Silica sol-gel and aerogel substrates were synthesized using a modified acid catalyzed hydrolysis of tetramethyl orthosilicate method that incorporated graphene oxide and silver nanoparticles into the matrix. The effectiveness of loading of graphene oxide was monitored by UV-vis and surface enhanced Raman spectroscopy (SERS). Characterization data suggests that graphene oxide is detectable through SERS while integrated into a sol-gel and that size of silver nanoparticles has an impact on the SERS spectrum of graphene oxide

Atkinson, Elizabeth J.O.

Wyatt, Brandyn A.

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Brandyn Wyatt and Elizabeth J. O. AtkinsonDepartment of Chemistry, Linfield College, McMinnville, ORSERS detection of graphene oxide in acid-catalyzed sol-gels38 nmFigure 4: Nanosight spectrum of the varioussized silver nanoparticles in solution (B) fromFigure 2 with a mean size of 38 nm.Figure 5: SERS spectra of graphene oxidesilica sol-gels using silver nanoparticlesolution (A) at various graphene oxideconcentrations. Concentrations of grapheneoxide were 0.066 mg/mL (▪ ▪ ▪), 0.123 mg/mL(- - -), and 0.198 mg/mL (──).Figure 6: SERS spectra of graphene oxidesilica sol-gels using silver nanoparticlesolution (B) at various graphene oxideconcentrations. Concentrations of grapheneoxide were 0.066 mg/mL (▪ ▪ ▪), 0.123 mg/mL(- - -), and 0.198 mg/mL (──).DiscussionGraphene oxide sol-gels with silvernanoparticles were successfully preparedthrough a modified acid catalyzed synthesisreaction. The graphene oxide was detectablethrough SERS (Figure 5, 6) when integratedinto the sol-gel matrix at its characteristicpeaks (1365 cm-1, 1612 cm-1)3. Other peaksappear (1030 cm-1, 1476 cm-1) and may becharacteristic peaks of methanol, a sideproduct of the modified reaction.Data suggests that as graphene oxideconcentration increases peak intensity alsoincreases (Figure 5, 6). Silver nanoparticlesolutions (A) and (B) were synthesized andhad an average size of 88 nm and 38 nm,respectively (Figure 3, 4). Figure 2 supportsthese results by showing that solution (A) ismore aggregated with a FWHM value of 96.2nm, whereas solution (B) had a FWHM valueof only 42.3 nm. Figure 5 shows thatgraphene oxides characteristic peaks areintensified and become more distinct whenlarger silver nanoparticles are present whencompared to those made with smaller silvernanoparticles that are shown in Figure 6. Thenext step for this research is to dry these sol-gels into aerogels, where graphene oxide canbe tested as a sensor.Conclusions• Graphene oxide in the presence of silvernanoparticles can be detected by SERSwhile encapsulated in a silica sol-gelmatrix.• The intensity of graphene oxidescharacteristic peaks (1365 cm-1, 1612 cm-1)increase as the concentration of grapheneoxide increases in the sol-gel matrix.• Data suggests that larger silvernanoparticles integrated into the silica sol-gels allow for greater intensity of grapheneoxide signature peaks.AcknowledgmentsThe authors would like to thank the LinfieldCollege Chemistry Department, the LinfieldCollege Collaborative Research Grant, Dr.Thomas Reinert, Dr. Brian Gilbert, and Dr.Julian Haigh.References1. X. Ling, L.M. Xie, Y. Fang, H. Xu, H.L.Zhang, J. Kong, M.S. Dresselhaus, J. Zhang,Z.F. Liu. Nano Lett. 10 2010 553–561.2. A. Wojcik, P.V. Kamat. ACS Nano 4 20106697–67063. G. Ding et al. / Appl. Surf. Sci. 345 2015310-318.4. Schlücker, S. Chem. Int. Ed. 53 20144756–4795.5. Rywak, A; Burlitch, J. Chem. Mater. 1996,8, 60-676. Allen. J, Rosenberg,. J, Johnston. E, Hart.C. ACS Appl. Mater. Interfaces 2012, 4, 1573-15847. Cai, S; Zhang, Y; Zhang, H; Yan, H; Lv, H;Jiang, B. ACS Appl. Mater. Interfaces 2014, 6,11470−114758. Nasrollahzadeh. M, Babaei. F, Fakhri. P,Jaleh. B. RSC Adv. 5 2015 10782-10789.9. P.C. Lee, D. Meisel, J. Phys. Chem. 861982 3391-3395• Silver nanoparticles were prepared using amodified citrate reduction method9. Silvernitrate (50 mL, 1 mM) and deionized water(25 mL) were mixed and brought to a boil.Sodium citrate (7.0 mL, 1% w/v) wasadded and the mixture was refluxed (30min).• Graphene oxide (1.0 mL, 2 mg/mL) wasadded to deionized water (6.5 mL) and thesolution sonicated until homogenous.Citrate buffer (0.035 mL, 0.4M, 4.6 pH) andTMOS (4.62 mL) were then added to themixture and further sonicated (10 min).Silver colloid (3.0 mL), Was added to thesolution and sonicated a final time (5 min).• Gels were aged (24 h).• Aged gels were washed several times inethanol, followed by acetone over threedays.Instrumentation:• Custom-built Raman spectrometer using a532 nm excitation beam andthermoelectrically cooled CCD• NanoSight LM10 HS• Shimadzu UV-Vis Spectrophotometer (UV-2600)Results (A)(B)Figure 2: UV-vis spectra for replicate samplepreparations of silver nanoparticlesolutions. Differences in particle size wereobserved using full width at half maximum(FWHM) values. The FWHM value for sample(A) was 96.2 nm whereas (B) was 42.3 nm.88 nmFigure 3: NanoSight spectrum of the varioussized silver nanoparticles in solution (A) fromFigure 2 with a mean size of 88 nm.IntroductionOverview: Graphene oxide has shownpromise as a sensor due to its manyinteresting physical and chemical properties,including its ability to induce strong chemicalenhancement1 and its high adsorptionproperties2. Moreover, graphene oxide isknown to be detectable using surface-enhanced Raman spectroscopy (SERS)3, asurface-sensitive spectroscopic technique withmany applications in the chemical andbiological fields4. The ability to detectgraphene oxides presence while integrated ina silica sol-gel could be an important step intesting its effectiveness as a sensor.Sol-gel materials: Silica Sol-gel and aerogelsare very low density solids, composed of ahighly porous matrix of metal-oxide bondsthat provide a cage-like structure, allowing forthe entrapment of desired target molecules.Silica gels can be synthesized using a varietyof different catalysts5-7. The synthesis methodused involves an acid-catalyzed reaction usingTMOS5, which acts as the building blocks forstructure of the porous silica gel.Figure 1: The structure of the targetmolecule, graphene oxide.8Goal: Little work has been done to investigatethe detection of graphene oxide while encagedin a sol-gel, nor as a sensor in an aerogel.Herein, the authors present an acid-catalyzedsilica sol-gel preparation that incorporatesgraphene oxide and silver nanoparticles whileusing SERS to monitor the efficiency of thegraphene oxide uptake. The concentrationeffect of graphene oxide loading wasmonitored by SERS. In addition, the impactof the silver nanoparticles size on thegraphene oxide SERS spectrum was observed.MethodsChemicals:• Graphene oxide• Tetramethyl orthosilicate (TMOS)• Silver nitrate, dihydrate sodium citrate,and citric acid monohydrate• Chemicals were purchased from Sigma-Aldrich (St. Louis, MO). All materials wereused as received.Procedures:• Silica sol-gels were prepared by the acid-catalyzed hydrolysis of TMOS5.00.10.20.30.40.50.60.7300 400 500 600 700 800AbsorbanceWavelength	(nm)0123456780 100 200 300 400 500 600 700Concentration	(Particles*e6/mL)Particle	Size	(nm)05101520250 100 200 300 400 500 600 700Concentration	(Particles*e6/mL)Particle	Size	(nm)500 1000 1500 2000 2500Intensity	(a.u.)Raman	Shift	(cm-1)500 1000 1500 2000 2500Intensity	(a.u.)Raman	Shift	(cm-1)

SERS Detection of Graphene Oxide in Acid Catalyzed Sol-Gels

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SERS Detection of Graphene Oxide in Acid Catalyzed Sol-Gels

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