Published at : 25 Nov 2019
Volume : IJtech Vol 10, No 6 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i6.3639
|Eny Kusrini||Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Atik Suhrowati||Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Anwar Usman||Department of Chemistry, Faculty of Science, Universiti Brunei Darussalam, Gadong BE1410, Negara Brunei Darussalam|
|Volkan Degirmenci||School of Engineering, The University of Warwick, Coventry CV4 7AL, UK|
|Munawar Khalil||Department of Chemistry, Faculty of Mathematic and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
In this paper, synthesis of graphite oxide, graphene oxide (GO), and reduced graphene oxide (rGO) from the spent pot lining (SPL) of aluminum industrial waste using modified Hummers’ method and zinc as reducing agent is examined. The effects of ultrasonication time from 1 to 2 h and Zn mass ranging from 8 to 24 g as reducing agent were observed in detail for reduction reaction of GO into rGO. The chemical structures and morphology of the samples were confirmed through FTIR, PSD, SEM-EDS, and XRD characterizations. The FTIR analysis confirmed the formation of GO. Although some restacking/unexfoliated graphite structures showed a diffraction peak at 2? of 26.54°, the XRD analysis clearly exhibited a peak at 2? of 20.04°, assigned to rGO after reduction of the GO. The smallest particle size of rGO graphene was observed in the range of 1 to 10 mm when under ultrasonication time of 1 h and Zn mass of 8 g. The FTIR spectrum of graphene oxide showed that there was a functional group C=C, which is an indication of rGO formation due to the covalent bonding of the graphene structure. SEM imagery of the rGO showed that the morphology seemed thick and layer stacking. The quality of rGO produced in this study needs to be improved further to meet requirements for applications.
Graphene oxide; Modified Hummers’ method; Reduced graphene oxide; Zinc as reducing agent
The aluminum smelting process using electrolysis produces a huge amount of waste of graphite electrodes (Reny et al., 2016). In this electrolysis process, graphite is used as both anode and cathode, since it is inert and capable of conducting heat and electric current efficiently. Some of the graphite used in the electrolysis processes will be recycled, while the remaining will be dumped as waste. To present, the reutilization of electrode graphite waste has only been as filler in the production of steel. To improve the use and value of this graphite waste, investigations for synthesis and characterization of graphite waste as valuable products, such as adsorbents, (Kusrini et al., 2017; Kusrini et al., 2018) have been reported.
The aluminum industry continues to grow rapidly year by year with rate increase of 5% per year, and the aluminum production was predicted to reach 68 million tons in 2020 (Pei & Cheng, 2012). Increasing aluminum production prompts an increase in the use of graphite electrodes in the electrolysis of Al2O3. The electrolytic cell lining should be replaced every 3–5 years, and spent pot lining (SPL) becomes solid waste. The main content of SPL is carbon in the form of graphite, which can actually be utilized as raw material for the production of graphene-related materials. As we know, graphite is the most common feedstock for the synthesis of graphene using a top-down method. The grade of graphite depends on flake size and carbon content; thus, the price ranges from $430 to $20,000 per MT (Lee et al., 2019). Increasing the carbon content in graphite makes it more valuable.
Graphene is commonly a monoatomic two-dimensional sheet-like material with sp2 hybridized carbon atoms configured in a hexagonal or honeycomb-like structure, and its thickness is similar to an atom diameter (Novoselov et al., 2004; Lee et al., 2019). Graphene is the world’s thinnest material—a single layer of carbon atoms that has a hexagonal structure (Geng et al., 2012). The excellent electrical properties of graphene can make it play a large role in energy storage, material composites, sensors, and other fields (Dikin et al., 2007). Graphene is recognized as an advanced material due to its advantages and unique properties. With a thickness of about one carbon atom, graphene has optical transparency of up to 97.7% (Nair et al., 2008). The structure of graphene, consisting of layers, makes graphene highly conductive with a carrying mobility of up to 200,000 cm2V-1s-1 and thermal conductivity of up to 5,300 Wm-1K-1 (Bolotin et al., 2008; Balandin et al., 2008). Graphene oxide (GO) and its reduced graphene oxide (rGO) are classified as graphene family materials and have many applications, such as optical, in biomedical water treatment, and as adsorbents (Raghavan et al., 2017; Ahmad et al., 2019).
Graphene can be synthesized using two methods, namely bottom-up and top-down (Supriadi et al., 2017). In this study, a top-down method including the exfoliation of graphite and the chemical reduction of graphite oxide and graphene oxide (Marcano et al., 2010) was used. Graphite oxide can be synthesized by oxidizing graphite. The Hummers method is commonly used to synthesize graphite oxide because the final product has a higher oxidation rate than the final product of the Staudenmaier method (Hummers & Offeman, 1958). The materials used in the Hummers method are also easier to obtain and are less dangerous than the Staudenmaier method. In the Hummers method, graphite oxide is reacted with potassium permanganate (KMnO4) and sodium nitrate (NaNO3) in a sulfuric acid solution (H2SO4). Several reducing agents, such as sodium borohydrate, hydrazine, and ascorbic acid, have been used for conversion of GO to rGO. On the other hand, chemically reducing GO into reduced graphene oxide (rGO) using Fe or Zn in an acidic medium under ambient conditions has also been reported (Wang et al., 2009; Jassby et al., 2012).
Herein, the synthesis of rGO from SPL aluminum industrial waste using modified Hummers’ method and Zn as a reduction agent is reported.
In this study, graphite oxide, graphene oxide (GO), and reduced graphene oxide (rGO) were successfully synthesized from graphite waste. The chemical structures and morphology of graphite oxide, GO, and rGO were confirmed through FTIR, PSD, SEM-EDS, and XRD characterizations. The FTIR analysis confirmed the formation of GO. Although some restacking/unexfoliated graphite structures showed a diffraction peak at 2? of 26.54°, the XRD analysis clearly exhibits a peak at 2? of 20.04°, assigned to rGO after reduction of the GO. The XRD patterns of the graphite oxide show that the oxidation reaction was not perfect, because there was no diffraction peak at 2? of 10.5°, which is peak of graphite oxide. Graphite oxide has a C/O ratio of 6.22 and an average particle size of 148.25 ?m. The FTIR spectrum of the graphene oxide showed that there was a functional group C=C, which is an indication of rGO formation due to the principal bonding of the graphene structure. The SEM images of the rGO showed that the morphology seemed thick and layer stacking. Further research, with pre-purification treatment of graphite waste using acid and base leachings, is important to obtaining high purity graphite as a starting material to produce graphene.
The authors gratefully acknowledge the Ministry of Research, Technology and Higher Education of the Republic of Indonesia for its research grant award through PTUPT, Grant No. 493/UN2.R3.1/HKP05.00/2018.
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