Research ArticleHydroxyapatite-Functionalized GrapheneA New Hybrid Nanomaterial
C Rodriacuteguez-Gonzaacutelez1 H E Cid-Luna1 P Salas1 and V M Castantildeo12
1 Centro de Fısica Aplicada y Tecnologıa Avanzada Universidad Nacional Autonoma de Mexico Boulevard Juriquilla 300176230 Santiago de Queretaro QRO Mexico
2 Centro de Tecnologıa Avanzada (CIATEQ) Avenida El Retablo 150 76150 Santiago de Queretaro QRO Mexico
Correspondence should be addressed to V M Castano menesesunammx
Received 26 March 2014 Accepted 16 June 2014 Published 20 July 2014
Academic Editor John Z Guo
Copyright copy 2014 C Rodrıguez-Gonzalez et alThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
Graphene oxide sheets (GO) were functionalized with hydroxyapatite nanoparticles (nHAp) through a simple and effectivehydrothermal treatment and a novel physicochemical process Microstructure and crystallinity were investigated by Fouriertransform infrared spectroscopy (FT-IR) Raman spectroscopy X-ray diffraction (XRD) ultraviolet-visible (UV-Vis) absorptionspectroscopy and thermogravimetric analysis (TGA) Transmission electronmicroscopy (TEM) and scanning electronmicroscopy(SEM) were performed to characterize the morphology of the functionalized material The resulting novel materials combine thebiocompatibility of the nHAp with the strength and physical properties of the graphene
1 Introduction
Graphene is a fascinating 2Dnanomaterial whose importancehas been recognized since it was isolated in 2004 [1] Thiscarbon allotrope which consists of a single layer of carbonatoms covalently bonded in a hexagonal network exhibitsexceptional properties such as high mechanical strengthoptimal thermal conductivity and excellent electrical con-ductivity [2ndash4] Since basically all atoms in its surfaceare exposed graphene presents an extremely large specificsurface area (theoretical value of 2600 gm2) making it anideal candidate for the addition for various molecules [56] Moreover graphene and graphene-related materials haveshown potential biocompatibility which is an essential issueif bioapplications ranging from biomaterials to drug deliverysystems are to be considered [7ndash9]
Graphene oxide (GO) is a heavily oxygenated graphenederivative [10] Structurally graphene oxide sheets consistof graphene sheets decorated with epoxy hydroxyl andketone functional groups above and below each plane aswell as carboxyl and carbonyl functionalities attached to theedges of the sheets The abundance of functional groups on
the surface of GO makes it highly hydrophilic [11] Thesefunctionalities can be used as chemical anchoring sites fordifferentmolecules thus generating new compositematerialswith enhanced properties as compared to their individualcomponents [12ndash19]
Hydroxyapatite (HAp) is a compound made of calciumphosphate the main crystalline component of the mineralphase of the bone [20] Given its chemical and structuralsimilarity with the biological apatite the synthetic hydrox-yapatite possesses exceptional biocompatibility and lack oftoxicity [21 22] In addition HAp is osteoconductive that isit promotes bone-cells growth when it is placed in the vicinityof viable bone [20] As a result HAp is being widely usedin coatings on metal implants as a filling for bone defectsin orthopedic and dental applications and also as reinforce-ment to polymer scaffold material for tissue regeneration[23]
Accordingly it seems very attractive to develop a newclass of hybrid material integrating mechanical propertiesand biological activity which is highly promising to beused as a scaffold to promote the growth and differen-tiation of several classes of cells It can also be used as
Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 940903 7 pageshttpdxdoiorg1011552014940903
2 Journal of Nanomaterials
a biocompatible phase reinforcement in biomedical compos-ites and a drug delivery carrier [8] by synergetically combin-ing GO and HAp However to date there are few reports onmethods for the fabrication of a GO-HAp nanocompositeNeelgund et al for instance reported the functionalizationof graphene sheets with hydroxyapatite through chemicalprecipitation [24] Liu et al showed the simultaneous surfacemodification and reduction of GO sheets by polymeriza-tion of dopamine and then deposited the hydroxyapatiteonto this surface by using a biomineralization method[25] Kim et al synthesized graphene oxide-CaCO
3vaterite
microspheres hybrid film which enhanced hydroxyapatiteformation when incubated in simulated body fluid solution[26] Liu et al reported the synthesis of reduced grapheneoxide and hydroxyapatite composite by chemical precip-itation followed by spark plasma sintering consolidation[27]
Hydrothermal processing offers an interesting and effec-tive route to synthesize nanocomposite materials usinggentle reaction conditions This approach produces highlycrystalline and chemically homogeneous hydroxyapatitenanoparticles Previous reports have also demonstrated itis convenient method for the reduction of graphene oxidesheets [28ndash30]
In this present study we report the surface functionaliza-tion of graphene oxide sheets with hydroxyapatite through alow temperature hydrothermal synthesis To the best of ourknowledge this synthesis method has not been reported yetIn our process the influence of hydrothermal reaction timeon the morphology of functionalized material was observedThe graphene-based hybrid material was morphological andmicrostructural characterized
2 Materials and Methods
21 Materials Pure crystalline graphite (300meshes) waspurchased from Electron Microscopy Science Ammoniumhydroxide (NH
4OH) and diammonium hydrogen phosphate
((NH4)2HPO4) were obtained from Baker All other reagents
and solvents were obtained from Aldrich All of the reagentswere of analytical grade and used without any furtherpurification
22 GO Functionalization with HAp Nanoparticles GO wassynthesized by the modified Hummers method [11] A typ-ical experiment for the functionalization of GO with HApnanoparticles is as follows 45mgGOwas dispersed in 15mLDI water by ultrasonic treatment for 3 h Then 4475mLof Ca(NO
3)2sdot4H2O (01M) and 2685mL of (NH
4)2HPO4
(01M) were added to the above system obtaining the molarCaP ratio of 16 which corresponds to pure hydroxyapatiteratio Furthermore NH
4OH was dropped in excess under
constant stirring adjusting the pH of the suspension toasymp10 The mixture was then transferred to a 70mL teflon-lined autoclave and heated at 90∘C under autogenous pres-sure for 6 and 24 hours The hydrothermal synthesis of
pure calcium hydroxyphosphate was based on the followingreaction10Ca(NO
3)
2+ 6(NH
4)
2HPO4+ 8NH
4OH
997888rarr Ca10(PO4)
6(OH)2+ 20NH
4NO3+ 6H2O
(1)
The resulting suspension was naturally cooled to roomtemperature and washed with deionized water several timesin order to remove the NH
4NO3 Finally the sample was
dried at room temperature for 24 h In order to compare theobtained functionalized materials pure HAp nanoparticleswere also prepared by the same method
23 Characterization The crystallinity and phase purity ofthe products were examined by powder X-ray diffraction(XDR) in a Rigaku Miniflex diffractometer with Cu Karadiation (120582 = 015418 nm) Fourier transform infrared(FTIR) spectra of KBr powder pressed pellets were recordedon a Bruker VECTOR 33 within the spectral region 400 to4000 cmminus1 Transmission electronmicroscopy (TEM) imageswere taken with a JEOL JEM1010 microscope The morphol-ogy and elemental analysis of nanomaterial were carried outusing a scanning electronmicroscopy (SEM) JEOL JSM-6060LV equipped with an energy dispersive X-ray spectroscopy(EDX) spectrometer Oxford Inca X-Sight Raman analysiswas performed at room temperature using a LabRAM Dilormicro-Raman system equipped with an Argon ion laser witha wavelength of 488 nm The absorption spectra of the sam-ples were obtained using an ultraviolet visible spectroscopy(UV-Vis) recorded on a Hach spectrophotometer DR 5000Thermal properties of GO and RGOHA were measuredby thermogravimetric analysis (TGA) on a SDT Q600 (TAInstruments) under a nitrogen atmosphere at a heating rateof 10∘Cmin
3 Results and Discussion
FTIR was performed to verify GO reduction and function-alization with HAp nanoparticles by the hydrothermal reac-tionThe characteristic absorption bands of GO (Figure 1(a))including alkoxy CndashO stretching (1030 cmminus1) epoxy CndashO stretching (1247 cmminus1) OndashH deformation vibrations oftertiary CndashOH (1400 cmminus1) and C=O stretching (1724 cmminus1)were identified Also a strong and broad absorption at3350 cmminus1 due to OndashH stretching vibrations and an intenseband at 1614 cmminus1 corresponding to the C=C benzene ringmode was observed [31] As to the spectrum of preparedHAp(Figure 1(b)) the bands at 1035 and 1093 cmminus1 correspondto the ]3 PO
4
3minus asymmetric stretching 603 and 567 cmminus1are ]4 PO
4
3minus antisymmetric deformation [32] The peaks at3570 and 631 cmminus1 derive from the stretching and librationalmodes of the OH-ions respectively [33] After hydrothermalreaction both spectra of RGOHAp 6 and 24 h (Figures 1(c)and 1(d)) showed that bands for oxygen functional groupsof GO were significantly reduced and some of them disap-peared entirely Moreover a new absorption band appearedat 1560 cmminus1 which may be attributed to the C=C stretchvibration of graphene sheets [34] The absence of the OndashH
Journal of Nanomaterials 3
(a)
(b)
(c)
(d)Tran
smitt
ance
(au
)
4000 3400 2800 2200 1600 1000 400
Wavenumber (cmminus1)
1192
1560
Figure 1 FT-IR spectra of GO (a) HAp (b) RGOHAp 6 h (c) andRGOHAp 24 h (d)
(a)
(b)
(c)
Inte
nsity
(au
)
Wavenumber shift (cmminus1)
960
600500400
554447
400 800 1200 1600 2000
Figure 2 Raman spectra of pristine GO sheets (a) RGOHAp 6 (b)and 24 h (c) Inset shows an amplification of RGOHAp 6 and 24 h
band at 631 cmminus1 compared toHap and the appearance of theCndashO stretch band at 1192 cmminus1 provided a solid indication ofgraphene oxide reduction and formation of the RGOHApcomposite The spectrum of RGOHAp at 24 h shows anincrease in the width of the band at 1035 (PO
4
3minus) and adecrease in the band at 3570 cmminus1 (OndashH) which could beattributed to an enhancement of the HAp particles on the GOsurface
Figure 2 shows the Raman spectra of GO (a) and HAp-graphene after 6 (b) and 24 (c) hours of hydrothermalreaction For GO there are two characteristic peaks in thespectra the119866 band at 1590 cmminus1 and the119863 band at 1353 cmminus1TheGband is associatedwith the119864
2119892modeof graphite which
(d)
(c)
(b)
(a)
10 20 30 40 50 60 70
2120579 (deg)
Inte
nsity
(au
)
001
002
111
002
110 210
211
300
202
301 310
311
113
222
213321
004
322 304
Figure 3 XRD patterns of pristine graphite (a) GO (b) RGOHAp6 (c) and 24 h (d)
is usually related to the in-phase vibrations of the graphitelattice whereas the 119863 band is ascribed to the presence ofdisorder vacancies and edges in the 1199041199012 network [35 36]In the Raman spectra of HAp-graphene 6 h and 24 h the 119866band was shifted towards 1601 cmminus1 while the intensity ofthe 119863 band decreased substantially The shifting of the 119866band may be due to the fact that the chemical interactionsbetween carbon atoms of GO and reactive sites of HApallow the formation of isolated double bonds which resonateat higher frequencies [37] The disorder and graphitizationdegree of carbon materials may be quantified by analyzingthe 119868119863119868119866 intensity ratio between 119863 and 119866 band [36] The119868119863119868119866 ratios of GOHAp-graphene 6 and 24 hwere 103 053and 032 respectively indicating that the functionalizationof graphene with HAp greatly enhances the size of the in-plane 1199041199012 domains of GO [38] In both HAp-graphene 6 and24 h spectra the characteristic peaks for HAp at 447 cmminus1 (]2(PO4
3minus)) 554 cmminus1 (]4 (PO4
3minus)) and 960 cmminus1 (]1 (PO4
3minus))[34 39] were shown
Figure 3 shows the XRD patterns of graphite (a) GO(b) and RGOHAp 6 h (c) and 24 h (d) Graphite showedthe characteristic (002) peak at around 2120579 = 264∘ corre-sponding to an average interlayer spacing of sim33 A Thepattern of GO displayed the most intense peak at 2120579 =119∘ which corresponds to the (001) reflection Due to thepresence of oxygen-containing functional groups attachedon both sides of the graphene sheet GO has an aver-age interlayer spacing of sim79 A indicating that individualgraphene oxide sheets are thicker than pristine graphenesheets [40] The diffraction patterns of both RGOHAp 6and 24 h show characteristic peaks of the HAp hexagonalphase (JCPDS card number 9-432) Well-defined peaksappeared at 2120579 around 259∘ 319∘ 329∘ 341∘ 398∘ 467∘and 505∘ which are attributed respectively to the (002)
4 Journal of Nanomaterials
CO
P
Ca
Ca
0 1 2 3 4 5 6 7 8 9
(keV)
Full scale 527 cts Cursor 0021 keV (801 cts)
Figure 4 EDX spectrum of RGOHAp after 24 hours of hydrother-mal treatment
(211) (300) (202) (310) (222) and (321) reflections of HA[41 42] The average particle size of HAp nanoparticles wascalculated to be ca 83 and 95 nm for RGOHap 6 and24 h respectively based on Scherrerrsquos equation No signalfor any other phases about GO (001) can be detected inthe RGOHAp composite (Figure 3(c)) This may be due tothe fact that GO can be reduced to graphene during thehydrothermal reaction producing a restacking of the sheetsforming poorly ordered graphitic structures consequentlytheir diffraction peaks might also turn weak until disap-pearing [43] Moreover because of functionalization HApnanoparticles act as spacers between graphene layers whichcannot be stacked to formdetectable graphite structures con-sequently this weakens the diffraction of single carbon sheets[44]
RGOHAp EDX spectrum (Figure 4) showed defined CaP C and O peaks that can be attributed to the presenceof GO and HAp Furthermore the CaP atomic ratio ofthe composite was 166 which is lower than the stoichio-metric composition of pure hydroxyapatite but close tothe calcium-deficient HAp present in natural bone tissue[45]
The UV-Vis spectra for GO and graphene-based hybridsdispersions are shown in Figure 5 The spectrum obtainedfor GO dispersion displays a maximum absorption peak at230 nm which is characteristic of 120587-120587lowast of aromatic C=Cbonds and a shoulder at about 300 nm attributed to 119899-120587lowasttransitions of CndashO bonds [46] When the GO is functional-izedwithHApnanoparticles the peak at 230 nm is red shiftedto 252 nm while the shoulder at 300 nm disappeared Thisresult suggests a strong interaction between graphene sheetsand HAp nanoparticles and also the reduction of grapheneoxide sheets [46 47]
According to Figure 6(a) large and transparent grapheneoxide sheets can be clearly observed in the TEMmicrographsTheGO sheets exhibit wrinkled and crumplingmorphologiesillustrating a flake-like shapeThe TEM images of RGOHAp6 h andRGOHAp 24 h hybridmaterials are shown in Figures6(b) and 6(c) respectively It is clearly seen in Figure 6(b)
12
10
08
06
04
02
00
200 300 400 500 600
Wavelength (nm)
GO
RGOHAp 24h
RGOHAp 6h
Abso
rban
ce (a
u)
Figure 5 UV-Vis spectra of GO RGOHAp 6 h and RGOHAp24 h
that rod-like HAp nanoparticles are well separated anddistributed randomly onto the transparent graphene oxidesheets indicating a strong interaction between grapheneand nanoparticles [48 49] Figure 6(c) reveals graphenesheets uniformly decorated by the nanosized HAp particlesAlso the nanocomposite displays a high density of HApnanoparticles It is interesting to note that HAp nanoparticlesare successfully dispersed onto graphene sheets in bothhydrothermal reaction conditions However the density ofHAp nanoparticles is higher in RGOHAp 24 h nanocom-posite because this hybrid material is subjected to a higherreaction time
The SEM micrograph of Figure 7(a) displays layers ofGO exhibiting a homogeneous surface with the characteristicwrinkles and ripples of graphene 2D structure SEM imagesof RGOHAp 6 h yRGOHAp 24 h Figures 7(b) and 7(c)respectively show a completely different morphology ascompared with the GO sheets In both hybrid materials itcan be observed that HAp nanoparticles are homogeneouslydeposited onto the graphene sheets The surface of thesenanocomposites shows a rough structure with many gran-ules indicating that GO sheets are covered by nHAp Theseresults are consistentwith the results obtained byTEMwhichshowed a homogeneous distribution of HAp nanoparticlesonto graphene oxide surface indicating that hydrothermalapproach is an effective method to form graphene-basedhybrid materials
The TGA curve of GO (Figure 8(c)) showed an initialweight loss (12 wt) before 100∘C attributed to evapora-tion of water molecules contained in the material Thesuccessive mass losses occurred below 250∘C and above550∘C which are attributed to the decomposition of labileoxygen-containing functional groups and the pyrolysis of thecarbon skeleton respectively [50] Compared with the GOweight loss at 250∘C (40wt) the weight loss of RGOHAp(Figure 8(b)) at 250∘C is much lower (9wt) indicatinga decreased amount of oxygenated functional groups afterhydrothermal reduction As for the TGA curve of HAp
Journal of Nanomaterials 5
(a)
(b)
(c)
Figure 6 TEM images of graphene oxide (a) RGOHAp 6 h (b)and RGOHAp 24 h (c) of hydrothermal treatment
(Figure 8(a)) there is no significant weight loss from roomtemperature up to 1000∘C which is consistent with thatreported in the literature [51] The curve of RGOHAp(Figure 8(b)) showed that the sample had lost a significant
(a)
(b)
(c)
Figure 7 SEM images of GO sheets (a) RGOHAp 6 h (b) andRGOHAp 24 h (c)
mass (42wt) from 550 to 880∘C possibly due to the decom-position of graphene sheets The residual weight measuredfor GO and RGOHAp at 1000∘C was found to be 4wtand 58wt respectively indicating the deposition of HApnanoparticles over GO Due to the thermal stability of HApand after subtracting thewater effect it is estimated that about61 wt of HA is contained in the RGOHAp composite
4 Conclusions
Graphene oxide sheets were functionalized with hydroxyap-atite nanoparticles through a hydrothermal reaction betweenCa(NO
3)2sdot4H2O and (NH
4)2HPO4in basic conditions at
a temperature of 90∘C Both conditions of hydrothermalreaction time (6 h and 24 h) produce the deposition of
6 Journal of Nanomaterials
(a)
(b)
(c)
Temperature (∘C)
Wei
ght (
)
100
80
60
40
20
0
0 200 400 600 800 1000
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
a biocompatible phase reinforcement in biomedical compos-ites and a drug delivery carrier [8] by synergetically combin-ing GO and HAp However to date there are few reports onmethods for the fabrication of a GO-HAp nanocompositeNeelgund et al for instance reported the functionalizationof graphene sheets with hydroxyapatite through chemicalprecipitation [24] Liu et al showed the simultaneous surfacemodification and reduction of GO sheets by polymeriza-tion of dopamine and then deposited the hydroxyapatiteonto this surface by using a biomineralization method[25] Kim et al synthesized graphene oxide-CaCO
3vaterite
microspheres hybrid film which enhanced hydroxyapatiteformation when incubated in simulated body fluid solution[26] Liu et al reported the synthesis of reduced grapheneoxide and hydroxyapatite composite by chemical precip-itation followed by spark plasma sintering consolidation[27]
Hydrothermal processing offers an interesting and effec-tive route to synthesize nanocomposite materials usinggentle reaction conditions This approach produces highlycrystalline and chemically homogeneous hydroxyapatitenanoparticles Previous reports have also demonstrated itis convenient method for the reduction of graphene oxidesheets [28ndash30]
In this present study we report the surface functionaliza-tion of graphene oxide sheets with hydroxyapatite through alow temperature hydrothermal synthesis To the best of ourknowledge this synthesis method has not been reported yetIn our process the influence of hydrothermal reaction timeon the morphology of functionalized material was observedThe graphene-based hybrid material was morphological andmicrostructural characterized
2 Materials and Methods
21 Materials Pure crystalline graphite (300meshes) waspurchased from Electron Microscopy Science Ammoniumhydroxide (NH
4OH) and diammonium hydrogen phosphate
((NH4)2HPO4) were obtained from Baker All other reagents
and solvents were obtained from Aldrich All of the reagentswere of analytical grade and used without any furtherpurification
22 GO Functionalization with HAp Nanoparticles GO wassynthesized by the modified Hummers method [11] A typ-ical experiment for the functionalization of GO with HApnanoparticles is as follows 45mgGOwas dispersed in 15mLDI water by ultrasonic treatment for 3 h Then 4475mLof Ca(NO
3)2sdot4H2O (01M) and 2685mL of (NH
4)2HPO4
(01M) were added to the above system obtaining the molarCaP ratio of 16 which corresponds to pure hydroxyapatiteratio Furthermore NH
4OH was dropped in excess under
constant stirring adjusting the pH of the suspension toasymp10 The mixture was then transferred to a 70mL teflon-lined autoclave and heated at 90∘C under autogenous pres-sure for 6 and 24 hours The hydrothermal synthesis of
pure calcium hydroxyphosphate was based on the followingreaction10Ca(NO
3)
2+ 6(NH
4)
2HPO4+ 8NH
4OH
997888rarr Ca10(PO4)
6(OH)2+ 20NH
4NO3+ 6H2O
(1)
The resulting suspension was naturally cooled to roomtemperature and washed with deionized water several timesin order to remove the NH
4NO3 Finally the sample was
dried at room temperature for 24 h In order to compare theobtained functionalized materials pure HAp nanoparticleswere also prepared by the same method
23 Characterization The crystallinity and phase purity ofthe products were examined by powder X-ray diffraction(XDR) in a Rigaku Miniflex diffractometer with Cu Karadiation (120582 = 015418 nm) Fourier transform infrared(FTIR) spectra of KBr powder pressed pellets were recordedon a Bruker VECTOR 33 within the spectral region 400 to4000 cmminus1 Transmission electronmicroscopy (TEM) imageswere taken with a JEOL JEM1010 microscope The morphol-ogy and elemental analysis of nanomaterial were carried outusing a scanning electronmicroscopy (SEM) JEOL JSM-6060LV equipped with an energy dispersive X-ray spectroscopy(EDX) spectrometer Oxford Inca X-Sight Raman analysiswas performed at room temperature using a LabRAM Dilormicro-Raman system equipped with an Argon ion laser witha wavelength of 488 nm The absorption spectra of the sam-ples were obtained using an ultraviolet visible spectroscopy(UV-Vis) recorded on a Hach spectrophotometer DR 5000Thermal properties of GO and RGOHA were measuredby thermogravimetric analysis (TGA) on a SDT Q600 (TAInstruments) under a nitrogen atmosphere at a heating rateof 10∘Cmin
3 Results and Discussion
FTIR was performed to verify GO reduction and function-alization with HAp nanoparticles by the hydrothermal reac-tionThe characteristic absorption bands of GO (Figure 1(a))including alkoxy CndashO stretching (1030 cmminus1) epoxy CndashO stretching (1247 cmminus1) OndashH deformation vibrations oftertiary CndashOH (1400 cmminus1) and C=O stretching (1724 cmminus1)were identified Also a strong and broad absorption at3350 cmminus1 due to OndashH stretching vibrations and an intenseband at 1614 cmminus1 corresponding to the C=C benzene ringmode was observed [31] As to the spectrum of preparedHAp(Figure 1(b)) the bands at 1035 and 1093 cmminus1 correspondto the ]3 PO
4
3minus asymmetric stretching 603 and 567 cmminus1are ]4 PO
4
3minus antisymmetric deformation [32] The peaks at3570 and 631 cmminus1 derive from the stretching and librationalmodes of the OH-ions respectively [33] After hydrothermalreaction both spectra of RGOHAp 6 and 24 h (Figures 1(c)and 1(d)) showed that bands for oxygen functional groupsof GO were significantly reduced and some of them disap-peared entirely Moreover a new absorption band appearedat 1560 cmminus1 which may be attributed to the C=C stretchvibration of graphene sheets [34] The absence of the OndashH
Journal of Nanomaterials 3
(a)
(b)
(c)
(d)Tran
smitt
ance
(au
)
4000 3400 2800 2200 1600 1000 400
Wavenumber (cmminus1)
1192
1560
Figure 1 FT-IR spectra of GO (a) HAp (b) RGOHAp 6 h (c) andRGOHAp 24 h (d)
(a)
(b)
(c)
Inte
nsity
(au
)
Wavenumber shift (cmminus1)
960
600500400
554447
400 800 1200 1600 2000
Figure 2 Raman spectra of pristine GO sheets (a) RGOHAp 6 (b)and 24 h (c) Inset shows an amplification of RGOHAp 6 and 24 h
band at 631 cmminus1 compared toHap and the appearance of theCndashO stretch band at 1192 cmminus1 provided a solid indication ofgraphene oxide reduction and formation of the RGOHApcomposite The spectrum of RGOHAp at 24 h shows anincrease in the width of the band at 1035 (PO
4
3minus) and adecrease in the band at 3570 cmminus1 (OndashH) which could beattributed to an enhancement of the HAp particles on the GOsurface
Figure 2 shows the Raman spectra of GO (a) and HAp-graphene after 6 (b) and 24 (c) hours of hydrothermalreaction For GO there are two characteristic peaks in thespectra the119866 band at 1590 cmminus1 and the119863 band at 1353 cmminus1TheGband is associatedwith the119864
2119892modeof graphite which
(d)
(c)
(b)
(a)
10 20 30 40 50 60 70
2120579 (deg)
Inte
nsity
(au
)
001
002
111
002
110 210
211
300
202
301 310
311
113
222
213321
004
322 304
Figure 3 XRD patterns of pristine graphite (a) GO (b) RGOHAp6 (c) and 24 h (d)
is usually related to the in-phase vibrations of the graphitelattice whereas the 119863 band is ascribed to the presence ofdisorder vacancies and edges in the 1199041199012 network [35 36]In the Raman spectra of HAp-graphene 6 h and 24 h the 119866band was shifted towards 1601 cmminus1 while the intensity ofthe 119863 band decreased substantially The shifting of the 119866band may be due to the fact that the chemical interactionsbetween carbon atoms of GO and reactive sites of HApallow the formation of isolated double bonds which resonateat higher frequencies [37] The disorder and graphitizationdegree of carbon materials may be quantified by analyzingthe 119868119863119868119866 intensity ratio between 119863 and 119866 band [36] The119868119863119868119866 ratios of GOHAp-graphene 6 and 24 hwere 103 053and 032 respectively indicating that the functionalizationof graphene with HAp greatly enhances the size of the in-plane 1199041199012 domains of GO [38] In both HAp-graphene 6 and24 h spectra the characteristic peaks for HAp at 447 cmminus1 (]2(PO4
3minus)) 554 cmminus1 (]4 (PO4
3minus)) and 960 cmminus1 (]1 (PO4
3minus))[34 39] were shown
Figure 3 shows the XRD patterns of graphite (a) GO(b) and RGOHAp 6 h (c) and 24 h (d) Graphite showedthe characteristic (002) peak at around 2120579 = 264∘ corre-sponding to an average interlayer spacing of sim33 A Thepattern of GO displayed the most intense peak at 2120579 =119∘ which corresponds to the (001) reflection Due to thepresence of oxygen-containing functional groups attachedon both sides of the graphene sheet GO has an aver-age interlayer spacing of sim79 A indicating that individualgraphene oxide sheets are thicker than pristine graphenesheets [40] The diffraction patterns of both RGOHAp 6and 24 h show characteristic peaks of the HAp hexagonalphase (JCPDS card number 9-432) Well-defined peaksappeared at 2120579 around 259∘ 319∘ 329∘ 341∘ 398∘ 467∘and 505∘ which are attributed respectively to the (002)
4 Journal of Nanomaterials
CO
P
Ca
Ca
0 1 2 3 4 5 6 7 8 9
(keV)
Full scale 527 cts Cursor 0021 keV (801 cts)
Figure 4 EDX spectrum of RGOHAp after 24 hours of hydrother-mal treatment
(211) (300) (202) (310) (222) and (321) reflections of HA[41 42] The average particle size of HAp nanoparticles wascalculated to be ca 83 and 95 nm for RGOHap 6 and24 h respectively based on Scherrerrsquos equation No signalfor any other phases about GO (001) can be detected inthe RGOHAp composite (Figure 3(c)) This may be due tothe fact that GO can be reduced to graphene during thehydrothermal reaction producing a restacking of the sheetsforming poorly ordered graphitic structures consequentlytheir diffraction peaks might also turn weak until disap-pearing [43] Moreover because of functionalization HApnanoparticles act as spacers between graphene layers whichcannot be stacked to formdetectable graphite structures con-sequently this weakens the diffraction of single carbon sheets[44]
RGOHAp EDX spectrum (Figure 4) showed defined CaP C and O peaks that can be attributed to the presenceof GO and HAp Furthermore the CaP atomic ratio ofthe composite was 166 which is lower than the stoichio-metric composition of pure hydroxyapatite but close tothe calcium-deficient HAp present in natural bone tissue[45]
The UV-Vis spectra for GO and graphene-based hybridsdispersions are shown in Figure 5 The spectrum obtainedfor GO dispersion displays a maximum absorption peak at230 nm which is characteristic of 120587-120587lowast of aromatic C=Cbonds and a shoulder at about 300 nm attributed to 119899-120587lowasttransitions of CndashO bonds [46] When the GO is functional-izedwithHApnanoparticles the peak at 230 nm is red shiftedto 252 nm while the shoulder at 300 nm disappeared Thisresult suggests a strong interaction between graphene sheetsand HAp nanoparticles and also the reduction of grapheneoxide sheets [46 47]
According to Figure 6(a) large and transparent grapheneoxide sheets can be clearly observed in the TEMmicrographsTheGO sheets exhibit wrinkled and crumplingmorphologiesillustrating a flake-like shapeThe TEM images of RGOHAp6 h andRGOHAp 24 h hybridmaterials are shown in Figures6(b) and 6(c) respectively It is clearly seen in Figure 6(b)
12
10
08
06
04
02
00
200 300 400 500 600
Wavelength (nm)
GO
RGOHAp 24h
RGOHAp 6h
Abso
rban
ce (a
u)
Figure 5 UV-Vis spectra of GO RGOHAp 6 h and RGOHAp24 h
that rod-like HAp nanoparticles are well separated anddistributed randomly onto the transparent graphene oxidesheets indicating a strong interaction between grapheneand nanoparticles [48 49] Figure 6(c) reveals graphenesheets uniformly decorated by the nanosized HAp particlesAlso the nanocomposite displays a high density of HApnanoparticles It is interesting to note that HAp nanoparticlesare successfully dispersed onto graphene sheets in bothhydrothermal reaction conditions However the density ofHAp nanoparticles is higher in RGOHAp 24 h nanocom-posite because this hybrid material is subjected to a higherreaction time
The SEM micrograph of Figure 7(a) displays layers ofGO exhibiting a homogeneous surface with the characteristicwrinkles and ripples of graphene 2D structure SEM imagesof RGOHAp 6 h yRGOHAp 24 h Figures 7(b) and 7(c)respectively show a completely different morphology ascompared with the GO sheets In both hybrid materials itcan be observed that HAp nanoparticles are homogeneouslydeposited onto the graphene sheets The surface of thesenanocomposites shows a rough structure with many gran-ules indicating that GO sheets are covered by nHAp Theseresults are consistentwith the results obtained byTEMwhichshowed a homogeneous distribution of HAp nanoparticlesonto graphene oxide surface indicating that hydrothermalapproach is an effective method to form graphene-basedhybrid materials
The TGA curve of GO (Figure 8(c)) showed an initialweight loss (12 wt) before 100∘C attributed to evapora-tion of water molecules contained in the material Thesuccessive mass losses occurred below 250∘C and above550∘C which are attributed to the decomposition of labileoxygen-containing functional groups and the pyrolysis of thecarbon skeleton respectively [50] Compared with the GOweight loss at 250∘C (40wt) the weight loss of RGOHAp(Figure 8(b)) at 250∘C is much lower (9wt) indicatinga decreased amount of oxygenated functional groups afterhydrothermal reduction As for the TGA curve of HAp
Journal of Nanomaterials 5
(a)
(b)
(c)
Figure 6 TEM images of graphene oxide (a) RGOHAp 6 h (b)and RGOHAp 24 h (c) of hydrothermal treatment
(Figure 8(a)) there is no significant weight loss from roomtemperature up to 1000∘C which is consistent with thatreported in the literature [51] The curve of RGOHAp(Figure 8(b)) showed that the sample had lost a significant
(a)
(b)
(c)
Figure 7 SEM images of GO sheets (a) RGOHAp 6 h (b) andRGOHAp 24 h (c)
mass (42wt) from 550 to 880∘C possibly due to the decom-position of graphene sheets The residual weight measuredfor GO and RGOHAp at 1000∘C was found to be 4wtand 58wt respectively indicating the deposition of HApnanoparticles over GO Due to the thermal stability of HApand after subtracting thewater effect it is estimated that about61 wt of HA is contained in the RGOHAp composite
4 Conclusions
Graphene oxide sheets were functionalized with hydroxyap-atite nanoparticles through a hydrothermal reaction betweenCa(NO
3)2sdot4H2O and (NH
4)2HPO4in basic conditions at
a temperature of 90∘C Both conditions of hydrothermalreaction time (6 h and 24 h) produce the deposition of
6 Journal of Nanomaterials
(a)
(b)
(c)
Temperature (∘C)
Wei
ght (
)
100
80
60
40
20
0
0 200 400 600 800 1000
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
Figure 1 FT-IR spectra of GO (a) HAp (b) RGOHAp 6 h (c) andRGOHAp 24 h (d)
(a)
(b)
(c)
Inte
nsity
(au
)
Wavenumber shift (cmminus1)
960
600500400
554447
400 800 1200 1600 2000
Figure 2 Raman spectra of pristine GO sheets (a) RGOHAp 6 (b)and 24 h (c) Inset shows an amplification of RGOHAp 6 and 24 h
band at 631 cmminus1 compared toHap and the appearance of theCndashO stretch band at 1192 cmminus1 provided a solid indication ofgraphene oxide reduction and formation of the RGOHApcomposite The spectrum of RGOHAp at 24 h shows anincrease in the width of the band at 1035 (PO
4
3minus) and adecrease in the band at 3570 cmminus1 (OndashH) which could beattributed to an enhancement of the HAp particles on the GOsurface
Figure 2 shows the Raman spectra of GO (a) and HAp-graphene after 6 (b) and 24 (c) hours of hydrothermalreaction For GO there are two characteristic peaks in thespectra the119866 band at 1590 cmminus1 and the119863 band at 1353 cmminus1TheGband is associatedwith the119864
2119892modeof graphite which
(d)
(c)
(b)
(a)
10 20 30 40 50 60 70
2120579 (deg)
Inte
nsity
(au
)
001
002
111
002
110 210
211
300
202
301 310
311
113
222
213321
004
322 304
Figure 3 XRD patterns of pristine graphite (a) GO (b) RGOHAp6 (c) and 24 h (d)
is usually related to the in-phase vibrations of the graphitelattice whereas the 119863 band is ascribed to the presence ofdisorder vacancies and edges in the 1199041199012 network [35 36]In the Raman spectra of HAp-graphene 6 h and 24 h the 119866band was shifted towards 1601 cmminus1 while the intensity ofthe 119863 band decreased substantially The shifting of the 119866band may be due to the fact that the chemical interactionsbetween carbon atoms of GO and reactive sites of HApallow the formation of isolated double bonds which resonateat higher frequencies [37] The disorder and graphitizationdegree of carbon materials may be quantified by analyzingthe 119868119863119868119866 intensity ratio between 119863 and 119866 band [36] The119868119863119868119866 ratios of GOHAp-graphene 6 and 24 hwere 103 053and 032 respectively indicating that the functionalizationof graphene with HAp greatly enhances the size of the in-plane 1199041199012 domains of GO [38] In both HAp-graphene 6 and24 h spectra the characteristic peaks for HAp at 447 cmminus1 (]2(PO4
3minus)) 554 cmminus1 (]4 (PO4
3minus)) and 960 cmminus1 (]1 (PO4
3minus))[34 39] were shown
Figure 3 shows the XRD patterns of graphite (a) GO(b) and RGOHAp 6 h (c) and 24 h (d) Graphite showedthe characteristic (002) peak at around 2120579 = 264∘ corre-sponding to an average interlayer spacing of sim33 A Thepattern of GO displayed the most intense peak at 2120579 =119∘ which corresponds to the (001) reflection Due to thepresence of oxygen-containing functional groups attachedon both sides of the graphene sheet GO has an aver-age interlayer spacing of sim79 A indicating that individualgraphene oxide sheets are thicker than pristine graphenesheets [40] The diffraction patterns of both RGOHAp 6and 24 h show characteristic peaks of the HAp hexagonalphase (JCPDS card number 9-432) Well-defined peaksappeared at 2120579 around 259∘ 319∘ 329∘ 341∘ 398∘ 467∘and 505∘ which are attributed respectively to the (002)
4 Journal of Nanomaterials
CO
P
Ca
Ca
0 1 2 3 4 5 6 7 8 9
(keV)
Full scale 527 cts Cursor 0021 keV (801 cts)
Figure 4 EDX spectrum of RGOHAp after 24 hours of hydrother-mal treatment
(211) (300) (202) (310) (222) and (321) reflections of HA[41 42] The average particle size of HAp nanoparticles wascalculated to be ca 83 and 95 nm for RGOHap 6 and24 h respectively based on Scherrerrsquos equation No signalfor any other phases about GO (001) can be detected inthe RGOHAp composite (Figure 3(c)) This may be due tothe fact that GO can be reduced to graphene during thehydrothermal reaction producing a restacking of the sheetsforming poorly ordered graphitic structures consequentlytheir diffraction peaks might also turn weak until disap-pearing [43] Moreover because of functionalization HApnanoparticles act as spacers between graphene layers whichcannot be stacked to formdetectable graphite structures con-sequently this weakens the diffraction of single carbon sheets[44]
RGOHAp EDX spectrum (Figure 4) showed defined CaP C and O peaks that can be attributed to the presenceof GO and HAp Furthermore the CaP atomic ratio ofthe composite was 166 which is lower than the stoichio-metric composition of pure hydroxyapatite but close tothe calcium-deficient HAp present in natural bone tissue[45]
The UV-Vis spectra for GO and graphene-based hybridsdispersions are shown in Figure 5 The spectrum obtainedfor GO dispersion displays a maximum absorption peak at230 nm which is characteristic of 120587-120587lowast of aromatic C=Cbonds and a shoulder at about 300 nm attributed to 119899-120587lowasttransitions of CndashO bonds [46] When the GO is functional-izedwithHApnanoparticles the peak at 230 nm is red shiftedto 252 nm while the shoulder at 300 nm disappeared Thisresult suggests a strong interaction between graphene sheetsand HAp nanoparticles and also the reduction of grapheneoxide sheets [46 47]
According to Figure 6(a) large and transparent grapheneoxide sheets can be clearly observed in the TEMmicrographsTheGO sheets exhibit wrinkled and crumplingmorphologiesillustrating a flake-like shapeThe TEM images of RGOHAp6 h andRGOHAp 24 h hybridmaterials are shown in Figures6(b) and 6(c) respectively It is clearly seen in Figure 6(b)
12
10
08
06
04
02
00
200 300 400 500 600
Wavelength (nm)
GO
RGOHAp 24h
RGOHAp 6h
Abso
rban
ce (a
u)
Figure 5 UV-Vis spectra of GO RGOHAp 6 h and RGOHAp24 h
that rod-like HAp nanoparticles are well separated anddistributed randomly onto the transparent graphene oxidesheets indicating a strong interaction between grapheneand nanoparticles [48 49] Figure 6(c) reveals graphenesheets uniformly decorated by the nanosized HAp particlesAlso the nanocomposite displays a high density of HApnanoparticles It is interesting to note that HAp nanoparticlesare successfully dispersed onto graphene sheets in bothhydrothermal reaction conditions However the density ofHAp nanoparticles is higher in RGOHAp 24 h nanocom-posite because this hybrid material is subjected to a higherreaction time
The SEM micrograph of Figure 7(a) displays layers ofGO exhibiting a homogeneous surface with the characteristicwrinkles and ripples of graphene 2D structure SEM imagesof RGOHAp 6 h yRGOHAp 24 h Figures 7(b) and 7(c)respectively show a completely different morphology ascompared with the GO sheets In both hybrid materials itcan be observed that HAp nanoparticles are homogeneouslydeposited onto the graphene sheets The surface of thesenanocomposites shows a rough structure with many gran-ules indicating that GO sheets are covered by nHAp Theseresults are consistentwith the results obtained byTEMwhichshowed a homogeneous distribution of HAp nanoparticlesonto graphene oxide surface indicating that hydrothermalapproach is an effective method to form graphene-basedhybrid materials
The TGA curve of GO (Figure 8(c)) showed an initialweight loss (12 wt) before 100∘C attributed to evapora-tion of water molecules contained in the material Thesuccessive mass losses occurred below 250∘C and above550∘C which are attributed to the decomposition of labileoxygen-containing functional groups and the pyrolysis of thecarbon skeleton respectively [50] Compared with the GOweight loss at 250∘C (40wt) the weight loss of RGOHAp(Figure 8(b)) at 250∘C is much lower (9wt) indicatinga decreased amount of oxygenated functional groups afterhydrothermal reduction As for the TGA curve of HAp
Journal of Nanomaterials 5
(a)
(b)
(c)
Figure 6 TEM images of graphene oxide (a) RGOHAp 6 h (b)and RGOHAp 24 h (c) of hydrothermal treatment
(Figure 8(a)) there is no significant weight loss from roomtemperature up to 1000∘C which is consistent with thatreported in the literature [51] The curve of RGOHAp(Figure 8(b)) showed that the sample had lost a significant
(a)
(b)
(c)
Figure 7 SEM images of GO sheets (a) RGOHAp 6 h (b) andRGOHAp 24 h (c)
mass (42wt) from 550 to 880∘C possibly due to the decom-position of graphene sheets The residual weight measuredfor GO and RGOHAp at 1000∘C was found to be 4wtand 58wt respectively indicating the deposition of HApnanoparticles over GO Due to the thermal stability of HApand after subtracting thewater effect it is estimated that about61 wt of HA is contained in the RGOHAp composite
4 Conclusions
Graphene oxide sheets were functionalized with hydroxyap-atite nanoparticles through a hydrothermal reaction betweenCa(NO
3)2sdot4H2O and (NH
4)2HPO4in basic conditions at
a temperature of 90∘C Both conditions of hydrothermalreaction time (6 h and 24 h) produce the deposition of
6 Journal of Nanomaterials
(a)
(b)
(c)
Temperature (∘C)
Wei
ght (
)
100
80
60
40
20
0
0 200 400 600 800 1000
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
Figure 4 EDX spectrum of RGOHAp after 24 hours of hydrother-mal treatment
(211) (300) (202) (310) (222) and (321) reflections of HA[41 42] The average particle size of HAp nanoparticles wascalculated to be ca 83 and 95 nm for RGOHap 6 and24 h respectively based on Scherrerrsquos equation No signalfor any other phases about GO (001) can be detected inthe RGOHAp composite (Figure 3(c)) This may be due tothe fact that GO can be reduced to graphene during thehydrothermal reaction producing a restacking of the sheetsforming poorly ordered graphitic structures consequentlytheir diffraction peaks might also turn weak until disap-pearing [43] Moreover because of functionalization HApnanoparticles act as spacers between graphene layers whichcannot be stacked to formdetectable graphite structures con-sequently this weakens the diffraction of single carbon sheets[44]
RGOHAp EDX spectrum (Figure 4) showed defined CaP C and O peaks that can be attributed to the presenceof GO and HAp Furthermore the CaP atomic ratio ofthe composite was 166 which is lower than the stoichio-metric composition of pure hydroxyapatite but close tothe calcium-deficient HAp present in natural bone tissue[45]
The UV-Vis spectra for GO and graphene-based hybridsdispersions are shown in Figure 5 The spectrum obtainedfor GO dispersion displays a maximum absorption peak at230 nm which is characteristic of 120587-120587lowast of aromatic C=Cbonds and a shoulder at about 300 nm attributed to 119899-120587lowasttransitions of CndashO bonds [46] When the GO is functional-izedwithHApnanoparticles the peak at 230 nm is red shiftedto 252 nm while the shoulder at 300 nm disappeared Thisresult suggests a strong interaction between graphene sheetsand HAp nanoparticles and also the reduction of grapheneoxide sheets [46 47]
According to Figure 6(a) large and transparent grapheneoxide sheets can be clearly observed in the TEMmicrographsTheGO sheets exhibit wrinkled and crumplingmorphologiesillustrating a flake-like shapeThe TEM images of RGOHAp6 h andRGOHAp 24 h hybridmaterials are shown in Figures6(b) and 6(c) respectively It is clearly seen in Figure 6(b)
12
10
08
06
04
02
00
200 300 400 500 600
Wavelength (nm)
GO
RGOHAp 24h
RGOHAp 6h
Abso
rban
ce (a
u)
Figure 5 UV-Vis spectra of GO RGOHAp 6 h and RGOHAp24 h
that rod-like HAp nanoparticles are well separated anddistributed randomly onto the transparent graphene oxidesheets indicating a strong interaction between grapheneand nanoparticles [48 49] Figure 6(c) reveals graphenesheets uniformly decorated by the nanosized HAp particlesAlso the nanocomposite displays a high density of HApnanoparticles It is interesting to note that HAp nanoparticlesare successfully dispersed onto graphene sheets in bothhydrothermal reaction conditions However the density ofHAp nanoparticles is higher in RGOHAp 24 h nanocom-posite because this hybrid material is subjected to a higherreaction time
The SEM micrograph of Figure 7(a) displays layers ofGO exhibiting a homogeneous surface with the characteristicwrinkles and ripples of graphene 2D structure SEM imagesof RGOHAp 6 h yRGOHAp 24 h Figures 7(b) and 7(c)respectively show a completely different morphology ascompared with the GO sheets In both hybrid materials itcan be observed that HAp nanoparticles are homogeneouslydeposited onto the graphene sheets The surface of thesenanocomposites shows a rough structure with many gran-ules indicating that GO sheets are covered by nHAp Theseresults are consistentwith the results obtained byTEMwhichshowed a homogeneous distribution of HAp nanoparticlesonto graphene oxide surface indicating that hydrothermalapproach is an effective method to form graphene-basedhybrid materials
The TGA curve of GO (Figure 8(c)) showed an initialweight loss (12 wt) before 100∘C attributed to evapora-tion of water molecules contained in the material Thesuccessive mass losses occurred below 250∘C and above550∘C which are attributed to the decomposition of labileoxygen-containing functional groups and the pyrolysis of thecarbon skeleton respectively [50] Compared with the GOweight loss at 250∘C (40wt) the weight loss of RGOHAp(Figure 8(b)) at 250∘C is much lower (9wt) indicatinga decreased amount of oxygenated functional groups afterhydrothermal reduction As for the TGA curve of HAp
Journal of Nanomaterials 5
(a)
(b)
(c)
Figure 6 TEM images of graphene oxide (a) RGOHAp 6 h (b)and RGOHAp 24 h (c) of hydrothermal treatment
(Figure 8(a)) there is no significant weight loss from roomtemperature up to 1000∘C which is consistent with thatreported in the literature [51] The curve of RGOHAp(Figure 8(b)) showed that the sample had lost a significant
(a)
(b)
(c)
Figure 7 SEM images of GO sheets (a) RGOHAp 6 h (b) andRGOHAp 24 h (c)
mass (42wt) from 550 to 880∘C possibly due to the decom-position of graphene sheets The residual weight measuredfor GO and RGOHAp at 1000∘C was found to be 4wtand 58wt respectively indicating the deposition of HApnanoparticles over GO Due to the thermal stability of HApand after subtracting thewater effect it is estimated that about61 wt of HA is contained in the RGOHAp composite
4 Conclusions
Graphene oxide sheets were functionalized with hydroxyap-atite nanoparticles through a hydrothermal reaction betweenCa(NO
3)2sdot4H2O and (NH
4)2HPO4in basic conditions at
a temperature of 90∘C Both conditions of hydrothermalreaction time (6 h and 24 h) produce the deposition of
6 Journal of Nanomaterials
(a)
(b)
(c)
Temperature (∘C)
Wei
ght (
)
100
80
60
40
20
0
0 200 400 600 800 1000
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
Figure 6 TEM images of graphene oxide (a) RGOHAp 6 h (b)and RGOHAp 24 h (c) of hydrothermal treatment
(Figure 8(a)) there is no significant weight loss from roomtemperature up to 1000∘C which is consistent with thatreported in the literature [51] The curve of RGOHAp(Figure 8(b)) showed that the sample had lost a significant
(a)
(b)
(c)
Figure 7 SEM images of GO sheets (a) RGOHAp 6 h (b) andRGOHAp 24 h (c)
mass (42wt) from 550 to 880∘C possibly due to the decom-position of graphene sheets The residual weight measuredfor GO and RGOHAp at 1000∘C was found to be 4wtand 58wt respectively indicating the deposition of HApnanoparticles over GO Due to the thermal stability of HApand after subtracting thewater effect it is estimated that about61 wt of HA is contained in the RGOHAp composite
4 Conclusions
Graphene oxide sheets were functionalized with hydroxyap-atite nanoparticles through a hydrothermal reaction betweenCa(NO
3)2sdot4H2O and (NH
4)2HPO4in basic conditions at
a temperature of 90∘C Both conditions of hydrothermalreaction time (6 h and 24 h) produce the deposition of
6 Journal of Nanomaterials
(a)
(b)
(c)
Temperature (∘C)
Wei
ght (
)
100
80
60
40
20
0
0 200 400 600 800 1000
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
Figure 8 TGA profiles of HAp nanoparticles (a) GO sheets (c) andRGOHAp (b) after 24 h of hydrothermal treatment
hydroxyapatite nanoparticles free of impurities and otherphases of calcium phosphates However a hydrothermaltreatment time of 24 h produces graphene sheets highlydecorated with nanohydroxyapatite with an average particlesize (95 nm) larger in size compared to the ones obtainedwith a reaction time of 6 h The results suggest that thehydrothermal process produced the functionalization andreduction of GO sheets to graphene simultaneously
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors are grateful to Beatriz M Millan-Malo forassistance with the XRD analysis Genoveva Hernandez-Padron for FTIR analysis Alicia del Real Lopez for assistancewith EDX and SEM Ma Lourdes Palma-Tirado for theTEM images Damaris Cabrero-Palomino for TGA analysisFrancisco Rodrıguez-Melgarejo for Raman analysis andMa Cristina Pina-Barba for technical support ClaramarıaRodrıguez-Gonzalez is recipient of a postdoctoral fellowshipfrom DGAPAUNAM
References
[1] K S Novoselov A K Geim S V Morozov et al ldquoElectric fieldin atomically thin carbon filmsrdquo Science vol 306 no 5696 pp666ndash669 2004
[2] C Lee X Wei J W Kysar and J Hone ldquoMeasurement ofthe elastic properties and intrinsic strength of monolayergraphenerdquo Science vol 321 no 5887 pp 385ndash388 2008
[3] A A Balandin S Ghosh W Bao et al ldquoSuperior thermalconductivity of single-layer graphenerdquo Nano Letters vol 8 pp902ndash907 2008
[4] R MWestervelt ldquoGraphene nanoelectronicsrdquo Science vol 320pp 324ndash325 2008
[5] S Zhang K Yang L Feng and Z Liu ldquoIn vitro and in vivobehaviors of dextran functionalized graphenerdquo Carbon vol 49pp 4040ndash4049 2011
[6] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[7] Y Chang S T Yang J H Liu et al ldquoIn vitro toxicity evaluationof graphene oxide on A549 cellsrdquo Toxicology Letters vol 200pp 201ndash210 2011
[8] K Yang H Gong X Shi J Wan Y Zhang and Z Liu ldquoInvivo biodistribution and toxicology of functionalized nano-graphene oxide in mice after oral and intraperitoneal admin-istrationrdquo Biomaterials vol 34 pp 2787ndash2795 2013
[9] K H Liao Y S Lin C W Macosko and C L Haynes ldquoCyto-toxicity of graphene oxide and graphene in human erythrocytesand skin fibroblastsrdquo ACS Applied Materials and Interfaces vol3 pp 2607ndash2615 2011
[10] S K Singh M K Singh P P Kulkarni V K Sonkar J J AGracio and D Dash ldquoAmine-modified graphene thrombo-protective safer alternative to graphene oxide for biomedicalapplicationsrdquo ACS Nano vol 6 pp 2731ndash2740 2012
[11] S Stankovich R D Piner S T Nguyen and R S RuoffldquoSynthesis and exfoliation of isocyanate-treated graphene oxidenanoplateletsrdquo Carbon vol 44 pp 3342ndash3347 2006
[12] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-l-lysinerdquo Langmuir vol 25 pp 12030ndash12033 2009
[13] S Park D A Dikin S T Nguyen and R S Ruoff ldquoGrapheneoxide sheets chemically cross-linked by polyallylaminerdquo TheJournal of Physical Chemistry C vol 113 no 36 pp 15801ndash158042009
[14] R Deepachitra M Chamundeeswari B Santhoshkumar etal ldquoOsteo mineralization of fibrin-decorated graphene oxiderdquoCarbon vol 56 pp 64ndash76 2013
[15] L Shao X Cheng Z Wang J Ma and Z Guo ldquoTuning theperformance of polypyrrole-based solvent-resistant compositenanofiltrationmembranes by optimizing polymerization condi-tions and incorporating graphene oxiderdquo Journal of MembraneScience vol 452 pp 82ndash89 2014
[16] J Zhu M Chen H Qu et al ldquoMagnetic field induced capaci-tance enhancement in graphene and magnetic graphene nano-compositesrdquo Energy and Environmental Science vol 6 pp 194ndash204 2013
[17] H Wei J Zhu S Wu S Wei and Z Guo ldquoElectrochromicpolyanilinegraphite oxide nanocomposites with endured elec-trochemical energy storagerdquo Polymer vol 54 pp 1820ndash18312013
[18] J Zhu M Chen H Qu et al ldquoInterfacial polymerized polyani-linegraphite oxide nanocomposites toward electrochemicalenergy storagerdquo Polymer vol 53 pp 5953ndash5964 2012
[19] L Shao X Chang Y Zhang Y Huang Y Yao and Z GuoldquoGraphene oxide cross-linked chitosan nanocomposite mem-branerdquo Applied Surface Science vol 280 pp 989ndash992 2013
[20] B D Ratner A S Hoffman F J Schoen and J E LemonsBiomaterials Science A Multidisciplinary Endeavor ElsevierAcademic Press New York NY USA 2nd edition 2004
[21] M P Ferraz F J Monteiro and C M Manuel ldquoHydroxyapatitenanoparticles a review of preparation methodologiesrdquo Journalof Applied Biomaterials and Biomechanics vol 2 pp 74ndash802004
Journal of Nanomaterials 7
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
[22] M Jevtic M Mitric S S Kapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitation CrystrdquoCrystal Growth amp Design vol 8 pp 2117ndash2222 2008
[23] D Lahiri S Ghosh and A Agarwal ldquoCarbon nanotube rein-forced hydroxyapatite composite for orthopedic application areviewrdquo Materials Science and Engineering C vol 32 no 7 pp1727ndash1758 2012
[24] G M Neelgund A Oki and Z Luo ldquoIn situ deposition ofhydroxyapatite on graphene nanosheetsrdquo Materials ResearchBulletin vol 48 pp 175ndash179 2013
[25] H Liu P Xi G Xie et al ldquoSimultaneous reduction and surfacefunctionalization of graphene oxide for hydroxyapatite miner-alizationrdquoTheJournal of Physical ChemistryC vol 116 pp 3334ndash3341 2012
[26] S Kim S H Ku S Y Lim J H Kim and C B ParkldquoGraphenemdashbiomineral hybrid materialsrdquoAdvancedMaterialsvol 23 no 17 pp 2009ndash2014 2011
[27] Y Liu J Huang and H Li ldquoSynthesis of hydroxyapatitendashreduced graphite oxide nanocomposites for biomedical appli-cations oriented nucleation and epitaxial growth of hydroxya-patiterdquo Journal of Materials Chemistry B vol 1 no 13 pp 1826ndash1834 2013
[28] I S Neira Y V Kolenrsquoko O I Lebedev et al ldquoAn effectivemorphology control of hydroxyapatite crystals via hydrother-mal synthesisrdquo Crystal Growth amp Design vol 9 no 1 pp 466ndash474 2009
[29] J Shen B Yan M Shi H Ma N Li and M Ye ldquoOnestep hydrothermal synthesis of TiO
2-reduced graphene oxide
sheetsrdquo Journal of Materials Chemistry vol 21 pp 3415ndash34212011
[30] C Nethravathi andM Rajamathi ldquoChemicallymodified graph-ene sheets produced by the solvothermal reduction of colloidaldispersions of graphite oxiderdquo Carbon vol 46 pp 1994ndash19982008
[31] M Jevtic M Mitric S Skapin B Jancar N Ignjatovic and DUskokovic ldquoCrystal structure of hydroxyapatite nanorods syn-thesized by sonochemical homogeneous precipitationrdquo CrystalGrowth amp Design vol 8 pp 2217ndash2222 2008
[32] P Lian X Zhu S Liang Z Li W Yang and H Wang ldquoLargereversible capacity of high quality graphene sheets as an anodematerial for lithium-ion batteriesrdquo Electrochimica Acta vol 55no 12 pp 3909ndash3914 2010
[33] S Park J An I Jung et al ldquoColloidal suspensions of highlyreduced graphene oxide in a wide variety of organic solventsrdquoNano Letters vol 9 pp 1593ndash1597 2009
[34] S Koutsopoulos ldquoSynthesis and characterization of hydroxyap-atite crystals a review study on the analytical methodsrdquo Journalof Biomedical Materials Research vol 62 pp 600ndash612 2002
[35] LMMalardM A Pimenta G Dresselhaus andM S Dressel-haus ldquoRaman spectroscopy in graphenerdquo Physics Reports vol473 pp 51ndash87 2009
[36] M SDresselhaus A JorioMHofmannGDresselhaus andRSaito ldquoPerspectives on carbon nanotubes and graphene Ramanspectroscopyrdquo Nano Letters vol 10 pp 751ndash758 2010
[37] K N Kudin B Ozbas H C Schniepp R K Prudrsquohomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 pp 36ndash412008
[38] A C Ferrari ldquoRaman spectroscopy of graphene and graphitedisorder electron-phonon coupling doping and nonadiabatic
effectsrdquo Solid State Communications vol 143 no 1-2 pp 47ndash572007
[39] M Markovic B O Fowler and M S Tung ldquoPreparation andcomprehensive characterization of a calcium hydroxyapatitereference materialrdquo Journal of Research of the National Instituteof Standards and Technology vol 109 pp 553ndash568 2004
[40] G Wang J Yang J Park et al ldquoFacile synthesis and char-acterization of graphene nanosheetsrdquo The Journal of PhysicalChemistry C vol 112 pp 8192ndash8195 2008
[41] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 pp 330ndash333 2007
[42] M Jevtic M Mitric S Skapin et al ldquoCrystal structure ofhydroxyapatite nanorods synthesized by sonochemical homo-geneous precipitationrdquo Crystal Growth amp Design vol 8 pp2217ndash2222 2008
[43] C Nethravathi and M Rajamathi ldquoChemically modifiedgraphene sheets produced by the solvothermal reduction ofcolloidal dispersions of graphite oxiderdquo Carbon vol 46 no 14pp 1994ndash1998 2008
[44] S Pan X Liu and X Wang ldquoPreparation of Ag2S-Graphene
nanocomposite from a single source precursor and its surface-enhanced Raman scattering and photoluminescent activityrdquoMaterials Characterization vol 62 no 11 pp 1094ndash1101 2011
[45] B Bourgeois O Laboux L Obadia et al ldquoCalcium-deficientapatite a first in vivo study concerning bone in growthrdquo Journalof Biomedical Materials Research vol 65 pp 402ndash408 2003
[46] Z Zhang H Chen C Xing et al ldquoSodium citrate a universalreducing agent for reductiondecoration of graphene oxide withau nanoparticlesrdquo Nano Research vol 4 pp 599ndash611 2011
[47] J Shen M Shi B Yan et al ldquoCovalent attaching protein tographene oxide via diimide-activated amidationrdquo Colloids andSurfaces B Biointerfaces vol 81 no 2 pp 434ndash438 2010
[48] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxidefor methanol electro-oxidationrdquo Carbon vol 48 pp 1124ndash11302010
[49] L Shao S Quan Y Liu Z Guo and Z Wang ldquoA novel ldquogel-solrdquo strategy to synthesize TiO
[50] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007
[51] I Mobasherpour M S Heshajin A Kazemzadeh and MZakeri ldquoSynthesis of nanocrystalline hydroxyapatite by usingprecipitation methodrdquo Journal of Alloys and Compounds vol430 no 1-2 pp 330ndash333 2007
