p, Jind Fun

, Ho

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nanoparticles are of particularentialxpecteies in orties all trackenvironanocounction

Due to their biocompatibility, excellent conductivity and facilesurface functionalization, the uorescent carbon nanoparticlesoffer great potential applications in biomedical imaging and photo-catalysis [9,25]. The emergence of uorescent carbon nanoparticlesmake the biological benign magnetic-uorescent nanomaterials

being a reality: magnetic Fe3O4 and uorescent carbon nanoparti-cle in one entity will endow the nanocomposite both strong mag-netic and stable uorescent properties.

2.1. Materials

Glucose, FeCl3 and FeSO47H2O, ethanol (analytical purity, Bei-jing Chemical Reagent Factory). They were used as received. Allthe aqueous solutions were prepared using de-ionized water.

2.2. Methods

Synthesis of carbon nanoparticles: Glucose was rst dissolvedin water (100 mL) to form a clear solution. Then, the solution

Corresponding authors. Address: Institute of Functional Nano & Soft Materials,Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, SoochowUniversity, Suzhou, Jiangsu 215123, China. Fax: +86 512 6588 2846.

Journal of Colloid and Interface Science 356 (2011) 107110

Contents lists availab

Journal of Colloid an

r .coE-mail addresses: yangl@suda.edu.cn (Y. Liu), zhkang@suda.edu.cn (Z. Kang).particles and quantum dots (QDs) based magnetic nanoparticlecomposites [8]. However, the introduction of traditional QDs(CdS etc.) would lead to the health and enviroment concerns;dye molecules are likely to be bleached due to their low photo-chemical stability. On the other hand, the synthetic approachesto their preparation also suffer from the complicated multi-stepprocess and quenching of uorescent entity by the magnetic core[8]. Therefore, the design and synthesis of environmental and bio-logical benign nanomaterials with magnetic-uorescent propertiesare still an urgent challenge.

sized by the hydrothermal reaction of Fe3O4 microspheres and glu-cose in water [12]. However, these microspheres lack uorescentproperties. Here, we report a facile chemical method for synthesiz-ing magnetic-uorescent Fe3O4/carbon nanocomposite. The fabri-cation details, characterization, feasibility and performance of theFe3O4/carbon nanocomposite are described in the followingsections.

2. Materials and methods1. Introduction

Magnetic and photoluminescentimportance due to their widely potscience and technology [14]. It is eof magnetic and uorescent propertgreatly enhance its versatile propeapplications in biological imaging, ceration, information technology andTo date, many magnetic-uorescentported, including silica-based, dye f0021-9797/$ - see front matter 2011 Elsevier Inc. Adoi:10.1016/j.jcis.2010.12.075applications in currentd that the combinationne nanocomposite willnd open up potentialing, magnetic biosepa-nmental science [57].mposites have been re-alized magnetic nano-

Carbon is an ideal candidate for outside coating material owingto its ease of functionalization, its reduction of the magnetic cou-pling between individual magnetic metal particles and stabilityin acid or alkali, which may protect the encapsulated materialsfrom environmental degradation [10]. Moreover, the carbon mate-rial in the composite can improve the electronic conductivity andthe surface area of Fe3O4 nanoparticles [11]. It is reported thatthe magnetic carbon microspheres (Fe3O4@C) have been synthe-Photoluminescent Fe3O4/carbon nanocom

Xiaodie He a, Yang Liu a,b,, Haitao Li a, Hui Huang a,ba Institute of Functional Nano & Soft Materials, Jiangsu Key Laboratory for Carbon-Baseb Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, ChinacCenter of Super-Diamond and Advanced Films (COSADF), City University of Hong Kong

a r t i c l e i n f o

Article history:Received 3 November 2010Accepted 24 December 2010Available online 1 January 2011

Keywords:CompositesMagnetic materialsLuminescenceMagnetic properties

a b s t r a c t

Fe3O4/carbon nanocomposdiffraction, X-ray photoelered spectroscopy and scanple were investigated by The results indicate thatranging from 425 to 550 n

www.elseviell rights reserved.osite with magnetic property

glin Liu b, Zhenhui Kang a,b,, Shuit-Tong Lee a,cctional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China

ng Kong SAR, China

as been prepared by a facile chemical method, and characterized by X-rayn spectroscopy, transmission electron microscopy, fourier transform infra-electron microscopy. The uorescent and magnetic properties of the sam-rescence spectroscopy and vibrating-sample magnetometer, respectively.Fe3O4/carbon nanocomposite exhibit good photoluminescent (emissionand strong magnetic (saturation magnetization of 44.2 emu/g) properties.

2011 Elsevier Inc. All rights reserved.

le at ScienceDirect

d Interface Science

m/locate / jc is

was placed in a 20 mL Teon-sealed autoclave and maintained at180 C for 4 h. After that, the obtained reddish-brown solutionwas centrifuged and washed three times with double-distilledwater and alcohol, and nally dried in a vacuum oven at 70 C toremove the residual solvent.

The morphology and structure of the as-prepared Fe3O4/carbonnanocomposite were investigated by TEM and SEM. SEM image of

108 X. He et al. / Journal of Colloid and Interface Science 356 (2011) 107110Synthesis of Fe3O4/carbon nanocomposite: The newly preparedcarbon nanoparticles were dispersed in water with the aid of ultra-sonication to give a 20 wt.% carbon suspension. FeCl3 (1.62 g) andFeSO47H2O (5.56 g) were dissolved in carbon suspension underN2 protection and vigorous stirring for 3 h. After that, 45 mL of1 mol/L NaOH was added dropwise into the resulting solution,and the mixture was vigorously stirred for 2 h. The suspensionwas then isolated by ltration, and cleaned by three cycles of cen-trifugation/washing/redispersion in water and alcohol. Finally, theas-prepared product was isolated from the mixture by externalmagnetic eld.

The morphology, structure and composition of Fe3O4/carbonnanocomposite were further investigated by X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), transmission elec-tron microscopy (TEM), FTIR spectroscopy, and scanning electronmicroscopy (SEM).

3. Results and discussion

Recently, with glucose as precursor, a microwave pyrolysis ap-proach to synthesize FCNPs has been reported [13]. In this commu-nication, we report a general and facile method for the synthesis ofmagnetic-uorescent Fe3O4/carbon nanocomposite. The synthesiswas done via sequential two-step reaction as follows (see Scheme1): the rst step is the hydrothermal treatment of glucose at 180 Cto obtain the uorescent carbon nanoparticles (FCNPs); the fol-lowed one is the formation of Fe3O4 nanoparticles in as-preparedcarbon nanoparticles (absorbtion of Fe2+/Fe3+ in carbon nanoparti-cles and then alkaline treatment) to obtain Fe3O4/carbon nanocom-posite. In our experiment, the FCNPs (300 nm) prepared in therst step show strong photoluminescence (PL) with different exci-tation wavelengths, and the PL spectra are shown in Fig. S1 (seeEIS). The nal Fe3O4/carbon nanocomposite possesses both mag-netic and uorescent properties, coming from the Fe3O4 nanoparti-cles and carbon materials, respectively.

Typical XRD patterns of the as-prepared Fe3O4/carbon nano-composite (red line) and Fe3O4 (black line) samples are presentedin Fig. 1a. For the XRD pattern of Fe3O4/carbon nanocomposite,the diffraction peaks at 30.1 (200), 35.4 (311), 43.0 (400), 53.7(422), 57.2 (511) and 62.6 (440) are consistent with the standardX-ray data of the Fe3O4 magnetite phase (JCPDS no.19-0629). Thebroad peak near 20 with a relatively low intensity is attributedto amorphous carbon [14]. Fig. 1b shows the XPS pattern ofFe3O4/carbon nanocomposite. The appearance of the characteristicpeaks of Fe2p (711.1 eV) and O1s is typical for iron oxide, while thepeaks ascribe to C1s at expected positions further indicate the exis-tence of carbon. The peak at 148 eV is attributed to Si2s, comingfrom the substrate (silicon wafer). As known, XPS mainly revealsthe information of the surface with a depth of 0.110 nm [15]. Inour experiment, only a weak peak of corresponding Fe2p was de-tected by XPS characterization, which may be due to the embed-ding of Fe3O4 nanoparticles in FCNPs.Scheme 1. Fabrication of Fe3O4/carbon nanocomposite via two-step chemicalreaction process.Fe3O4/carbon nanocomposite is shown in Fig. S2, from which wecan see that all the particles present a spherical shape, and thediameter of the nanocomposite is about 300 nm (see EIS). The insetphotograph shows the TEM image of the as-prepared Fe3O4/carbonnanocomposite. Obviously, the spherical Fe3O4 nanoparticles withdiameter about 510 nm have been embedded in FCNPs, which isconsistent with the result of XPS.

The UVvis absorption and PL spectra of the as-prepared Fe3O4/carbon nanocomposite are shown in Fig. 2. The absorption spec-trum (1blue line) exhibits a full absorption band in the visible rangeof 400700 nm, which corresponds to the absorption of Fe3O4nanoparticles [16]. The absorption band ranging from 300 to400 nm is comparable to those previously reported for the carbondots [17]. The peak at 250300 nm represents the typical absorp-tion of an aromatic pi system, which is similar to that of polycyclicaromatic hydrocarbons [18]. The extended conjugation in thestructure of carbon leads to the red shift of the pp transition[19]. This result further indicates that the as-prepared nanocom-posite is a composite of carbon and Fe3O4. As shown in Fig. 2, thePL spectra of Fe3O4/carbon nanocomposite are broad and depen-dent on excitation wavelengths (the emission peak ranges from425 to 550 nm). Comparing the PL spectra of Fe3O4/carbon nano-composite with that of FCNPs (Fig. S1), the Fe3O4/carbon and FCNPshave similar PL properties. It should be noted that the PL of theFe3O4/carbon composite should come from the carbon nanoparti-cles or the interface between Fe3O4 nanoparticles and carbon, be-cause the Fe3O4 nanoparticles are not photoluminescent. Furthercontrol experiments show that the expected PL spectra (Fig. S3,see EIS) can still be observed after the Fe3O4/carbon nanocompos-ite samples were treated by the HCl solution (to remove the Fe3O4nanoparticles). Therefore, we can conclude that the PL propertiesof the as-prepared Fe3O4/carbon nanocomposite are attributed tothe presence of FCNPs. The structure of carbon nanoparticles wascharacterized by TEM and HRTEM (Fig. S5). As shown, there is nodiscernible lattice structures on the HRTEM image, indicating thatthe resultant carbon nanoparticles are amorphous. Thus, the ob-served luminescence emission may be due to the presence of sur-face functional groups and surface energy traps that becomeemissive upon stabilization as a result of the surface passivation,for which a widely accepted mechanism for luminescence emis-sion is the radiative recombination of excitations [9,17].

To study the magnetic properties, the magnetization curves ofthe as-prepared Fe3O4/carbon nanocomposite were measured atroom temperature by a vibrating-sample magnetometer. It canbe seen from Fig. 3 that the saturation magnetization of the as-pre-pared Fe3O4/carbon nanocomposite is 44.2 emu/g. The decrease ofthe saturation magnetization of the as-prepared nanocompositecompared to the bulk magnetite (84 emu/g) [20] would be attrib-uted to the existence of the carbon. The hysteresis loop at roomtemperature gives a negligible coercivity, indicating the superpara-magnetic behavior. With increasing the applied eld from 0 to8000 Oe, the magnetization increases sharply, and the magnetiza-tion is nearly saturated at about 2000 Oe. Further experimentsshow that the as-prepared Fe3O4/carbon nanocomposite is effec-tive in magnetic separation. As shown in the inset photographsin Fig. 3, a color change from black to transparent was observedwhen an external magnetic eld was applied for 510 min. Afterremoval of the magnet, the Fe3O4/carbon nanocomposite can beeasily redispersed in water with slight hand shaking.1 For interpretation of color in Fig. 2, the reader is referred to the web version ofthis article.

InteX. He et al. / Journal of Colloid andThe FTIR spectrum (Fig. S4, see EIS) was used to identify thefunctional groups of the Fe3O4/carbon nanocomposite. The broadcharacteristic band from 3600 to 3100 cm1 should be assignedto OH stretching vibration arising from hydroxyl groups on nano-particles [9]. The two peaks around 1700 and 1615 cm1 are attrib-uted to the stretching vibration mode of C@O, COOH group andaromatic ring structures, respectively [9]. The peaks in the rangeof 10001300 cm1 including the COH stretching and OH bend-ing vibrations [9], imply the existence of large numbers of hydroxyl

liquids) or more suitable reaction conditions (i.e. ultrasonic power,

Fig. 1. (a) XRD patterns of Fe3O4/carbon nanocomposite (red line) and Fe3O4 (black line);substrate). The inset image is the corresponding XPS pattern of Fe2p. (For interpretationversion of this article.)

Fig. 2. UVvis absorption and PL spectra (with different excitation: 300, 350, and400 nm) of the as-prepared Fe3O4/carbon nanocomposite.

Fig. 3. Magnetization curves of the Fe3O4/carbon nanocomposite. The insetphotograph: (a) the aqueous solution of the Fe3O4/carbon nanocomposite; (b) theseparation of the Fe3O4/carbon nanocomposite with external magnetic eld.reaction temperature, microwave reaction) may further optimizethe present reaction process and improve the photoluminescent/magnetic properties of the Fe3O4/carbon nanocomposite. Notably,this kind of Fe3O4/carbon nanocomposite will bring a new wayfor hosting many other applications including separating materials,drug delivery systems, bio-imaging and data storage etc. The exis-tence of carbon also make them suitable for further functionaliza-tion by the attachment of another species (metal, oxide, organic,polymeric, etc.) to construct multi-functional novel hybrids withexcellent catalytic, magnetic, conductive, optical and electronicalproperties [2225].

4. Conclusions

In summary, the Fe3O4/carbon nanocomposite (300 nm) hasbeen prepared by a two-step chemical route. The as-preparedFe3O4/carbon nanocomposite exhibits both magnetic (44.2 emu/gof saturation magnetization) and uorescent (emission peak rang-ing from 425 to 550 nm) properties, coming from the Fe3O4 nano-groups. The FeO vibration is detected at around 570 cm1, whichis consistent with the previously reported results [21]. Based onthe above results, it is can be concluded that the presence of carbonnot only provides PL active center but also enhances their dispersi-bility and prevents the nanocomposites from aggregating in water.

We can expect that a better carbon sources (i.e. fructose, su-crose or starch), other additives (i.e. acid, alkali or different ionic

(b) full XPS pattern of the as-prepared Fe3O4/carbon nanocomposite (silicon wafer asof the references to colour in this gure legend, the reader is referred to the web

rface Science 356 (2011) 107110 109particles and carbon materials, respectively. The Fe3O4/carbonnanocomposite combining both magnetic and uorescent proper-ties in one entity is expected to hold promise in potential biomed-ical uses, including biological imaging, cell tracking, magneticbioseparation, bio- and chemo-sensoring.

Acknowledgments

This work was supported by the National Basic ResearchProgram (973 Program) (No. 2010CB934500), the National NaturalScience Foundation of China(Nos. 20801010, 20803008, 21073127,21071104), A Foundation for the Author of National Excellent Doc-toral Dissertation of PR China (FANEDD) (No. 200929), andResearch Grants Council of Hong Kong SAR (Grant No. CityU5/CRF/08).

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jcis.2010.12.075.

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110 X. He et al. / Journal of Colloid and Interface Science 356 (2011) 107110

Photoluminescent Fe3O4/carbon nanocomposite with magnetic propertyIntroductionMaterials and methodsMaterialsMethods

Results and discussionConclusionsAcknowledgmentsSupplementary materialReferences