Graphene oxide reduction using green chemistry

Graphene oxide reduction using green chemistry

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Materials Today: Proceedings xxx (xxxx) xxx

Contents lists available at ScienceDirect

Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr

Graphene oxide reduction using green chemistry Sonal Rattan a,b,⇑, Suresh Kumar b, J.K. Goswamy b a b

Centre for Nanoscience and Nanotechnology, Panjab University, Chandigarh, India Department of Applied Sciences, UIET, Panjab University, Chandigarh, India

a r t i c l e

i n f o

Article history: Received 5 August 2019 Received in revised form 19 September 2019 Accepted 28 September 2019 Available online xxxx Keywords: Nanomaterial Hummer’s Graphene Diffraction Spectroscopy

a b s t r a c t Graphene, a very attractive two-dimensional single atom thick carbon nanomaterial with excellent mechanical flexibility, superior electrical conductivity, high thermal and chemical stability has attracted scientific researchers from all across the world. Synthesis of graphene can be done by epitaxial growth, exfoliating graphite mechanically, chemical vapour deposition, and by reducing graphene oxide (GO). Here we report Graphene Oxide’s synthesis using Improved Hummer’s method by overcoming the flaws of Hummer’s method. A crucial step in synthesizing and exercising GO is the reduction, which helps in restoring its structure and attributes. Popular method of GO reduction is by treatment with hydrazine hydrate which is not environment friendly. Hence we report a green method to reduce GO using fresh ginger and garlic extracts. Different reduction procedures give rise to different attributes of reduced GO (rGO), ultimately affecting the outcome of the devices or materials constituting rGO. The prepared reduced GO is characterized by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and UV–Visible Spectroscopy. The results confirmed that GO was reduced by using green chemistry. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on functional materials and simulation techniques.

1. Introduction Graphene is a unique atom thick sheet of two dimensional (2D) sp2 hybridized carbon atoms that is steady at room temperature conditions; it has exceptional electrical properties like atypical quantum Hall effect [1] and superior carrier mobility at comparatively higher charge carrier concentrations and ambient temperature [2,3]. As a novel nanomaterial, graphene has been immensely analysed for the electronic applications [4], sensors [5], catalysis [6] and conserving and storing of energy [7,8] etc., since many interesting properties like thermal [9], mechanical [10]and electrical [11] have been published confirming graphene’s superiority to conventional materials [12]. For these reasons, huge level manufacturing of graphene materials at reasonable price is an essential obligation. The structure of Graphite oxide has oxygenated groups which densely decorates carbon’s atomic plane, increasing the interlayer distance as well as making the layers hydrophilic. As a result, soft ultrasonication can exfoliate these oxidized layers in

⇑ Corresponding author at: Department of Applied Sciences, UIET, Panjab University, Chandigarh, India. E-mail address: [email protected] (S. Rattan).

water. These one/few layers of carbon atom sheets just like graphene, are called as graphene oxide. Graphene possesses a unique property of tailoring different functional groups on its surface based upon the precursors and methodology used for its synthesis [13]. Till now, Graphene can be synthesized by a few approaches that mainly divide into two broad categories: the ‘‘top-down” approach involving cutting down from different carbon source, and ‘‘bottom-up” approach involving synthesis from different organic molecules or polymers as well as surface functionality or passivation. Bottom-up approaches including transforming C60 molecules, microwave, combustion, pyrolysis in concentrated acid are more favourable as compared to Topdown approaches including hydrothermal cutting, solvothermal cutting, nanotomy-assisted exfoliation, electrochemical cutting, nanolithography and ultrasonic shearing, since different physical attributes and electrical properties of Graphene can be tuned by using different carbon source and carbonization conditions in bottom-up routes [14–17].The most extensively used approach for synthesising Graphene Oxide (GO) was given by Hummers and Offeman in 1958 (Hummers method) [18], because of its satisfying reaction safety and high efficiency. However, the method still contains the following drawbacks: (1) the oxidation process

https://doi.org/10.1016/j.matpr.2019.09.168 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on functional materials and simulation techniques.

Please cite this article as: S. Rattan, S. Kumar and J. K. Goswamy, Graphene oxide reduction using green chemistry, Materials Today: Proceedings, https:// doi.org/10.1016/j.matpr.2019.09.168

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Fig. 1. (i) Synthesis of reduced graphene Oxide (ii) aqueous dispersion of (a) GO (b) rGO(1) (c) rGO(2).

Fig. 2. XRD pattern for GO, rGO(1) and rGO(2). Fig. 3. Raman spectra for GO, rGO(1) and rGO(2).

liberates hazardous gases such as NO2 and N2O4; (2) it is difficult to remove the Na+ and NO3 ions from the residual water obtained after the process. Hummers methodology was improved by Tour and his co-fellows by raising the concentration of KMnO4, excluding NaNO3 and carrying out the reaction in a 9:1 vol ratio of H2SO4/ H3PO4 [19]. This change in the precursors as of introducing H3PO4 and using double the amount of KMnO4 and almost 5 times the amount of H2SO4 used in the Hummers method, increased the yield and reduced the liberation of harmful gases. GO getting easily converted to graphene by detaching the oxygenated groups, is an interesting aspect. Some synonyms for rGO are chemically modified graphene, functionalized graphene or reduced graphene [20]. GO and rGO are subjects of intensive study for various implementations. Different reduction processes lead to variable attributes further affecting the final performance of the rGO based materials/devices. Graphene oxide sheets have been chemically reduced using various reducing agents including hydrazine [21–24], sodium borohydrate [25,26], hydroquinone [27] and strongly alkaline solutions [28]. Thermal reduction is another way of reducing graphene oxide which utilizes the heat treatment to get rid of the oxide functional groups from the surface of graphene oxide [29,30]. Popular method

of GO reduction is by treatment with hydrazine hydrate which is not environment friendly. There are risks to one’s health as well as surroundings when dealing with toxic chemicals. Using plants or their extracts have been investigated by several researchers for synthesising nanoparticles since they offer many advantages some of them being easily available and safe to handle. Also nanoparticles synthesised by using plant extracts are relatively more stable in nature [31]. Hence, treatment with eco friendly materials is the need of the hour; therefore, we used a green and economic method using natural reducing agents for reducing Graphene Oxide. 2. Experimental 2.1. Preparing graphene oxide (GO) Natural graphite powder was used to prepare GO by following the Hummers method with a slight alteration of eliminating NaNO3 from the precursors [18]. To Start with, graphite powder (2.0 g) was mixed with concentrated H2SO4 (83 mL) and H3PO4

Please cite this article as: S. Rattan, S. Kumar and J. K. Goswamy, Graphene oxide reduction using green chemistry, Materials Today: Proceedings, https:// doi.org/10.1016/j.matpr.2019.09.168

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Fig. 4. (a) FTIR spectra of GO (b) GO reduced with Ginger extract rGO(1) (c) GO reduced with Garlic extract rGO(2).

Fig. 5. HRTEM image of the reduced graphene oxides (a) rGO(1) and (b) rGO(2).

unexfoliated graphite content. Lastly it was dried at room temperature and stored for future purposes. 2.2. Ginger extract 20 g of ginger was peeled off and washed with distilled water, then sonicated in 100 mL of DI for half an hour. Filtration was done and pure ginger extract was obtained. 2.3. Garlic extract 10 g of garlic was peeled off, washed with DI and then sonicated in 50 mL of DI for an hour. After that filtration was done and fresh garlic extract was obtained. 2.4. Reduction of GO

Fig. 6. UV–Visible spectra for GO, rGO(1) and rGO(2).

(17 mL) while stirring. Next, gradual addition of KMnO4 (9.0 g) to sustain suspension temperature below 20 °C was done. 150 mL of Distilled water (DI) was then added to the solution while stirring for 15 min at 95 °C. It was further diluted with 500 mL of DI and then 15 mL H2O2 was slowly added, changing the appearance of the solution from dark brown to yellow. Filtration and washing of the mixture was done with HCl aqueous solution for removing metal ions. The resulting solution was diluted to 1000 mL, making an aqueous dispersion of graphite oxide. The resultant dispersion was then sonicated for 30 min exfoliating it to GO. Afterwards centrifugation was performed at 9000 rpm to eliminate the

2.4.1. Reduction using ginger extract rGO(1) 10 mL of ginger extract was poured in 90 mL of GO solution and sonicated for half an hour. The solution was then kept at 90 °C for continuous stirring at 950 rpm. 2.4.2. Reduction using garlic extract rGO(2) 10 mL of garlic extract was poured in 90 mL of GO solution and sonicated for half an hour. The solution was then kept at 90 °C for continuous stirring at 950 rpm. Both the processes gave reduced graphene oxide as shown in Fig. 1(i). Physical observation is the simplest way to predict graphene oxide’s reduction. GO on being reduced changes it color to black from the original yellow–brown suspension as can be seen from Fig. 1(ii). This possibly happens due to an increasing hydrophobic-

Please cite this article as: S. Rattan, S. Kumar and J. K. Goswamy, Graphene oxide reduction using green chemistry, Materials Today: Proceedings, https:// doi.org/10.1016/j.matpr.2019.09.168

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Fig. 7. I-V characteristics of GO, rGO(1) and rGO(2).

ity of the sample resulting from a decrease in the polar groups on the surface of the sheets [32]. 3. Characterisation X-ray diffraction (XRD) of the powder was performed using a Bruker D8 Advance X-ray diffractometer using Cu Ka with k = 0.154 nm. Fourier transform infrared spectroscopy (FTIR) ranging from 400 to 4000 cm 1 was studied using a Shimadzu IR affinity1S spectrometer. The TEM images were captured using FEI Tecnai G2 20 Twin transmission electron microscope. The UV–visible spectrum (200–800 nm) was observed with a Shimadzu UV2600 spectrometer. Distilled water served the purpose for background signal. Raman Spectroscopy was done by alpha-300 Raman confocal microscope at a laser wavelength of 532 nm. I-V calculations were done using keithley source meter 2461 within a voltage range of 5V to +5 V. 4. Results and discussion GO was prepared by Hummers method without using NaNO3 and later on purified by filtration and centrifugation. The X-ray Diffractometry (XRD) of dried GO gives a (0 0 1) reflection peak at 2h 10.4° confirming a d-space of 0.83 nm. This peak vanishes in the XRD pattern for reduced GO whereas rGO, on the other hand, exhibits a new broad peak at 2h = 28° approximately as shown in Fig. 2.

Raman spectral studies also show that Graphene Oxide formed by this method is in fair harmony with the reports present. The Raman spectrum of GO, in Fig. 3, shows a D-band at 1352 cm 1 and a G-band at 1600 cm 1. Here, the D-band is related to the defects present in the structure or partially disordered graphitic domains and the G-band occurs due to the existence of graphitic carbons [33]. The Raman spectrum of rGO shows a D-band at 1350 cm 1 and a G-band at 1590 cm 1. The D-band for rGO in spectrum is strong, verifying the lattice distortions of graphene basal planes. The intensity ratio of D to G bands indicates the quality of graphitization. Id/Ig ratio decreased from 0.996 for GO to 0.989 for rGO (1) and 0.891 for rGO (2) due to the repair of defects by recovery of the aromatic structure of graphite lattice [34]. Furthermore, the FTIR spectrum of GO in Fig. 4(a) shows the below mentioned characteristic functional groups of GO [35]:1740 cm 1 [email protected] (carbonyl/carboxy); 1400 cm 1 CAO (carboxy); 1216 cm 1 CAO (epoxy). Peaks occurring because of the oxygenated groups are absent in rGO(1) and rGO(2). Peak around 1618 cm-1corresponds to [email protected] The OAH stretching vibrations occurring in-between the 3600 and 3300 cm 1 range are due to the presence of the hydroxyl and carboxyl groups of GO as well as some water left in between the GO sheets. These oxygenated functional groups having a strong affinity for water provide GO sheets with a uniform dispersability in aqueous medium [36]. These can be seen from Fig. 4(b), (c). Fig. 5(a) and (b) is a representative HRTEM images of the reduced graphene oxides rGO(1) and rGO(2) which display clear

Please cite this article as: S. Rattan, S. Kumar and J. K. Goswamy, Graphene oxide reduction using green chemistry, Materials Today: Proceedings, https:// doi.org/10.1016/j.matpr.2019.09.168

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and wrinkled surfaces. From the SAED pattern shown in the inset of Fig. 5(a) small spots making up a ring can be seen indicating the polynanocrystallinity of rGO(1) and of Fig. 5(b) multiple dots in a hexagonal pattern confirm the crystallinity of reduced graphene oxide rGO(2). This could be caused by back-folding of edges, intrinsic rotational stacking faults, or overlapping domains of graphene layers [37]. Fig. 6 shows the UV–visible spectrum of GO as well as rGO dispersed in Distilled water. It displays absorption peaks at 232 nm and 300 nm, occurring because of g–g* transition of [email protected] bonds and n–g* transition of [email protected] bonds, respectively. This spectrum resembles the UV–Visible spectrum of Graphene Oxide synthesized by the conventional Hummers method and are also identical to the spectrum of GO samples recorded in literature [19]. A red shift was observed in the absorption spectra of reduced GO to 260 nm. This characteristic helps in confirming the reduction of GO. Fig. 7 shows the Current-Voltage (I-V) response of GO, rGO(1) and rGO(2). Graphene Oxide is non conducting by nature but it starts conducting after getting reduced. Conductivity progressively increases as oxygen is removed. From the graph it can be calculated that the resistance in case of GO comes out to be in the range of MO whereas in case of rGO(1) and rGO(2) resistance is in the range of KO. The possible rise in conductivity occurs most likely because of higher concentration of sp2 clusters, paving way for enhanced electrical transportation via percolation. 5. Conclusion Here we have prepared GO products by modifying the conventional Hummers method and its properties are nearly the same as already available in literature. Next, we have reduced GO using ginger and garlic extracts which are environment friendly and as such there is no potential hazard to human health as well as environment. This can be an interesting route for producing a substantial amount of graphene. The method used is very economic as well as completely safe making it significant. Further research in this area should concentrate on controlling graphite’s oxidation and deeper understanding of the reduction mechanism. It is necessary since a controlled functionalization altering the attributes of graphene to accomplish certain conditions is equally crucial for obtaining a non-defective graphene. Acknowledgements This research work is supported by Technical Education Quality Improvement Project III, India (TEQIP III) of MHRD, Government of India assisted by World Bank under grant number P154523 and sanctioned to UIET, Panjab University, Chandigarh (India). The authors would also like to acknowledge Director UIET and Chairperson, Centre for Nanoscience and Nanotechnology, for providing necessary facilities.

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Please cite this article as: S. Rattan, S. Kumar and J. K. Goswamy, Graphene oxide reduction using green chemistry, Materials Today: Proceedings, https:// doi.org/10.1016/j.matpr.2019.09.168