Graphene from discharged dry cell battery electrodes

Graphene from discharged dry cell battery electrodes

Accepted Manuscript Title: Graphene from Discharged Dry Cell Battery Electrodes Authors: Suresh Bandi, Syamsai Ravuri, Dilip Ramkrishna Peshwe, Ajeet ...

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Accepted Manuscript Title: Graphene from Discharged Dry Cell Battery Electrodes Authors: Suresh Bandi, Syamsai Ravuri, Dilip Ramkrishna Peshwe, Ajeet Kumar Srivastav PII: DOI: Reference:

S0304-3894(18)31145-2 https://doi.org/10.1016/j.jhazmat.2018.12.005 HAZMAT 20038

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

17 August 2018 26 October 2018 1 December 2018

Please cite this article as: Bandi S, Ravuri S, Peshwe DR, Srivastav AK, Graphene from Discharged Dry Cell Battery Electrodes, Journal of Hazardous Materials (2018), https://doi.org/10.1016/j.jhazmat.2018.12.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphene from Discharged Dry Cell Battery Electrodes

Suresh Bandi1, Syamsai Ravuri2, Dilip Ramkrishna Peshwe1, and Ajeet Kumar Srivastav1*

Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of

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Center for Nanotechnology Research, VIT University, Vellore – 632014, India.

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Technology, Nagpur, 440010, India.

Corresponding author

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Graphical Abstract

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E-mail: [email protected]

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Highlights

Waste dry cell battery electrodes were used for graphene synthesis using electrochemical

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exfoliation route. Significant yield (88%) of graphene oxide was achieved.



This method opens the path for both waste management and low cost production of

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Current approach can be extended for large scale synthesis of graphene.

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graphene.

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Abstract

Utilization of extracted graphite rods from discharged dry cell batteries for synthesis of

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graphene oxide / graphene serves two purposes, one is waste management which supports environmental safety and the second is low cost production of graphene oxide / graphene which are highly promising 2D materials in various fields of research. In the present work, a

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sustainable feasibility for the synthesis of graphene oxide / graphene from graphite rods of waste dry cell batteries is demonstrated. The graphite rods separated from the waste dry cell batteries were subjected to electrochemical exfoliation (ECE) in an acidic media. The graphene oxide (GO) obtained from this method was subjected to reduction heat treatment under argon atmosphere at suitable temperature and time period. Finally, the reduced graphene oxide (rGO) i.e., graphene was characterized using XRD, FTIR, Raman Spectroscopy, TGA, BET, SEM and TEM. The few layer graphene structure is supposed to

be less defective in comparison to similar exfoliation techniques due to less oxygenfunctional groups associated with the intermediate graphene oxide.

Keywords: Waste battery electrodes; Electrochemical exfoliation; Graphene oxide (GO); Reduced graphene oxide (rGO)

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1. Introduction

Dry cell batteries, in particular the Zinc-Carbon batteries, are low cost and high in demand

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for various portable applications including, flash lights, remote controls, clocks, toys,

watches, transistor radios and portable electronic devices etc. As these batteries constructed with immobilized electrolytes, these are called as dry cell batteries. The typical construction of these batteries comprises of graphite/carbon rod at the center portion which acts as positive

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electrode (cathode). The mixture of manganese oxide and carbon powder is filled around the

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positive electrode. NH4Cl or ZnCl2 aqueous paste is surrounded as a second layer which is separated by an impregnated paper from outer shell made by zinc. This zinc container acts as

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negative electrode i.e. anode [1]. Being non-rechargeable, yearly thousands of these batteries

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are getting disposed (landfilled / incinerated) worldwide. These disposed dry cell batteries disintegrate with time and the chemicals and metals inside the batteries leach to the

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environment. Their toxicity, abundance and permanence in the environment results in severe impact on nature and poses grievous health consequences [2]. Also, the limited storage

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availability of landfills/dumpsites and increased expenses of disposal necessitates recycling of these batteries. The organizations like European battery recycling association (Belgium), Australian battery recycling initiative (Australia) and EUCOBAT (Belgium) are already

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active in various countries for collection and recycling of several types of batteries. Majority of the battery recycling processes are only focusing on recovery of valuable Zn, Mn, Fe and other metals [3,4]. The graphite in these batteries is being burnt during the process or leaving

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as residue or being neglected [5]. Whoever looking forth for recycling/reusing of these batteries should also ponder about the graphite rod placed at the center of battery. With the rise of new technologies and materials for various fields, graphite and its

derivatives (mainly carbon nanotubes and graphene) playing a crucial role in various applications like energy, structural, catalysis, electronics and etc. Owing to Graphite as a source material, the synthesis of such materials are of superior interest for current growing research and technology. In view of production of these materials, heavy exploitation of

graphite became widespread. Apart from China and India (world’s largest graphite mining countries), the natural graphite resources are not plentiful worldwide [6]. Whereas, synthetic graphite production is complex with various process steps, raw materials and efforts involved. Thus, extracting graphite from waste product is an inevitable, cost-effective and modest choice to overcome the limited available sources. Accordingly, the graphite rods from waste dry cell batteries can be useful for recycling / reusing. Reutilization of these batteries/ battery components for some other application serves two purposes. First one is waste

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management and the second one is decrease in amount of energy and resources spending for that particular applications. Graphite in the form of powder or rods is already being used for

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synthesis of graphene[7]. In this concern, we have preferred graphite rods from waste dry cell batteries for graphene synthesis.

Graphene is a two dimensional single atomic layer material [8]. High theoretical surface area, high intrinsic mobility [9], high Young’s modulus [10], high thermal &

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electrical conductivity [11] and optical transmittance [12] are unique features owned by

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graphene. As a consequence, this material acquired huge research interest in various

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applications viz., catalysis [13], electronics [14], transistors [15], photonics [16], electrochemical sensors [17], biosensors [18], anticorrosive coatings [19], fuel cells [20],

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energy storage [21] and hydrogen storage [22] etc. Various routes of synthesis techniques have been established till now for the synthesis of such materials of great interest. Chemical

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vapor deposition (CVD) [23], GO and subsequent graphene synthesis (Brodie’s [24], Staudenmaier’s [25], Hofmann’s [26] and Hummer’s [27] methods) and Exfoliation

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(micromechanical exfoliation [28], solvent exfoliation [7,29,30], and electrochemical exfoliation (ECE) [31]) are well known existing routes for synthesis of graphene. CVD involves epitaxial growth of graphene on substrate of interest with appropriate lattice match.

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Brodie’s, Staudenmaier’s and Hummer’s methods convert graphite to various levels of oxidation i.e. graphene oxide (GO), the subsequent reduction treatment converts it to graphene. In Exfoliation techniques, micromechanical exfoliation involves separating single

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layer of graphene from graphite with some externally applied force. Solvent exfoliation is dissolving graphite in to certain solvents (organic solvents like N, N- dimethylformamide or N-Methyl-2-pyrrolidone) and exposure of high intensity ultrasounds results in GO dispersions. Whereas, ECE is an electrochemical synthesis of GO. Among all the above methods mentioned, CVD, Hummer’s method and electrochemical exfoliation are common and widely practiced techniques for graphene synthesis. However, CVD is an expensive synthesis route which involves sophisticated and high end equipment. Hummer’s method is

chemically tedious. ECE can be labeled as an effective method due to its unique features like higher yield of production, ease of operation and cost effective [32]. The product of ECE is GO, which should be reduction treated further at higher temperature for its conversion to graphene. There are three reports where graphene was synthesized through waste dry cell battery electrodes. Roy et al. [33] prepared graphene using waste battery graphite electrodes through Hummer’s method followed by chemical reduction route. Tiwari et al. [34] reported

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the graphene synthesis by ECE using sodium dodecyl benzenesulfonate as electrolyte.

However, there were few inexplicable aspects. There also found a patent (CN102534643A)

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on reusing of primary battery graphite electrodes for graphene generation. Where, the authors examined electrochemical exfoliation with various cathode electrodes (inert/noble metals or alloys) and electrolytes [35].

In the current work, we have adopted ECE [36] for synthesis of GO and subsequent

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thermal annealing for reduction treatment for the synthesis of rGO/graphene. Unlike, earlier

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two reports [47,48] Su [36] and coworker's approach, the discharged battery electrodes were

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used for both the source of graphene (anode) as well as cathode in place of inert/noble materials. To the best of our knowledge, this is the first report of its kind to demonstrate the

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higher yield of graphene/graphene oxide with better efficiency using graphite rods from discharged dry cell battery electrodes (both anode and cathode) through ECE. Initial graphite

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rod, GO and rGO obtained were subjected to various characterization techniques in order to

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investigate the quality of the produced graphene/graphene oxide.

2. Materials and Methods

2.1. Extraction of graphite electrodes from waste dry cell batteries

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The waste dry cell batteries were dismantled carefully without disturbing the graphite rods held inside. The graphite rods were taken apart, rubbed and cleaned with distilled water rigorously to remove the other chemicals attached to them. The initial diameter, length and

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weight of the graphite rods were observed to be 7 mm, 5.6 cm and 4.37 g respectively as illustrated in Fig. 1. 2.2 Synthesis of GO Two thoroughly cleaned graphite rods were chosen to serve as anode and cathode for ECE process. The electrolyte of 0.5M H2SO4 was prepared and transferred to a glass container. Two cleaned graphite rods were fixed to the top cover of the container with 10 cm distance from each other. The container was covered in such a way that, the near complete immersion

of electrodes in electrolyte should be achieved. Thereafter, the electrical connections were fixed and DC voltage supply was switched-on. Initially, the voltage bias of 2 V was given for 2 min, then it was ramped up to 10 V for 1.5 – 2 h [37]. This experimental conditions were adopted from the earlier reports [36–38]. The exfoliation of anode graphite rod and hydrogen bubbles evolution were simultaneously observed during the voltage supply. The process was terminated once the anode becomes thin enough. The settled graphene oxide was separated from the container, subjected to repeated washing with distilled water and ethanol followed

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by ultrasonication for few minutes. Finally, it was dried in the oven at 60 °C for 12 h. The

diameter of the graphite rod used for anode was observed to be thinned down to around ~ 3

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mm (Fig. 2) after ECE and the weight was reduced to 2.2 g. The yield of the GO obtained was measured to be 1.91 g. The percentage of yield obtained was 88%. The visuals of complete process and experimental setup is displayed in Fig. S1 of the supplementary information.

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The initial weight of the anode (Ai) = 4.37 g

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The final weight of the anode (Af ) = 2.2 g

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The GO obtained = 1.91 g The percentage of efficiency (E) = GO / (Ai-Af)

= 88%

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= (1.91 / (4.37-2.2)) * 100

washing and handling.

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The loss of the GO was 11% which would have been lost in electrolyte and / or during

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2.3 Reduction treatment of GO

The GO obtained was taken in to alumina boats. The boats were placed exactly at the center of uniform high temperature heating zone in the horizontal tubular furnace. The temperature

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of the furnace was fixed to the 650 °C. Furnace was cooled down to the room temperature after holding time of 3 h at fixed temperature. The entire process was carried out in argon atmosphere to eliminate the interaction of oxygen in the air with GO. The final product

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incurred was reduced graphene oxide (rGO) i.e. graphene. 2.4 Characterization X-ray diffraction (XRD) patterns were obtained using PANalytical X'Pert Pro Multi-Purpose Diffractometer in Bragg-Brentano geometry equipped with X’Celerator detector with Cu Kα (λ=1.5406 Å) radiation (45 kV, 30 mA). The measurements were carried out in 2θ range of 10 – 70° using step size of 0.02 with 30 s time per step. Raman spectra were recorded using a Horiba Scientific spectrometer fitted with a CCD detector and a grating that enables the

measurement of the full spectrum in the range 1000 – 3000 cm-1 within a single acquisition. All the measurements were made in back scattered configuration at room temperature. The samples were excited with a 532 nm (2.33 eV) laser through 50X objectives (Numerical Aperture 0.5). Optimized focus conditions were checked for each measurement using the real time display (RTD) mode. A standard silicon wafer was used as the Raman intensity reference to ensure reproducibility. The Fourier Transform Infrared (FTIR) spectroscopic data was collected using Perkin Elmer Spectrum One over the range of 1000 – 4000 cm-1.

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Thermal stability of Graphite, GO and rGO were investigated using thermogravimetric

analysis (TGA) on TA SDT600 (V20.9 Build 20) thermal analyzer. The analysis was carried

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out in N2 atmosphere with a heating rate of 10 °C / min in the temperature range of 36 – 800

°C. The surface area evaluation for GO and rGO was measured on Micromeritics ASAP 2020 V3.04 H using Brunauer-Emmet-Teller (BET) method by N2 adsorption-desorption measurements at -196 °C. Morphological features of rGO was investigated using field

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emission scanning electron microscope (FE-SEM, JEOL – JSM-7610F). The high resolution

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characterization of rGO was performed using transmission electron microscope (JEOL JEM

3.1 ECE mechanism

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3. Results and Discussion

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2100 HRTEM).

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Generally, the anodic electrochemical exfoliation is intercalation of negatively charged ion species in to the positively charged anode which leads to the exfoliation of graphene sheets

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from anode electrode [31].

Once DC voltage supply starts, there should be a smooth and continuous flow of electrons between anode and cathode graphite rods. Incomplete wetting of electrodes in

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electrolyte results in to uneven flow of electrons which leads to the uneven voltage gradient along the anode surface. As a result, the exfoliation will be disproportionate. Hence, the exfoliated graphite gives irregular thickness and surface characteristics of sheets. In order to

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overcome this, the initial voltage bias of 2 V was supplied for first 2 min then it was increased to 10 V for 1.5 – 2 h. Also, the initial low voltage promotes the gentle intercalation of ion species [31,36]. The applied voltage bias promotes water reduction at the cathode site [29,39] which leads to the generation of hydroxyl ions (OH-) and evolution of hydrogen bubbles. The OH- ions take the role of strong nucleophile in electrolyte and attacks on certain positions of graphite rod [29]. Initially, the edge sites and grain boundaries of graphite gets attacked, which leads to the oxidation at that particular sites [29]. As a consequence,

depolarization and expansion of graphite layers occur. It facilitates possible entrapment for SO4-2 and HSO4- ions i.e. called graphite intercalated compounds (GIC). Also, these ions interacts with water molecules. Reduction of SO4-2 and HSO4- ions and self-oxidation of water leads to graphite oxidation, functional groups formation on graphite and generation of gaseous species like SO2, O2 and the other [40,41]. The gaseous products evolution exerts sufficient forces on the graphite layers which helps to apart the weakly bonded graphene sheets from its bulk. The schematic of ECE mechanism for the graphene oxide exfoliation is

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illustrated in Fig. 3.

The yields of GO obtained through various approaches as reported in the literature is

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tabulated in table.1. It can be observed that, for obtaining higher yields through Hummer’s method, it takes huge exertions involving time, various chemicals and

modifications/improvements. However, Luo et al. [42] and Huang et al. [43] have reported higher yields of 90% and 100% through few modifications in Hummer’s method. Luo et al.

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[42] implemented a pre-expansion treatment for graphite using microwave heating which

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increased its volume by ~200 times. Further, the pre-expanded graphite was utilized for

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synthesis of GO through Hummer’s method. Haung et al.’s [43] approach consumes 3 days of time and which also involves various chemicals in the process. Thus, apart from achieving

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maximum yields these two approaches might place difficulty to scale it up at the large scale. Whereas, most of the ECE techniques showing better and consistent yields with less

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durations and modest experimental approaches. The yield obtained in the current study was significantly high and in competence with the existing technologies or methods. Also, it

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could be extended to the industrial level for large scale production. 3.2 Reduction treatment

The GO produced through the ECE can be termed as chemically derived graphene [44]. The

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only difference from the graphene to chemically derived graphene is attached oxygen functional groups over its surface due to the chemical reactions occurred during the ECE process. In order to eliminate the oxygen and other functional groups, it should be reduction

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treated. The thermal reduction treatment was performed at 650 °C in a tubular furnace with continuous purging of argon which facilitates the oxygen free environment in the chamber (Fig. 4). Hence, this reduction treatment decomposes the oxygen containing functional groups attached to the chemically derived graphene. Also, this decomposition might result in removal of carbon atoms from the graphene layers and thereby creating defects [44]. Eventually, the oxygenated graphene (GO) converts to rGO. Fig. 4a shows the illustration of

reduction heat treatment. The photograph of the rGO obtained after the heat treatment is showen in Fig. 4b. 3.3 Characterization 3.3.1 XRD All three XRD profiles of Graphite, GO and rGO showing (Fig. 5) (002) peaks at ~26.6°. The most intense peak of 002 in graphite corresponds to the well-organized AB stacking of graphite layers with interlayer distance of 0.34 nm. However, the intensity of the same peak

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in case of GO and rGO was broadened with reduced intensity in comparison to the graphite. In general, the shifting down of 002 peak from 26.6° to 10-11° is the most common feature

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exhibited by XRD profiles of GO. This is an evidence for destruction of periodicity in AB

stacking, oxidation of graphite sheets and finally exfoliation. In contrast, the XRD pattern of GO in present work showing the 002 peak at 26.6°. Though the peak was at 26.6°, the appearance of peak changed significantly compared to the equivalent peak in graphite. It was

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broadened with reduced intensity which could be attributed to the distortion in the

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periodicity of AB stacking in graphite due to mild oxidation [45]. In order to explore the

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presence of 002 peak at 26.6° in GO, we found few studies where people have discussed the same [45–49]. Jeong et al. [46,47] Krishnamurthy et al. [45] and Zhou et al. [48] have

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described the presence of 002 peak at 26.6° due to the low degree of oxidation. Morimoto et al. [50] reported that, the position of peak in XRD pattern of GO depends on the degree of

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oxidation. The GO containing O percentage up to 24.1 wt. % exhibited the 002 peak only at ~ 26.6°. The evolution of peak at 10° started once the percentage of O reached to 29.1%.

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However, there also existed peak of 002 until 49.3% of O. Complete disappearance of 002 peak was observed at 55.2%. In the present work, the degree of oxidation estimated with TGA and SEM-EDS was below 24.1%. Which was below the limit that requires to shift the

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002 peak of GO from ~26.6° to ~10° [50]. Thus, the peak broadening effect and position of 002 peak of GO in this work were in good agreement with above mentioned results [45,46]. The degree of oxidation for the GO synthesized by ECE exfoliation was said to be lower

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compared to other chemical methods (like Hummer’s method). Also, the nature of electrolyte and its concentration using in the process is one more aspect which also affects degree of oxidation [29,37]. In general, the degree of oxidation for GO synthesized through Hummers method is ~ 43.5%. Nonetheless, GO produced from ECE of graphite in 1M (NH4)2SO4 was reported as containing 28.3 % of oxygen content by Parvez et al. [51] The value was in line to our results. The degree of oxidation of GO plays a crucial role in tailoring the functionalities suitable for various applications. The level of oxygen containing functional

groups present on the surface of GO affects: 1) the ability of establishing composites with other materials and 2) the quality of graphene acquired after thermal reduction. Presence of these groups in higher density enhances the composite formation capability with metal and other organic compounds [30,52]. Nevertheless, decrease in oxygen functional groups on the surface of GO gives highly conductive and defect free high-quality graphene after reduction treatment [50]. The intensity of 002 peak in rGO was observed to be increased slightly in

functional groups during the reduction treatment could be the reason for this. 3.3.2 Raman spectroscopy

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comparison to GO as illustreated in Fig. 5. The decomposition of oxygen / oxygen containing

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The Raman spectroscopic data of carbon intercalated compounds is generally explained by

few characteristic peaks / bands present therein viz., D band (1350 cm-1), G band (1580 cm-1) and 2D or Gʹ band (2700 cm-1) [53]. The D peak is due to breathing modes of six atom hexagon rings. The appearance of D peak demands the activation of defects [54]. The G peak

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involves the in-plane stretching of C sp2 atoms. It does not require six fold rings. Hence, this

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stretching occurs at all sp2 atoms in the system [53]. Also, this is a characteristic peak in

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graphite compounds [55]. 2D band is an overtone of the D band. It is also called as Gʹ peak since it is a second most promising peak visible in graphitic samples [56]. D and 2D peaks

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are called as second order Raman scattering which consists one elastic and one in-elastic scatterings for D band and two in-elastic scatterings for 2D band [57]. The intensity of D

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peak (ID) increases with the increase in defects such as structural disorder, decrease in six fold rings and presence of functional groups. Whereas, the intensity of G peak (IG) roughly

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estimated to be constant with change in density of defects as it is not related to six fold hexagon rings [29,54,55]. ID can be termed as measure of order of defectiveness in the graphene.

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The spectroscopic data of graphite rod, GO and graphene are shown in Fig. 6 and the

corresponding details are tabulated in table.2. The G peak was observed at 1569.4 cm-1 for graphite. Whereas, the G peak of GO was broadened and shifted to 1572.82 cm-1 in

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comparison with graphite. Also the D peak became spectacular at 1345.15 cm-1 which could be attributed to the size reduction of sp2 in-plane domains due to the heavy oxidation during the exfoliation [7]. The prominence of D and G peaks were observed at 1338.96 cm-1 and 1571.33 cm-1 even after reduction of GO to rGO. The ID/IG calculated for GO and rGO were 0.95 and 1.06 respectively. The increase in this value for rGO resembles the reduction of GO to rGO and decrease in average size of sp2 domains upon reduction treatment [7,55,58,59]. The ID/IG ratio is also a measure for degree of defects associated with the graphene layer. The

value ID/IG (1.06) of rGO was in accord to the graphene reduced in chemical/thermal routes [60]. The peaks observed at ~ 2440 cm-1 in GO and rGO Raman spectra are reported as D + Dʺ in literature. There observed an upshift of ~3 cm-1 in G peak of GO from G peak of graphite which could be attributed to the presence of impurities or chemicals doped in to the resulted GO layers [56]. Whereas, the reduction of GO to graphene tried to bring back the position of G peak and shifted ~ 1.5 cm-1 down. Thus, various chemicals or impurities entrapped during electrochemical exfoliation gets reduced in subsequent reduction heat

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treatment. 3.3.3 FTIR

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FTIR spectra of GO and rGO are illustrated in Fig. 7. In the spectra of GO, the broad band

appears at 3335 cm-1 indicates the oxidation of graphite [61]. The appeared peak was due to O-H stretching vibrations. The peaks at 3042 cm-1 and 2888 cm-1 could be attributed to the asymmetric stretching and symmetric vibrations of CH2 groups respectively [62]. The peak at

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1628 cm-1 was C=C stretching vibration or skeletal vibrations of unoxidized graphite domains

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and 1079 cm-1 peak is due to the C-O stretching vibrations which was an evidence of alkoxy

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(C-OH) and epoxide functional groups (C-O-C) [62,63]. Whereas, intensity of all peaks were reduced in the spectra of rGO (in fact few peaks were disappeared). Which suggests the

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significant removal of oxygen containing functional groups from GO and formation of rGO through reduction heat treatment [64].

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3.3.4 TGA

The TGA data of graphite, GO and rGO are shown in Fig. 8. The weight % residue at the end

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of experiment for graphite, GO and rGO was 94%, 78.44% and 86.81% respectively. The graphite is observed to be thermally stable with very less mass loss of 6%. GO has shown highest mass loss of 21.56% amongst all three samples. The mass loss of GO was in 2 stages.

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Initial degradation was at 127 °C which could be due to the loss of moisture/OH groups attached to the surface of GO and the major degradation was occurred after 127 °C until 800 °C. The latter case could be attributed to the reduction of GO /decomposition of oxygen

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functional groups attached therein. Whereas, the rGO showed mass loss of 13.19% which indicates that the GO supports its conversion to rGO after reduction heat treatment. If we consider % of mass loss is the % of oxygen containing functional groups present in the material, the XRD data of GO was well matched with the literature with the corresponding % O presence. 3.3.5 BET

The N2 adsorption – desorption isotherms and pore size distribution histograms of GO and rGO are shown in Fig. 9. The BET surface area of GO and rGO was measured as 17 m2/g and 27 m2/g respectively. The increase in surface area from GO to rGO could be attributed to the reduction heat treatment [65]. The lower degree of oxygen containing functional groups present on the GO surface could be reason for the lower surface area of rGO after heat treatment [66]. Also, the method of GO synthesis could have an impact on estimated BET surface area. Gurzeda et al. [67] identified that, the increase in BET surface area depends on

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the worsening order of graphene layers. As the GO prepared from ECE methods is less

disordered/oxidized, the resultant BET surface area given was also relatively lower [67]. The

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formation of tridimensional layers from GO due to expansion on heating is responsible for

porosity in graphene materials. Particularly mesoporous pores formation increases the BET surface area. Nonetheless, these are less abundant in ramp heated sample which lowers their BET surface area [65]. The pore volume of the GO was observed to be increased from 0.0154

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cc/g to 0.0253 cc/g after thermal reduction to rGO. However, The BET surface area of GO

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and rGO highly depends on various factors viz. method of oxidation/exfoliation, reduction

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treatments, degree of oxygen containing functional groups, reduction temperature and period of time. Moreover, BET method is highly precise for nonporous materials.

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3.3.6 SEM

Fig. 10 illustrates the FE-SEM micrographs of graphite (a and b), GO (d and e) and rGO (g

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and h). The SEM micrographs of graphite rod (Fig. 10 a and b) shows, tightly stacked/packed graphite layers in graphite rod. Whereas, the SEM micrographs of GO exhibited the large,

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flexible, freely oriented and loosely stacked graphite sheets disassembled from graphite. The sponge / foam like nature was due to extensive exfoliation. As GO and rGO looks similar in view of morphology, the SEM micrographs of rGO also exhibited the same morphological

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features. The only difference between GO and rGO is the presence of oxygen containing functional groups. The variance in presence of oxygen percentage in graphite rod, GO and rGO can be observed from the elemental analysis as shown in the EDS spectra in Fig. 10 (c),

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(d) and (e) respectively. As discussed earlier (in section 3.1), during the ECE process the negatively charged species entraps in to the tightly packed graphite flakes in graphite rod. These graphite flakes exfoliates from the rod, as negative ion species entrapped between the graphite flakes which get oxidized. The energy dispersive spectroscopy (EDS) data was in good agreement with the prior statement. The EDS of graphite rod showed 6.1% O presence. Where, the GO encompassed 22.8% O. The increase in % O could be attributed to the intercalation of oxygen containing groups in to the graphitic layers and subsequent

exfoliation of graphite flakes which results in GO. However, the EDS of rGO showed reduced oxygen content to 13.6% compared to GO. Which attributes the removal of oxygen containing functional groups from GO during reduction heat treatment. Interestingly, the percentage of oxygen detected for each material was in good agreement with the percentage of material loss obtained from the TGA analysis.

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3.3.7 TEM

Similar to the SEM observations the TEM also revealed the crumpled and aggregated

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behavior of the rGO (Fig. 11 a and b). The dark and thick regions resembles the multi layered graphene whereas the thin transparent regions are symbol of few layer graphene [68] and which is said to be the general behavior of graphene synthesized through oxidation or reduction based methods [64,69]. The SAED ring pattern in Fig. 11 (c) reveals that, the rGO

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was showing a turbostratic nature/ random stacking of layers. The similar kind of results were

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reported elsewhere [70,71].

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Stacking of graphene layers was observed from HRTEM images (Fig. 12 a, b and c). It appears to be multilayerd graphene. The interlayer spacing of stacked layers was measured

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to be ~ 0.34 nm. Fig. 12 (c) shows the multilayer stacking in a crumpled / corrugated graphene edge. The right side of the image was HRTEM of marked region from the image

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showing crumpled graphene edges (left side).

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4. Conclusion

Waste dry cell battery electrodes were used for synthesis of graphene oxide / graphene following the ECE route. The yield of GO through ECE in present investigation was 88%.

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XRD, TGA and SEM-EDS revealed that, the degree of oxidation of obtained GO was moderate which could be helpful for synthesizing quality and defect free graphene through reduction treatment. The GO was transformed to rGO after reduction treatment. The degree

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of oxidation in GO was observed to be less than 24% which was corroborated by XRD pattern. The same was supported by TGA and FE-SEM-EDS analysis. The Raman spectroscopy analysis revealed that, the synthesized graphene was multilayered in structure. Also, the crumpled and multilayer stacking behavior of graphene was revealed by SEM and TEM analysis. The further optimization of process parameters like voltage supply, electrolyte concentration and change in electrolyte may result in improved quality of graphene. In conclusion, the synthesis of graphene from waste dry cell battery electrodes was realized

through this work and the technique can be extended to the industry level for large scale synthesis of graphene. It also helps environment in view of waste management and recycling of resources.

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ACKNOWLEDGEMENT

The authors are grateful to Dr. Pavithra for fruitful suggestions during the work. Mr.

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Devathade Vidyasagar is thankfully acknowledged for his rich accompaniment. Also, the

authors are thankful to Mr. Nikhil Cherukupalli, Mr. Vikram Hastak for their help during the

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synthesis and Mr. S. L. Gadge for his constant support and motivation for the work.

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[2]

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A

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[75]

[76]

[77]

A

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ED

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U

SC R

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Conductive Electrodes for Organic Electronics., ACS Nano. 7 (2013) 3598–3606. doi:10.1021/nn400576v. [78] X. Huang, S. Li, Z. Qi, W. Zhang, W. Ye, Y. Fang, Low defect concentration fewlayer graphene using a two-step electrochemical exfoliation, Nanotechnology. 26 (2015) 105602. doi:10.1088/0957-4484/26/10/105602. [79] L. Wu, W. Li, P. Li, S. Liao, S. Qiu, M. Chen, Y. Guo, Q. Li, C. Zhu, L. Liu, Powder, paper and foam of few-layer graphene prepared in high yield by electrochemical intercalation exfoliation of expanded graphite, Small. 10 (2014) 1421–1429. doi:10.1002/smll.201302730.

U

SC R

IP T

Figures

Fig. 1. The visuals of a) separating graphite electrodes from the used dry cell batteries, and b)

CC E

PT

ED

M

A

N

the separated and cleaned graphite electrode for ECE.

A

Fig. 2. The photographs of graphite rods used as anode and cathode; a) prior to the ECE process, b) after ECE, the anode got thinned down, and c) The GO powder obtained at the end of the experiment.

IP T SC R U

N

Fig. 3. The schematic representation of ECE mechanism. 1) The graphitic layers arranged in

A

the graphite rod, 2) intercalation of negative charged ion species and their oxidation which leads to the separation of stacked graphene layer in the graphite, 3) exfoliated graphene layers

A

CC E

PT

ED

illustration of single GO layer.

M

which are containing oxygenated functional groups which will be called as GO, and 4)

Fig. 4. a) Illustration of reduction heat treatment of GO for the formation of rGO, and b) the rGO obtained after the heat treatment.

IP T

SC R

Fig. 5. The XRD patterns of graphite, GO and rGO showing the most intense 002 peak. The

CC E

PT

ED

M

A

N

U

reference pattern (JCPDS card No. 89-8487) is shown at the top.

A

Fig. 6. Raman spectra showing the characteristic peaks of graphite, GO and rGO

IP T SC R

Fig. 7. FTIR spectra of GO and rGO showing the peaks corresponding to the attached

PT

ED

M

A

N

U

functional groups.

CC E

Fig. 8. TGA profiles of graphite, GO and rGO showing the mass loss and inset table shows

A

the quantitative % mass loss in comparison to each other.

IP T SC R

Fig.9. Nitrogen adsorption and desorption isotherms of a) GO and b) rGO. The histograms

A

CC E

PT

ED

M

A

N

U

shows the pore volume vs. pore radius as shown in the insets.

Fig. 10. The FE-SEM micrographs of graphite rod (a and b), GO (d and e), rGO (g and h) and their respective EDS spectrum (c, f and i).

IP T SC R U N A M ED PT

CC E

Fig.11. (a, b and c) The TEM micrographs of rGO, and (d) The SAED pattern of rGO for the

A

area of (c).

IP T SC R U N A M ED PT

CC E

Fig. 12. HRTEM stacked multilayered micrographs of rGO (a and b), and the HRTEM of

A

crumpled edge showing in right side for the selected region from the left portion (c).

Tables Table.1. The comparison of yields of GO obtained by various methods reported in literature. Method

Initial material

Oxidants

Modifications

Dura

Yield

tion

of GO

Ref

(%) Modified Hummer’s

Graphite

-

-

-

Graphite

H2SO4, H3PO4

Controlled stirring duration for 72 h

70

[72]

Hummer’s method

Hummer’s method

62.5

[73]

-

90

[42]

KMnO4 replaced partly with K2FeO4 and amount of concentrated H2SO4 was controlled.

5h

84

[24]

Oxidation of graphite (by modified

6h

84

[74]

24 h

43

[74]

3

100

[43]

-

96

[75]

-

-

>70

[76]

H2SO4

-

2h

>80

[77]

-

-

>85

[29]

and KMnO4

Graphite

-

Pre-expansion of graphite by microwave heating

Graphite

KMnO4 and

free Hummer's

K2FeO4

U

Improved NaNO3-

method

method followed by

Graphite oxide

-

N

Natural

Hummer's method) prior to ultra-

A

Modified Hummer's

sonication.

Synthetic

method followed by

Graphite oxide

Ultra sonication Graphite flakes

Electrochemical

Graphite paper

Graphite

expansion

A

H2SO4, H3PO4

sonication. -

and KMnO4

CC E

Electrochemical

Oxidation of graphite (by modified Hummer's method) prior to ultra-

PT

Hummer's method

-

ED

Modified Hummer's

M

Ultrasonication

Simplified

72 h

SC R

Controllable

IP T

method

H2SO4

days Two step oxidation: 1) EC intercalation in conc. H2SO4.2) EC exfoliation in dilute H2SO4 by using intercalated compounds as anodes

Electrolyte of LiClO4 and Propylene carbonate (PC)

Electrochemical

Natural graphite

exfoliation

flakes adhered on carbon tape

Electrochemical

Natural graphite

Electrolyte

exfoliation

flakes adhered

made

of(NH4)2SO4,

on carbon tape

Na2SO4, K2SO4, etc. Electrochemical

Graphite foil

exfoliation

NaOH and

Two step exfoliation. NaOH as

H2SO4

electrolyte in step.1 and H2SO4 as

1h

>56

[78]

electrolyte in Step.2 Graphite rods

(NH4)2SO4

-

2h

>80

[51]

Electrochemical

Pellet of

H2SO4

+1 V for 10 min followed by +2 V for

30

> 75

[79]

intercalated

expanded

exfoliation

graphite flakes

Electrochemical

Waste battery

88

Curr

exfoliation

graphite

(Current work)

electrodes

Electrochemical

next 20 min

min

-

~ 1.5

SC R

H2SO4

IP T

exfoliation

ent

-2h

U

work

G band

Sample

1345.15

rGO

1338.96

CC E A

Position I2D

1457.44 2699.71

271

0.18

0.04

214.478 1572.82

225.15

2681.06

13.96 0.06

0.95

84.29

79.33

2674.83

11.29 0.14

1.06

PT

GO

55.27

1569.84

ED

Graphite 1338.96

Position IG

12D/IG ID/IG

M

Position ID

2D band

A

D band

N

Table.2 Details extracted from Raman spectra of graphite, GO and rGO.

1571.33