Nnomterils Volume 2012, Article ID 135138, 5 pges doi:10.1155/2012/135138 Reserch Article Simple Synthesis nd Enhnced Performnce of Grphene Oxide-Gold Composites MinSong,LuluYu,ndYiminWu Key Lortory of Energy Therml Conversion nd Control, School of Energy nd Environment, Southest University, Ministry of Eduction, Nnjing 210096, Chin Correspondence should e ddressed to Min Song, sm@seu.edu.cn Received 23 Jnury 2012; Accepted 10 Mrch 2012 Acdemic Editor: Anukorn Phurungrt Copyright 2012 Min Song et l. This is n open ccess rticle distriuted under the Cretive Commons Attriution License, which permits unrestricted use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. Grphene oxide-gold composites were prepred y one-step rection in queous solution, where the gold nnoprticles were deposited on the grphene oxide during their synthesis process. Trnsmission electron morphology, X-ry diffrction, Romn spectr, nd UV-Vis sorptionspectr were used tochrcterize the otined composites. Furthermore, sed on the BET nlysis results, it ws found tht the surfce re of the composite film ws oviously enhnced compred with the synthesized grphene oxide. Electrochemicl mesurements indicted tht the modifiction of the composites on electrode could efficiently enhnce the voltmmetric response, suggesting the potentil ppliction for mking electrochemicl sensors. 1. Introduction Grphene, two-dimensionl mteril, hs ttrcted tremendous ttention from oth the experimentl nd theoreticl scientific communities due to its unique nnostructure nd properties, such s the high therml conductivity, high strength, nd high specific surfce re. These properties mke grphene very promising for mny pplictions such s solr cells, hydrogen storge [1], sensors [2], tteries [3], supercpcitors [4], nd nnocomposites [5, 6]. Beside pure grphene, the study of grpheme-sed nnocomposites is lso importnt. The comintion of grphene with inorgnic prticles, such s metllic, semiconducting, nd insulting nnoprticles (NPs), my result in some excellent mterils used for ctlysts nd tteries [7 10]. Grphene-sed composite mterils prepred y dispersing in polymers show significnt improvement in the electronic nd therml conductivity [11, 12]. Also, the integrtion of grphene with certin functionl prticles presents specil fetures in the new hyrids tht cn e used in opticl, electricl, ctlysis, sensors, nd so forth [13]. The grphene cn e otined in ulk quntity y chemicl reduction of grphene oxide in solution [14 16]. However, the strong vn der Wls interctions mong these reduced grphene sheets result in their tendency to ggregte in solution. Both electrosttic stiliztion [17] nd chemicl functionliztion [18, 19] methods hve een proven to e useful to suppress ggregtion of exfolited grphene sheets, such s the ttchment of some molecules or polymers onto the sheets [11, 20]. Furthermore, severl investigtions hve een crried out to produce grphene-metl composites to prevent the restcking of these cron sheets during the chemicl reduction process [8 10, 21, 22]. Electrochemicl deposition, metl evportion, nd hydrogen reduction of metllic slts-grphite composite cn e used to prepre grphite-metl composites. In this study, we hve explored new strtegy to deposit gold nnoprticles on grphene oxide y one-step rection in queous solution, where the gold nnoprticles re deposited on the grphene oxide during their synthesis process. The s synthesized composites re chrcterized y using trnsmission electron morphology, X-ry diffrction, Romn spectr, nd UV-Vis sorption. Moreover, we investigte the signl enhncement of the composite y electrochemicl detection, suggesting the potentil ppliction for electrochemicl sensors.
2 Nnomterils 2. Experimentl Section 2.1. Preprtion of Grphene Oxide-Gold Composites. The nturl grphite ws ought from Sigm. The grphite oxide (GO) ws prepred from purified nturl grphite ccording to Hummers method. The 2 mg GO ws suspended in 1 wt % HAuCl 4 solution (2 ml) y soniction for 5 minutes to mke GO dispersed equly. The suspended solution ws then diluted to 200 ml with douly distilled wter nd heted to oiling while stirring. Afterwrd, 20 ml sodium citrtes ws dded to the oiling solution which ws kept heting for 30 min with mgnetic stirring until the color of the solutions did not chnge. Then, the smple ws cooled to room temperture, then seprted in the centrifuge, nd wshed with douly distilled wter five times. The resulting products were dried in vcuum oven t 80 Cfor12h. 2.2. Chrcteriztion. TEM imges were otined y using JEM2000FX (JEOL). The composition nd structure were nlyzed using powder X-ry diffrction (XRD, Rigku D/ mx-2500 diffrctometer with Cu Kα rdition). Brunuer- Emmett-Teller (BET) surfce res nd pore volumes were mesured on Micromeritics ASAP 2020 sorptometer using nitrogen dsorption t 77 K. UV-Vis sorption spectroscopy ws performed on Hitchi U-4100. Rmn spectr were recorded with surfce enhnced Rmn spectrophotometer (JY HR800). 2.3. Electrochemicl Mesurements. Initilly, 1 mg grphene oxide or grphene oxide-gold composites were suspend in 10 ml doule-distilled wter. Then 5 mls of the reltive solution ws spred evenly onto the surfces of the GCE electrode. Afterwrds, the electrode surfces were completely dried under flow of nitrogen. Electrochemicl mesurements were performed on CHI 660B electrochemicl worksttion t room temperture (22 ± 2 C) under the nitrogen tmosphere. A three-electrode system ws used in the reltive electrochemicl study, which contined the composites-modified glssy cron electrode (GCE) s the working electrode, Pt electrode s the counter electrode, nd sturted clomel electrode (SCE) s the reference electrode. 3. Results nd Discussion To demonstrte the effective coting of gold nnoprticles on the grphene oxide surfce, TEM, XRD, Romn spectr, nd UV-vis sorption spectr re used to chrcterize the grphene oxide nd grphene oxide-au composites. Figures 1() nd 1() show the typicl TEM imges of the synthesized grphene oxide nd grphene oxide-au composites. The TEM imge of grphene oxide nnosheets illustrtes the flke-like shpes of grphene oxide. Trnsmission electron microscopy (TEM) microgrphs demonstrte tht the gold nnoprticles re deposited on grphene oxide sheets. In this imge, Au nnoprticles pper s drk dots with dimeter of 20 to 30 nm on lighter shded sustrte corresponding to the plnr grphene oxide sheet. Furthermore, Figure 1(c) shows the XRD ptterns of the s-synthesized grphene oxide nd Au-grphene oxide composites. From the results, we oserve tht GO shows position pek t 11.3, suggesting the successful oxidtion of the strting grphite. Menwhile, the diffrction peks of the Au-grphene oxide composite re similr to tht of pure Au. The peks t 2θ = 39.9, 46.2, 67.9, nd 81.4 cn e ssigned to the (111), (200), (220), nd (311) crystlline plnes of Au. In ddition, we lso oserve tht the regulr lyered structure of grphite oxide or grphite is destroyed. The possile mechnism is tht the ttched prticles prevent the restcking of these cron sheets nd therefore the chrcteristic diffrctions peks of the lyered structure dispper [23]. Figure 1(d) shows the Rmn spectr of grphene oxide nd grphene oxide-aunps composites. As for grphene oxide, the peks t 1590 cm 1 (G nd) nd 1360 cm 1 (D nd) re clerly present. In the menwhile, the D-nd nd G-nd for grphene oxide-aunps composites re lso locted t 1360 nd 1590 cm 1,respectively.Thertio etween the D nd G nds (I D /I G )cneusedtoestimte the degree of structurl disorder. The Rmn spectrum of grphene oxide-aunps composites mteril is very similr to the Rmn spectrum of the grphene oxide with prcticlly identicl D/G nd rtio, indicting the nondestructive chrcter of the method. However, the pek intensities of ll reltive nds for grphene oxide-aunps composites re oviously higher thn those for the corresponding nds oserved for the grphene oxide, suggesting strong coting of the lignd on the grphene oxide surfce. Furthermore, ll Rmn spectr hve the sme pttern, which implies tht the inding procedure does not ffect the structure of grphene. The successful synthesis of AuNPs-decorted grphene oxideisconfirmedyuv-visspectroscopy(figure 1(e)). The UV-vis spectrum of grphene oxide (curve in Figure 1(e)) in wter shows tht no sorption pek from 300 to 700 nm. As shown in Figure 1(e) (curve c), when AuNPs re decorted onto the grphene oxide surfce, the sorption peks of grphene oxide-aunps composites re oserved t 520 nm, which is corresponding to the sorption of AuNPs (curve ), indicting the formtion of AuNPs. The redox proe Fe(CN) 3 6, which is sensitive to surfce chemistry of cron-sed electrodes, ws used to chrcterize the re nd modified GCEs. Figure 2 shows the enhnced electrochemicl response of K 3 (FeCN) 6 t the respective modified glssy cron electrodes. It is oserved tht s for the re GCE, the pek current of K 3 (FeCN) 6 is 4.0 10 5 A, while the relevnt pek current increses to 4.8 10 5 A t pure grphene oxide modified GCE. Thus, the pek current intensity of K 3 (FeCN) 6 is incresed out 20% in the presence of grphene oxide. In comprison, in the presence of grphene oxide-aunps composites, the respective pek current of K 3 (FeCN) 6 increses to 9.0 10 5 A. It ppers tht the pek current of K 3 (FeCN) 6 increses out 125% in the presence of grphene oxide-aunps composites under identicl experimentl conditions. The results indicte tht the current response of K 3 (FeCN) 6 t the grphene oxide- AuNPs composites modified electrode is much stronger thn tht of grphene oxide modified GCE s well s the re
Nnomterils 3 () Au(111) Au(311) Au(200) Au(220) (001) 0 10 Intensity Intensity () 20 30 40 50 2θ (deg) 60 70 80 1200 1000 1400 1600 1800 2000 Rmn shift/cm 1 (c) (d) 1 Adsorption 0.8 0.6 0.4 0.2 0 300 400 500 Wvelength (nm) 600 700 c (e) Figure 1: TEM imges of the grphene oxide () nd grphene oxide-au composites (). (c) XRD imges of the grphite oxide () nd grphene oxide-au composites (). (d) Rmn spectr of the grphene oxide () nd grphene oxide-au composites (). (e) UV-vis sorption spectr of the grphene oxide (), Au nnoprticles () nd grphene oxide-au composites (c).
4 Nnomterils Tle 1: The texture property of grphene oxide nd grphene oxide-aunps composites. Smples Properties Pore dimeter/nm BET surfce re/m 2 /g Pore volume/cm 3 /g Grphene oxide 31.5 23 0.18 Grphene oxide -AuNPs composites 4.18 985 1.03 Current (μa) 400 200 0 200 400 600 c 1 0.5 0 Potentil (V) 0.5 Figure 2: Cyclic voltmmogrm of K 3 (FeCN) 6 t the re GCE (), pure grphene oxide modified GCE (), nd grphene oxide-aunps composites modified GCE (c). GCE. The enhnced current response on composites should e scried to the effective intercltion of Au NPs onto the grphene oxide sheets, which contriute to the surfce re enhncement of the composite film. To confirm this, the surfce re nd pore structures properties of grphene oxide nd grphene oxide-aunps composites re elucidted y BET methods in Tle 1. From the results, we cn oviously oserved tht the surfce re of composites incresed y incorportion of Au NPs. 4. Conclusion In summry, gold nnoprticles re ttched on the grphene oxide surfce during their synthesis process. Our results indicte tht the premixing of grphene oxide with HAuCl 4 solution could contriute to the distriution of HAuCl 4 molecule on the grphene oxide surfce nd further induce the nice deposition of gold nnoprticles on grphene oxide sheets. The enhncement of surfce re nd respective electrochemicl response shows potentil ppliction of the composite for electrochemicl sensing. Acknowledgments The uthors re grteful for the Ntionl Nturl Science Foundtion of Chin (20907008) nd the finncil support of the Ntionl Hi-tech Reserch nd Development Progrm of Chin (973) (2010CB732206 nd 2011CB201505), Specilized Reserch Fund for the Doctorl Progrm of Higher Eduction (20090092120010). Dr. M. Song specilly thnks the support of the Foundtion for Southest University excellent young techer. References [1] X. Wng, L. Zhi, nd K. Müllen, Trnsprent, conductive grphene electrodes for dye-sensitized solr cells, Nno Letters, vol. 8, no. 1, pp. 323 327, 2008. [2] J. D. Fowler, M. J. Allen, V. C. Tung, Y. Yng, R. B. Kner, ndb.h.weiller, Prcticlchemiclsensorsfromchemiclly derived grphene, ACS Nno, vol. 3, no. 2, pp. 301 306, 2009. [3] C. Wng, D. Li, C. O. Too, nd G. G. Wllce, Electrochemicl properties of grphene pper electrodes used in lithium tteries, Chemistry of Mterils, vol. 21, no. 13, pp. 2604 2606, 2009. [4] Y. Wng, Z. Shi, Y. Hung et l., Supercpcitor devices sed on grphene mterils, Physicl Chemistry C, vol. 113, no. 30, pp. 13103 13107, 2009. [5] G. Ed nd M. Chhowll, Grphene-sed composite thin films for electronics, Nno Letters, vol. 9, no. 2, pp. 814 818, 2009. [6]J.L.Vickery,A.J.Ptil,ndS.Mnn, Frictionofgrphene-polymer nnocomposites with higher-order three-dimensionl rchitectures, Advnced Mterils, vol. 21, no. 21, pp. 2180 2184, 2009. [7] R. Ptkflvi, D. Diz, P. Sntigo-Jcinto, G. Rodriguez- Gttorno, nd R. Sto-Berru, Anchoring of silver nnoprticles on grphite nd isomorphous lttices, Physicl Chemistry C, vol. 111, no. 14, pp. 5331 5336, 2007. [8] M. Shiri, K. Iget, nd M. Ari, Formtion of pltinum nnosheets etween grphite lyers, Chemicl Communictions, no. 7, pp. 623 624, 2000. [9] S. K. Shikhutdinov nd F. J. C. Sntos Aires, Evolution of the rhodium colloid supported on grphite studied y tomic force microscopy in the tpping mode, Lngmuir, vol. 14, no. 13, pp. 3501 3505, 1998. [10] X. Yng, Y. Mkit, Z. H. Liu, nd K. Ooi, Novel synthesis of lyered grphite oxide-irnessite mngnese oxide nnocomposite, Chemistry of Mterils, vol. 15, no. 6, pp. 1228 1231, 2003. [11] S. Stnkovich, D. A. Dikin, G. H. B. Dommett et l., Grphene-sed composite mterils, Nture, vol. 442, no. 7100, pp. 282 286, 2006. [12] A. Yu, P. Rmesh, M. E. Itkis, E. Bekyrov, nd R. C. Hddon, Grphite nnopltelet-epoxy composite therml interfce mterils, Physicl Chemistry C, vol. 111, no. 21, pp. 7565 7569, 2007. [13] H. Yng, Q. Zhng, C. Shn, F. Li, D. Hn, nd L. Niu, Stle, conductive suprmoleculr composite of grphene sheets with
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