Int. J. Nano and Biomaterials, Vol. X, No. Y, xxxx
Preparation and characterisation of graphene oxide nanofluid and its electrical conductivity Md. Arifur Rahman, Md. Abu Naser Shatez, K. Yamun Nahar Ritee and Papia Yasmin Department of Chemical Engineering, Jessore University of Science and Technology, Jessore 7408, Bangladesh Email:
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Md. Shahadat Hossain Department of Chemistry, Government M.M. College, Jessore, Bangladesh Email:
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Md. Zaved H. Khan* Department of Chemical Engineering, Jessore University of Science and Technology, Jessore 7408, Bangladesh Email:
[email protected] *Corresponding author Abstract: Recently, two dimensional honeycomb lattice structural graphene grants unique properties that are currently being pursued for conductive composites, advanced electronics, membranes, etc. In this work, we report the preparation of graphene oxides (GO) nanofluids by dispersion of GO nanosheets in base fluid. Firstly, GO sheets were synthesised in controlled size using improved Hummer method by simply oxidation and facile exfoliation procedure. As prepared samples are characterised by UV-vis spectrometer, Fourier transform infrared spectroscopy (FTIR) spectrometer, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The XRD pattern revels that GO were form in nanoscale with crystalline structure. SEM image confirmed that GO were form in ultra small sheet state with smooth surface. UV-vis absorption spectrum reveals that GO nanosheets disperse well in the base fluid. FTIR result reveals the presence of functional group in the lattice which helps the graphene oxide sheets to interact with water molecules and good dispersion. In terminology of electrical conductivity, the result suggests that the samples with 0.1% volume of GO had the highest conductivity with the value of 5,310 µS/cm. Keywords: graphene oxide; GO; nanofluids; electrical conductivity; crystalline structure; nanosheets. Copyright © 20XX Inderscience Enterprises Ltd.
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M.A. Rahman et al. Reference to this paper should be made as follows: Rahman, M.A., Shatez, M.A.N., Ritee, K.Y.N., Yasmin, P., Hossain, M.S. and Khan, M.Z.H. (xxxx) ‘Preparation and characterisation of graphene oxide nanofluid and its electrical conductivity’, Int. J. Nano and Biomaterials, Vol. X, No. Y, pp.xxx–xxx. Biographical notes: Md. Arifur Rahman recently finished his BSc in Chemical Engineering from the Jessore University of Science and Technology and is currently working as a Research Assistant at the NAME Laboratory. He has strong interest in working with electrochemistry and nanotechnology. Md. Abu Naser Shatez recently finished his BSc in Chemical Engineering from the Jessore University of Science and Technology and is currently working as a Research Assistant at the NAME Laboratory. He has strong interest in working with electrochemistry. K. Yamun Nahar Ritee recently finished his BSc in Chemical Engineering from the Jessore University of Science and Technology and is currently working as a Research Assistant at the NAME Laboratory. He has strong interest in working with electrochemistry and nanotechnology. Papia Yasmin recently finished his BSc in Chemical Engineering from the Jessore University of Science and Technology and is currently working as a Research Assistant at the NAME Laboratory. He has strong interest in working with electrochemistry and nanotechnology. Md. Shahadat Hossain is working as an Assistant Professor in the Dept. of Chemistry at M.M. College, Jessore. He finished his BSc and MSc from the Department of ACCE, Islamic University, Kushtia, Bangladesh. Currently, he is doing his PhD in China. Md. Zaved H. Khan is working as an Associate Professor in the Department of Chemical Engineering at the Jessore University of Science and Technology, Bangladesh. He finished his PhD and postdoc from Japan. He is currently working as a Postdoctoral Research Fellow at the Henan University, China. He has a long experience in working with nanotechnology and materials engineering. He has contributed over fifty international peer reviewed journal papers and presented his work in different international conferences in home and abroad.
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Introduction
Graphene is a single plait of sp2 bonded carbon atom having two dimension (2D) honeycomb lattice structure (Novoselov et al., 2004; Allen et al., 2009), attracting interest from both research and various applications due to its tremendous electronic, mechanical, optical, rheological and thermal properties (Lu et al., 2006; El Achaby et al., 2012). Therefore, graphene has been widely looked for the applications in highly conducting composite (Stankovich et al., 2006a; Watcharotone et al., 2007), electronic materials (Eda et al., 2008; Avouris et al., 2007; Son et al., 2006), sensor (Schedin et al., 2007; Khan, 2017), batteries (Takamura et al., 2007), catalysis (Huang et al., 2012) and storage (Yoo et al., 2008; Wang et al., 2009b).
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Nanofluids, which are suspensions prepared by dispersing nanometre-sized solid particles, rods or tubes in the base fluids, have attracted much attention due to the anomalous thermal conductivity enhancement, electrical conductivity, viscosity and heat transfer (Zhu et al., 2006; Kole and Dey, 2013; Park et al., 2010). Generated graphene-based materials, like modification of graphene oxide (GO), prepared by oxidation of graphite (Hummers and Offeman, 1958) is arguably the most versatile and easily scalable method. Notably, the well-dispersed solutions of GO sheets in solvent (Stankovich et al., 2006b, 2006c) providing more possibilities for applications in materials science and nanocomposites, GO paper, enhancement of thermal, electrical conductivity (Stankovich et al., 2006a, 2007; Watcharotone et al., 2007; Dikin et al., 2007). Many technique have been developed to prepare graphene sheet, such as micromechanical cleavage (Novoselov et al., 2004), intercalation, sonication in various solvents (McAllister et al., 2007), solvothermal synthesis (Wang et al., 2009a) and chemical processing involve graphite oxidation, exfoliation and reduction (Reina et al., 2008). Recently, chemical reduction of exfoliated graphite oxide (GO), a soft chemical synthesis route using graphite as the initial material was reported. All these are efficient approaches to bulk production of graphene-based sheets at low cost (Hummers and Offeman, 1958; Wang et al., 2009a; Stankovich et al., 2007). Herein, we reported that the preparation of GO nanofluids by two step method where GO nanosheet were prepared via modified Hummer method. The main objective of this research was to prepare and significant enhancements of electrical conductive properties of GO nanofluids upon dispersion of GO sheet in base fluid.
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Materials and method
2.1 Materials and chemicals Table 1
Materials and chemicals used in this work
Precursor Graphite flakes
Quantity 1g
Sulphuric acid (H2SO4, 98% concentration)
100 ml
Phosphoric acid (H3PO4, 98% concentration)
10 ml
Potassium permanganate (KMnO4, 99.9% pure)
5g
Hydrogen peroxide (H2O2, 30% concentration)
70 ml
Hydrochloric acid HCI, 37% concentration)
1 mole
2.2 Preparation of GO GO was synthesised by oxidation of graphite powder by using Hummer method with a modification of removing sodium nitrate from the reduction formula. Typically, 10 mL of phosphoric acid introduced to 100 mL of sulphuric acid under stirring for two hours at room temperature. After that 1.0 gm of graphite flakes was added to the mixture and vigorous stirring for 10 minutes in an ice bath. Next, additional 6 gm of KMnO4 was added slowly to the mixture and stirring for one day. Finally, 10 mL of 30% H2O2 was
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added to the mixture slowly under vigorous stirring for 30 minutes in an ice bath to remove excess KMnO4. The reaction progressed, the mixture colour turned light yellow to dark brown indicating presence of GO. The GO mixture was filtered and washed with HCl and de-ionised water thoroughly yielding pure GO. The GO suspension is dried in a dryer for 24 hours at 500°C to remove water molecules from GO sheet.
2.3 Preparation of GO nanofluids The prepared GO sheets were dispersed in de-ionised water to prepare the GO nanofluids. After dispersion of GO sheet in de-ionised water, the solution was sonicated for two hours for well dispersion of GO sheet in base fluid.
2.4 Characterisation X-ray powder diffraction (XRD) was done to investigate the oxidation and crystalline of graphite and formation of GO sheet. XRD measurement was done with Cu-Kα radiation of 0.154187 nm wavelength in the region of 2θ from 300 to 800 at 0.02/min and the time constant was 2 s. Scanning electron microscopy (SEM) measurement of GO sheet was done to investigate the surface morphology. Fourier transform infrared spectroscopy (FTIR) was done to indentify the presence of functional group and oxidation of graphite into GO. UV-vis adsorption spectrum was done to investigate the presence and homogeneous dispersion of GO sheet in base fluid. EC analysis was done to monitor the electrical conductivity of GO.
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Results and discussion
3.1 XRD pattern Figure 1 shows the XRD patterns of GO. In the pattern, a very wide peak is observed that clearly indicates that the damage of the regular crystalline of pattern graphite during the oxidation (Chen et al., 2010) GO refrains the layer structure of graphite but with a larger and irregular basal plane spacing. In addition, it can be described that, the broad peak at 260 two theta due to a disordered components generated during the chemical processing of graphite to make GO or which apprise incomplete oxidation of graphite. Moreover, some small peaks arising in pattern which also apprising the incomplete oxidation of graphite.
3.2 SEM analysis SEM measurement of was done to deduce the formation of GO nanosheet. Figure 2 shows the GO sheet after successfully oxidised of graphite into GO which is not aggregated. SEM image reveals that the GO sheet form in ultra small size, thin, ordered solid sheet. This image also prove the presence of individual of sheet of GO.
Preparation and characterisation of graphene oxide nanofluid Figure 1
XRD pattern of prepared grapheme oxide
Figure 2
SEM image of go sheet, (a) single GO sheet with clear wrinkle and folding (b) close image of GO with sharp edge
(a)
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(b)
3.3 FTIR spectrometer analysis The FTIR analysis was done to analyse the presence of functional groups and interaction of GO molecules with base fluid molecules. Figure 3 shows the FTIR spectrum of GO which confirm the presence of different oxygen and water containing functional groups were present in the sample. The peaks in FTIR spectrum at 3,483.44 cm–1 and 1,043.48 cm–1 were raises due to hydroxyl functional group. The sharp peak at 1,730 cm–1 may be correspond to the C=O group. The peaks at about 1,630 cm–1 apprises the retention of C=C even after the oxidation process of graphite. The sharp peak at 1,240 cm–1 can be the epoxy of C-O group.
3.4 UV-vis spectrometer analysis The optical absorbance of GO was monitored by UV-vis spectrometer. Figure 4 shows the absorption spectrum of GO varying with weight. Formation of GO confirm by colour change from yellow to dark brown as shown in Figure 1 followed by UV-vis
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spectroscopy. Figure 2 delimitate the absorbance spectrum of GO, showing the absorbance peak at 228 nm for both 1 gm and 1.5 gm and absorption peak shifted at 226 nm for 2 gm of graphite powder which is attributed to the π – π* transition of C=C bonds. After that the peak for 2 gm of graphite shifted to 300 nm which attribute to n – π* transition of C=O bonds, respectively. These observation indicate the homogeneous dispersion of GO and also the tunability of optical properties of GO. Figure 3
FTIR spectrum of GO dispersion
Figure 4
UV absorption spectrum of GO dispersion (see online version for colours)
3.5 Stability of GO According to the zeta potential values and the distance between zeta potential and isoelectric point, the stability of nanofluid is varying. The zeta potential values represent the electrostatic value of the particle dispersion. The zeta potential values greater than 30 mV or lass than –30 mV due to electrostatic force greater than the attraction force
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between the particles which represents the nanofluid stable over a period of time. pH one of the key parameter which affect the zeta potential value. According to change of pH, the electrostatic charge of the surface will change. The GO nanofluid is stable when the pH values kept around seven by adding drops of NaOH (Park et al., 2012). The stability of GO also depends on the dispersion of the GO nanofluid. A longer ultrasonication time will give the better stability. Therefore as it is shown in Table 2 the most stable GO nanofluid is located at 65 min. sonication time and pH around 7.3. Table 2
pH value and the stability results with different ultrasonic durations
Sample number
Initial pH
Final pH
Ultrasonic time (min)
Stability (days)
1
2.6
7.5
65
2
2
2.1
7.2
65
2
