A glycerolwater-based nanofluid containing graphene oxidenanosheets

Ali Ijam A. Moradi Golsheikh R. Saidur

P. Ganesan

Received: 1 February 2014 / Accepted: 7 May 2014 / Published online: 23 May 2014

Springer Science+Business Media New York 2014

Abstract Nanofluids are simply the dispersion of nano-

meter-sized particles in different fluids. Graphene oxide

nanosheets (GONs) were prepared by exfoliating the

graphite oxide. The GONs were investigated using Fourier

transform-infrared spectroscopy, Raman spectroscopy,

XRD analysis, high-resolution emission electron micros-

copy, transmission electron microscopy, and UVvisible

spectroscopy. GONs/glycerolwater-based nanofluid was

prepared by the two-step method. The stability of the

nanofluid was investigated with respect to time. Thermal

and electrical conductivity of the prepared nanofluid was

examined with different temperatures (2545 C) andweight fractions (0.020.1 wt%). The nanofluid is found to

be stable for more than 5 months. The results showed an

enhancement in thermal conductivity of about 4.5 % at

25 C with a weight fraction of 0.02 %. The improvementwas up to 11.7 % with a weight fraction of 0.1 wt% at

45 C. The electrical conductivity was increased withincreasing the weight fraction and temperature. The

improvement in electrical conductivity was about 5890 %

at 25 C and 0.1 wt%.

Introduction

The rapid development across all the sectors, such as

industrial, transportation, defense, and space, generate a

numerous amount of heat. A small heat transfer system is

required for many applications like electronic cooling in

computers and microprocessors, engine cooling in the

automobile, cooling in space, etc. The conventional fluids,

such as water, ethylene glycol, glycerol, mineral oil, etc.,

have very low thermal conductivities. A better technique is

continuously being explored to improve the thermal per-

formance of the conventional fluid. Thus, dispersing of

nano-sized particle of highly thermal conductivity to the

base fluid was introduced by Choi and Eastman [1] in

Argonne National Laboratory, which termed as nano-

fluid. Eastman et al. [2] examined the thermal conduc-

tivity of ethylene glycol containing copper nanoparticles. It

was found that the thermal conductivity improved by 40 %

by dispersing 0.3 vol%. Choi et al. [3] found that the

thermal conductivity of poly(a-olefin) oil nanofluid raisedby 160 % by adding CNT with 1 vol%. Assael et al. [4]

inspected the enhancement of the thermal conductivity of

water in the presence of MWNT and sodium dodecyl sul-

fate (SDS) as a surfactant. The enhancement of 38 % was

obtained by dispersing 0.6 vol%.

The discovery of graphene by Novoselov and co-

authors [5] has attracted much attention due to two-

dimensional structure, unique physical and chemical

properties [6]. Graphene is a single atom thick nanosheet

of sp2-bonded packed into a honeycomb lattice. Graphene

has shown unusual mechanical, thermal, and electrical

properties such as very high carrier mobility [6], long-

range ballistic transport at room temperature [7], quantum

confinement in nanoscale ribbons [8], single molecule gas

detection sensitivity [9], and high young modules and

A. Ijam R. Saidur (&) P. GanesanDepartment of Mechanical Engineering, University of Malaya,

50603 Kuala Lumpur, Malaysia

e-mail: saidur@um.edu.my

A. Moradi Golsheikh

Low Dimensional Materials Research Centre (LDMRC), Physics

Department, Faculty of Science, University of Malaya,

50603 Kuala Lumpur, Malaysia

R. Saidur

UM Power Energy Dedicated Advanced Centre (UMPEDAC),

University of Malaya, Level 4, Wisma R & D,

50603 Kuala Lumpur, Malaysia

123

J Mater Sci (2014) 49:59345944

DOI 10.1007/s10853-014-8312-2

fracture strength [5]. The thermal conductivity of graph-

ene near room temperature was about 30005000 W/m K

[10]. Due to superb thermal conduction of graphene, it

became an excellent candidate for the thermal manage-

ment [10]. The thermal conductivity of graphene oxide

ethylene glycol nanofluid was reported for the first time

by Yu et al. [11]. An improvement of 61 % at loading of

5 vol% of graphene oxide nanosheets (GONs) was

obtained in room temperature. Thermal conductivity of

graphene oxide with different based fluids (distilled water,

propyl glycol, and liquid paraffin) was reported [12]. At a

load of 5 vol%, the enhancement of the thermal conduc-

tivity for nanofluid was about 30.2, 62.3, and 76.8 % for

the distilled water, propyl glycol, and liquid paraffin,

respectively. Baby and Ramaprabhu [13] prepared and

study the thermal and electrical conductivity of the ther-

mal exfoliated graphene (TEG) water and ethylene glycol-

based nanofluid with a volume fraction of about

0.0050.056 vol% with temperature range (2550 C).They found that the thermal and electrical conductivity

(TEGwater nanofluid) was enhanced about 64 and

1400 % for a volume fraction 0.056 %. For the ethylene

glycol, an enhancement in thermal conductivity of about

67 % was reported.

Yu et al. [14] reported a high thermal conductivity

improvement of about 86 % for the graphene/water nano-

fluid at 30 C and loading of 5 vol%. The sodium dodecyl-benzenesulfonate (SDBS) was used as a surfactant. Arav-

ind and Ramaprabhu [15] reported the in-situ reduction of

the graphite oxide nanofluid under strong alkaline treat-

ment. The investigation of the thermal and electrical con-

ductivity of the graphene ethylene glycol and water

nanofluid was carried out. The maximum enhancement for

the thermal conductivity was about 94.1 % for the water

and 36.1 % for the ethylene glycol with a loading of

0.14 vol%. Furthermore, the electrical conductivity

improvement was about 190 and 55 % for ethylene glycol

and water, respectively.

In this paper, graphene oxide was prepared by the

chemical method. To the best of our knowledge, there is no

report about the thermal and electrical conductivity for the

graphene oxide glycerolwater mixture nanofluid. The

stability and the effect of temperature and weight fraction

on them were investigated.

Experimental

Preparation of the exfoliated graphite GO

Graphite flakes (code no. 3061) were purchased from

Asbury Graphite Mills, Inc (Asbury, NJ). Sulfuric acid

(H2SO4, 98 %), phosphoric acid (H3PO4, 85 %), potassium

permanganate (KMnO4, 99.9 %), hydrogen peroxide

(H2O2, 30 %), and glycerol (C3H8O3, 86 wt%) were pur-

chased from Merck (Darmstadt, Germany). Hydrogen

chloride (HCl, 37 %) was purchased from Sigma-Aldrich

(St Louis, MO).

Exfoliated graphite oxide has been prepared based on

modified Hummers method [16]. Typically, graphite flakes

were oxidized by mixing H2SO4 and H3PO4 with a ratio 4:1

(v/v) at the room temperature. The graphite and potassium

permanganate were added slowly to the above mixture

solution. Then, the mixtures were left for stirring for 3 days

to complete the oxidation of the graphite. After that, hydro-

gen peroxide was added to stop the reaction. The mixture was

sonicated and washed with HCl and water for several times

until pH became neutral. During the washing and sonication

process, the graphite oxide was exfoliated to GONs. The

product was dried in a vacuum oven overnight at 60 C. Theobtained powder was a loose brown with hydrophilic nature.

Figure 1 shows the chemical exfoliation of graphite oxide.

Nanofluid preparation

Two-step method was used to prepare the nanofluid. First,

based fluid was obtained by mixing glycerol (Gly) with

water with the ratio of 4:1 (w/w) and stirred for 1 h to

ensure the homogenization of the base fluid. Then, the

dried (GO) was added to Gly/water with different mass

fractions of (0.020.1) wt%. The mixture was sonicated

and stirred for 1 h using sonication bath (40 kHz, 280 W).

Figure 2 shows the two-step method for preparing the

nanofluid. This is to confirm the uniform suspension of GO

in (Gly ? water).

Characterization, thermal, and electrical conductivity

measurements

Fourier transforms infrared spectroscopy (FTIR) was used

to examine the functional group on the surface of the GO.

FTIR measurements were carried out using a Perkin

Elmer System series 2000 spectrophotometer (USA) in the

range of 4004000 cm-1. The Raman spectra were gained

with a Renishaw Invia Raman Microscope using a laser

with a wavelength of 514 nm. Power X-ray diffraction

characterization was performed using a PANalytical

XPERT Pro X-ray diffractometer with nickel-filtered

Cu Ka radiation as the X-ray source (k = 1.54056 A).The pattern was recorded in the 2h range of 5 to 60 withstep size of 0.026 and scanning speed of 0.1/s. The UVabsorption spectra were achieved by using Cary 50 Bio

UV/visible spectrophotometer with wavelength of

800200 nm. The morphology of GO was identified by

field emission scanning electron microscopy (FESEM,

Hitachi SU8000). Transmission electron microscopy was

J Mater Sci (2014) 49:59345944 5935

123

Fig. 1 Chemical exfoliation of graphite oxide

Fig. 2 An illustration shows the nanofluid preparation and the detail of the experiment set up

5936 J Mater Sci (2014) 49:59345944

123

carried out using (TEM, Hitachi HT7700). For TEM

characterization, the graphene oxide was suspended in

absolute ethanol by the aid of sonication. Then, drop the

dispersion on carbon-coated copper grid, and drying it in

air.

The measurement of nanofluids thermal conductiv-

ity was accomplished by KD2 Pro instrument based on

transient hot wire (THW) method. KD2 Pro has three

sensors for measuring different types of materials with

accuracy of 5 %. As suggested by the manufacture

(decagon devices), the KS-1 sensor with length of 6 cm

and 1.3 mm diameter was used for the liquid. In order

to investigate the effect of temperature on the thermal

conductivity of nanofluid, thermal circulating bath

(polyScience) was used to control the temperature. The

nanofluid samples were sealed in glass container and

immersed in thermal bath. The KD2 Pro was cali-

brated daily with glycerin and distilled water before

taking the measurements. The measured value was

0.288 and 0.6 W/m K at 20 C for glycerin and watercorrespondingly, which are in good agreement with the

literature values of 0.285 and 0.602 W/m K,

respectively.

The error of the measurements was less than 1 %. The

manufacture asserted that the sensor has accuracy within

5 %. Minimum of five readings were taken for each

temperature, and the average value was reported. EU-

TECH instruments, Bench conductivity/TDS meter was

used to measure the electrical conductivity of nanofluid.

The meter was calibrated with distilled water and ethyl-

ene glycol. The error of the measurements was less than

5 %. The sample was placed in a water jacket of the

adapter which was connected to the overstated thermal

circulating bath in order to investigate the effect of tem-

perature on the electrical conductivity. Figure 2 shows the

details of the experiment set up. Five measurements were

taken for each temperature, and the average value was

reported.

Results and discussion

FTIR, Raman spectra, and XRD

Figure 3 shows the FTIR spectra for graphite and graphene

oxide, respectively. For the graphite curve, two peaks at

2925 and 2856 cm-1 are corresponding to the asymmetric

and symmetric vibrations of CH2 groups [17]. The peak at

1634 cm-1 is assigned to the presence of a C=C bond in

graphite [18]. For graphene oxide, a very broad band at

3406 cm-1 refers to stretching vibration of OH [19]. The

peak at 1622 cm-1 is ascribed to the contribution from the

vibration of the aromatic C=C group [20]. The peaks at

1733 and 1367 cm-1 are attributed to C=O and CC

stretching vibration of carboxylic group [21]. This result

shows that the function groups are extensively introduced

to the structure of the carbon. The peak at 1225 cm-1

contributed to COC stretching [22]. Furthermore, the

peaks at 1162 and 1040 cm-1 could be assigned to CO

vibration of epoxy or alkoxy group [23]. This confirms the

successful formation of graphene oxide.

Raman spectroscopy is a powerful technique that used

for characterization of the structure of graphitic materials.

The Raman spectrum for graphite displays a highly strong

peak at 1582 cm-1 (G band) and a very weak peak at

1353 cm-1 (D band). The G band refers to the first-order

scattering of the E2g vibration in sp2 carbon atoms. The D

band represents the sp3 hybridization of carbon atoms and

structure defects, which are caused by breathing mode of

the K-point phonons of A1g symmetry [24]. The ratio of D

band to G band intensities (ID/IG) was only 0.02 indicating

that the graphite is highly ordered structure with low

defects [25]. In graphene oxide, the G band was shifted and

broadened to 1608 cm-1; however, the D band became

eminent in 1349 cm-1. The ratio of D band to G band

intensities for graphene oxide (ID/IG = 0.81) was higher

than graphite. This is due to severe oxidation of graphite by

strong acid during the preparation, which causes destruc-

tion of the sp2 character and creation defects in the

graphene sheets (Fig. 4).

The structure of the crystal was examined using XRD.

Figure 5 shows the XRD result for graphite and graphene

oxide. The graphite shows a strong peak at 26.54 associ-ated with (002) reflection of graphite and interlayer spacing

of 0.335 nm estimated by Braggs equation. Moreover, it

demonstrates an extra peak (004) at 2h = 54.6, corre-sponding to an interlayer distance of 0.167 nm. The peak

of (002) has been shifted to 9.21 after oxidation of

Fig. 3 FTIR for graphite and graphene oxide

J Mater Sci (2014) 49:59345944 5937

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graphite. The d-spacing of GO now rises to 0.95 nm. The

increase in interlayer spacing is due to the formation of a

large number of oxygen containing function groups in

between the graphene sheets. Additionally, there is a small

lump close to 18.1 reveals that the graphite was notcompletely oxidized [20].

Morphology, stability, and UVvisible

The morphology of graphene oxide has been inspected by

high-resolution field emission electron microscopy (FE-

SEM) and TEM as shown in Fig. 6ac. The images show a

winkled surface and folds at the edges of the nanosheets.

Furthermore, the TEM image shows the transparent

graphene nanosheets which appeared in style of few layer.

The size of the graphene nanosheets is in the range of

0.52 lm, and few of them are larger than 3 lm. Thestability of the graphene oxide nanofluid is checked by

measuring the thermal conductivity with time for several

days. The stability of the nanofluid is reflected with time

through the constancy in thermal conductivity of it.

According to Fig. 7, it can be seen that the thermal

conductivity of all the samples remains constant with time

(14 days). This confirmed that the nanofluid is highly sta-

ble. Figure 6d, e shows the nanofluid just prepared and

after 5 months. The digital photographs of the graphene

oxide with different loadings show that there are no sedi-

mentations observed after 5 months of the prepared nano-

fluid. Additionally, the stability of the nanofluid was

confirmed by UVvisible spectroscopy.

UVvisible spectroscopy is an appropriate procedure to

investigate the stability of nanocolloids quantitatively.

Figure 8 shows the UVvisible spectrum of GO suspended

in Gly/water. The main absorption peak at 230 nm which

refers to the p ? p* transition of aromatic CC. There is asmall shoulder peak around 300 nm assigned to n ? p*transition of C=O bond [18]. The UVvisible was mea-

sured after 5 months and there are no distinguish differ-

ences in intensity between the nanofluid just prepared and

after 5 months. It exhibited a long-term stability due to

hydrophilic nature of the graphene oxide and glycerol

water mixture (Fig. 8).

Thermal conductivity of nanofluid

The thermal conductivity of nanofluid was measured with

the different weight fractions at 30 C as shown in Fig. 9.The results showed that the thermal conductivity was

increased with increasing the loading of the graphene

oxide. Figure 10 shows the effect of temperature on the

thermal conductivity enhancements with different weight

fraction. The thermal conductivity increased with raising

the temperature. It exhibited a nonlinear behavior with

temperature, and the nonlinear behavior was already stated

for the carbon-based nanofluid [2]. The enhancement per-

centage was calculated based on the formula below:

%Enhancment knf koko

100; 1

where knf and ko are the thermal conductivity of nanofluid

and the base fluid, respectively. A maximum enhancement

of 4.5 % was achieved at 25 C with 0.02 wt%. Thehighest improvement in thermal conductivity of Gly

water-based nanofluid is about 11.7 % at 45 C with0.1 wt%.

The enhancement in thermal conductivity was reported

by several researches due to effect of the Brownian motion

of the nanoparticles and the micro-convection caused by

Brownian motion [2628]. On the other hand, the

Fig. 4 Raman spectra for graphite and graphene oxide (GO)

Fig. 5 XRD analysis for graphite and graphene oxide (GO)

5938 J Mater Sci (2014) 49:59345944

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enhancement in thermal conductivity is owing to the per-

colation structure formed by the nanoparticles, which acts

as conducting path [29, 30]. The thermal conductivity and

the stability were compared with other reports based on the

enhancement as explained in Tables 1 and 2. Yu et al. [12,

14] examined the thermal conductivity of the graphene

oxide in distilled water and ethylene glycol with the vol-

ume fraction of 15 %. His results showed that an

improvement was about 30.2 and 61 % with a loading of

5 %. The enhancements were almost constant with respect

to the temperature. It can be seen that the high concen-

tration of the graphene oxide in the base fluid will limit the

effect of the Brownian motion of the nanoparticle induced

by micro-convection. The GONs became nearer to each

other and cause the formation of percolation structure [31].

Unlike, Baby and Ramaprabhu [13] showed a high

improvement (64 %) in thermal conductivity of the water

by dispersing graphene nanosheets with 0.056 vol% at

50 C. Similarly, he prepared nanofluid by dispersingfunctionalized hydrogen exfoliated graphene (f-HEG) in

deionized water [32]. His results claimed that an

enhancement of 75 % was achieved. In both studies, the

enhancements were dependent on the temperature. The

mechanism of the Brownian motion of the nanoparticle

Fig. 6 a FESEM and b, c TEM for graphene oxide nanosheets. Digital photo of the nanofluid d just prepared and e after 5 months

Fig. 7 Thermal conductivity of nanofluid with timeFig. 8 UVvisible spectroscopy of GOGly/water

J Mater Sci (2014) 49:59345944 5939

123

caused the raising the thermal conductivity of the nano-

fluid. Gupta et al. [33] examined the thermal conductivity

of the graphene nanosheets nanofluid and a maximum

enhancement of 27 % was obtained. According to his

study, the size of the particle and amount of loading play an

important role in interconnected network formation.

In the present study, the based fluid thermal conductivity

did not display much enhancement with respect to tem-

perature. The size of the GO sheets was claimed to be from

0.5 to 2 lm, and the concentration was from 0.02 to0.1 wt%. It was larger than size of the graphene nanosheets

obtained in Gupta and smaller than Yu. In our opinion, the

enhancement in the thermal conductivity of the base fluid

because of two reasons. First, the larger size of GONs will

be near each other, and form interconnects network like

chain structure subsequent percolation theory. Second, the

random motion of the smaller size of the nanosheets will

cause Brownian motion. As a result, the micro-convection

produced by Brownian motion will enhance the thermal

conductivity with an increase in temperature. This result

has a good agreement with previous report [33]. It was

suggested by Jang and Choi [27] that the random motion of

the nanoparticles (Brownian motion) will increase, and the

viscosity of the base fluid will decrease due to the raising

the temperature. The micro-convection happened because

the Brownian motion of nanoparticle, which results in

increased the thermal conductivity. The pure glycerol is

highly viscous but in this study the glycerol contains about

14 % water. Moreover, it was mixed with water, and the

viscosity decreased. However, Tadjarodi and Zabihi [34]

measured the thermal conductivity of the mSiO2glycerol

nanofluid. Their results showed that there is no obvious

effect on the thermal conductivity while increasing the

temperature. The fact is that the suspension was converted

to gel-like form because of the high concentration, which

reduces the effect of Brownian motion. In addition, the

thermal conductivity enchantment was lower than other

reports [13, 32, 33, 35]. The graphite flakes were treated by

strong acid which can cause defects on the structure of the

graphite oxide sheets. The graphene oxide was prepared by

exfoliating the graphite oxide by using sonication. The

sonication process has a bad impact, which can cause

breaking the large sheets of the graphene oxide. It was

confirm earlier by Raman spectra which shows that the

graphene oxide contains higher defects than the graphite

flakes. These defects have a great effect on the thermal

conductivity of the graphene oxide.

Meanwhile other researchers [3638] reported a very

high thermal conductivity improvement because of the

presence of the nanoparticles which formed on the surface

of the graphene nanosheets.

Electrical conductivity of nanofluid

The effect of weight fraction and temperature on the

electrical conductivity of the graphene oxide nanofluid has

been examined as shown in Figs. 11 and 12. The results

showed that the electrical conductivity increased with

increasing the weight fraction. For example, the electrical

conductivity of the base fluid at 25 C is 0.32 lS/cm.However, the electrical conductivity has been increased to

19.17 lS/cm when the weight fraction increased to 0.1 %.Furthermore, the electrical conductivity improved when the

temperature rose. The temperature and weight fraction

have a positive effect on the electrical conductivity of the

nanofluid. The maximum enhancement for electrical con-

ductivity was computed based on the below formula:

Fig. 9 Effect of the loading on the thermal conductivity

Fig. 10 Effect of temperature on the thermal conductivityenhancements

5940 J Mater Sci (2014) 49:59345944

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%Enhancment r roro

100; 2

where r is the electrical conductivity of the nanofluid andro is electrical conductivity of the based fluid. A max-imum enhancement of about 5890 % was achieved at

25 C with 0.1 %. Baby and Ramaprabhu [13] examinedthe electrical conductivity of the graphene/DI water. His

results showed an enhancement of 1400 % was achieved at

25 C. Table 3 summaries the previous studies on electri-cal conductivity of nanofluid. The electrical double-layer

(EDL) characteristics, weight fraction, ionic concentra-

tions, and other physicochemical properties are the factors

that significantly change the electrical conductivity of

colloidal nanosuspensions in a liquid [40]. An enhance-

ment in electrical conductivity with respect to the base

fluid is resulted from the related EDL interactions and the

net charge effect of the solid [41, 42]. When GONs

dispersed in polar solvent (Gly ? water), electric charges

develop on the surfaces/surrounding of the particle. This is

because of the development of the charged diffuse layer

when ions of charge opposite to that of the particle surface

are attached.

This charged diffuse layer, which is known as EDL [41], can

be characterized using j-1 (Debye length) parameter. Conse-quently, conduction mechanisms through the suspension are

enhanced. In addition, the presence of uniformly dispersed

nanoparticles increases the electrophoretic mobility. There-

fore, the effective electrical conductivity of the nanofluid sus-

pension increases [40]. The availability of conducting

pathways increases in the solution as the particle volume

fraction increases and as a result the overall electrical con-

ductivity of the solution increases. An increase in temperature

has a positive effect on the enhancement in the electrical con-

ductivity of the nanoparticle suspension [40] (i.e., j-1 (i.e.,EDL thickness) increases) according to DLVO theory [41].

Table 1 Thermal conductivity of graphene materials nanofluid and their enhancements

Researcher Base fluid Material Synthesis method Loading TC

(%)

Yu et al. [11] Ethylene glycol GONs Modified Hummers

method

15 vol% 61

Yu et al. [12] Distilled water GONs Modified Hummers

method

15 vol% 30.2

Baby and Ramaprabhu

[13]

Water GNs Hummers method 0.0050.056 vol% 64

Baby and Ramaprabhu

[13]

Ethylene glycol GNs Hummers method 0.0050.05 vol% 67

Yu et al. [14] Ethylene glycol GNs Modified Hummers

method

15 vol% 86

Baby and Ramaprabhu

[36]

Deionized water HEG coated with Ag

nanoparticles

Hummers method 0.0050.05 vol% 86

Ethylene glycol HEG coated with Ag

nanoparticles

Hummers method 0.010.07 vol% 14

Baby and Ramaprabhu

[37]

Deionized water HEG coated with CuO

nanoparticles

Hummers method 0.0050.05 vol% 90

Ethylene glycol HEG coated with CuO

nanoparticles

Hummers method 0.010.07 vol% 23

Baby and Ramaprabhu

[32]

Deionized water f-HEG Hummers method 0.0050.05 vol% 75

Ethylene glycol f-HEG Hummers method 0.050.08 vol% 5

Gupta et al. [33] water GNs Hummers method 0.010.2 vol% 27

Aravind and Ramaprabhu

[15]

Deionized water GNs Hummers method 0.0090.14 vol% 94.3

Ethylene glycol GNs Hummers method 0.0080.14 vol% 36.1

Aravind and Ramaprabhu

[38]

Deionized water GNs wrapped MWNT Hummers method 0.0110.04 vol% 97.5

Ethylene glycol GNs wrapped MWNT Hummers method 0.0110.04 vol% 24

Kole and Dey [39] Distilled water/ethylene

glycol

f-HEG Hummers method 0.0410.395 vol% 17

Ghzatloo et al. [35] Deionized water FG CVD method 0.010.05 % 13.5

Present study Gly/water GONs Modified Hummers

method

0.020.1 wt% 11.7

J Mater Sci (2014) 49:59345944 5941

123

Conclusion

In this study, the graphene oxide nanosheets (GONs) has

been prepared by using chemical method. The stability of

the GONs/glycerolwater nanofluid was investigated. The

effect of concentration and temperature on the thermal and

electrical conductivity has been examined. The following

conclusion can be gained:

(1) The thermal conductivity of the nanofluid remained

almost constant within 14 days. It reflects the high

Table 2 The stability ofgraphene materials nanofluid

with different base fluid

Researcher Base fluid TC

measurement

Temperature

(C)Stability

Yu et al. [11] Ethylene glycol THW 1060 More than 2 months

Yu et al. [12] Distilled water THW 1060 Long-term stability

Yu et al. [14] Ethylene glycol THW 1060 Stable

Baby and

Ramaprabhu [13]

Water KD2 Pro 2550 N/A

Baby and

Ramaprabhu [36]

Deionized water KD2 Pro 2570 No visible settling of HEG/Ag

after 2 months

Ethylene glycol KD2 Pro 2570 No visible settling of HEG/Ag

after 2 months

Baby and

Ramaprabhu [37]

Water KD2 Pro 2550 N/A

Ethylene glycol KD2 Pro 2550 N/A

Baby and

Ramaprabhu [32]

Deionized water KD2 Pro 2550 No sedimentation was

observed after 2 months

Ethylene glycol KD2 Pro 2550 No sedimentation was

observed after 2 months

Gupta et al. [33] Water THW 20 Stable for more than 6 months

Aravind and

Ramaprabhu [15]

Deionized water KD2 Pro 2550 Stable more than 1 month

Ethylene glycol KD2 Pro 2550 Stable more than 1 month

Aravind and

Ramaprabhu [38]

Deionized water KD2 Pro 2550 Stable for more than 6 months

Ethylene glycol KD2 Pro 2550 Good stability

Kole and Dey [39] Distilled water/

Ethylene glycol

THW 1070 Stable for more than 5 months

Ghzatloo et al. [35] Deionized water KD2 Pro 1050 Long-term stability

Present study Gly/water KD2 Pro 2545 Stable more than 5 months

Fig. 11 Electrical conductivity versus weight fractionFig. 12 Electrical conductivity of nanofluid with the temperature

5942 J Mater Sci (2014) 49:59345944

123

stability of the nanofluid. UVvisible was confirmed

the stability of the nanofluid after 5 months.

(2) The thermal conductivity of the Glywater was

increased by suspending the GONs. The thermal

conductivity increased with raising the temperature

in a nonlinear manner.

(3) An improvement of 4.5 % in thermal conductivity

for GONs/Glywater nanofluid was gained at 25 Cwith a weight fraction of 0.02 %. In addition, the

thermal conductivity enhanced up to 11.7 % at

45 C with a weight fraction of 0.1 wt%.(4) The electrical conductivity increased linearly with

increasing the temperature and weight fraction. A

maximum enhancement of 5890 % in electrical

conductivity at 25 C and 0.1 % weight fractionwas obtained.

Acknowledgements The first author would like to thank Mr.Mohammed Ijam for his kind support and valuable discussion. This

work was supported by the High Impact Research Grant (HIRG)

Scheme (UM-MOHE) Project No. UM.C/HIR/MOHE/ENG/40.

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enhancements

Researcher Base fluid Material Temperature

(C)EC

enhancement

Baby and Ramaprabhu

[13]

Water GNs 2550 1400 %

Ethylene glycol GNs 2550 220 %

Baby and Ramaprabhu

[37]

Deionized water HEG/CuO 2550 N/A

Ethylene glycol HEG/CuO 2550 N/A

Baby and Ramaprabhu

[32]

Deionized water f-HEG 2550 N/A

Ethylene glycol f-HEG 2550 N/A

Aravind and

Ramaprabhu [15]

Deionized water GNs 2550 55 %

Ethylene glycol GNs 2550 190 %

Aravind and

Ramaprabhu [38]

Deionized water GNs wrapped

MWNT

2550 N/A

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glycol

GNs 1070 8620 %

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Ganguly et al. [40] Water Al2O3 2445 2127 %

White et al. [44] Propylene glycol ZnO 25 100-fold

Wong and Kurma [45] Water Al2O3 250 3457.1 %

Present study Gly/water GONs 2545 5890 %

J Mater Sci (2014) 49:59345944 5943

123

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A glycerol--water-based nanofluid containing graphene oxide nanosheetsAbstractIntroductionExperimentalPreparation of the exfoliated graphite GONanofluid preparationCharacterization, thermal, and electrical conductivity measurements

Results and discussionFTIR, Raman spectra, and XRDMorphology, stability, and UV--visibleThermal conductivity of nanofluidElectrical conductivity of nanofluid

ConclusionAcknowledgementsReferences