O4composite beads are more

resistant at relatively low pH (pH 3.5–4) than Fe3O4-free CS, which can

be explained by more rigid and more stable structure, reinforced by

magnetite particles of beads compared to that of naked CS

3.2.2 SEM/EDS analyses after metal ion adsorption

SEM micrographs of chitosan/magnetite composite beads before and

after their exposure to metal ion solutions were shown onFig 8 These

images illustrated that the surface texture and porosity of chitosan/

magnetite composite beads, having holes and small openings on the

surface, thereby increasing the contact area, were responsible for metal

ion adsorption The general morphology before adsorption can be

characterized as rough and folded After adsorption, surface morphology

was observed to have much asperity and to be more coarsely grained

Rod-like (Fig 8d) and plate-like (Pb adsorption,Fig 8f) morphologies,

corresponding to Ni and Pb posterior adsorptions respectively could be a

result of NiO·H2O or PbO·H2O formation on the surface

The EDS spectra of unexposed chitosan/magnetite composites (Fig 9a) showed the peaks of C, O and Fe, which were three major constituents 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 new appearing peaks, corresponding to Ni and Pb elements The EDS spectra provided an evidence for efficient metal uptake by chitosan/ magnetite composite beads: strong peak values at 2.34; 10.5 and 13.5 keV were due to uptake of Pb(II); the peaks at 7.46 and 8.30 keV indicated 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 OH group in chitosan, the atomic ratio of Fe and O could not be calculated and correlated with magnetic VSM and XRD measurements on phase structure of magnetite

4 Conclusions Chitosan/magnetite nanocomposite beads have been proven to be

an effective adsorbent for removal of toxic metal ion such as Pb(II), Ni (II) The adsorption parameters demonstrated good compatibility with Langmuir model and adsorption capacities of chitosan/magnetite composite beads reached maxima at pH 6.0 for both Pb(II) and Ni(II) The metals ion adsorption on surface of chitosan/magnetite composite was observed via SEM and EDS analyses Having a high saturation magnetization value (Ms) after coating with chitosan made these beads advantageous for heavy metal ion removal from water with the help of an external magnet

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Fig 9 EDS spectra of chitosan/magnetite composite beads (CS/Fe 3 O 4 = 4/1) before