Green reduction of graphene oxide using Indian gooseberry (amla) extract for gas sensing applications

Journal Pre-proof Green reduction of graphene oxide using Indian gooseberry (Amla) extract for gas sensing applications Fiona Crystal Mascarenhas, Nagaraju Sykam, M. Selvakumar, Mahesha M G

PII:

S2213-3437(20)30060-9

DOI:

https://doi.org/10.1016/j.jece.2020.103712

Reference:

JECE 103712

To appear in:

Journal of Environmental Chemical Engineering

Received Date:

2 January 2020

Revised Date:

16 January 2020

Accepted Date:

20 January 2020

Please cite this article as: Mascarenhas FC, Sykam N, Selvakumar M, Mahesha MG, Green reduction of graphene oxide using Indian gooseberry (Amla) extract for gas sensing applications, Journal of Environmental Chemical Engineering (2020), doi: https://doi.org/10.1016/j.jece.2020.103712

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Green reduction of graphene oxide using Indian gooseberry (Amla) extract for gas sensing applications Fiona Crystal Mascarenhas1, Nagaraju Sykam2, M. Selvakumar3 and Mahesha M G1* 1

Department of Physics, Manipal Institute of Technology, Manipal Academy of Higher Education 576104,

India 2

Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India

3

Department of Chemistry, Manipal Institute of Technology, Manipal Academy of Higher Education,

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Manipal, 576104, Karnataka, India *

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Corresponding Author. Tel: +91 820 2925624; Fax: +91 820 2571071; Email: [email protected]

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Graphical abstract

Highlights

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Synthesized rGO using Indian gooseberry (Amla) extract as green reducing agent.

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XPS, Raman, FTIR and UV-Vis spectroscopy have confirmed the reduction of GO to rGO.

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Demonstrated application of rGO in ammonia gas detection using chemiresistor.

Abstract

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Graphene preparation from reduction of graphene oxide (GO) which is known as reduced graphene oxide (rGO) is considered as one of the promising methods for the development of graphene-based

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devices on a large scale at low-cost. In the present work, rGO has been successfully prepared using Indian gooseberry (Amla) extract, a green reducing agent, and its sensitivity for ammonia gas

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molecules has been studied using chemiresistor configuration. About 5% sensitivity was observed for 3 ppm concentration of ammonia gas. Raman and X-ray photoelectron spectroscopy (XPS)

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spectra have confirmed the formation of rGO. Fourier transform infrared spectroscopy (FTIR), ultraviolet visible (UV-Vis) spectroscopy and electron microscopy have been adopted for evaluating the quality of synthesized rGO. In addition, the green synthesized rGO has been

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evaluated for the device suitability by comparing its quality and performance with rGO synthesized using chemical reducing agent (hydrazine hydrate).

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Keywords: rGO; Green reducing agent; Chemical sensor; Raman spectroscopy; XPS

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1. Introduction

In recent years, various toxic gases brought about by fast industrialization causing natural unevenness and an unnatural weather change. Toxic gases such as carbon monoxide, ammonia, nitrogen dioxide etc. have to be detected since they have an adverse effect on our ecosystem [1]. Hence developing a simple and reliable sensor is necessary. A gas sensor could detect the harmful gas present in the area of inspection. Because of its substantial surface– to– volume ratio,

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controllable structure, and effectively modified chemical and physical properties, nanomaterials are considered to be promising gas detectors, which result in high affectability, quick unique procedure, and high specificity [2]. Graphene, a 2D crystal, can be used as a catalyst [3] gas sensor. The advantage of using graphene over all the materials is its high surface area [4] and unique electronic property [5]. The discovery of graphene was in 2004 using the scotch tape peeling method [6]. Recently a lot of work on gas sensing applications has been done using graphene prepared by various methods which include electrolytic exfoliation [7], liquid-phase exfoliation [8], chemical vapor deposition [9], plasma-

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enhanced chemical vapor deposition [10]. Among all these methods graphene synthesized by reducing Graphene oxide (GO) which is known as reduced graphene oxide (rGO) is used as gas

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sensors because of its cost-effectiveness, high yield, easy functionalization with oxygencontaining groups and creation of defects which can lead to the increase in gas sensing

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performance [11]. Gas molecules cannot interact with pristine graphene as they do not have chemical bonds hence it has low sensitivity but the derivative of it such as GO and rGO are rich in functional group and can easily form bond with gas molecules adsorbed and hence has a good

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sensitivity compared to the pristine [12]. rGO which has similar structural, physical and chemical properties as of graphene has some oxygen functional group on the edge and on its basal plane

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[13]. Several reducing agents have been used to reduce GO. In recent days, studies on environmental friendly green reducing agent has been done to reduce GO. Reported reducing agents include Psidiumguajava [14], Vitamin C [15], Eucalyptus [16], and Green Tea Extract [17]

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and Thiourea dioxide [18].

Gas / vapor sensors can be categorized into chemiresistor, siliconebased field effect transistor (FET), capacitance sensor (CS), surface work function (SWF) change transistor, surface acoustic wave (SAW) change transistor, and optical fiber sensor (OFS), according to different forms of

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reaction with external atmospheres [19]. Among them, chemiresistor is the most widely used gas sensors [20], [21] where gases were identified by estimating the change in the resistance of detecting layers incited by adsorbing the gas molecules and its viability is due to the simple fabrication procedure [22]. The performance of this sensor depends on temperature and it can be used to detect many gases including ammonia, nitrogen dioxide etc. [22]. The adsorption of gas molecules on the surface of graphene contributes to changes in its electrical conductivity that can be due to changes in the local carrier concentration caused by surface adsorbents acting as donors 3

or acceptors of electrons [23]. Thus based on whether the gas adsorbed is an electron donor (e.g., NH3, CO, ethanol) or electron acceptor (e.g., NO2, H2O,iodine) the sign of the resistivity changes [24]. Even though Indian gooseberry has high percent of ascorbic acid, a good reducing agent for rGO, its application has not been explored. Also, its availability in Indian subcontinent and cost effectiveness are the additional advantages. Hence, in this present work, rGO was prepared using Indian gooseberry extract (green reducing agent) and hydrazine hydrate (chemical reducing agent) and their sensitivity in ammonia detection was analyzed in chemiresitor configuration.

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2. Experimental Details. 2.1 Preparation of graphene oxide

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From natural graphite, GO was prepared using improved Hummer’s method [1]. Acid mixture (360 ml of concentrated H2SO4 and 70 ml of H3PO4) was added to 3 g of graphite flakes in an ice

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bath under agitation. 18 g of KMNO4 was added pinch wise to this under constant stirring. The mixture was stirred for about 12 hours. After that, 400 ml of ice was taken in a beaker and to this;

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3 ml of H2O2 and the entire mixture was slowly added in an ice bath, to make sure that the temperature do not exceed 5°C. The color of the suspension then turned into yellow from brown.

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The mixture was then washed with 200 ml water, 200 ml of 30% HCl, 200 ml ethanol and 200 ml ether. Finally, the GO suspension was collected.

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2.2 Reduction of graphene oxide using hydrazine hydrate (rGO-5) 20 mg of GO was dispersed uniformly in 20 ml of distilled water for about 45 minutes using ultrasonication and 5 ml of hydrazine hydrate was added to this. The mixture was kept in an oven for about 5 min. The color of the mixture turned from yellow to black, which showed the successful

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reduction of GO to rGO. The suspension was dried up to obtain rGO powder [25]. 2.3 Reduction of graphene oxide using gooseberry extract (rGO-G) 20 mg of GO was uniformly dispersed in 20 ml of distilled water for about 45 minutes using

ultrasonication. It was further diluted by taking 5 ml GO from dispersion and adding it to 13 ml of DI water with constant stirring for about 30 min. To this solution, gooseberry extract was added and again stirred for 30 min. This solution was then transferred to a Teflon lined autoclave and kept for 6 hours at 120°C followed by cooling it down to room temperature [26]. The obtained 4

solution was then centrifuged, washed with DI water and ethanol. Finally, dried it at 60°C for 12 hours to obtain a solid residue. The schematic representation of the synthesis process is depicted in Figure 1. 2.4 Characterization Techniques Synthesized rGO was examined by transmission electron microscope (TEM). To prepare the sample for TEM, a drop of rGO dispersion was transferred to copper grid and it was allowed to dry completely at room temperature. Raman spectroscopic analysis of GO and rGO samples were done by recording the spectra using LABRAM - HR800 instrument in which the samples were

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excited by Ar-ion laser of 514 nm wavelength. A Nicolet Nexus 670 Fourier transform infrared (FT-IR) spectrometer was used to identify the functional groups of the EG material in the range of

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4000 – 400 cm−1. Shimadzu UV-1800 PC spectrophotometer was used to record the absorption spectra. X-ray diffractogram was recorded with Rigaku MiniFlex600 XRD (Cu K radiation

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source having a wavelength of 1.54 Å) at the scan speed of 2° /min. XPS analysis was done using

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3. Results and Discussions

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PHI 5000 VersaProbe III (C60 ion gun and X ray source of Al Kα 1486.6 eV and step size 0.05

In the present work, gooseberry extract has been used as the green reducing agent and hydrazine hydrate as the chemical reducing agent to form rGO from GO. A multilayer structure is observed

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for rGO-G under TEM examination, which is depicted in Figure 2 and the estimated particle size was about 230 nm.

3.1 Raman Spectroscopy

The Raman spectra of GO and rGO are mainly distinguished by D (due to the edges and grain

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boundary disorder) and G (due to the bond stretching of all pairs of sp2 atoms in both rings and chains) bands. Spectra of natural graphite powder (NGP), GO and rGO are shown in Figure 3. The D band for NGP, GO, rGO-5 and rGO-G are observed at 1348, 1348, 1356 and 1369 cm-1 whereas the G band is observed at 1578, 1605, 1606 and 1595 cm-1 respectively. The G band is common to all types of sp2 carbon and is derived from C - C bond stretch [27]. G band of GO is more broadened and blue-shifted to 1605cm-1 in comparison to that of NGP, which shows the deviation from sp2 hybridization due to extensive oxidation. The D band of NGO is less intense 5

indicating that NGO is less defective than GO. The intensities of D and G bands can be used to determine the degree of defects. The ratio, ID/IG represents defects and also creation of small sp2 domains [28] which is given in Table 1. As the number of layers increases, the intensity of G band increases significantly. The increase in the ratio from 0.85 (NGP) to 1.08 (GO) confirms the introduction of oxygen containing functional group to the graphitic plane. The increase in the intensity ratio ID/IG from 1.08 (for GO) to 1.18 (for rGO-5) shows the creation of defects, this may be due to the smaller sized new graphitic in-plane sp2 domains created [29]. The decrease in the ratio of rGO-G to 0.87 could be attributed to the decrease in the size of in-plane sp2 domains, an increase of the edge planes, as well as the expansion of the disorder in the prepared rGO [30].

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3.2 FTIR Spectroscopy

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FTIR spectra gives information on the various functional groups present in the sample. FTIR spectra of NGP, GO and rGO are shown in Figure 4. In GO, peaks were observed at 1049 cm-1

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corresponding to C – O, 1204 cm-1 corresponding to C = C, 1626 cm-1 corresponding to C – O – C and 1720 cm-1, which corresponds to C = O stretching band. These peaks were not observed in NGP indicating that a large number of functional groups were introduced during the oxidation

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step. Moreover, we observed a broad peak at 3400 cm-1 which corresponds to the hydroxyl group. This is also the evidence of presence of carboxylic, carbonyl, epoxy and hydroxyl in GO. The

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functional group at the sheet edge were - COOH and C = O whereas on the basal plane we observed C – O - C and - OH. On reduction with hydrazine hydrate, almost all the peaks disappeared which showes the removal of oxygen functional group whereas the intensity of some peaks had reduced.

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The decrease in the intensity peak for rGO-G showed that oxygen was removed to a certain extent. The disappearance as well as decrease in the intensity peak showed successful reduction of GO [31] via chemical and green route. 3.3 UV – Visible Spectroscopy

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UV-VIS spectra of GO, rGO-5, and rGO-G are shown in Figure 5. The maximum absorption peak for GO is at 230 nm and a small shoulder at 300 nm. The maximum absorption peak corresponds to the π - π* transitions of the aromatic C - C bonds and a small peak corresponds n - π* transitions of the C = O bonds, respectively. The maximum absorption peak is at 270 nm of rGO reduced with hydrazine hydrate and reduction with gooseberry extract shows absorption peak at 255 nm, which means there is a redshift in the absorption peak which can be attributed to the restoration of sp2 hybridized carbon network [32]. 6

3.4- X-ray diffraction study The XRD patterns for NGP, GO, rGO-5 and rGO-G are presented in Figure 6. A sharp peak observed at 2θ = 26.66 degree for NGP corresponds to (002) plane, using Bragg’s law we got the interlayer spacing (d spacing) of 3.34 Å. And, for GO, a peak appeared at 9.18 degree, which corresponds to (001) plane. Compared to NGP, GO has a large interlayer spacing 9.62 Å which could be due to formation of water molecules and oxygen functional groups during the oxidation process. This also indicates a weakening of interlayer Vander Waals interaction, therefore it is relatively easier for GO to exfoliate [17]. However, after reduction using hydrazine hydrate and

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also amla extract, we obtained a broad peak in the range 22° to 26° which corresponds to (002) plane and a peak at 9.82° disappeared which shows the successful reduction of GO. The interlayer

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spacing for rGO was almost in the range of NGP which shows the reformation of graphite microcrystal on graphene sheets [33]. XRD data also gives information on whether the given

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sample is crystalline or amorphous (polycrystalline) solid. NGO has an intense sharp peak indicating it to be a crystalline solid. rGO -5 and rGO-G peaks are very broad which implies it’s

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an amorphous or polycrystalline solid. 3.5 XPS analysis

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XPS survey spectra and core spectra for C 1s, O 1s are shown in Figure 7 (a-c), and results are shown in Table 2. Analysis of C1s XPS spectrum of rGO showed different states of carbon in the sample. Considerable reduction is confirmed from the area ratio [34]. Deconvolution of C 1s peak

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lead to four peaks with energies 284.80, 285.41, 286.35 and 288.60 eV corresponding to C=C, CN, C-O and C=O groups respectively. Higher area fraction of C=C compare to other groups confirms the reduction. O1s spectra is concurrent with the result with peaks at 531.49 and 532.98 eV originating from C=O and C-O groups respectively. This implies trace amount of C–O groups

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are associated with rGO.

3.6 Gas Sensing Application Raman, FTIR, UV and XRD analysis confirmed the formation of rGO from GO using gooseberry extract as reducing agent. The rGO thus formed was used as a gas sensor and its performance was compared with that reduced by using hydrazine hydrate as reducing agent. The sensing tests were carried out in a gas chamber using a two-electrode configuration. The sensitivity of the sensor was achieved by applying a constant bias voltage of 1 V and measuring the change in resistance 7

(Chemiresistor). As a carrier gas, dry synthetic air was used to dilute the test gas and purge the device before and after measurements. A mass control unit was used to control the concentration of ammonia. The sample was maintained at temperature of 60°C. On the adsorption of gas molecules on the surface of rGO, its electrical conductivity changes due to the change in local carrier concentration induced by the molecules which are either electron donors or electron acceptors. The gaseous analytes (ammonia molecules) were detected by measuring the resistance change of sensing layers induced by adsorbing NH3 (ammonia) molecules which is an electron donor. Upon exposure to ammonia molecules, resistance increases because of the increase in the

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concentration of holes. The sensitivity of given gas sensors can be calculated by the following formula. 𝑅𝑎 − 𝑅𝑔

𝑎

𝑅𝑎

| × 100 %

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𝑅

𝑆 = |𝑅 | × 100 % = |

where Ra is the resistance of the device under the clean atmosphere and Rg is the resistance of the

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device the gas atmosphere. The sensitivity of rGO-5 and rGO-G was calculated for the different concentration of ammonia. The resistance values and sensitivity of rGO-5 is given in Table 3.

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With increase in the concentration of ammonia molecules, resistance values were also increased as expected. The maximum sensitivity of 39.88% was observed at 250 ppm.

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rGO-G has exhibited high resistance compared to rGO-5 under clean atmosphere. Hence, the sensitivity study for rGO-G has been restricted the concentration up to 3 ppm. The resistance values and sensitivity of rGO-G is given in Table 4. However, rGO-G shows a good response to

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ammonia gas even for lower concentration. Response time defined as period of time from gas sensor contact with gas to be detected to variation of resistance reach to 90 % of |Ra-Rg| and recovery time defined as period of time from gas sensor away from gas to be detected to variation of resistance reach to 90 % of |Ra-Rg| are two important parameters that define the quality of the sensor apart from sensitivity. The response and the recovery time was also calculated for rGO-G

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for 3-ppm ammonia gas concentration (Figure 8) and found to be 70 sec and 55 sec respectively.

4. Conclusion

Successful reduction of GO by using Indian gooseberry extract as reducing agent in a hydrothermal autoclave has been demonstrated and its properties have been compared with rGO reduced by hydrazine hydrate. The reduction of GO to rGO has been confirmed through various characterization techniques including XRD, Raman, FTIR, XPS and UV – VIS spectroscopy. Reduction in the peak intensity of FTIR spectra confirms the removal of some oxygen functional 8

groups. Also, C/O ratio, obtained from XPS, supports the observation made from FTIR. The gas sensing ability of green synthesized rGO is proven for ammonia gas and the performance was compared with that of rGO reduced by chemical route. Green synthesized rGO has exhibited higher resistance compare to that reduced by chemical method, which is concurrent with the Raman results where higher disorder has been registered for rGO-G compared to rGO-5. Sensitivity of rGO-G has increased with higher concentration and about 5% sensitivity is achieved

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for 3 ppm concentration of ammonia.

CRediT author statement

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Nagaraju Sykam: Experiment - Gas sensing

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Fiona Crystal Mascarenhas: Experiment – synthesis, characterization and paper writing

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M. Selvakumar: Experiment and analysis – TEM, Raman, FTIR

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Mahesha M G: Building the concept, XPS analysis, reviewing and editing

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DECLARATION OF INTEREST STATEMENT

Title: Green synthesis of rGO using Indian gooseberry (Amla) extract as green reducing agent for gas sensing applications

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Authors: Fiona Crystal Mascarenhas, Nagaraju Sykam, M. Selvakumar and Mahesha M G Declaration: We have no conflict of interest to declare.

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Figure 1: Process flow for the synthesis of rGO from graphite via chemical and green synthesis route

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Figure 2: TEM image of rGO-G sample

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Figure 3: Raman Spectroscopy for natural graphite powder (NGP), Graphene oxide (GO), rGO5, and rGO-G.

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Figure 4: FTIR spectra for natural graphite powder (NGP), Graphene oxide (GO), rGO-5, and rGO-G.

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Figure 5: Absorbance vs. wavelength for Graphene oxide (GO), rGO-5 and rGO-G.

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Figure 6: XRD pattern for natural graphite powder (NGP), Graphene oxide (GO), rGO-5, and

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rGO-G.

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Figure 7: XPS (a) wide spectra and core spectra for (b) C1s and (c) O1s of rGO-G sample

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Figure 8: Response and recovery time for rGO-G gas sensor

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Table 1: ID/IG for NGP, GO, rGO-5 and rGO-G Sample

ID/IG

NGP

0.85

GO

1.08

rGO-5

1.18

rGO-G

0.87

Table 2: XPS analysis of rGO-G sample

284.80 285.41 286.35 288.60 531.49

1327.6 106.9 1184.4 426 631.8

43.60 3.51 38.90 13.99 14.86

1.18 0.8 1.61 1.86 1.3

Chemical State C=C C-N C-O C=O C=O

532.98

3619.8

85.14

2.17

C-O

Area % FWHM

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Area

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C1s

Peak

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Region

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O1s

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Table 3: The resistance values and sensitivity of rGO-5 Ra(mῼ) Rg(mῼ) 703.86 769.46 710.72 794.96 713.64 819.45 717.57 853.71 719.59 888.98 729.36 935.04 735.20 988.84 739.14 1033.88

Sensitivity (%) 9.32 11.85 14.82 18.97 23.53 28.20 34.49 39.88

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Concentration (ppm) 5 10 25 50 100 150 200 250

Table 4: The resistance values and sensitivity of rGO-G Concentration (ppm)

Ra (Mῼ)

Rg (Mῼ)

Sensitivity (%)

0.3

1.79

1.82

1.68

22

1.95 1.95

2.02 2.05

3.59 5.12

Jo

ur na

lP

re

-p

ro

of

1.5 3

23