Bioresource Technology 114 (2012) 703–706

Contents lists available at SciVerse ScienceDirect

Bioresource Technology

journal homepage: www.elsevier .com/locate /bior tech

Short Communication

Preparation of novel magnetic chitosan/graphene oxide composite as effectiveadsorbents toward methylene blue

Lulu Fan, Chuannan Luo ⇑, Min Sun, Xiangjun Li, Fuguang Lu, Huamin QiuKey Laboratory of Chemical Sensing & Analysis in Universities of Shandong (University of Jinan), School of Chemistry and Chemical Engineering, University of Jinan,Jinan 250022, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 12 November 2011Received in revised form 14 February 2012Accepted 14 February 2012Available online 22 February 2012

Keywords:Magnetic chitosanGraphene oxideMethylene blueAdsorption

0960-8524/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.biortech.2012.02.067

⇑ Corresponding author. Fax: +86 53189736065.E-mail addresses: fanlu1949@126.com (L. Fan), chm

A novel magnetic composite bioadsorbent composed of magnetic chitosan and graphene oxide (MCGO)was prepared as the magnetic adsorbent toward methylene blue. The magnetic composite bioadsorbentwas characterized by SEM, FTIR and XRD measurements. The effect factors including pH, contact time andtemperature on the adsorption properties of methylene blue onto MCGO were investigated. The resultingshows extraordinary adsorption capacity and fast adsorption rates for removal of methylene blue. Thekinetics are well-described by pseudo-second-order kinetic. The experimental data of isotherm followedthe Langmuir isotherm model and the Freundlich model, respectively. This work shows that the MCGOcould be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction GO is that it is hydrophilic with very high negative charge density

Dyes from the industries such as dye synthesis, paper, printing,electroplating, food and cosmetic are the major source of water pol-lution. Dyes are harmful to flora, fauna and some of the organic dyesand their products have a mutagenic or carcinogenic influence onhuman beings (Aksu, 2005). The adsorptive removal of various dyesis the most widely used method because of the ease of operation andcomparable low cost of application (Barquist and Larsen, 2010; Den-izli et al., 2003; Safarik et al., 1995). Chitosan has been reported to bea suitable biopolymer for the removal of dyes from aqueous solution,because of its high amino and hydroxyl functional group content(Crini, 2006). Coating chitosan with magnetic fluids is a new methodto expand function of the chitosan, and the method has been re-ported that it can improve the surface area for adsorption and reducethe required dosage for the adsorption of dyes (Babel and Kurnia-wan, 2003; Fan et al., 2011; Wang et al., 2008).

Graphene is a fascinating new member of carbon materials withhoneycomb and one-atom-thick structure. This excitement isgreatly attributed to its excellent mechanical and physicochemicalproperties (Rao et al., 2009). Recent researches have indicated thatgraphene oxide proved to be a promising material to adsorb dyesand support for catalyst due to their extraordinary mechanicalstrength and relatively large specific area (Ramesha et al., 2011).Graphene oxide (GO) is an oxidized form of graphene (Dreyeret al., 2010) consisting of various functional groups such as hydro-xyl, carboxyl, and epoxy groups. One of the major advantages with

ll rights reserved.

_luocn@ujn.edu.cn (C. Luo).

arising due to the oxygen containing functional groups. In solutionphase, GO exists as single layer. GO can act as weak acid cation ex-change resin because of the ionizable carboxyl groups, which allowion exchange with metal cations or positively charged organic mol-ecules (Ramesha et al., 2011). Based on favorable adsorption prop-erties of chitosan and inherent properties of GO, some researchershave explored the possibility of chitosan–GO composite as bioad-sorbents (Depan et al., 2011). However, magnetic chitosanstrengthened by graphene oxide has not been synthesized and ap-plied in removing methylene blue (MB) from aqueous solution.

In this work, the MCGO have been prepared, where the carboxylgroups of GO chemically react with the amine group of magneticchitosan with the consequent formation of a chemical bond be-tween GO and the biopolymer (magnetic chitosan) (Depan et al.,2011). The aim of this study was to explore MCGO composite bio-adsorbent with higher adsorption capacity and excellent separa-tion properties. The kinetic and thermodynamic of the dyeadsorption on the MCGO composite have been investigated. Theresulting MCGO composite could be utilized as a magnetically sep-arable and efficient adsorbent for dye removal from water. Theapplication of MCGO for removal of MB with the help of an exter-nal magnetic field is shown in Scheme 1.

2. Methods

2.1. Materials

Chitosan with 80 mesh, 96% degree of deacetylation and aver-age-molecular weight of 6.36 � 105 was purchased from Qingdao

Scheme 1. The application of MCGO for removal of MB with the help of an external magnetic field.

704 L. Fan et al. / Bioresource Technology 114 (2012) 703–706

Baicheng Biochemical Corp. (China). The reagents 1-ethyl-3-(3-dimethylaminoprophy) carbondiimide hydrochloride (EDC), N-hy-droxyl succinimide (NHS), sodium hydroxide, glutaraldehyde andacetic acid were Aldrich products. All other reagents used in thisstudy were analytical grade, and distilled or double distilled waterwas used in the preparation of all solutions.

2.2. Preparation of MCGO

The preparation process of MCGO was as follows: 2% (w/v) ofchitosan solutions were prepared by dissolving 0.4 g of chitosaninto 20 mL of 2.0 (v/v) acetic acid aqueous solutions under ultra-sonic stirring for 2 h at room temperature. Subsequently, 0.1 g ofmagnetic nanosized Fe3O4 was added into the colloidal solutionand the reaction system was continued to be stirred for 1.5 h. Someparaffin oil was slowly dispersed in the prepared mixture understirring. After 0.5 h of emulsification, 3 mL of glutaraldehyde wasadded to crosslink chitosan. Then, 0.3 g of GO was added and themixed system was stirred continuously for 90 min in a water bathat 50 �C. pH of the reaction system was adjusted to 9–10 by using1 mol L�1 NaOH and kept in a water bath for a further 60 min at80 ± 0.2 �C. Black products (MCGO) were washed with petroleumether, ethanol and distilled water in turn until pH was about 7.Then, the precipitate was dried in a vacuum oven at 50 �C. The ob-tained product was MCGO.

2.3. Adsorption experiments

All batch adsorption experiments were performed on a modelKYC-1102 C thermostat shaker (Ningbo, China) with a shakingspeed of 180 rpm. Typically, a 25 mL solution of known dye con-centration and 0.05 g of MCGO were added into 100 mL glass flasksand then shook under 30 ± 0.2 �C. At the completion of preset timeintervals, 10 mL dispersion was drawn and separated immediatelyby the aid of a magnet to collect the bioadsorbent. Residual MBconcentration in supernatant was determined by using a ShimadzuUV-2550 UV–vis spectrophotometer. The adsorption amount andadsorption rate are calculated based on the difference in the MBconcentration in the aqueous solution before and after adsorption,according to the following equation:

Q ¼ ðC0 � CeÞV=W; E ¼ ðC0 � CeÞ=C0 � 100% ð1Þ

where, C0 and Ce are the initial and equilibrium concentrations ofMB in milligrams per liter, respectively, V is the volume of MB solu-tion, in liters, and W is the weight of the MCGO used, in grams.

3. Results and discussion

3.1. Characterization of MCGO

The GO and MCGO had been characterized by the FTIR. Thecharacteristic IR features of GO indicate the presence of the abun-dant oxygen-containing functional groups on the surface of GO.The characteristic bands at 1071, 1404, 1630 and 1730 cm�1 corre-spond to the C–O–C stretching vibrations, the O–H deformation ofthe C–OH groups, the C@C stretching mode of the sp2 C networkand the C@O stretching vibrations of the –COOH group, respec-tively. As for the CS, there are two characteristic absorbance bandscentered at 1636 and 1578 cm�1, which correspond to the C@Ostretching vibration of –NHCO– (amide I) and the N–H bendingof –NH2, respectively (Depan et al., 2011). However, in the caseof MCGO nanocomposites, it can be distinctly observed that the–NH2 absorbance band has vanished and the intensity of –NHCO–(amide I) has increased remarkably, which proves that some –NH2

groups on the CS chains have already reacted with the –COOHgroups on the surfaces of GO and therefore have been convertedto –NHCO– groups (Depan et al., 2011). The results demonstratedthat the amidation reaction assisted by microwave radializationwithin a very short time is effective and that the chitosan chainswere successfully grafted onto the surface of GO nanosheets viaamido bonds. In addition, 580 cm�1 is the characteristic peak ofFe3O4. These indicated that MCGO was successfully synthesized.

The XRD analysis results of pure Fe3O4 and MCGO were mostlycoincident. Six characteristic peaks for Fe3O4 (2h = 30.1, 35.5, 43.3,53.4, 57.2 and 62.5), marked by their indices ((220), (311), (400),(422), (511), and (440)), were observed in samples.

The GO presents the sheet-like structure with the large thick-ness, smooth surface, and wrinkled edge. After the combinationwith magnetic chitosan to form the MCGO composite, the MCGOhad a much rougher surface, revealing that many small magneticchitosan had been assembled on the surface of GO layers with ahigh density. Notably, high surface area of sheet biomaterials en-hanced adsorption active sites as it provided an advantageous con-dition for attracting more target substances around the sites and

Table 1Adsorption kinetic parameters of MB onto MCGO.

Initial conc. C0(mg/L) Pseudo-first-order Pseudo-second-order

K1 (min�1) Qe,cal (mg/g) R2 Qe,cal (mg/g) K2, g/(mg.min) Qe,exp (mg/g) R2

50 0.0017 107.1 0.69 130.1 0.0309 132.6 0.992100 0.0042 134.6 0.71 180.2 0.0124 179.6 0.995

L. Fan et al. / Bioresource Technology 114 (2012) 703–706 705

correspondingly improved the adsorption rate and adsorptioncapacities.

3.2. Effect of pH value on adsorption

Through experiment, MB removal capacity had great change atthe pH 2–10. This may be due to the more functional groupsformed on the surface of MCGO which increase their surface com-plexation capability (Li et al., 2010; Kyzas and Lazaridis, 2009).Chitosan becomes strongly anionic after grafting with GO. Increas-ing the pH of solution, deprotonation of (MCGO) derivative is real-ized and strong attractive forces, between the positive charged dyeand negatively charged MCGO, result in high uptakes as follows(Crini et al., 2008):

RCOO� þ DANþ ! RCOO�DANþ;

ACH2O� þ DANþ ! ACH2O�DANþ

Thus, pH of 10.0 was selected as the optimum pH value of MB solu-tion for the following adsorption experiment.

3.3. Adsorption kinetics

The pseudo-first-order kinetic model is expressed by the fol-lowing equation:

lnðQ e � Q tÞ ¼ ln Qe � K1t ð2Þ

where Qe and Qt are the amount adsorbed in mg/g at equilibrium,time ‘t’ in min, and K1 is the rate constant of adsorption (min�1).The values of experimental Qe do not agree with the calculated onesand the values of correlation coefficient (R2) are relatively low formost of the adsorption data (Table 1). This shows that the adsorp-tion process may not be the correct fit to the first-order rate equa-tion. Another kinetic model is pseudo-second-order model, which isexpressed by:

t=Q t ¼ 1=ðK2Q e2Þ þ t=Qe ð3Þ

where K2 is the rate constant for the pseudo-second-order adsorp-tion process. The linear plots of t/Qt versus t show good agreementbetween experimental and calculated Qe values at different initialconcentrations. The correlation coefficient (R2) (Table 1) for thepseudo-second-order adsorption model has high value (>99%) foradsorbent. These facts suggest that the pseudo-second-orderadsorption mechanism is predominant.

3.4. Adsorption isotherms

The Langmuir adsorption isotherm can be expressed as:

Ce=Q e ¼ 1=ðKLQ0Þ þ Ce=Q 0 ð4Þ

where Ce is the equilibrium concentration of MB in solution (mg/L),Qe is the adsorbed value of MB at equilibrium concentration (mg/g),Q0 the maximum adsorption capacity (mg/g), and KL is the Langmuirbinding constant, which is related to the energy of adsorption. Plot-ting Ce/Qe against Ce gives a straight line with slope and interceptequal to 1/Q0 and 1/(KL Q0), respectively.

By calculating, the results are as follows:

Ce=Qe ¼ 0:00553Ce þ 0:0144; ðR2 ¼ 0:991Þ;Q0 ¼ 180:83 mg g�1; KL ¼ 0:38 L mg�1

The MB maximum adsorption capacity of MCGO was 180.83 mg/g,which was higher than the reported values of pyrophylite(4.2 mg/g) (Wang et al., 2005) and graphene (Liu et al., 2011) indi-cating that MCGO is a good adsorbent to remove dyes from aqueoussolutions. In addition, the coefficients of determination R2 of theLangmuir equation demonstrated that the adsorption of MB ontoMCGO follows the Langmuir’s model.

Freundlich isotherm is an empirical equation based on adsorp-tion on a heterogeneous surface. The equation is commonly repre-sented by:

ln Q e ¼ ln KF þ ð1=nÞ ln Ce ð5Þ

KF (mg/g (L/mg)1/n) and n are the Freundlich constants characteris-tics of the system, indicating the adsorption capacity and theadsorption intensity, respectively. If the value of 1/n is lower than1, it indicates a normal Langmuir isotherm; otherwise, it is indica-tive of cooperative adsorption.

By calculating, the results are as follows:

ln Q e ¼¼ 5:12þ 0:08 ln Ce; 1=n ¼ 0:08; R2 ¼ 0:96

The Langmuir and Freundlich adsorption constants and the corre-sponding correlation coefficients are got. The adsorption of MBwas well fitted to the Langmuir isotherm model with the higherR2 (0.999). It indicated the adsorption took place at specific homo-geneous sites within the adsorbent forming monolayer coverage ofMB at the surface of the MCGO. The Freundlich constant 1/n wassmaller than 1, indicating a favorable process. Furthermore, theessential characteristics of the Langmuir isotherm can be describedby a separation factor, which is defined by the following equation(Kadirvelu et al., 2001; Atia et al., 2006).

4. Conclusions

In summary, MCGO composite was successfully prepared. TheMCGO acted as a good adsorbent to adsorb MB from aqueous solu-tions. In batch adsorption experiments, the adsorption kinetics,isotherms and thermodynamics were investigated in detail. The ki-netic study revealed the adsorption process was well fitted thepseudo-second-order kinetic model. The equilibrium data werewell-modeled by the Langmuir and Freundlich isotherm models.This work showed that the MCGO composite could be utilized asa magnetically separable and efficient adsorbent for the environ-mental cleanup.

References

Aksu, Z., 2005. Application of biosorption for the removal of organic pollutants: areview. Process Biochem. 40, 997–1026.

Atia, A., Donia, A.M., El-Boraey, H.A., Mabrouk, D.H., 2006. Adsorption of Ag(I) onglycidyl methacrylate/N,N-methylene bis-acrylamide chelating resins withembedded iron oxide. Sep. Purif. Technol. 48, 281–287.

Babel, S., Kurniawan, T., 2003. Low-cost adsorbents for heavy metals uptake fromcontaminated water: a review. J. Hazard. Mater. 28, 219–243.

Barquist, K., Larsen, S.C., 2010. Chromate adsorption on bifunctional, magneticzeolite composites. Microporous Mesoporous Mater. 130, 197–202.

706 L. Fan et al. / Bioresource Technology 114 (2012) 703–706

Crini, G., 2006. Non-conventional low-cost adsorbents for dye removal: a review.Bioresour. Technol. 97, 061–1085.

Crini, G., Robert, C., Martel, F.B., Adam, O., De Giorgi, F., Badot, P.M., 2008. Theremoval of basic blue 3 from aqueous solutions by chitosan-based adsorbent:batch studies. J. Hazard. Mater. 153, 96–106.

Denizli, A., Say, R., Piskin, E., 2003. Removal of aluminium by alizarin yellow-attached magnetic poly(2-hydroxyethyl methacrylate) beads. React. Funct.Polym. 55, 99–107.

Depan, D., Girase, B., Shah, J.S., Misra, R.D.K., 2011. Structure–process–propertyrelationship of the polar graphene oxide-mediated cellular response andstimulated growth of osteoblasts on hybrid chitosan network structurenanocomposite scaffolds. Acta Biomater. 7, 3432–3445.

Dreyer, D.R., Park, S., Bielawski, C.W., Ruoff, R.S., 2010. The chemistry of grapheneoxide. Chem. Soc. Rev. 39, 228.

Fan, L.L., Luo, C.N., Lv, Z., Lu, F.G., Qiu, H.M., 2011. Preparation of magnetic modifiedchitosan and adsorption of Zn2+ from aqueous solutions. Colloids. Surf., B 88,574–581.

Kadirvelu, K., Thamaraiselvi, K., Namasivayam, C., 2001. Adsorption of Cu (II) andCr(VI) ions by chitosan: kinetics and equilibrium studies. Sep. Purif. Technol. 24,497–505.

Kyzas, G.Z., Lazaridis, N.K., 2009. Reactive and basic dyes removal by sorption ontochitosan derivatives. J. Colloid Interface Sci. 331, 32–39.

Li, Y.H., Du, Q.J., Wang, X.D., Zhang, P.D., Wang, C., Wang, Z.H., Xia, Y.Z., 2010.Removal of copper from aqueous solution by carbon nanotube/calcium alginatecomposites. J. Hazard. Mater. 177, 876–880.

Ramesha, G.K., Vijaya Kumara, A., Muralidhara, H.B., Sampath, S., 2011. Grapheneand graphene oxide as effective adsorbents toward anionic and cationic dyes. J.Colloid Interface Sci. 361, 270–277.

Rao, C.N.R., Sood, A.K., Subrahmanyam, K.S., Govindaraj, A.A., 2009. Graphene: thenew two dimensional nanomaterial. Angew. Chem. Int. Ed. 48, 7752.

Safarik, I., Safarikova, M., Buricova, V., 1995. Sorption of water soluble organic dyeson magnetic poly(oxy-2,6-dimethyl-1,4-phenylene). Collect. Czech. Chem.Commun. 60, 1448–1456.

Wang, S., Li, L., Wu, H., Zhu, Z.H., 2005. Unburned carbon as a low-cost adsorbent fortreatment of methylene blue-containing wastewater. J. Colloid Interface Sci.292, 336–343.

Wang, Y.J., Wang, X.H., Luo, G.S., 2008. Adsorption of bovin–serum–albumin (BSA)onto the magnetic chitosan nanoparticles prepared by a microemulsion system.Bioresour. Technol. 99, 3881–3888.