Reduction of graphene oxide in ethanol solution by gamma irradiation for preparing reduced graphene oxide material with water desalination
Nuclear Science and Technology, Vol.9, No. 1 (2019), pp. 34-40
Reduction of graphene oxide in ethanol solution by gamma
irradiation for preparing reduced graphene oxide material
with water desalination
Pham Thi Thu Hong*, Nguyen Thanh Duoc, Nguyen Thi Ly,
Chu Nhut Khanh, Cao Van Chung, Doan Binh.
Research and Development Center for Radiation Technology,
202A street 11, Linh Xuan ward,Thu Duc district, HCM. City, Vietnam;
(Received 07 September 2019, accepted 20 September 2019)
Abstract: Reduction of graphene oxide (GO) for preparing the reduced graphene oxide (rGO) by γ–
ray irradiation was investigated. GO was dispersed in the ethanol solution with the GO concentration
of 1 mg/ml, then irradiated with γ–ray in presence of oxygen at dose range of 0 – 100 kGy for
preparation of rGO product. The characteristic properties of GO and rGO were determined by UV-Vis
spectroscopy, X–ray diffraction (XRD), Transmission Electron Microscopy (TEM), contact angle
measurement and test of water desalination. The result showed that water desalination efficiency of
rGO was about 46 – 48%.
Keywords: graphene oxide, gamma, irradiation, desalination.
In recent years, graphene material was
prepared by reduction process of graphene
oxide (GO) through many different methods:
I. INTRODUCTION
Graphene can be defined as a mono-
layer of carbon atoms connected by the sp2
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].
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.
Fig.1. Structure of graphene material
©2019 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
PHAM THI THU HONG et al.
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 70oC and ground
into a fine powder for next experiments.
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=
o
1.5406Å) at a scanning rate of 0.04 /s in a
wide angle range (2q = 5 - 30o) 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.
Fig. 2. Suspensions of GO and rGO irradiated at
doses of 25, 50 and 100 kGy
Preparation of rGO films
-
Contact angle measurement: A rGO
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 80oC for
48 hours and kept in a desiccator before use.
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
35
REDUCTION OF GRAPHENE OXIDE IN ETHANOL SOLUTION BY GAMMA IRRADIATION FOR…
water). NaCl solution with the volume of 150
ml was filtered through rGO films by vacuum
filtration. NaCl concentration in filtered
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.
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:
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
DE (%)
Where C0 is the initial concentration of
NaCl solution and C1 is the concentration of
filtered NaCl solution through rGO film.
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.
III. RESULTS AND DISCUSSION
UV-vis spectra
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.
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 nπ* 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*
36
PHAM THI THU HONG et al.
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].
Fig. 5a. XRD patterns of Graphite and GO
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 ± 0.7o for GO 58.3
± 0.5o, 61.2 ± 1.1o and 74.2 ± 0.9o for
irradiation-reduced GO at dose of 25, 50 and
100 kGy, respectively.
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
b
a
Fig.6. TEM images of GO sheet (a) and rGO-50 kGy (b)
37
REDUCTION OF GRAPHENE OXIDE IN ETHANOL SOLUTION BY GAMMA IRRADIATION FOR…
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
GO
Dose, kGy
Contact angle, degree
58.2 ± 0.7
0
rGO-25
rGO-50
rGO-100
25
58.3 ± 0.5
50
61.2 ± 1.1
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
33.4 ± 0.6
GO
15.4 ± 0.9
19.6 ± 0.6
20.3 ± 0.8
rGO-25
rGO-100
46.0 ± 1.2
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].
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.
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 30oC. The results showed that
rGO exhibited higher desalination efficiency
than that of GO, for example the salt filtering
38
PHAM THI THU HONG et al.
[6]. C. Xu, R. Yuan, and X. Wang, “Selective
IV. CONLUSIONS
reduction of graphene oxide”, New Carbon
Materials, 29, 61-66, 2014.
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.
[7]. X. Li, T. Tang, M. Li, and X. He,
“Photochemical doping of graphene oxide thin
films with nitrogen for electrical conductivity
improvement”, Journal of Material Science:
Materials in Electronics, 26, 1770-1775, 2015.
[8]. V. Singh, D. Joung, L. Zhai, S. Das, S.I.
Khondaker, and S. Seal, “Graphene based
materials: Past, present and future”, Progress in
Materials Science, 56, 1178-1271, 2011.
[9]. Z. Wang, P. Li, Y. Chen, J. He, B. Zheng, J.
Liu, and F. Qi, “The green synthesis of reduced
graphene oxide by the ethanol-thermal reaction
and its electrical properties”, Materials Letters,
116, 416-419, 2014.
ACKNOWLEGEMENTS
[10]. M. Park, H.K. Shin, B.S. Kim, B. Pant,
N.A.M. Bakakat, and H.Y. Kim, “Facile
preparation of graphene induced from electron-
beam irradiated graphite”, Materials Letters,
105, 236-238, 2013.
The authors would like to thanks
VINAGAMMA Center for helping in gamma
irradiation.
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