This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

Synthesis of magnetic citric acid-functionalized graphene oxide and its

application in the removal of methylene blue from contaminated water

Mina Namvari1, Hassan Namazi

1,2,*

1Laboratory of Dendrimers and Nano-Biopolymers, Faculty of Chemistry, University of

Tabriz, Tabriz, Iran

2Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Science,

Tabriz, Iran

This article has been accepted for publication and undergone full peer review but has not

been through the copyediting, typesetting, pagination and proofreading process, which

may lead to differences between this version and the Version of Record. Please cite this

article as doi: 10.1002/pi.4769

*

Corresponding author. Tel.: + 98 411 339 3121, Fax: +98 411 334 0191, E-mail address: namazi@tabrizu.ac.ir (H. Namazi).

Abbreviations

GO: graphene oxide; CA: citric acid; GO-COCl : acyl chloride-functionalized grapehen oxide; GO-CA: citric acid-grafted graphene oxide;

MNPs: Fe3O4 magnetic nanoparticles; GO-CA-Fe3O4: magnetic nanocomposite of citric acid-grafted graphene oxide; GNS: graphene

nanosheets; MB: methylene blue; FTIR: Fourier transform infrared spectrometer; XRD: X-ray diffraction spectrometry; SEM: scanning

electron microscopy; VSM: vibrating sample magnetometer; TEM: transition electron microscopy; UV–Vis : Ultraviolet-visible

spectroscopy.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

Acc

epte

d A

rtic

le

Abstract

Magnetic nanocomposite of citric acid-functionalized graphene oxide was prepared with an

easy method. First, citric acid (CA) was covalently attached to acyl chloride-functionalized

graphene oxide. Then, Fe3O4 magnetic nanoparticles (MNPs) were chemically deposited onto

the resulted adsorbent. CA, as a good stabilizer for MNPs, was covalently attached to

graphene oxide (GO), thus MNPs were adsorbed much strongly to this framework and

subsequently leaching would decrease and less agglomeration occurred. The attachment of

CA onto GO and the formation of the hybrid were confirmed by Fourier transform infrared

spectroscopy, scanning electron microscopy, X-ray diffraction spectrometry and transition

electron microscopy. The specific saturation magnetization of the magnetic CA-grafted GO

(GO-CA-Fe3O4) was 57.8 emu g-1

and the average size of the nanoparticles was obtained to

be 25 nm using TEM micrograph. The magnetic nanocomposite has been employed as

adsorbent of methylene blue from contaminated water. The adsorption tests demonstrated that

it only took 30 min to attain the equilibrium. The adsorption capacity in the concentration

range studied was 112 mg g-1

. GO-CA-Fe3O4 nanocomposite was easily manipulated in an

external magnetic field which eases the separation and leads to the removal of dyes. Thus the

prepared nanocomposite has great potential in removing organic dyes.

Keywords

Graphene oxide; Citric acid; Magnetic nanoparticles; Adsorption; Dye removal; Magnetic

separation.

1. Introduction

Water pollution control is presently one of the major areas of scientific activity. While

colored organic compounds (dyes) generally impart only a minor fraction of the organic load

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

to wastewater, their color renders them totally unacceptable. Effluent discharges from the

textile industries to neighboring water bodies and wastewater treatment systems have been

given of much concern specially, in recent years. Accordingly, several conventional

technologies have been proposed for separation of dyes from wastewater e.g., biological

treatment [1], coagulation/flocculation [2], ozone treatment [3], chemical oxidation [4],

membrane filtration [5], ion-exchange [6], photocatalytic degradation [7] and adsorption [8].

Oxidation and adsorption are two most widely used methods for dye removal. The ability of

oxidation to eliminate very low concentrations of organic compounds limits its application

[9]. Adsorption techniques have gained favor recently because of their proven efficiency in

the removal of dyes, ease of operation and insensitivity to toxic material [10]. Adsorption by

activated carbon has been widely used for wastewater treatment however, its widespread use

is restricted due to high cost [11]. Therefore, researchers have been looking for low cost

adsorbents as alternatives to activated carbon. In search for high-performance and low-cost

adsorbents, clay materials, zeolites, siliceous material, activated alumina, polymeric porous

materials/frameworks and biosorbents such as chitosan and peat have been reported [12-18].

Recently, carbon based materials such as graphene and carbon nanotubes are the most

popular adsorbent and have been used with great success [19-21].

Graphene oxide (GO) is basically a wrinkled two-dimensional one-atom thick carbon sheet

with various oxygenated functional groups on its basal plane (hydroxyl and epoxide) and

peripheries (carboxylic acid), with the thickness around 1 nm and lateral dimensions varying

between a few nanometers and several microns. Since the breakthrough work of A. K. Geim

et. al [22], GO is rapidly gaining attraction due to its scientific significance as a basic form of

oxidized carbon and technological importance as a platform for all kinds of derivatives and

composites, which have already demonstrated various interesting applications [23]. As

previously mentioned, GO has multiple oxygen-containing functional groups which result in

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

a negatively charged surface and this enables interactions between GO and different materials

such as nanoparticles (NPs) and dyes [20, 21, 24-27].

Recently, magnetic loaded adsorbents have proven to be highly efficient and easily separable

[28]. Fe3O4 magnetic nanoparticles (MNPs) are either physically adsorbed onto GO [29, 30]

or covalently attached to it [31, 32]. However, nano-sized particles tend to aggregate to

minimize their surface energy due to their large ratio of surface area per unit volume.

Therefore, to achieve stability, NPs are usually functionalized with specific groups, for

instance surfactants, polysaccharides, zeolite, activated carbon and cyclodextrin. The coating

method can also hamper the aggregation of the particles at a distance where the attraction

energy between the particles is larger than the disordering energy of thermal motion. Since

carboxylates have important effect on the growth of MNPs and their magnetic properties,

citric acid (CA) [33, 34] is proved to be one of the most suitable and easily available

materials used to stabilize MNPs [35-39] which happens via the coordination of one or two of

the carboxylate functionalities, depending upon steric necessity and the curvature of the

surface [40-43]. Thus, we decided to use the advantages of both GO and CA to synthesize a

hybrid which can stabilize MNPs and efficiently adsorb dyes and the ease of separation from

the aqueous solution would finalize the work. The novelty of the current study involves two

aspects. (i) CA, as a stabilizer for MNPs, is covalently attached to GO, so MNPs are adsorbed

much strongly to this framework and subsequently leaching will be decreased. (ii) CA-

grafted GO (GO-CA) is well-dispersed in water; therefore it reduces the hydrophobic nature

of MNPs and leads to stable NPs. This feature enhances the efficacy of this nanocomposite in

dye removal systems.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

2. Experimental section

2.1. Materials

Graphite (average particle size 30 µm) is commercially available and it was used without

further purification. Thionyl chloride (SOCl2) was distilled from boiled linseed oil prior to

use. Triethylamine (Et3N) was dried over calcium hydride (CaH2) and then distilled.

Tetrahydrofuran (THF) was dried over sodium. Methylene Blue (MB) was used to prepare

stock solutions of 100 mg L-1

, which was further diluted to the required concentrations. All

other reagents and solvents employed for the synthesis were commercially available and used

as received without further purification. All the reagents, except graphite, were purchased

from Merck. Deionized water (DI water) was used in all experiments.

2.2. Preparation of acyl chloride-functionalized GO (GO-COCl)

The as-prepared GO by modified Hummers’ method [44, 45] (1 g) was well-dispersed in 10

mL of dry N,N’-dimethylformamide by sonification for 1 h and then was treated with SOCl2

(60 mL, 0.82 mol) at 80 oC for 3 days. The product was separated by centrifugation, washed

with anhydrous THF and dried under vacuum.

2.3. Preparation of GO-CA hybrid

CA-grafted GO was synthesized through an esterification reaction between GO-COCl and

CA. Briefly, to a dispersion of GO-COCl (0.05 g) in 30 mL dry THF under argon

atmosphere, previously dried CA in 2 mL THF and Et3N (1 mL) were added dropwise at 0

°C. The mixture was stirred at 0 °C for 1 h, at room temperature for 6 h and reflux for 24 h.

The powder was washed with an excess amount of DI water and ethanol. After washing, the

resulting powder was dried in vacuum overnight.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

2.4. Preparation of magnetic GO-CA nanocomposite (GO-CA-Fe3O4)

The GO-CA-Fe3O4 hybrid was prepared by chemical deposition of iron ions using soluble

GO-CA as carriers. During synthetic process, ideal Fe3O4 NPs were obtained under the molar

ratio of Fe3+

:Fe2+

as 2:1. 0.5 g GO-CA was first sonicated in 30 mL diluted NaOH aqueous

solution (pH 12) for an hour to transform the carboxylic acid groups to carboxylate anions,

followed by thorough dialysis until the dialysate became neutral. The resulting product was

condensed to 20 mL and placed in a 100 mL three-necked round bottom flask. A solution of

FeCl3⋅6H2O (0.022 mol) and FeCl2⋅4H2O (0.011 mol) in water (20 mL) was added to the

flask. The mixture was stirred at 70 °C for 15 min. Then 2 mL ammonium hydroxide was

added. The mixture was kept stirring at 70 °C for a further 4 h. Then the mixture was washed

with water to neutral pH and dried under vacuum at 45 °C for 12 h.

2.5. Characterization

Infrared spectra were obtained on a Fourier transform infrared (FTIR) spectrometer (Bruker

Instruments, model Aquinox 55, Germany) in the 4000–400 cm-1

range at a resolution of 0.5

cm-1

as KBr pellets. The pattern of X-ray diffraction (XRD) of the samples was obtained by

Siemens diffractometer with Cu-ka radiation at 35 kV in the scan range of 2 h from 2 to 70°

and scan rate of 1°/min. All of analyzed samples were in powdery form. The d-spacing was

calculated by Bragg’s equation where k was 0.154 nm. Transmission electron micrograph

(TEM) was conducted by LEO 906E transmission electron microscope operating at 80 kV.

Room temperature magnetic properties of the nanocomposite were characterized using

vibrating sample magnetometer (Iran). Scanning electron micrographs (SEM) were obtained

with a LEO 1430VP scanning electron microscope operating at 15 kV. Ultraviolet-visible

(UV–Vis) spectroscopy was carried out on a Perkin-Elmer Lambda 35 UV-Vis absorption

spectrometer at room temperature.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

2.6. Adsorption experiments

Effects of contact time, solution pH and the related isotherm were studied individually.

Typically, adsorption experiments were carried out in glass bottles at 25 °C. 25 mL of dye

solution of a known initial concentration was shaken with 0.025 g of magnetic GO-CA-Fe3O4

on a shaker at 200 rpm at 25 °C. To evaluate the time effect, at the completion of preset time

intervals, a 5 mL dispersion was drawn and separated immediately by the aid of a magnet to

collect the adsorbent. The equilibrium concentrations of dyes were measured with a UV-Vis

spectrophotometer at appropriate wavelength corresponding to the maximum absorbance, 664

nm for MB. The amount of dye adsorbed was calculated using the following equation.

qe = (Co − Ce)V/m

Where, qe is the concentration of dye adsorbed (mg g-1

), Co and Ce are the initial and

equilibrium concentrations of dye in mg L-1

, respectively, V is the volume of dye solution (L)

and m (g) is the weight of the adsorbent used.

The effect of pH on the adsorption of MB was studied in a pH range of 2-10 using 25 mL of

solutions with MB concentrations of 20 mg L-1

. The initial pH values of the solutions with

certain amount of adsorbent and dye were adjusted with 0.1 M HNO3 or NaOH using a pH

meter. After magnetic separation using a magnet, the equilibrium concentrations of dyes were

measured as mentioned earlier.

For adsorption equilibrium experiments, fixed adsorbent dose (25 mg) was weighed into 50

mL conical flasks containing 25 mL of different initial concentrations (20–120 mg L-1

) of

MB. The mixture was shaken for 5 h at 25 °C until equilibrium was obtained. Then the

adsorbent was separated from solution by an external magnet. The concentration of MB in

the solution was measured using a UV–Vis spectrophotometer.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

2.7. Desorption experiments

The desorption experiments were carried out as follows: 0.025 g of GO-CA-Fe3O4 was

shaken with 25 mL of dye (20 mg L-1

) for 5 h. After the magnetic separation, the supernatant

dye solution was discarded and the adsorbent alone was separated. Then, the MB-adsorbed

was added into 25 mL of 0.5 mol/L of HCl. After shaking for 5 h, the MB-loaded adsorbent

was collected by a magnet and reused for adsorption again. The supernatant solutions were

analyzed by UV–Vis spectra. The cycles of adsorption–desorption processes were

successively conducted five times.

3. Results and Discussion

By far, GO has been functionalized through condensation reactions between the functional

groups such as carboxyl and epoxide on GO and amine or hydroxyl groups of the

functionalizers. In this work, peripheral carboxylic acids were partially converted into acyl

chloride by treating GO with SOCl2. After removing the excess of SOCl2 with dry THF,

anhydrous CA was covalently grafted onto GO through a simple esterification reaction. GO-

CA-Fe3O4 nanocomposite was prepared via co-precipitation. The process is schematically

illustrated in Fig. 1.

This article is protected by copyright. All rights reserved

The XRD patterns of GO, graphene nanosheets (GNS, reduced by hydrazine hydrate), GO-

CA and GO-CA-Fe3O4 are presented in Fig. 2. GO shows a sharp (0 0 1) peak at 10.44°.

Oxidation generates oxygen-containing groups on the originally atomically flat graphene

sheets which makes individual GO sheets thicker than individual pristine graphene sheets

[46]. In GNS, which are prepared by reducing GO with hydrazine hydrate, this peak shifted

back around the original 0 0 2 peak and is observed at 24.09°. CA-functionalized GO shows

an XRD pattern similar to

Acc

epte

d A

rtic

le

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

GNS and the related peak is seen at 2θ = 23.73°. Besides, the (0 0 1) peak of GO is barely

there. This indicates that layered GO has been exfoliated largely and CA was intercalated into

interlayer spacing of GO, partially restoring its electronic conjugation [46]. It can be

suggested that functionalization of GO with CA has led to the formation of graphene-like

platelets [47]. For GO-CA-Fe3O4 nanocomposite, characteristic peaks at 2θ values of 18.34°

(1 1 1), 29.93° (2 2 0), 35.49° (3 1 1), 43.12° (4 0 0), 56.99° (4 2 2), and 62.52° (5 1 1) are

observed. The equivalent particle size of the NPs was calculated to be 25 nm using the

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

Scherrer’s equation which was confirmed by TEM. Furthermore in the XRD pattern of GO-

CA-Fe3O4 nanocomposite, the presence of GO-CA is not clearly demonstrated and this also

confirms that GO-CA has almost completely been exfoliated and less agglomorated GO-CA

sheets are presented in the nanocomposite [30].

Fig. 3 shows the FTIR spectra of GO, GO-CA and GO-CA-Fe3O4. The presence of several

characteristic peaks of GO confirms successsful oxidation of graphite. In detail, C=O (1735

cm-1

), aromatic C=C (1626 cm-1

) and alkoxy C-O (1074 cm-1

) stretching vibrations were

obsereved and were in good agreement with previous works reports [30, 48]. The FTIR

spectrum of GO-CA differs from that of GO. The peak at 3392 cm-1

in GO spectrum is

related to O-H and CO-H. This peak is reduced in broadness and shifts to 3431 cm-1

due to

esterifaction of carboxylic acid groups of GO and the presence of aliphatic carboxylic groups

of CA. The absorbtion band at 1740 cm-1

is attributed to the ester and the upcoming new

bands at 2927 cm-1

are asigned to CH2 groups of CA. The signals of C=O in carboxylic acids

of CA are observed at 1694 and 1647 cm-1

. In addition, a sharp band at 1560 cm-1

is

connected to the skeletal vibration of reduced graphene sheets [49]. McAllister et al. have

reported that in nucleophilic substitution between epoxy groups of GO and alkylamine or

diaminoalkane, deoxygenation occurs which leads to reduction of GO. The peak at 1560 cm-1

is related to the out-of-plane A2u, increased disorder, bending graphite sheets and a change in

the interplanar bonding [50]. In the reaction between GO and 1-bromooctadecane in the

presence of pyridine, a peak at 1560 cm-1

was observed and indicated that GO has been

effectively reduced during the functionalization process [51]. Using excess of Et3N in our

reaction and the reflux condition, it can be speculated that Et3N can act like pyridin [39] and

reduction of GO has happened associated with the nucleophilic attack of Et3N. This is in

good agreement with XRD spectrum of GO-CA which shows a pattern similar to GNS.

Furthuremore, a considrable change is seen in the fingerprint region of the GO-CA spectrum

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

(2000-800 cm-1

) which suggests that a chemical modification of the GO structure had

occurred [47]. In the FTIR spectrum of GO-CA-Fe3O4 charactristic peak of Fe3O4 is seen at

580 cm-1

. The bands assigned to carboxylic acid groups of CA were reduced in intensity and

shifted to lower wavenumbers displaying the binding of a CA radical to the surface of Fe3O4

NPs by chemi-sorptions of carboxylate (citrate) ions [40]. In addition, since the –OH groups

of GO and –COOH groups of CA are in interaction with MNPs, the peak around 3500 cm-1

is

significantly reduced in intensity.

Comparing the FTIR spectra of GO-CA-Fe3O4 and GO-CA-Fe3O4/MB-loaded, total absence

of the peak attributed to –COOH groups of CA at 3500 cm-1

in the latter one, in addition to

other obvious changes, confirm the complexation of MB with functional groups present in the

adsorbents.

The morphology and structure of the GO-CA hybrid and GO-CA-Fe3O4 nanocomposite

wereanalyzed by SEM and TEM. Fig. 4a-c show the SEM images of GO-CA. The layered

morphology of GO is clearly visible in SEM images. White round objects seen at the edges of

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

the GO sheets are CA groups since the functionalization was performed on the edges. The

SEM images of GO-CA-Fe3O4 are displayed in Fig. 4d-f. It can be observed that the

functionalized GO sheets are completely coated with MNPs and as expected, the CA groups

were covered with MNPs as well. By paying attention to Fig. 4d, the layer-by-layer assembly

of GO-CA sheets is seen. These sheets are distributed between MNPs and prevented their

aggregation to a certain extent. The average size of MNPs determined from SEM images is

25 nm. As observed from TEM morphology and size distribution of GO-CA-Fe3O4

nanocomposite micrographs (Fig. 4g), the magnetic particles are specifically well shaped

spherical and not much agglomeration is seen which implies that GO-CA can efficiently

stabilize the MNPs. The mean size of the MNPs was found to be 25 nm from the TEM image

which is in consistent with the average particle size calculated from the Scherrer’s relation in

the XRD pattern.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

The magnetization curve of GO-CA-Fe3O4 was measured at room temperature and is shown

in Fig. 5. The magnetic hysteresis loop is S-like curve. The saturation magnetization (Ms) is

57.8

emu g-1

. The prepared nanocomposite exhibited zero coercivity and permanence indicating its

superparamagnetism.

As seen in Fig. 6a, the magnetic nanocomposite could readily be dispersed in water by

sonicating for 3 min, resulting in a stable brown suspension. When a magnet was placed close

to the glass vial, the magnetic nanocomposite was separated fleetly from the aqueous solution

within a few seconds using an ordinary magnet (Fig. 6b and 6c). Since high magnetic

response is essential for magnetic separation, we decided to use this nanocomposite in

adsorbing dyes from aqueous solutions.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

The adsorption of MB by GO-CA-Fe3O4 was studied. The effect of contact time and pH on

the amount of dye adsorbed and adsorption isotherm were investigated individually with a

fixed adsorbent does (25 mg) and 25 mL of dye at an initial concentration of 20 mg L-1

.

3.1 Adsorption studies

There are plenty of oxygen atoms on GO which give a negative charge to its surface.

Interaction of GO with cations and positively charged surfactants has been reported [52-59].

MB is a heterocyclic aromatic chemical compound and a basic cationic dye, thus it is likely

to interact with negatively charged compounds such as GO. GO-CA has additional carboxylic

groups that

make the electrostatic interaction between MB and GO-CA more intense. In addition, π-π

stacking can contribute to the whole binding strength, but for instance, the affinity of carbon

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

nanotubes and MB is low [60] and the absorption capacity of MB on expanded graphite is

three orders of magnitude lower than that on GO [61]. These facts suggest that electrostatic

interaction plays the major role and π-π stacking plays the minor role in adsorption of MB

onto GO. This is schematically presented in Fig. 7.

3.1.1. Effect of contact time

The effect of contact time on the adsorption of MB is shown in Fig. 8. The adsorption process

reaches equilibrium in only 30 min. which is an excellent merit for the synthesized

nanocomposite. Adsorption of MB onto Fe3O4@graphene [30] and covalently attached GO-

Fe3O4 [31] was reported to be 30 min. as well. Therefore, this novel nanocomposite can be a

promising adsorbent for cationic dyes.

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

3.1.2. Effect of pH

The effect of pH on the adsorption of MB was investigated over the range of pH values from

2-10. The adsorption capacity of MB increases rapidly with increasing solution pH from 2 to

6 and it remains constant until 10 (Fig. 9). Electrostatic interactions greatly control the

adsorption of ionic compounds. The solution pH affects the degree of ionization of the

pollutant and the adsorbent. The surface of GO is negatively charged due to the presence of

oxygene-containing groups and the CA groups add up to it. The electrostatic attraction

between the negatively charged surface of the GO-CA-Fe3O4 nanocomposite and positively

charged MB molecules increases as the pH increases and this leads to higher adsorption

capacity of the dye. As it is shown in Fig. 9, adsorption decreases in low pH which can be

due to the protons competition with the dye molecules for the available adsorption sites [41].

The obtained result is in good agreement with the adsorption of MB by solvothermal-

synthesized graphene-magnetic nanocomposite [52, 20].

3.1.3. Adsorption equilibrium

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

The adsorption isotherm of MB for the GO-CA-Fe3O4 is shown in Fig. 10. To study the

distribution of the adsorption molecules between the liquid phase and solid phase at the

equilibrium state, the adsorption isotherm is used. The maximum adsorption capacity was

attained 112 mg g-1

at an initial concentration of 20 mg L-1

. The obtained result is comparable

with the adsorption of MB onto GO-Fe3O4 [31] and Fe3O4@graphene [30].

Table 1 shows the results obtained in this study with those in the previously reported works

on adsorption capacities of various adsorbent in aqueous solution for MB. The adsorption

isotherm data of MB onto pure graphene has already been studied [30]. GO shows the highest

adsorption capacity [31]. Fe3O4 has no ability to adsorb dye molecule [30]. The adsorption

capacity for GO-CA and GO-CA-Fe3O4 are 19.2 and 19.0, respectively. These facts suggest

that electrostatic interaction plays the major role in adsorption of MB onto GO. As mentioned

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

previously, MB is a basic cationic dye, thus it is likely to interact with negatively charged

compounds such as GO. GO-CA has additional carboxylic groups that make the electrostatic

interaction between MB and GO-CA more intense and comparable to GO. The slight

difference in the adsorption capacities of GO-CA and GO-CA-Fe3O4 is that the magnetic

nanoparticles may occupy some active sites on GO [30]. Thus the synthesized GO-CA-Fe3O4

shows a pretty good adsorption.

3.2 Desorption studies

Reversibility of dye adsorption is one of the important properties of the adsorbent in the

combined system. Desorption is expected to play an important role in the mechanism and the

effectiveness of the combined system.

To evaluate the possibility of regeneration and reusability of GO-CA-Fe3O4 as an adsorbent,

the desorption experiments were performed. Desorption of MB from GO-CA-Fe3O4 was

demonstrated using 0.5 mol/L HCl as an eluent. The cycles of adsorption–desorption

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

experiments were also carried out, as shown in Fig. 11. The adsorption capacity decreased for

each new cycle after desorption with five cycles. These results show that the adsorbents can

be recycled for MB adsorption with 0.5 mol/L HCl, and the adsorbents can be reused. This

could be ascribed to the fact that, in the acidic solution, the negatively charged carboxylate

anions were protonated and the electrostatic interaction between GO-CA-Fe3O4 and dye

molecules became much weaker.

4. Conclusions

We have prepared a well-dispersed and highly efficient adsorbent to remove MB from

contaminated water. The adsorbent was synthesized by a simple esterification of acyl

chloride-functionalized GO which was well-dispersed in water. The MNPs were chemically

deposited onto this hybrid. Due to the presence of CA groups, MNPs were strongly attached

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

to the hybrid and covered its surface which was observed in the SEM images. The specific

saturation magnetization of the GO-CA-Fe3O4 is 57.8 emu g-1

and the average size of the NPs

was obtained to be 25 nm using TEM micrographs and XRD pattern. Since the surface of the

hybrid was negatively charged, the nanocomposite had a great interaction with the cationic

dye of MB and showed high adsorption capacity of 112 mg g-1

. High adsorption capacity

accompanied with the ease of separation by an external magnetic field makes the synthesized

nanocomposite a powerful separation tool to be utilized in wastewater treatment.

Acknowledgements

Authors are pleased to acknowledge the University of Tabriz and Research Center for

Pharmaceutical Nanotechnology (RCPN), Tabriz University of Medical Science for financial

support of this work.

References

[1] Kornaros M and Lyberatos G, J Hazard Mater 136:136:95–102 (2006).

[2] Guibal E and Roussy J, React Funct Polym 67:33–42 (2007).

[3] Zhao W, Wu Z and Wang D, J Hazard Mater 137:1859–1865 (2006).

[4] Dutta K, Mukhopadhyaya S, Bhattacharjee S and Chaudhuri B, J Hazard Mater 84:57–61

(2001).

[5] Capar G, Yetis U and Yilmaz L, J Hazard Mater 135:423–430 (2006).

[6] Liu C H, Wu JS, Chiu HC, Suen SY and Chu KH, Water Res 41:1491–1500 (2007).

[7] Muruganandham M and Swaminathan M, J Hazard Mater 135:78–86 (2006).

[8] De Lisi R, Lazzara G, Milioto S and Muratore N, Chemosphere 69:1703–1712 (2007).

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

[9] Sun G and Xu X, Ind Eng Chem Res 36:808–881 (1997).

[10] Juang RS, Wu FC and Tseng RL, Colloids Surf A 201:191–199 (2002).

[11] Crini G, Bioresour Technol 97:1061-1085 (2006).

[12] Aleboyeh A and Aleboyeh H, J Hazard Mater 133:167–171 (2006).

[13] Kawasaki N, Ogata F and Tominaga H, J Hazard Mater 181:574-579 (2010).

[14] Camacho LM, Torres A, Saha D and Deng SG, J Colloid Interface Sci 349:307-313

(2010).

[15] Hamada K, Kaneko T, Chen MQ and Akashi M, Chem Mater 19:1044-1052 (2007).

[16] Costanzo JA, Ober CA, Black R, Carta G and Fernandez EJ, Biomaterials 31:2857-2865

(2010).

[17] Fu X, Chen X, Wang J and Liu J, Microporous Mesoporous Mater 139:8–15 (2011).

[18] Crini G, Gimbert F, Robert C, Martel B, Adam O, Morin-Crini N, et al, J Hazard Mater

153:96-106 (2008).

[19] Aia L, Zhang C, Liao F, Wang Y, Li M, Meng L, et al, Hazard Mater 198:282–290

(2011).

[20] Ramesha GK, Vijaya Kumara A, Muralidhara HB and Sampath S, J Colloid Interface

Sci 361:270−277 (2011).

[21] Zhang W, Zhou C, Zhou W, Lei A, Zhang Q, Wan Q, et al, Bull Environ Contam

Toxicol 87:86−90 (2011).

[22] Geim AK and Novoselov KS, Nat Mater 6:183–191 (2007).

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

[23] Dreyer DR, Park S, Bielawski CW and Ruoff RS, Chem Soc Rev 39:228–240 (2010).

[24] Shi WH, Zhu JX, Sim DH, Tay YY, Lu ZY, Sharma XJ, et al, J Mater Chem 21:3422-

3427 (2011).

[25] Yang XY, Wang YS, Huang X, Ma YF, Huang Y, Yang RC, et al, J Mater Chem

21:3448-3454 (2011).

[26] Zhou GG, Wang DW, Li F, Zhang LL, Li N, Wu ZS, et al, Chem Mater 22:5306-5313

(2010).

[27] Xu C, Wang X, Zhu JW, Yang XJ and Lu LD, J Mater Chem 18:5625-5629 (2008).

[28] Ambashta RD and Sillanpää M, J Hazard Mater 180:38–49 9(2010).

[29] Geng Z, Lin Y, Yu X, Shen Q, Ma L, Li Z, et al, J Mater Chem 22:3527-3535 (2012).

[30] Yao Y, Miao S, Liu S, Ma L P, Sun H and Wang S, Chem Eng J 184:326– 332 (2010).

[31] Xie G, Xi P, Liu H, Chen F, Huang L, Shi Y, et al, J Mater Chem 22:1033-1039 (2012).

[32] He F, Fan J, Ma D, Zhang L, Leung C and Chan HL, Carbon 48:3139–3144 (2010).

[33] Namazi H and Adeli M, Eur Polym J 39:1491–1500 (2003).

[34] Namazi H, Motamedi S and Namvari M, BioImpacts 1:63-69 (2011).

[35] Oliveira LCA, Petkowicz DI, Smaniotto A and Pergher SBC, Water Res 38:3699-3704

(2004).

[36] Oliveira LCA, Rios RVRA, Fabris JD, Garg V, Sapag K and Lago RM, Carbon

40:2177-2183 (2002).

[37] Crini G, Dyes Pigments 77:415-426 (2008).

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

[38] Crini G and Badot P M, Prog Polym Sci 33:399-447 (2008).

[39] Chang PR, Yu J, Ma X and Anderson DP, Carbohyd Polym 83:640–644 (2011).

[40] Nigam S, Barick KC and Bahadur D, J Magn Magn Mater 323:237–243 (2011).

[41] Cheraghipour E, Javadpour S and Mehdizadeh AR, J Biomed Sci Eng 5:715-719 (2012).

[42] Răcuciu M, Creangă DE and Airinei A, Eur Phys J E 21:117-121 (2006).

[43] Goodarzi A, Sahoo Y, Swihart MT, Prasad PN, Mat Res Soc Symp Proc 789:129-136

(2004).

[44] Hummers WS, William S and Offeman REJ, J Am Chem Soc 80:1339-1339 (1958).

[45] Zhang K, Zhang LL, Zhao XS and Wu J, Chem Mater 22:1392–1401 (2010).

[46] Shen J, Li N, Shi M, Hu Y and Ye M, J Colloid Interface Sci 348:377–383 (2010).

[47] Salvio R, Krabbenborg S, Naber WJM, Velders AH, Reinhoudt DN and van der Wiel

WG, Chem Eur J 15:8235–8240 (2009).

[48] Yang Q, Pan X, Clarke K and Li K, Ind Eng Chem Res 51:310–317 (2012).

[49] Szabo T, Berkesi O and Dekany I, Carbon 43:3186–189 (2005).

[50] McAllister MJ, Abdala AA, McAllister MJ, Aksay IA and Prudhomme RK, Langmuir

23:10644–10649 (2007).

[51] Liu J, Wang Y, Xu S and Sun DD, Mater Lett 64:2236–2239 (2010).

[52] Aia L, Zhang C, Chen Z. J Hazard Mater 192:1515–1524 (2011).

[53] Yang ST, Chang Y, Wang H, Liu G, Chen S, Wang Y, et al, J Colloid Interface Sci

351:122-127 (2010).

This article is protected by copyright. All rights reserved

Acc

epte

d A

rtic

le

[54] Xu C, Wang X, Yang L and Wu Y, J Solid State Chem 82:2486-2490 (2009).

[55] Machida M, Mochimaru T and Tatsumoto H, Carbon 44:2681-2688 (2006).

[56] Cho HH, Wepasnick K, Smith BA, Bangash FK, Fairbrother DH and Ball WP,

Langmuir 26:967-981 (20100.

[57] Seredych M nad Bandosz TJ, J Colloid Interface Sci 324:25-35 (2008).

[58] Matsuo Y, Niwa T and Sugie Y, Carbon 37:897–901 (1999).

[59] Liu Z, Wang Z, Yang X and Ooi K, Langmuir 18:4926-4932 (2002).

[60] Yao Y, Xu F, Chen M, Xu Z and Zhu Z, Bioresour Technol 101:3040-3046 (2010).

[61] Zhao M and Liu P, Desalination 249:331-336 (2009).

[62] Xie LM, Ling X, Fang Y, Zhang J and Liu ZF, J Am Chem Soc 131:9890-9891 (2009)

[63] Hu YW, Li FH, Bai XX, Li D, Hua SC, Wang KK, et al, Chem Commun 47:1473-1475

(2011)

[64] Juang RS, Wu FC, and Tseng RL, J Colloid Interface Sci 227:437-444(2000)

[65] Qu S, Huang F, Yu SN, Chen G and Kong JL, J Hazard Mater 160:643-647 (2008)

[66] Thuy-Duong NP, Viet Hung P, Kim EJ, Oh ES, Hur SH, Chung JS, et al, Appl Surf Sci

258:4551–4557 (2012)

[67] Ai L and Jiang J, Chem Eng J 192:156–163 (2012)