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Sensors and Actuators B 188 (2013) 1218– 1224

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l h om epage: www.elsev ier .com/ locate /snb

raphene oxide as carboelectrocatalyst for in situ electrochemicalxidation and sensing of chemical warfare agent simulant

irendra V. Singh, Anil K. Nigam, Sardar S. Yadav, Brajesh K. Tripathi, Anchal Srivastava,annan Boopathi ∗, Beer Singh

efence Research and Development Establishment, DRDO, Gwalior 474002, India

r t i c l e i n f o

rticle history:eceived 26 March 2013eceived in revised form 18 July 2013ccepted 4 August 2013vailable online 15 August 2013

eywords:raphene oxide

a b s t r a c t

The graphene oxide (GO) was prepared via the chemical oxidation of natural graphite powder followedby microwave irradiation and then used to modify the surface of gold (Au) electrode. The morphologyof GO was characterized using transmission electron microscopy, X-ray diffraction, scanning electronmicroscopy and Raman spectroscopy. The synthesized GO was used as a carboelectrocatalyst for theelectrochemical oxidation of chemical warfare agent simulant thiodiglycol (TDG) at room temperatureby modifying the gold (Au) electrode with GO. The electrochemical behavior of TDG on GO modifiedAu electrode (GO/Au electrode) was investigated by cyclic voltammetry and differential pulse voltam-

hemical warfare agenthiodiglycollectrocatalysisarboelectrocatalyst

metry. The results with GO/Au electrode indicated involvement of excellent electrocatalytic activitytoward the TDG oxidation and gas chromatography–mass spectrometry (GC–MS) results revealed theformation of 2-(2-hydroxy-ethanesulfinyl)-aldehyde as main oxidation product. Degradation studieswere also performed and products were identified by GC–MS which indicated the formation of thio-glycolic acid, 2-(2-hydroxy-ethanesulfinyl)-ethanol, 1,4-oxathione and 1,4-oxathiane 4 oxide as maindegradation products.

© 2013 Elsevier B.V. All rights reserved.

. Introduction

The sulfur mustard commonly known as mustard gas is aytotoxic and vesicant chemical warfare agent (CWA). It readilyliminates a chloride ion to form a reactive cyclic sulfonium ion,hich tends to permanently damage the DNA strands, finally pose a

isk to animals and humans. Hence, CWAs have drawn considerablenvironmental, social and scientific concern in recent years as these of such compounds by terrorists, organizations, or even states isignificant [1–3]. In the environment, hydrolysis of sulfur mustardeads mainly to the formation of thiodiglycol [TDG, bis(2-hydroxy-thyl) sulfide] a polar and stable compound. Both compounds arencluded in the scheduled list of the chemical weapon convention;ulfur mustard in Schedule-1 and TDG in Schedule-2 [4].

A number of oxidation methodologies using oxidizing sub-tances such as hydrogen peroxide [5], ozone [6], metal oxides [7]nd Fenton reagents [8] were reported for the oxidation and degra-

ation of sulfides. However, these methodologies have its own

nherent disadvantages in terms of efficiency, corrosiveness, cost,egeneration and secondary pollution, etc. [9]. Hence, to avoid the

∗ Corresponding author. Tel.: +91 751 2390162.E-mail address: boopathi@drde.drdo.in (M. Boopathi).

925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2013.08.013

drawbacks associated with the fore mentioned methods; in presentstudy electrochemical oxidation methodology is adopted due to itsrobust oxidation capacity, relatively simple equipment, environ-mental friendliness, strong corrosion stability, long service life andweak electrode fouling [10–14]. Furthermore, the direct electro-chemical oxidation of CWAs at bare electrodes is generally difficultdue to non electrochemical activity of these agents, which usuallyresults in low selectivity, poor sensitivity and poor reproducibility.This can be overcome by modifying the electrode surfaces with dif-ferent transition metals [15,16] and metal oxide [17] that are oftenexpensive, toxic and are frequently obtained from limited naturalresources [18]. As such, the search for a catalyst that provides ben-efits of a metal-free degradation or conversion of one chemical toanother is a continuing effort in the research and development.

In recent years, graphene oxide (GO) has drawn an enormousamount of scientific attention since its discovery because of itsimportance in nanoscience. GO is a pseudo two-dimensionalnanomaterial, possessing a variety of chemically reactive function-alities, such as epoxy and hydroxyl groups on the basal plane andcarboxylic acid groups along the sheet edge [19–24]. The sorption

and intercalation of ions or molecules are possible because of thefunctional groups present in GO [25]. The unique properties suchas hydrophilicity, availability of functional group, good chemicalstability and easy fabrication ability make GO as the star material

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V.V. Singh et al. / Sensors and A

n the fields of electrocatalysis [26–28] material science [29] andlectronic devices [30]. Moreover, GO often exhibits excellentlectroanalytical performance than carbon nanotubes [31].

Herein, first time we report the use of GO, a readily availablend inexpensive material, as a mild and efficient carbon electro-atalyst for the electrochemical oxidation of TDG in to respectivexidized products, a process refer as “carboelectrocatalysis”. More-ver, GO modified Au (GO/Au) electrode was characterized usingcanning electron microscopy (SEM) and energy dispersive-X-raypectroscopy (EDS), transmission electron microscopy (TEM), X-ay diffraction (XRD), and Raman spectroscopy. The effect of pH onhe electrocatalytic behavior of GO/Au electrode with TDG was alsoarried out and optimized.

. Experimental

.1. Chemicals and reagents

Graphite powder (99.8%, 325 mesh), thiodiglycol TDG were pro-ided by Alfa Aesar, Germany. Disodium hydrogen phosphate,odium dihydrogen phosphate, phosphorus pentoxide, potassiumersulphate, potassium permanganate, hydrochloric acid, sodiumydroxide, sulfuric acid (H2SO4) and hydrogen peroxide solution30 wt%) are obtained from Merck-Germany. Buffer solutions wererepared using Milli-Q water (18 M� cm at 25 ◦C) throughout thexperiment. The pH of the buffers was measured using a pH meterhich was standardized with 0.05 M potassium hydrogen phtha-

ate (pH 4.0 at 25 ◦C) and 0.05 M borax (pH 9.0 at 25 ◦C). Differentuffer solutions are used in this study depending on pH [pH 4–5sodium acetate–acetic acid), pH 6–8 (phosphate solution), pH 9,0 (glycine–NaOH)] for the optimization of pH. The common chem-

cals used for preparation of buffers and other reagents were ofnalytical grade.

.2. Instruments and electrochemical studies

TEM images were obtained with an FEI Technai G2 F20 micro-cope at 200 kV; the samples were air dried before using the TEMo characterize the size and morphology of the GO. The samplesor TEM analysis were obtained by placing a drop of the colloidalispersion of nanoparticles onto the 200 mesh carbon-coated cop-er grid. They were dried at room temperature and then examinedsing the TEM without any further modification. The crystal struc-ure of sample was studied using a Bruker D8 Advance X-rayiffractometer (XRD) operating at 40 mA and 40 kV, Cu K�1 radia-

ion. Raman spectrum was obtained using Renishaw Invia Ramanicroscope (Gloucestershire, UK). ESEM-EDX (Quanta 400-ESEMith EDAX-FEI, The Netherlands) system was used to know the

urface morphology and elemental composition of the modifica-ions. The pH of solutions was measured with a EUTECH instrumentpH-1500, Singapore). Microwave irradiation was carried out in a

icrowave oven (LG) at 700 W for 300 s.Electrochemical experiments were performed at room temper-

ture 25 ± 2 ◦C by using potentiostat/galvanostat with a frequencyesponse analyzer (Autolab-302 with FRA-II, The Netherlands).he three-electrode system contained a GO/Au electrode as theorking electrode, a saturated Ag/AgCl electrode and a platinum

piral as reference electrode and counter electrode, respectivelyf Metrohm make. Cyclic voltammetry (CV) scans were performedsing 50 mV/s as scan rate in phosphate buffer pH 7.0 between 0.0 Vnd 1.2 V unless otherwise stated.

The GC–MS system consisted of an Agilent 7890 A gas chro-atograph combined with a 5975 quadrupole mass spectrometer

Agilent Technology, USA). GC was performed on a DB5-MSapillary column (30 m × 0.25 mm i.d., 0.25 �m thickness, J&W

rs B 188 (2013) 1218– 1224 1219

Scientific, Folson, CA). The carrier-gas (helium) flow-rate and splitratio were adjusted to 1.0 ml/min and 50:1, respectively. Theinjection port and transfer line were maintained at 250 and 280 ◦C,respectively. The temperature program for the separation was asfollows, initial temperature, 50 ◦C (2 min hold), then a ramp to250 ◦C at 10 ◦C/min (5 min hold). Mass spectrometric acquisitionwas started 3 min after sample injection. For the qualitative anal-ysis, electron ionization (EI, ionization energy, 70 eV; ionizationcurrent, 34.6 �A) was used as the ionization mode. The ion sourceand quadrupole analyzer were maintained at 230 and 150 ◦C,respectively. The data acquisition mass range was 50–550, andsampling was 0.8 scan/s.

2.3. Synthesis of GO nanosheets

GO nanosheets were synthesized from 325 mesh size graphitepowder by a modified Hummers method as shown in Scheme 1.Briefly, 2 g of graphite powder was added into a mixed solution of20 mL of concentrated H2SO4, 1 g of K2S2O8 and 1 g of P2O5 and thesolution was kept at 80 ◦C for 5 h. Then, the resulting preoxidizedproduct was filtered and dried. After this preoxidization process,the preoxidized graphite was put into 50 mL of concentrated H2SO4.Then, 6 g of KMnO4 was added gradually under stirring and ice-cooling to ensure that the temperature of the mixture was below20 ◦C. The mixture was then stirred at 35 ◦C for 10 h, followed byadding 100 mL of Milli-Q water. After 1 h, another 300 mL of Milli-Qwater was added to dilute the solution and then 5 mL of 30% H2O2was added into the solution to terminate the reaction. A bright yel-low solution was obtained. The mixture was filtered and washedwith HCl (3%) solution, and the obtained graphite oxide was sus-pended in Milli-Q water. The obtained brown dispersion solutionwas then subjected to 20 min of centrifugation at 3000 rotation perminute (r.p.m.) to remove any large agglomerates of graphite oxide.Exfoliation of graphite oxide to GO was achieved by microwave irra-diation in a microwave oven. Under microwave irradiation, rapidexfoliation occurs along with the sudden release of various gasesresulting the formation of GO. Precaution should be taken whileusing microwave oven; it should be carried out well ventilatedroom or inside a fume hood. A dialysis process in Milli-Q waterwas further performed with the above resultant material for 2 daysin order to neutralize the pH as well as to remove the metal impu-rities of the suspension solution and then the resultant solid wasdried under vacuum (60 ◦C) for about 2 days.

2.4. Fabrication of GO/Au electrode

The Au electrodes were polished using 0.3 and 0.05 �m alu-mina slurry, then sonicated in nitric acid (1:1), ethanol and doublydistilled water in turn. Firstly, GO was treated with 0.05 M NaOHsolution and then it was centrifuged and dried at 80 ◦C in oven.1.0 mg GO was dispersed in 1 mL ethanol to form a homogenousmixture. 7 �L of 1.0 mg mL−1 mixture was dropped on the surfaceof Au electrode and allowed to dry in ambient air with the help ofspin coater. Finally, the electrodes were rinsed with Milli-Q waterand again dried in air.

3. Results and discussion

3.1. Characterization of GO/Au electrode

The prepared GO was characterized for morphologies by SEM

and TEM, non crystalline nature by XRD and elemental analysis byEDS. Supplementary Fig. 1 shows the SEM image of the GO film onthe surface of Au, revealing the typical crumpled and wrinkled GOnanosheet over the Au electrode, as reported elsewhere [32].

1220 V.V. Singh et al. / Sensors and Actuators B 188 (2013) 1218– 1224

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Scheme 1. Procedure used in t

A typical TEM image is shown in Fig. 1. From this figure, it is evi-ent that the GO nanosheets are rippled and entangled with eachther, as such they ripple and as such they resembled crumpled

ilk veil waves. Moreover, the thin wrinkled structure represents aurled and crumpled morphology that the GO owns intrinsically33]. The inset of Fig. 1 is the selected-area electron diffractionSAED) of GO showing diffraction rings and the diffraction dots

ig. 1. TEM image of GO. The inset is the selected area electron diffraction patternSAED).

dy to prepare graphene oxide.

are unresolved, unambiguously indicating that the GO flakes areamorphous in nature. The XRD pattern of GO (Fig. 2) reveals its char-acteristic peak at 11.8◦ and is in good agreement with the reportedvalue earlier [34].

Raman spectroscopy is a powerful tool for investigating thestructural changes that occur in carbon materials [35–37]. Asshown in Supplementary Fig. 2A, the D band around 1312 cm−1

corresponding to sp3 and prominent G band around 1583 cm−1 isattributed to first order scattering of the E2g mode a characteristic

band of crystalline graphite [37]. As shown in Supplementary Fig.2B the increased intensity of D band indicates the formation of GOdue to the reduction in size of the in-plane sp2 domains causedby the oxidation [37]. Moreover, the vibration frequency of the G

10 20 30 40 50 60

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Fig. 2. X-ray diffraction pattern of GO.

V.V. Singh et al. / Sensors and Actuato

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ig. 3. CV in phosphate buffer pH = 7.0 (a) bare Au electrode and (b) GO/Au electrode.can rate 50 mV/s vs. Ag/AgCl.

and increased to 1597 cm−1, reflects the influence of defects andsolated double bonds.

.2. CV characterization of the modified electrode

Bare and GO/Au electrodes were characterized by CV in pH 7.0hosphate buffer in the potential window from 0.0 V to 1.2 V. Fig. 3ahows CV response for bare Au electrode and Fig. 3b is the CVesponse with GO/Au electrode in phosphate buffer. In case of bareu electrode, no peak is observed in the forward scan and in reversecan one peak is seen at 0.51 V, this peak is due to reduction of goldxide [38]. However, with GO/Au electrode (Fig. 3b) in the forwardcan one peak at 0.955 V is observed with peak current of 3.48 �A,ue to electrochemical activity of GO and one peak in the reversecan at 0.541 V due to reduction of GO species as it is having manyxygen group functionalities. In case of GO/Au electrode a peak isbserved at 0.955 V in the forward scan and this peak is absent inare electrode and this confirms the modification of Au electrodeith GO.

In order to know the electrocatalytic activity of GO/Au electrodeoward TDG, CV studies are performed with TDG by using bare Aund GO/Au electrodes under the optimal conditions. In case of bareu electrode, after the addition of 1.93 × 10−4 M TDG (Fig. 4Ab)

n a pH = 7.0 phosphate buffer solution, a decrease in anodic peakurrent is observed when compared to without TDG and after sub-equent addition this current response is not having regular trends shown in Fig. 4A and this observation is due to the adsorption ofDG on bare electrode surface.

Fig. 4B shows CV response for GO/Au electrode in absence ofDG (Fig. 4Ba) and in presence of 3.86 × 10−4 M TDG (Fig. 4Bb) and.79 × 10−4 M (Fig. 4Bc) in a pH 7.0 phosphate buffer solution. Afterddition of 3.86 × 10−4 M TDG (Fig. 4Bb), an increase in anodic cur-ent (7.5 �A) is observed at 0.990 V, however, in absence of TDGhis peak is present at 0.955 V, from the above, a shifting of peakotential of 45 mV toward positive direction is observed when com-ared to without TDG. This type of peak shifting and current areot observed in bare Au and thereby confirming the presence oflectrocatalysis in GO/Au electrode due to the presence of GO. Theubsequent increase in current with GO/Au electrode in presencef different increasing concentration of TDG indicates the in situ

lectrocatalytic oxidation of the TDG due to the presence of modi-cation on electrode surface as GO is having a edge and basal planeontaining functional group like hydroxyl, epoxy, lactones and car-oxylic groups and these groups are responsible for electrocatalytic

rs B 188 (2013) 1218– 1224 1221

oxidation of TDG and this is in agreement with an earlier studywhere alcohol is chemically converted to aldehyde using GO [39].Moreover, a probable mechanism involved in this electrocatalyticoxidation is provided in supplementary material.

It is also observed that the peak potential slightly shifts posi-tively with the increase of the scanning rate, which is caused bythe irreversible reaction of TDG.

3.3. Electrochemical characterization of TDG

In order to know the nature of TDG oxidation on GO/Au elec-trode, scan rate variation studies were carried out from 25 mV/s to150 mV/s with an increment of 25 mV/s Supplementary Fig. 3a. Theresultant CVs are shown in Supplementary Fig. 3a and an increasein peak current is seen as scan rate was increased. Analysis of thedata by plotting the current versus scan rate (�) variation profile(not shown) exhibited a linearity with anodic peak with a correla-tion coefficient of 0.999 while correlation coefficient of current vs.root scan rate (�1/2) was 0.990 (Supplementary Fig. 3b).

To further confirm the TDG oxidation peak, log i vs. log � graphwas plotted (Supplementary Fig. 3c), and the regression equationis log ip = 0.70 log � + 1.76 (r2 = 0.996) with a slope value of 0.70 inthe scan rate range of 25–150 mV/s and this observation is meantfor an adsorption controlled process [40].

As shown in Supplementary Fig. 3d the plot of Ep vs. ln � isa linear relationship in the potential scan rate ranging from 25to 150 mV/s, following the linear equation: Ep = 0.076 ln � + 1.22(r2 = 0.971), from the slope of this plot product of ̨ and n isestimated to be 0.337, which also confirms the electrocatalytic oxi-dation of TDG on GO/Au electrode as a totally irreversible one.According to Laviron theory [41,42] for an irreversible anodic reac-tion, the relationship between Ep and ln � is described based on thefollowing equation:

Ep = Eo + RT

˛nF

ln RTks

˛nF− RT

˛nFln � (1)

where all the symbols have their usual meaning. The estimatedvalue of heterogeneous rate constant (ks) from Eq. (1) was found tobe 0.309 s−1. The adsorbed amount of GO on the surface of Au wasfurther calculated by earlier reported method [43] According to thismethod, the peak current is related to the surface concentration ofelectroactive species � , by Eq. (2):

ip = nFA��

4RT= nFQ�

4RT(2)

where n represents the number of electrons involved in thereaction, A is the geometric surface area (0.0314 cm2) of the elec-trode, � (mol cm−2) the surface coverage, � the scan rate; R(8.314 J mol−1 K−1), F (96,485 C mol−1) and T (298 K) denote the gasconstant, the temperature, and the Faraday constant, respectively.

From the slope of the plot of anodic peak currents vs. scanrates, the surface concentration of GO was calculated to be0.774 × 10−5 mol cm−2 for n = 2, indicating good adsorption of theGO on Au electrode. This may be resulted from that GO is a strictlytwo-dimensional material, whose whole volume is exposed to sur-face adsorbates, maximizing their size effect [31].

Moreover, in order to know the number of electron involvedduring oxidation, bulk electrolysis was performed using coulome-try according to Faraday equation [44]:

n = �Q

FcV(3)

where �Q is charge involved in the reaction (�Q = QTDG − Qblank),

c is concentration of TDG, V is volume of electrolyte and F isFaraday constant. From the result of bulk electrolysis with coulom-etry (�Q = 0.050 C, c = 1.21 × 10−5 M and V = 20.0 mL), the electrontransfer number was calculated as n = 2.14 ≈ 2. This result suggests

1222 V.V. Singh et al. / Sensors and Actuators B 188 (2013) 1218– 1224

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hat the electrocatalytic oxidation of TDG as two electron trans-er reaction with charge transfer coefficient (˛) of 0.17. Thus, thelectrooxidation of TDG is a two-electron involvement process andhe suggested mechanism of electrooxidation of TDG is shown inupplementary Scheme 1 (refer to supporting information) and its also supported by GC–MS data [45].

.4. Parameters optimization for TDG response on GO/Aulectrode

The influence of amount of GO on Au electrode for the in situlectrocatalytic oxidation of TDG is also optimized as it wasbserved that different amount of GO cause different electrocat-lytic catalytic activity for a particular species. Supplementary Fig.a shows the effect of amount of GO on the oxidation peak cur-ent of TDG that measured using CV. The oxidation peak current ofDG remarkably increases with the volume of GO solution from

to 7 �L. During this period, the amount of GO at Au surfacebviously increases, leading to stronger enhancement effect. As aesult, the oxidation peak current of TDG greatly increases. With

urther increasing the amount of GO solution from 8 to 11 �L, thexidation peak current of TDG gradually decreases, maybe due tohe fact that the GO film becomes too thick and blocks the electronransfer of TDG. Therefore the 7 �L of GO volume was used for the

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ig. 5. DPV curve for different concentration of TDG oxidation in phosphate buffer (A) wd) 0.965 × 10−4 M, (e) 1.93 × 10−4 M, (f) 3.86 × 10−4 M, (g) 5.79 × 10−4 M and (h) 0.772 ×A.

without TDG, (b) with 1.93 × 10−4 M TDG and (c) with 3.86 × 10−4 M TDG and (B)TDG.

preparation of GO/Au electrode and then it was used for the elec-trocatalytic oxidation of TDG in order to shorten the time of solventevaporation and to achieve high sensitivity.

To find out the optimum performance pH of the GO/Au elec-trode and also to know the stability of modification, pH variationstudy was carried out in the pH range from 4.0 to 10.0 and a varia-tion in peak current with respect to the change in pH of the buffer isshown in Supplementary Fig. 4b. It can be seen from SupplementaryFig. 4b the anodic peak current of TDG increases with an increasein the solution pH until it reaches pH 7.0, and then it decreaseswhen the pH increased further. This decrease in peak current ofTDG can be explained by the phenomenon of electrostatic repul-sion between these anionic species of TDG with anionic part of GO.From Supplementary Fig. 4b, it is observed that a highest current isobtained at pH 7.0 for TDG oxidation; hence, all the electrochemicalexperiments were performed at pH 7.0.

3.5. Analytical application

Differential pulse voltammetry (DPV) was performed to inves-

tigate the relationship between the anodic peak current andconcentration of TDG. Well-defined peaks were obtained withinthe range scanned (0–1.2 V vs. Ag/AgCl) with a current proportionalto the concentration of TDG. Thus, this oxidation peak is attributed

By =0.663x+3.67

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o TDG and the peak current can be used as the analytical signal forDG. As can be seen in Fig. 5A, under the optimal conditions, thenodic peak current of TDG exhibited a good linearity with the log-rithmic value of TDG concentration ranging from in the range from.21 × 10−5 M to 0.772 × 10−3 M (Fig. 5B). The regression equation

s Ipa (�A) = 3.67 + 0.663 log c (Ipa: �A, c: M) (r2 = 0.994) and theetection limit was 0.020 × 10−5 M (S/N = 3).

.6. Identification of TDG degradation products by GC–MS

In order to see the in situ electrocatalytic degradation capa-ility of GO/Au electrode degradation study is performed withDG in phosphate buffer. The degradation study of TDG was per-ormed by holding the potential to 1.5 V for a time period of00 min. After this electrolysis, the degradation products werextracted with dichloromethane, purged with N2 and identifi-ation of the degradation products are carried out by GC–MS.ue to polar and non-volatile nature of degradation productf TDG, they are derivatized before GC–MS analysis. GC–MSata was obtained after silylating the extracted reaction mix-ure using BSTFA [bis(trimethylsilyl) trifluoro acetamide]. GC–MSata indicated the formation of thioglycolic acid, 2-(2-hydroxy-thanesulfinyl)-ethanol, 1,4-oxathione and 1,4-oxathiane 4 oxides main degradation products with m/z 92, 138, 104 and 120,espectively. These oxidized products are attributed due to oxy-en functionalities of GO which help to oxidize the TDG. It is alsoorth mentioning here, that in case of fixed potential electrolysis

he product 2-(2-hydroxy-ethanesulfinyl)-aldehyde is not identi-ed it may be due to the overoxidation. The suggested mechanismf degradation products of TDG is shown in Supplementary Scheme

(refer to supporting information).

. Conclusions

GO was prepared by oxidizing natural graphite powder withtrong oxidants followed by microwave irradiation and used toodify the Au electrode surface. GO/Au electrode was used for

egradation and sensing applications and the material was exten-ively investigated by various characterization methods, includingEM, XRD and Raman spectroscopy. This material is proved to ben excellent carboelectrocatalyst for the electrocatalytic oxidationf TDG in to its oxidized products. This study also indicates thatO will be a better alternative material for transition metals in theegradation of chemical warfare agents as well as environmentalollutants.

cknowledgements

The authors thank Prof. Dr. M.P. Kaushik, Director, Defenceesearch and Development Establishment, DRDO, Gwalior 474002,

ndia for his keen interest and encouragement.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.snb.2013.08.013.

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[

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iographies

Dr. Virendra V. Singh obtained his M.Sc. in AnalyticalChemistry from Banaras Hindu University in 2006. He didhis Ph.D. from Jiwaji University, Gwalior, M.P. in 2011.He joined the DRDO in June 2009, as Scientist. His cur-rent fields of interest are in the development of detectionsystem based on conducting polymers; graphene nano-material and ionic liquids using electrochemical methods.

Anil K. Nigam is working as Technical Officer in DRDO.His area of work is detection and decontamination of CWagents.

Sardar S. Yadav is working as Technical Officer A in DRDO.His area of work is detection and decontamination of CWagents.

rs B 188 (2013) 1218– 1224

Brajesh K. Tripathi obtained his M.Sc. in Physics from BhojOpen University in 2012. He joined the DRDO as a STA.His area of work is characterization of nanomaterials anddifferent composite polymer.

Anchal Srivastava is working as Technical Officer A inDRDO. His area of work is characterization of nanomate-rials and different composite polymer. He is also workingon extensive electron microscopy/EDS analysis of materialand biological specimens to establish structure–functioncorrelations.

Dr. Mannan Boopathi obtained his M.Sc., M.Phil. andPh.D. Analytical Chemistry degrees in 1993, 1994 and2000, respectively from University of Madras, India. Heworked as a visiting researcher with Prof. Yoon-Bo Shimin Pusan National University, Korea between 2000 and2003 and subsequently joined for his present post in DRDOas Scientist. His current filed of interest is in the devel-opment of detection systems for chemical and biologicalagents using conducting polymers, molecularly imprintedpolymers and ionic liquids based on electrochemical andoptical methods.

Dr. Beer Singh is Scientist “G” at present and joined DRDOas a Scientist “C” at the Defence Research & DevelopmentEstablishment (DRDE), Gwalior in 1988. He is working on