Amide Functionalized Graphene Oxide Thin Films for ... - IEEE Xplore

IEEE SENSORS JOURNAL, VOL. 16, NO. 9, MAY 1, 2016

2929

Amide Functionalized Graphene Oxide Thin Films for Hydrogen Sulfide Gas Sensing Applications Sumita Rani, Mukesh Kumar, Ravish Garg, Sumit Sharma, and Dinesh Kumar

Abstract— Amide graphene oxide (AGO) has been achieved by functionalization of graphene oxide (GO) through chemical route using 2-aminothiazole. GO and AGO were characterized and compared using Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction, energy dispersive X-ray, and Raman spectroscopy. Gas sensor devices were developed by depositing film of GO/AGO between aluminum electrodes on SiO2 /Si substrate. The sensing performance of AGO and GO has been investigated in terms of change in conductivity. It has been found experimentally that AGO exhibits significantly better reversible sensing response to hydrogen sulphide (H2 S) gas in comparison with GO. Index Terms— Amide graphene oxide (AGO), graphene oxide (GO), gas sensor, hydrogen sulphide (H2 S).

I. I NTRODUCTION

G

RAPHENE is an admirable two dimensional (2D) material having monolayer of hexagonally arranged carbon atoms in a honeycomb structure and has received an increasing attention of researchers in recent years due to its inherent electrical, mechanical, physiochemical and biocompatible properties [1]–[3]. Graphene based material have great prospects in the field of nanoscience and nanotechnology due to its flexible nature and large interfacial area [4]. Its 2D structure epitomizes every carbon atom as a surface atom and provides increased electro-active surface area for the interaction of analyte, hence electron mobility in graphene becomes highly sensitive to adsorbed molecules. The gas sensing mechanism of graphene is generally attributed to the adsorption/desorption of gaseous molecules that act as donors/acceptors on the graphene surface which facilitate to change in electrical conductivity of graphene [5]. Furthermore, graphene oxide (GO) is another type of 2D carbon Manuscript received December 2, 2015; accepted January 21, 2016. Date of publication February 3, 2016; date of current version March 16, 2016. The work of S. Rani was supported by the Innovation in Science Pursuit for Inspired Research within the Department of Science and Technology, India. The associate editor coordinating the review of this paper and approving it for publication was Prof. Tony Huang. S. Rani and S. Sharma are with the Electronic Science Department, Kurukshetra University, Kurukshetra 136119, India (e-mail: [email protected]; [email protected]). M. Kumar with Electrical Engineering Department, College of Engineering at Prince Sattam Bin Abdulaziz University, Wadi Aldawasir 11991, Saudi Arabia (e-mail: [email protected]) R. Garg is with the Biomedical Engineering Department, Guru Jambheshwar University of Science and Technology, Hisar 125001, India (e-mail: [email protected]). D. Kumar is with the Electronic Science Department, Kurukshetra University, Kurukshetra 136119, India, and also with the YMCA University of Science and Technology, Faridabad 121001, India (e-mail: [email protected]). Digital Object Identifier 10.1109/JSEN.2016.2524204

based material, having different oxygen-containing functional groups (such as epoxy, hydroxyl and carboxyl groups) on the surface produced by oxidative exfoliation of graphite, which can be transformed to conductive material by exposing it to reducing agents such as hydrazine, sodium borohydrate [5]– [8], known as reduced graphene oxide (rGO). It is recently reported that the conductivity of GO/rGO based gas sensor can be changed by changing the interface charge layer where adsorption of reducing or oxidizing gases takes place [9]. GO has high affinity for a wide range of gases which when chemisorbed onto its surface results a change in the electronic structure of the GO as the adsorbed molecules act as electron donors or acceptors on GO surface. This phenomena enhances the change in the conductance of GO [10]. The rGO is adequate conductive to act as a channel material for electronic devices as it is sensitive to the surface adsorbents. Mass production of GO/rGO can be achieved using chemical approaches and can easily be processed in continuous sheets/films. The properties of rGO such as conductivity, tensile strength, sensitivity etc., can be tuned by altering reduction conditions and chemical modification by attaching various types of functional groups that makes GO/rGO as a potential versatile material for gas sensing, humidity sensing, biomolecule detection, as an antibacterial material and many other applications. Various chemical species and toxic gases are present in the nature possessing pungent and suffocating odors such as ammonia, hydrogen sulphide (H2 S), hydrogen chloride, and various hydroxyl acids that can be harmful to human society [11]. Among these chemical species, H2 S is one of the harmful gas as its concentration (∼250 ppm) can produce severe effects on the human nervous system and pulmonary edema, and can be fatal [10]. H2 S gas often result from effective reduction of sulphur from petroleum refineries and natural gas processing plants and have harmful effects on the environment as it causes acidification of rivers and lakes, damage to fish stocks and flora, destruction of trees, degradation of stone and metals in buildings and monuments etc. Reliable and efficient sensors having fast response/recovery time with high sensitivity are still desirable for detecting H2 S gas in industries as well as in natural sulphur reservoirs. Enlarged-surface area and facile-portable geometry of sensing material are also considered as most important factors in chemiresistive gas sensor design and applications. Commercial devices developed so far for H2 S monitoring, suffer from high operating temperature, power consumption and cost. On the other hand, the sensor based on functionalized GO/rGO

1558-1748 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

2930


operates at lower temperature and comparatively have low cost. Several materials have been investigated for the detection and sensing of toxic gases such as, conductive polymers [11], metal oxides [12]–[14] carbon nanotubes [15]. These materials have low sensitivity, complex processing and high cost of fabrication [12], [16]. Recently, there are also some studies on the application of GO/rGO as a gas sensing material operating at low temperature range (25-85°C) [14], [17], [18]. In spite of above discussed advantages, GO/rGO gas sensors required many improvements to be made for achieving higher sensitivity for the toxic gases in terms of change of its conductivity. Functionalization of GO is the consummate way to improve sensing performance because gas molecules are more strongly adsorbed on functionalized GO than on GO/rGO [10], [19]. Covalent attachments of functional groups on GO can change the electronic structure which provides increased electro-activity on the sensor surface for the gas molecule interaction [20], [21]. Zhou et al. [22] reported that sensor based on Cu2 O nanocrystals, grown on functionalized graphene sheets (Cu2 O-FGS), can be utilized to monitor H2 S gas at room temperature. Further, they observed that sensor based on functionalized GO/rGO have potential applications for monitoring air pollution at room temperature with low cost and power consumption. From this motivation, here the authors present the work of functionalization of GO by the condensation of amine group of heteroaryl amine with carboxyl and lactone groups of GO. Amide GO (AGO) was dispersed into water through ultrasonication and the sensor was obtained by preparing the sensing film through drop casting method on SiO2 /Si substrate between the aluminum electrodes. The prepared sample was examined via two probe method for the detection of H2 S gas and it was observed that AGO has significant better response/ recovery time.

to the mixture while continuing the stirring. Now, the container of the mixture was taken out from ice bath and again stirred to form thick paste at 40°C for 30 minutes. Subsequently, 80 ml of de-ionized (DI) water was added to the paste and blending was done using magnetic stirrer for 90 minutes at 90°C. After that, more water (200 ml) was added to stop the oxidation reaction and then, 6 ml of 30% H2 O2 was added to destroy the excess KMnO4 . The changes of color of the solution from dark brown to yellowish indicate the complete removal of KMnO4 . Subsequently, the solution was filtered and washed several times with DI water. The filtered paste was dissolved in 100 ml of DI water and solution was bath sonicated (having frequency 35kHz) by maintaining temperature below 20°C for 60 minutes to exfoliate the layers of GO followed by centrifugation at the rate of 4000 rpm for 20 minutes. Then, obtained GO powder was dried at room temperature. AGO was synthesized by dispersing GO (0.3 g) in 30 ml of DMF by ultrasonication for 60 minutes at room temperature. After that, NaOH (0.3 g) was added and solution was stirred for 60 minutes at room temperature. NaOH open the rings of lactone groups (–CO–O–) on the surface of GO and convert them into hydroxyl and carboxyl groups. Subsequently, 2–aminothiozole (0.3 g), HOBt (0.48 g) was added to reaction mixture followed by DCC (0.65 g) and stirred for 24 hours at room temperature. The resulting reaction of 2–aminothiozole amine with GO in the presence of DCC and HOBt leads to the amidation of the carboxyl groups to give AGO. Powder form of AGO was collected by centrifugation. The resulting suspension was repeatedly centrifuged after adding pure DMF to remove side products, followed by three times further centrifugation with water to remove DMF from AGO. The prepared AGO was dried at 60°C for 12 hours.

II. E XPERIMENTAL D ETAILS

The sensor was obtained by preparing the sensing film of GO/AGO by drop casting method on SiO2 /Si substrate (0.5 × 0.5 mm) between the aluminum electrodes separated by a distance of 0.1mm. To make the sensitive film, 1 mg of the GO/AGO was dispersed in 5 mL of DI water by ultrasonic vibration for 1 hour to achieve the homogenous suspension. The aluminum electrodes were developed on the substrate by thermal vacuum coating technique followed by annealing at 50°C to obtain good contact of GO/AGO film with electrodes [23]. The prepared sample was examined for the detection of H2 S gas via two probe method and it was observed that AGO has significant better response/recovery time.

A. Materials Graphite powder (purity 99.99%), sodium nitrate (NaNO3 ), sulphuric acid, Sodium hydroxide (NaOH), potassium permanganate (KMnO4 ), hydrogen peroxide (H2 O2 ) of AR grade were procured from Rankem RFCL Pvt. Ltd., India. 2-aminothiazole, hydroxybenzotriazole (HOBt), N,N’-dicyclohexylcarbodiimide (DCC), dimethylformamide (DMF) were purchased from Karl Fisher Co., Ltd., India. For the preparation of sensor, silicon substrate (Macwin, India, Pvt. Ltd.) was used and 70 nm thin insulating layer of silicon dioxide (SiO2 ) was grown on it by wet etching method and bulk aluminum was used for development of electrodes via thermal vacuum coating technique. B. Synthesis of GO and AGO Hydrophilic GO have been achieved by oxidation of graphite through chemical method. Graphite (2 g), NaNO3 (1 g) were mixed in concentrated sulphuric acid (46 ml) using magnetic stirrer under cool environment in ice bath maintaining the temperature between 10–15°C [21]. Afterwards, KMnO4 (6 g) was gradually added

C. Sensor Preparation

D. Experimental Setup Figure 1 shows the schematic of experimental setup utilized for H2 S gas sensing. The prepared sensors of GO and AGO were kept in the chamber one by one and the gas injected into the glass chamber by inlet using nitrogen as a carrier gas. The gas flow is linear and the sensor was initially exposed to H2 S gas and I-V characteristics were measured at regular interval of time using Keithley 2400 Series Source Measurement Unit via two probe method by stepping the

RANI et al.: AMIDE FUNCTIONALIZED GO THIN FILMS FOR HYDROGEN SULFIDE GAS SENSING APPLICATIONS

Fig. 1.

2931

Experimental setup for I-V characteristics of H2 S sensor.

voltage in the range of 0V to 5V. Later, the inlet of chamber was closed and the cover of the chamber was opened to expose the sensor to air. Again I-V characteristics were measured with time and change in conductivity was estimated.

Fig. 2.

FTIR spectra of GO and AGO.

E. Characterization The functional surface groups on GO and AGO were studied by Fourier Transform Infra Red (FTIR) spectra using Perkin Elmer model FTIR SPETRUM 65 system. Dried solid samples were mixed with KBr powder and were pelletized before performing the FTIR scan from wave number 4000 to 400 cm−1 . The morphological characterization of GO and AGO was carried out by Scanning Electron Microscopy (SEM) using JSM-6510LV Series Electron Microscope at accelerating voltage of 20kV. The percentage composition of the carbon, oxygen and nitrogen was analyzed by the Energy-Dispersive X-ray (EDX) spectroscopy using Oxford Instruments INCAx-act X-ray detector at accelerating voltage 20 kV and current 0.34 nA. Structural characterization of GO and AGO was carried out by X-ray diffraction (XRD) at ambient temperature using an X-ray diffractometer (XPERT-PRO diffractometer) equipped with a Giono-meter PW3050/60 working with Cu Kα radiation of wavelength 1.5406Å in the 2θ range from 5 to 80°. Structural defects had been analyzed by Raman spectroscopy using Renishaw InVia Raman spectrometer. I-V characteristics of GO and AGO were measured in ambient and H2 S environment using Keithley 2400 Series Source Measurement Unit via two probe method by stepping the voltage 0 to 5V. III. R ESULTS AND D ISCUSSION A. Sample Analysis Amidation of GO take place mainly through the reaction between –COOH group of GO and –NH2 group of the 2–aminothiozole functional molecule. Amidation is a two step process which comprises firstly to activate the carboxylic groups by using an activation agent followed by attachment of a leaving group (X) to acyl carbon (RCO–) of the acid which can further be replaced by amino group. This mechanism can be represented by the following reaction equation: RCOOH

Activation agent

RCOX Activation

R NH2

RCONHR

Aminolysis

Fig. 3. (a, b, c) SEM images of graphite, GO and AGO and (d, e) AFM image of GO and AGO, respectively.

The attachment of the functional groups was investigated by comparing the FTIR spectra of GO and AGO as shown in Figure 2. The most characteristic features in the FTIR spectrum of GO are the adsorption bands corresponding to the C = O carbonyl stretching at 1721 cm−1 , the stretching bands for C = C bonds at 1591 cm−1 , the O–H deformation vibration at 1392 cm−1 and the C–O stretching at 1051 cm−1 . The FTIR spectra of AGO reveals a new peak at about 1630 cm−1 corresponding to the amide carbonyl (C = O) stretch (amide I) and the peak at about 1578 cm−1 for amide II (C–N in-plane stretching and CHN deformation) [24] which demonstrate that amine has been grafted upon GO as amide bond. The SEM images in Figure 3 (a, b, c) represents the surface morphology of the synthesized samples of graphite, GO and AGO respectively. Figure 3a illustrates that natural graphite flakes is composed of thousand of graphene layers compactly stacked upon each other [25]. Strong oxidation of graphite converts it into graphite oxide from which GO was exfoliated by ultrasonication. Figure 3b shows the SEM image of GO which depicts that GO have relatively lesser number of layers and larger surface about the size of micrometer. This observation depicts very good exfoliation of graphite during oxidation process [26]. Figure 3c shows the fluffy and discontinuous edges of the flakes after

2932


Fig. 4.

Raman spectra of (a) GO and (b) AGO.

Fig. 6. EDX images of (a) GO and (b) AGO showing the presence of carbon, oxygen and nitrogen peaks measured from EDX spectroscopy.

Fig. 7. Variation in current of GO (a) in H2 S gas environment (b) on removal of H2 S gas environment.

Fig. 5.

XRD patterns of graphite, GO and AGO.

functionalization which evidence that amide functional groups have been attached onto GO. AFM images in Figure 3 (d, e) confirm that most of GO and AGO films are thin having average roughness of 1 to 2 nm and thickness of about 15nm. Raman spectroscopy is widely used technique to characterize crystal structure, disorder and defects in graphene-based materials [27]. Figure 4 (a, b) shows the Raman spectra of GO and AGO respectively. The D peaks of GO and AGO located at 1341 cm−1 reflects a defect-induced breathing mode of sp2 rings which arise due to stretching of C-C bond. The G peak at 1587 cm−1 for GO and at 1595 cm−1 for AGO represents the first order scattering of the E2g phonon of sp2 carbon atoms. The relative intensity ratio of both peaks (D/G) is a measure of defects and disorder degree, and is inversely proportional to average size of the sp2 clusters [27], [28]. Figure 4, the D/G intensity ratio for AGO (1.04) is larger than GO (0.93) that indicates AGO has more defective and disordered sites which act as active sites for the adsorption of foreign molecules. Effects of amidation on the interlayer distance of GO is analyzed using XRD spectra depicted in Figure 5. It has been observed that the graphite has characteristic diffraction peak at 2θ = 26.3° and GO has characteristic diffraction peak 2θ = 11.42°. The XRD of AGO shows the characteristics peak at 2θ = 10.48°, 17.08°, 20.1° and 21.69° which are correspond to presence of amide groups. The interlayer spacing of graphite, GO and AGO was found 0.34 nm,

0.77 nm and 0.84 nm respectively. The large value of interlayer spacing implies more attachment of functional groups on the surface of basal plane of graphite based materials. EDX images of GO and AGO, as shown in Figure 6 (a, b), reveal the presence of nitrogen only in the sample of AGO originating from the attachment of amide functional group. The relative atomic concentration (%) of carbon and oxygen in GO is found as 61.3% and 38.8%. In AGO, relative atomic concentration (%) of carbon, oxygen and nitrogen is found as 73.2%, 22.7% and 4.1%. It is observed that relative atomic concentration of carbon increases and oxygen decreases in AGO than GO due to presence of nitrogen in AGO by the consequence of attachment of amide group. B. Gas Sensing Application To investigate the gas sensing properties of the prepared sensor (GO/AGO), sensor was placed into the chamber to equilibrate by dry air for 30 minutes prior to introduction of H2 S gas into the chamber. I-V characteristics were measured with the passage of time in the environment of H2 S gas and subsequently in ambient environment. The Figure 7 (a, b) represents the I-V characteristics of GO on the exposure of H2 S gas and ambient environment which predict that conductivity of GO decreases with exposure of H2 S gas and recovered in ambient environment with the passage of time. On contrary, the I-V characteristics in Figure 8 (a, b) depict that the conductivity of AGO increases with the passage of time in H2 S gas environment and recovers back on the removal of H2 S gas with time. It is evident from the I-V characteristics that variation in conductivity is more for AGO in comparison to GO with the exposure of H2 S gas. The plausible mechanism of this observation may be described on the basis of bond theory. A reducing gas (H2 S) depletes the charge carrying sensing layer of GO by transfer of electrons causing

RANI et al.: AMIDE FUNCTIONALIZED GO THIN FILMS FOR HYDROGEN SULFIDE GAS SENSING APPLICATIONS

2933

its film between aluminum electrodes on SiO2 /Si substrate. The H2 S gas sensing performance of the AGO sensing device has been investigated and compared with that of sensor based on GO. The experimental results show that AGO exhibits significantly better reversible sensing response to H2 S gas in comparison to GO in terms of change in conductivity. The AGO has faster response/recovery time than GO. Hence, AGO is a potential candidate for futuristic gas sensing applications due to its high sensitivity and reusability. Fig. 8. Variation in current of AGO (a) in H2 S gas environment (b) on removal of H2 S gas environment.

Fig. 9.

Response/recovery time graphs of (a) GO (b) AGO.

decrease of hole carrier density which leads to decrease in conductivity. Thus electrical resistance of the GO sensors specifically increases upon exposure of H2 S due to the adsorption of gas molecules. The adsorption of electron-donating (H2 S) gas reduces the number of holes, so the Fermi level is shifted to valence band and increase in electrical resistance is observed. These results support the p-type semiconducting behavior of the GO [10]. Amide functionalization of GO alters the carrier concentration to negative since amine group (–NH2 ) donates electron on the GO surface. Thereby, AGO behaves as n-type semiconductor. AGO when brought in contact with reducing H2 S gas, the n-type AGO exhibit increase in conductivity occurs as shown in Figure 8 (a) due to enhancement of the charge density in AGO by the presence of amine groups on the surface. Reverse process takes place on exposure to air and conductivity decreases as shown in Figure 8 (b). It can be seen from the I-V characteristics in Figure 7 and Figure 8 that AGO sensor exhibit better response to H2 S than GO. The sensor response is derived by ratio of the resistance of sensor in ambient air (Rair ) with the resistance in H2 S gas (Rgas ) environment. Figure 9 (a, b) illustrate that both GO and AGO sensors recovered their initial state with small drift when placed in ambient environment after the exposure to H2 S gas. It is also observed that AGO has fast response and recovery time for sensing of H2 S gas which infers that AGO has better sensitivity as gas sensing material than GO and hence, it is a potential candidate for futuristic gas sensing applications. IV. C ONCLUSION Amide functionalized GO was successfully synthesized through chemical method using 2-aminothiozole at room temperature and was used to develop gas sensor by depositing

R EFERENCES [1] P. Yao et al., “Electric current induced reduction of graphene oxide and its application as gap electrodes in organic photoswitching devices,” Adv. Mater., vol. 22, no. 44, pp. 5008–5012, Nov. 2010. [Online]. Available: http://onlinelibrary.wiley.com/doi/10.1002/adma.201002312/abstract [2] Y. Yao, X. Chen, J. Zhu, B. Zeng, Z. Wu, and X. Li, “The effect of ambient humidity on the electrical properties of graphene oxide films,” Nanosc. Res. Lett., vol. 7, p. 363, Jul. 2012. [Online]. Available: http://www.nanoscalereslett.com/content/7/1/363 [3] H. Yang et al., “Covalent functionalization of chemically converted graphene sheets via silane and its reinforcement,” J. Mater. Chem., vol. 19, no. 26, pp. 4632–4638, May 2009. [Online]. Available: http://pubs.rsc.org/en/Content/ArticleLanding/2009/JM/ B901421G#!divAbstract [4] U. K. Sur, “Graphene: A rising star on the horizon of materials science,” Int. J. Electrochem., vol. 2012, p. 12, Aug. 2012. [Online]. Available: http://www.hindawi.com/journals/ijelc/2012/237689 [5] G. Lu, L. E. Ocola, and J. Chen, “Gas detection using lowtemperature reduced graphene oxide sheets,” Appl. Phys. Lett., vol. 94, no. 8, pp. 083111-1–083111-3, Feb. 2009. [Online]. Available: http://www4.uwm.edu/nsee/publications/upload/26.pdf [6] S. Borini et al., “Ultrafast graphene oxide humidity sensors,” ACS Nano, vol. 7, no. 12, pp. 11166–11173, Nov. 2013. [Online]. Available: http://pubs.acs.org/doi/abs/10.1021/nn404889b [7] A. Lipatov, A. Varezhnikov, P. Wilson, V. Sysoev, A. Kolmakov, and A. Sinitskii, “Highly selective gas sensor arrays based on thermally reduced graphene oxide,” Nanoscale, vol. 5, no. 12, pp. 5426–5434, Jun. 2013. [Online]. Available: http://www.ncbi. nlm.nih.gov/pubmed/23661278 [8] C. Piloto et al., “Highly NO2 sensitive caesium doped graphene oxide conductometric sensors,” Beilstein J. Nanotechnol., vol. 5, pp. 1073–1081, Jul. 2014. [9] Y. Zhou, Y. Jiang, T. Xie, H. Tai, and G. Xie, “A novel sensing mechanism for resistive gas sensors based on layered reduced graphene oxide thin films at room temperature,” Sens. Actuators B, Chem., vol. 203, pp. 135–142, Nov. 2014. [10] M. M. Alaie, M. Jahangiri, A. M. Rashidi, A. H. Asl, and N. Izadi, “A novel selective H2 S sensor using dodecylamine and ethylenediamine functionalized graphene oxide,” J. Ind. Eng. Chem., vol. 29, pp. 97–103, Sep. 2015. [Online]. Available: http://www. sciencedirect.com/science/article/pii/S1226086X15000970 [11] R. Garg, V. Kumar, D. Kumar, and S. K. Chakarvarti, “Polypyrrole microwires as toxic gas sensors for ammonia and hydrogen sulphide,” J. Sensors Instrum., vol. 3, no. 1, pp. 1–13, Jan. 2015. [Online]. Available: http://www.researchgate.net/profile/Ravish_Garg2/ publication/271135767/links/54dab3a90cf233119bc3b37c.pdf [12] X.-J. Huang and Y.-K. Choi, “Chemical sensors based on nanostructured materials,” Sens. Actuators B, Chem., vol. 122, no. 2, pp. 659–671, Mar. 2007. [Online]. Available: http://www. sciencedirect.com/science/article/pii/S0925400506004503 [13] F.-L. Meng et al., “Parts per billion-level detection of benzene using SnO2 /graphene nanocomposite composed of sub-6 nm SnO2 nanoparticles,” Anal. Chim. Acta, vol. 736, pp. 100–107, Jul. 2012. [14] F.-L. Meng, Z. Guo, and X.-J. Huang, “Graphene-based hybrids for chemiresistive gas sensors,” TrAC Trends Anal. Chem., vol. 68, pp. 37–47, May 2015. [15] M. Asad, M. H. Sheikhi, M. Pourfath, and M. Moradi, “High sensitive and selective flexible H2 S gas sensors based on Cu nanoparticle decorated SWCNTs,” Sens. Actuators B, Chem., vol. 210, pp. 1–8, Apr. 2015. [16] S. Capone et al., “Solid state gas sensors: State of the art and future activities,” J. Optoelectron. Adv. Mater., vol. 5, no. 5, pp. 1335–1348. [Online]. Available: http://joam.inoe.ro/arhiva/pdf5_5/Capone.pdf

2934

[17] S. Basu and P. Bhattacharyya, “Recent developments on graphene and graphene oxide based solid state gas sensors,” Sens. Actuators B, Chem., vol. 173, pp. 1–21, Oct. 2012. [Online]. Available: http://www. sciencedirect.com/science/article/pii/S092540051200785X [18] Y. Wang et al., “Ammonia gas sensors based on chemically reduced graphene oxide sheets self-assembled on Au electrodes,” Nanosc. Res. Lett., vol. 9, p. 251, May 2014. [Online]. Available: http://www.nanoscalereslett.com/content/9/1/251 [19] S. Yoo, X. Li, Y. Wu, W. Liu, X. Wang, and W. Yi, “Ammonia gas detection by tannic acid functionalized and reduced graphene oxide at room temperature,” J. Nanomater., vol. 2014, p. 6, Mar. 2014. [Online]. Available: http://www.hindawi.com/journals/jnm/2014/497384/ [20] N. Hua et al., “Gas sensor based on p-phenylenediamine reduced graphene oxide,” Sens. Actuators B, Chem., vol. 163, no. 1, pp. 107–114, Mar. 2012. [Online]. Available: http://www.sciencedirect.com/science/ article/pii/S0925400512000391 [21] S. Rani, M. Kumar, S. Sharma, D. Kumar, and G. Singh, “Characterization and dispersibility of improved thermally stable amide functionalized graphene oxide,” Mater. Res. Bull., vol. 60, pp. 143–149, Dec. 2014. [Online]. Available: http://www.sciencedirect.com/science/ article/pii/S0025540814003845 [22] L. Zhou, F. Shen, X. Tian, D. Wang, T. Zhang, and W. Chen, “Stable Cu2 O nanocrystals grown on functionalized graphene sheets and room temperature H2 S gas sensing with ultrahigh sensitivity,” Nanoscale, vol. 5, pp. 1564–1569, Dec. 2013. [23] F. Y. Ban, S. R. Majid, N. M. Huang, and H. N. Lim, “Graphene oxide and its electrochemical performance,” Int. J. Electrochem. Sci., vol. 7, pp. 4345–4351, May 2012. [24] H. Gunzler and H. U. Gremlich. (2002). IR spectroscopy. Wiley-VSH, Weinheim, Germany, pp. 223–227. [Online]. Available: http://onlinelibrary.wiley.com/store/10.1111/j.1471 [25] M. M. Gudarzi and F. Sharif, “Enhancement of dispersion and bonding of graphene-polymer through wet transfer of functionalized graphene oxide,” Exp. Polym. Lett., vol. 6, no. 12, pp. 1017–1031, May 2012. [Online]. Available: http://www.expresspolymlett.com/letolt.php? [26] G. Sobon et al., “Graphene oxide vs. reduced graphene oxide as saturable absorbers for Er-doped passively mode-locked fiber laser,” Opt. Exp., vol. 20, no. 17, pp. 19463–19473, 2012. [Online]. Available: http://www.osapublishing.org/oe/abstract.cfm?uri=oe-20-17-19463 [27] J. Shen et al., “Fast and facile preparation of graphene oxide and reduced graphene oxide nanoplatelets,” Chem. Mater., vol. 21, no. 15, pp. 3514–3520, Jul. 2009. [Online]. Available: http://pubs.acs.org/doi/abs/10.1021/cm901247t [28] S. Stankovich et al., “Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide,” Carbon, vol. 45, no. 7, pp. 1558–1565, Jun. 2007. [Online]. Available: http://bimat-org.cf1-princetonol-com.vps.ezhostingserver.com/assets/ pdf/nu_07_45stankovich.pdf

Sumita Rani received the M.Sc. degree in physics from the Physics Department, Kurukshetra University, Kurukshetra, India, in 2006, the M.Tech. degree in nanotechnology from the National Institute of Technology Kurukshetra (NIT Kurukshetra), in 2008, and the Ph.D. degree from the Electronic Science Department, Kurukshetra University, Kurukshetra, in 2015. She was an Assistant Professor with Banasthali University, Jaipur, from 2008 to 2010, and then joined the Electronic Science Department, Kurukshetra University. She carried out work on carbon nanotubes at NIT Kurukshetra. She received the Gold Medal in M.Tech. Nanotechnology from NIT Kurukshetra. She has authored eight research papers in different journals and attended national and international conferences. Her current research interests include the functionalization of graphene and applications of graphene-based composites in sensor, photocatalysis, and advance oxidation process. She was awarded the Inspire Fellowship in 2011 from the Department of Science and Technology, India, in 2011.


Mukesh Kumar received the Ph.D. degree from Kurukshetra University, India, while working on the development of diffusion barrier layers for copper metallization in silicon-based integrated circuits. He was a Visiting Researcher with Sultan Qaboos Univesity, Oman, and involved in deputation at Prince Sattam Bin Abdulaziz Univesity, Saudi Arabia. He is currently an Assistant Professor with the Electronic Science Department, Kurukshetra University, India. He has been involved in the developing semiconductor materials for electronic applications since last 15 years. He received the TRIL Fellowship by ICTP-Trieste in 2002, for doing postdoctorate in Italy. He spent almost one and half years there while working on the characterization of GaAs-based heterostructures at low temperature. Dr. Kumar has authored about 60 research papers in various journals with high impact factor. His current research interests include development of materials for photocatalytic activities and sensing applications.

Ravish Garg received the M.S. degrees in electronics from DAVV, Indore, India, in 1994, the M.Tech. degree in instrumentation from NIT Kurukshetra, India, in 1999, and the D.Phil. degree in electronic science from Kurukshetra University, Kurukshetra, in 2015. He is currently a Chairperson and an Associate Professor with the Department of Biomedical Engineering, Guru Jambheshwar University of Science and Technology, Hisar. He is teaching and guiding students in the field of electronics, instrumentation, and biomedical engineering for more than 18 years. He has authored over 20 research papers in journals and conferences and attended more than 30 workshops, training courses, and staff development program to keep him abreast with the advances in his profession. His present interest area of research is medical electronics and instrumentation and biomedical applications of synthetic membranes. He is a Life Member and Executive Council Member (for the period 2015 to 2017) of the Nuclear Track Society of India. Sumit Sharma received the master’s degree from the Electronic Science Department in 2007, and the Ph.D. degree from the Electronic Science Department in 2013, and carrying out work on SAM and diffusion barrier. He is currently a Research Scholar with the Electronic Science Department, Kurukshetra University, Kurukshetra, India. Following his master’s degree, he moved to the laboratory of the Electronic Science Department and worked as a Project Assistant for three years. He is currently interested in SAM, Langmuir–Blodgett films, diffusion barrier, and graphene sensor. He has six publications and attended national and international conferences/workshops. Dinesh Kumar received the M.Phil. degree in microelectronics engineering in 1991 and the Ph.D. degree from Cambridge University, U.K., under the supervision of Prof. A. M. Campbell at the Department of Engineering. He was a Vice Chancellor of YMCA Faridabad, India. He traveled to INFM-TASC, Trieste, Italy, in 1998, and worked there as a Post-Doctoral Research Associate with Prof. A. Franciosi on MBE grown Schottky barrier tuned devices. He again joined Cambridge University in Prof. M. Blamire’s Group. During his stay at Cambridge University, he worked on Cr-doped AlN thin films and was a Bye Fellow of Selwyn College, Cambridge. He is currently a Professor with Kurukshetra University. In 2003, he received the Commonwealth Fellowship by the Association of Common Wealth Universities, London. He joined the Electronic Science Department, Kurukshetra University, in 1987, where he worked as the Coordinator of the National Program for developing MEMS and microsystems. He also received a Nanomission Project by DST worth Rs. 2.96 Crore to support M.Tech. degree in the nanoscience and technology program at the Electronic Science Department. He was the Director at UIET, Kurukshetra University, India, from 2010 to 2015.