Reduction of graphene oxide in ethanol solution by gamma irradiation for preparing reduced graphene oxide material with water desalination

esalination efficiency of 
rGO was about 46 – 48%. 
Keywords: graphene oxide, gamma, irradiation, desalination. 
I. INTRODUCTION 
Graphene can be defined as a mono-
layer of carbon atoms connected by the sp
2
bonds forming the hexagonal lattice in 
structure [1] (Fig.1). It was discovered by two 
scientists of Novoselov and Gein (2004) with 
its attractive properties including good thermal 
conductivity, large theoretical specific surface 
area, high electron mobility, good optical 
transmittance; in addition, it is so thin and 
harder than diamonds [1,2]. Until now, 
graphene has been studied for application in 
many high-technique fields such as bio-sensor, 
solar cells, energy storage and so on [1,2]. 
Fig.1. Structure of graphene material 
In recent years, graphene material was 
prepared by reduction process of graphene 
oxide (GO) through many different methods: 
chemical, solvothermal, electrochemical 
method, ultrasonic irradiation, gamma rays or 
electron beam irradiation and so on [3-11]. 
And GO is usually synthesized via an 
oxidizing process of graphite using oxidants 
based on Hummers’method and modified 
Hummers’approach [5]. There are lots of 
reduction routes of GO sheets to produce rGO 
with a good improvement of its properties as 
graphene’s ones. One of useful properties of 
graphene and GO is its ability of water 
desalination [12-14]. 
In this work, we focus on the reduction 
of GO to prepare reduced GO (rGO) by gamma 
rays irradiation in ethanol/water medium to 
improve the ability of desalination aiming at 
the development and production of membrane 
filter applied in treatment of salt water or 
brackish water. 
PHAM THI THU HONG et al. 
35 
II. EXPERIMENTAL 
Sample irradiation to prepare rGO 
Graphite oxide was synthesized from 
graphite powder (SEC Carbon, Japan) by the 
modified Hummer’s method [5, 11]. GO 
suspension was prepared by adding an amount 
of 0.01 g of GO in 10 ml of ethanol/water 
solution (25%, v/v) and dispersed under 
ultrasonic for 1 hour in an ultrasonic bath 
(Elma Elmasonic S40H, Germany). The 
prepared suspension was sealed and irradiated 
at a room temperature by gamma Co-60 rays in 
the range of absorbed doses from 0 to 100 kGy 
with the dose rate of 1.0 kGy/h. Irradiated GO 
(or rGO) was filtrated and washed by distilled 
water several times, dried at 70
o
C and ground 
into a fine powder for next experiments. 
Fig. 2. Suspensions of GO and rGO irradiated at 
doses of 25, 50 and 100 kGy 
Preparation of rGO films 
The rGO films were prepared by 
dispersing 0.04 g of rGO in 200 ml of ethanol 
solvent under ultrasonic for 2 hours in the 
ultrasonic bath. Then, the suspension was 
centrifuged at 2000 rpm by a centrifuge (EBA 
12, Hettich, Germany) and decanted the 
supernatant. rGO films were obtained by 
vacuum filtration of the prepared rGO with an 
alpha-cellulose membrane, washing with 
distilled water several times, dried at 80
o
C for 
48 hours and kept in a desiccator before use. 
Fig. 3. rGO film (a) and rGO films on cellulose 
acetate membrane (b) 
Characterization 
- UV-vis absorption spectra were 
measured with a JASCO V630 
spectrophotometer, Japan in the wavelength 
region of 200 – 800 nm. Gamma ray pre-
irradiated and post-irradiated GO samples in 
ethanol/water solution were prepared at a 
concentration of 0.025 mg/ml. 
- X-ray diffraction patterns of the 
samples were taken on a XRD D8 Advance 
diffractometer, Bruker, Germany with 
monochromatized Cu-K radiation (l= 
1.5406Å) at a scanning rate of 0.04 
o
/s in a 
wide angle range (2q = 5 - 30
o
) at ambient 
temperature. 
- The TEM measurements of all samples 
were performed on a JEM 1010 instrument, 
JEOL, Japan with the high resolution scanning 
electron micro-scope plus a transmission 
mode. 
- Contact angle measurement: A rGO 
film was prepared with diameter of 33 
millimeters and weight of 20 mg. Surface 
wettability of all sample films was measured 
on an OCA 20L instrument (Germany) using 
distilled water as a wettable solvent in 
condition of room temperature. 
- Test of water desalination: NaCl 
solution was prepared at the concentration of 
4% (like the salt concentration in seawater) and 
1% (like the salt concentration in brackish 
REDUCTION OF GRAPHENE OXIDE IN ETHANOL SOLUTION BY GAMMA IRRADIATION FOR 
36 
water). NaCl solution with the volume of 150 
ml was filtered through rGO films by vacuum 
filtration. NaCl concentration in filtered 
solution was measured by indirect 
potentiometric method determining electrical 
conductivity [15], in which a standard line 
shows the relationship between NaCl 
solution’s concentration and its electrical 
conductivity at temperature of 25 °C. 
Desalination efficiency (DE) of rGO films was 
evaluated by the following formula: 
DE (%) 
Where C0 is the initial concentration of 
NaCl solution and C1 is the concentration of 
filtered NaCl solution through rGO film. 
III. RESULTS AND DISCUSSION 
UV-vis spectra 
Fig.4. The UV-Vis spectra of GO and rGO 
irradiated at different absorbed doses 
Fig. 4 shows UV-Vis spectra GO and 
resulted rGO at dose of 25, 50 and 100 kGy. 
As indicated in Fig. 4, the UV-vis spectrum of 
GO with the shoulder peak around 240 nm due 
to n π* transition of C=O bonds but this peak 
was changed after gamma rays irradiation with 
doses from 25 to 100 kGy. It was 
characterized with the strong absorption peak 
of GO at around 240 nm regarding to π π* 
transition of aromatic C – C bonds red-shifted 
to 264, 266 and 268 nm corresponding to the 
absorbed doses of 25, 50 and 100 kGy, 
respectively. It suggested that the reduced GO 
was formed in the presence of ethanol/water 
by the gamma ray irradiation at high absorbed 
dose. This meant that the electronic 
conjugation in the graphene sheets was re-
arranged and partially restored. 
It is sure that the radiolysis of water is the 
main mechanism that induced the reduction 
process. On the radiation chemistry, water 
molecular was decomposed into some products 
which are 
H, 
OH, OH
-
, eaq, H2, H2O2, H3O
+
and 
H2O by gamma irradiation. Hydrated 
electron (eaq) and 
H are the major reducing 
species among the products of water radiolysis, 
while hydroxyl radical, 
OH is the major 
oxidizing species produced [18]. In this work, 
ethanol was used as radical scavenger to 
eliminate the hydroxyl radical, thereby 
accelerating the reduction process of GO. In the 
reduction process, hydrated electron interacts 
with hydroxyl and carboxyl group attached to 
GO, removing oxygen to form rGO. 
XRD pattern 
XRD patterns of graphite and GO are 
shown in Fig.5a. It can be observed a sharp 
peak with high intensity at 2θ = 26.3o, 
corresponding to d002 = 3,395Å. It implied that 
graphite has an orderly crystalline structure. 
Meanwhile, GO's XRD pattern appeared a 
larger peak with low intensity at 2θ = 11.6o, 
corresponding to d002 = 7,617Å. 
This result indicated that orderly 
crystalline structure of graphite was changed 
and the gap between the graphite layers has 
been widened because the oxidation of 
Hummer’s method prepared the polar 
functional groups such as hydroxyl, carboxyl 
on the carbon layers. 
PHAM THI THU HONG et al. 
37 
Fig. 5a. XRD patterns of Graphite and GO 
Fig. 5b. The XRD patterns of GO and rGO 
irradiated at 25, 50 and 100 kGy. 
The results as shown in Fig.5b indicated 
that rGO resulted by gamma ray irradiation in 
the dose range of 25-100 kGy had diffraction 
peak at 2θ ~ 12 – 13o, which was the 
characteristic peak of GO. It suggested that a 
few hydrophilic functional groups still existed in 
the structure of rGO after gamma irradiation of 
GO in the ethanol/water solution. And the 
intensity decreased with the increase of 
absorbed doses for irradiated GO. Thus, the 
obtained result proved that the crystalline 
structure of GO had changed due to gamma ray 
irradiation of GO in the ethanol/water solution. 
TEM images 
TEM images of non-irradiated and 
irradiated GO suspensions at 50 kGy are 
shown in Fig.6. The non-irradiated suspension 
of GO with a structure of stacked layers by a 
lot of GO layers was observed in Fig.6a. The 
image of rGO was observed on highly 
exfoliated graphite as shown in Fig.6b. The 
high transparent areas indicated the creation of 
thin layer structure by a few exfoliated GO 
layers after –ray irradiation-induced reduction 
in the solutions [16]. 
Contact angle measurement 
Results in Table 2 and Fig.7 showed the 
differences in the contact angles of GO and 
rGO films for the water drops formed on their 
surface, which was used to evaluate the surface 
wettability of these films [9]. It indicated that 
the water droplet was dropped on the GO and 
rGO film, resulting in an increase of the 
contact angle of from 58.2 ± 0.7
o
 for GO 58.3 
± 0.5
o
, 61.2 ± 1.1
o
 and 74.2 ± 0.9
o
 for 
irradiation-reduced GO at dose of 25, 50 and 
100 kGy, respectively. 
Fig.6. TEM images of GO sheet (a) and rGO-50 kGy (b) 
C
o
u
n
ts
 (
a
.u
) 
a b 
REDUCTION OF GRAPHENE OXIDE IN ETHANOL SOLUTION BY GAMMA IRRADIATION FOR 
38 
Fig.7. Photos for contact angle measurement of GO (a), rGO-25 kGy (b), 
rGO-50 kGy (c) and rGO-100 kGy (d). 
Table I. The results of contact angle of GO and rGO films 
Sample Dose, kGy Contact angle, degree 
GO 0 58.2 ± 0.7 
rGO-25 25 58.3 ± 0.5 
rGO-50 50 61.2 ± 1.1 
rGO-100 100 74.2 ± 0.9 
Table II. The results of water desalination of GO and rGO films 
Sample Desalination efficiency, % 
4% NaCl solution 1% NaCl solution 
GO 15.4 ± 0.9 33.4 ± 0.6 
rGO-25 19.6 ± 0.6 46.0 ± 1.2 
rGO-100 20.3 ± 0.8 48.0 ± 0.7 
It meant that the GO was reduced 
remarkably to form rGO due to the resulted rGO 
films were non-wetting with water and became 
more hydrophobility than GO films [17]. 
Test of water desalination 
Table III shows the filtration efficiency 
of saline solution in GO and rGO films at a 
pressure of 2 psi in vacuum filtration at 
temperature 30
o
C. The results showed that 
rGO exhibited higher desalination efficiency 
than that of GO, for example the salt filtering 
efficiency of GO and rGO-25 for NaCl 4% 
solution was 15.4% and 19.6%, respectively. 
The dose does not significantly affect the salt 
filtration efficiency of rGO membrane, 
particularly the desalination efficiency of 
rGO-25 and rGO-100 for NaCl 4% solution 
was 19.6% and 20.3%, respectively. In 
addition, the concentration of salt in the 
initial solution also affects the salt filtration 
ability of the film, the higher the salt 
concentration, the lower the salt filtration 
efficiency of the film. 
PHAM THI THU HONG et al. 
39 
IV. CONLUSIONS 
Graphene oxide can be simply reduced 
and exfoliated by gamma Co-60 ray irradiation 
in alcohol/water solution. The transparent 
solution of rGO was obtained after gamma 
irradiation-induced reduction, which was 
confirmed by analysis of rGO through UV-Vis 
spectra, XRD pattern and TEM images. 
Hydrophobic properties of rGO increased 
steadily with the increase of absorbed dose. 
Desalination ability of rGO film was better 
than that of GO one. Further research should 
be carried out to analyze the effect of filtration 
pressure and desalination capacity of rGO film. 
ACKNOWLEGEMENTS 
The authors would like to thanks 
VINAGAMMA Center for helping in gamma 
irradiation. 
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