DSpace at VNU: Pre-irradiation grafting of acrylonitrile onto chitin for adsorption of arsenic in water

Radiation Physics and Chemistry 106 (2015) 235–241

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Radiation Physics and Chemistry
journal homepage: www.elsevier.com/locate/radphyschem

Pre-irradiation grafting of acrylonitrile onto chitin for adsorption
of arsenic in water
Truong Thi Hanh a,n, Ha Thuc Huy b, Nguyen Quoc Hien a
a
Research and Development Center for Radiation Technology, Vietnam Atomic Energy Institute, 202A, Street 11, Linh Xuan Ward, Thu Duc District,
Ho Chi Minh City, Viet Nam
b
The University of Science, Vietnam National University, 227, Nguyen Van Cu Street, District 5, Ho Chi Minh City, Viet Nam

H I G H L I G H T S







Partially deacetylated chitin was used for grafting AN by pre-irradiation.
The maximal grafting degree of AN onto chitin was 114%.
The cyano- of AN was converted into amidoxime to enhance adsorption.
The adsorption capacity of As(III) onto modified chitin was 19.724 mg/g.
Removal of arsenic in groundwater samples was tested by continuous adsorption.

art ic l e i nf o

a b s t r a c t

Article history:
Received 16 May 2014
Accepted 2 August 2014
Available online 12 August 2014

Radiation-induced grafting is an effective technique for preparation of novel materials. In this study,
partially deacetylated chitin with deacetylation degree (DDA) of about 40% was graft-copolymerized
with acrylonitrile (AN) by a γ-ray pre-irradiation method. The maximal grafting degree of AN onto preirradiated chitin at 25 71.2 kGy was 114% for AN concentration in dimethylformamide of 40% (v/v) at
70 1C for 8 h. The mixture ratio of 0.1 N NH2OH Á HCl to 0.1 N NaOH was selected to be 7:3 (v/v) for
amidoxime conversion of cyano-groups on grafted chitin (Chi-g-AN). The characteristics of modified
chitin were depicted by the FT-IR spectra, BET area and SEM images. Adsorption equilibrium of As(III)
onto Chi-g-AN converted amidoxime (Chi-g-AN-C) fits with the Langmuir model and the maximal
adsorption capacity was 19.724 mg/g. The break-through times of As(III) on Chi-g-AN-C in column
adsorption experiments increased with the increase in bed depths.
& 2014 Published by Elsevier Ltd.

Keywords:
Chitin
Acrylonitrile
Arsenite
Pre-irradiation
Grafting
Adsorption

1. Introduction
Modification of polymer by radiation grafting techniques has
been applied to prepare novel materials, including adsorbents for

environmental and industrial applications (Tamada, 2004; Chen
et al., 2007). A large amount of free radicals is produced in
the irradiated polymer without the use of chemical initiators
and these radicals easily reacted with a functional monomer by
covalent bonds to form macromolecular chains. In this way, the
polymer properties were improved and thus the graft copolymerization was commonly used.
In the past decades, besides studying the degradation effect of
natural polymers by radiation, modification by grafting monomers
on these substrates has also been carried out by many scientists

n

Corresponding author. Tel.: þ 84 8 62829159; fax: þ84 8 38975921.
E-mail address: (T.T. Hanh).

/>0969-806X/& 2014 Published by Elsevier Ltd.

(Barakat, 2011; Boddu et al., 2008; Laus et al., 2010). Chitin and its
deacetylated form chitosan are bio-renewable, biodegradable, biocompatible, inexpensive and environmentally friendly polymers.
Chitin is a heteropolymer made up of β-(1-4)-2-acetamido2-deoxy-β-D-glucopyranose units. It can be extracted from crustacean shell such as prawns, crabs, fungi, insects and other crustaceans (Wan Ngah and Isa, 1998).
Chitosan can be used as an adsorbent to remove heavy metals
and dyes due to the presence of amino and hydroxyl groups, which
can serve as the active sites (Wu et al., 2001). The heavy metal ions
such as As(III), As(V), Cd2 þ , Hg2 þ and Pb2 þ in the groundwater
and industrial wastewater caused pollution. High arsenic concentration in groundwater has been reported recently from USA,
China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland,
Canada, Hungary, Japan and India (Mohan and Pittman, 2007).
The current WHO recommended guideline value for arsenic in
drinking water is less than 10 mg/l, whereas many countries are
still having a value of 50 mg/l (Jack et al., 2003). Especially, in

236

T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

Vietnam the water from Red River delta with average arsenic
concentrations of 159 mg/l threatened human health (Kien and
Ross, 2009). Chitosan has been extensively investigated as adsorbents (Wan Ngah et al., 2011). However, chitosan is very sensitive
to pH as it can either form gel or dissolve depending on the pH
values (Chiou et al., 2004). Therefore chitin is a potential starting
polysaccharide to modify for application in different fields, including metal ion adsorbents for wastewater treatment. Chitin even
with low adsorption capacity of metal ion exhibits good stability
and insolubility in acidic media, is also available in large quantity
and a recyclable material that can be used for modification.
In order to enhance the adsorptive property of chitin, partially
deacetylated chitin has been prepared and used at the same time
to modify through grafting with functional monomers. In this
work, acrylonitrile monomer was grafted onto deacetylated chitin
with DDA of about 40% by a pre-irradiation method; then the
cyano-groups (–CN) were converted into amidoxime groups
(–C(NH2)¼N–OH) by treatment with hydroxylamine (NH2OH) to
enhance the adsorption capacity. The resultant chitin was used for
adsorption of arsenic from aqueous solutions of arsenic salt and
groundwater samples.

2. Experimental
2.1. Materials
Shrimp shell chitin was supplied by a factory in Vung Tau
province, Vietnam. Chitin was further deacetylated in 30% sodium

hydroxide at 30 1C for 24 h to obtain a degree of deacetylation
(DDA) of about 40%. This value was determined based on FT-IR
spectra according to absorbances of chitin at 1320 and 1420 cm À 1
(Brugnerotto et al., 2001). All other chemicals, including acrylonitrile (AN), hydroxyl ammonium chloride (NH2OH.HCl), tetrahydrofuran (C4H8O), N,N-dimethylformamide (HCON(CH3)2), and
sodium arsenite (NaAsO2), were of analytical reagent grade.
2.2. Grafting acrylonitrile onto pre-irradiation chitin and
modification of poly-acrylonitrile grafted on chitin
Chitin flakes from shrimp shells with DDA of about 40% were
irradiated in air by γ- rays in the dose range from 4 to 35 kGy at a
dose rate of 1.3 kGy/h under ambient conditions. The gammairradiation dose was determined by using an ethanol–chlorobenzene (ECB) dosimetry system from mean value of absorbed doses
of three dosimeters at 30 1C (ASTM International, 2004). Preirradiated chitin was immersed into a glass flask containing
acrylonitrile (AN) in dimethylformamide (DMF) with ratios from
10:100 to 70:100 (v/v) and Mohr's salt additive of 0.1% (w/v). The
flask was connected to a reflux system and heated by an electric
oven at 70 1C for 8 h. The AN grafted chitin (Chi-g-AN) was
extracted with tetrahydrofuran to remove homopolymers and
unreacted monomers and then dried in a forced air oven at 60 1C.
The degree of grafting (DG) was calculated from the weight gain as
follows:
DGð%Þ ¼ 100ðW 1 À W 0 Þ=W 0

ð1Þ

where W0 and W1 are the weights of the original and grafted
samples, respectively.
The Chi-g-AN was converted to amidoxime by hydroxyl amine
(NH2OH) in sodium hydroxyl (NaOH) at the ratios of 7:3, 1:1 and
1:0 (v:v) at 70 1C to introduce the functional adsorption units. The
content of substituted amidoxime groups was determined by
titration. The converted Chi-g-AN (Chi-g-AN-C) was immersed in

100 ml of 1 M NaCl aqueous solution and equilibrated for 24 h.
For this purpose, the NH2–C ¼N–OH group was converted to

NH2–C ¼N–ONa þ . The exchange proton from amidoxime group
was titrated with a 0.05 N NaOH solution. The content of amidoxime group (M) was determined as follows:
Mðmmol=gÞ ¼ ð0:05V NaOH Þ=W d

ð2Þ

where VNaOH is the volume of 0.05 N NaOH solution and Wd is the
dried weight of Chi-g-AN-C.
2.3. Characteristics of modified chitin
The modified chitin samples were characterized by FT-IR (Fourier
Transform Infrared Spectrophotometer) spectra with an FTIR – 8400s
(Shimadzu, Japan). The change of surface morphology of chitin was
observed by SEM (scanning electron microscope) pictures using a
JEOL scanning electron microscope, model JSM-6480 LV; specific
surface area was determined by the BET (Brunauer–Emmett–Teller)
method following the standard ISO 9277 (2010) (E) on a Quantachrome Nova 1200 instrument.
2.4. Batch adsorption experiments
The adsorption properties of As(III) on Chi-g-AN-C were estimated with sodium arsenite (NaAsO2). An amount of Chi-g-AN-C
flakes of 3 g was shaken with 200 ml of NaAsO2 solution in the
range of concentration from 0.5 to 5 mmol/l of NaAsO2 or from 65
to 650 mg/l of As(III) for 24 h. The adsorbent was removed by
filtration. The equilibrated arsenic concentration was quantified by
means of a Perkins-Elmer 5300DV inductively coupled plasma
atomic emission spectroscope (ICP-AES). The Langmuir isotherm
equation is expressed as follows (Kamari and Wan Ngah, 2009):
Ce=Ye ¼ 1=Q bþ Ce=Q

ð3Þ

where Ce is the concentration of As(III) after adsorption (mg/l), Ye
is the capacity of As(III) adsorbed (mg/g), Q is maximum adsorption capacity (mg/g) and b is the Langmuir constant (l/mg).
All collected data were expressed as mean 7 SE – standard
error, in this study. The differences between sample values were
assessed using two-tailed unpaired Student's t-tests. The standard
error should be o 7 5% at a 95% confidence level, and number of
samples analyzed per condition is three (N ¼3).
2.5. Continuous adsorption experiments
Adams and Bohart describe the relationship between Ct/Co and
t in a continuous system (Sharma and Singh, 2013). It is used to
predict the breakthrough curves for modified chitin column
design.
A Shengbo-G3 column (Zhejiang, China) with an internal diameter of 3 cm with flow rate of 5 ml/min was used for continuous
adsorption experiment. In order to investigate the effect of bed
height on removal efficiency of As(III) ions, depths of Chi-g-AN-C
packed column 10, 20 and 30 cm (equivalent to, respectively, 2.846,
5.538 and 7.923 g) were used for adsorption of As(III) ions at
concentration of 75 mg/l. Effluent samples from column were
collected at specified time interval of 30 min, and the As(III)
concentrations in the effluent were measured by ICP-AES. In all
experiments, the temperature and pH values were adjusted to 30 1C
and 6.5, respectively.
Adsorption of arsenic from groundwater samples with the
depth of about 30 m was also determined. One liter of groundwater sample was flowed through the Chi-g-AN-C packed column
from the top to the bottom with a column height of 30 cm. The
concentration of arsenic was measured before and after flowing
through the column.

T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

3. Results and discussion

140

3.1. Effect of pre-irradiation dose, concentration of acrylonitrile and
reaction temperature on grafting degree

120

DG (%)

140

80
60
40
20
0

0

10

20

30

40

50

60

70

80

Conc. AN (%)
Fig. 2. Relationship between the degree of grafting and concentration of acrylonitrile.

50 and 70 1C for 8 h. However, at higher doses than 25 kGy the DG
levelled off at all temperatures. Thus, the dose of 257 1.2 kGy was
selected as the optimal dose for grafting AN onto chitin.
Temperature is also an important factor that controls the
kinetics of grafting copolymerization. Fig. 1 shows that the DG
gradually increases corresponding to temperatures of 30, 50 and
70 1C at all absorbed doses. It had been reported that the increase
in DG at high temperature was due to the increased monomer
diffusion into polymer substrates as well as mobility of monomer
molecules, accelerating reactions among the monomer and the
active sites of graft chains (Chapiro, 1962; Sharif et al., 2013).
Furthermore, in the method of grafting on peroxidized polymers,
an increase in temperature leading to further increases the rate of
initiation, and thus enhances the graft polymerization rate
(Bhattacharya and Mirsa, 2004).
The concentrations of AN in DMF from 10:100 to 70:100 (v/v)
were used for grafting onto 25 kGy irradiated chitin. The DG

increased with the increase of concentration of AN and reached
an optimal value of 114% or 2.15 mmol/g for 40% AN concentration
(Fig. 2). The deep diffusion of monomers inside chitin membranes
will be advantageous when the concentration of AN is high
enough. However, at a higher concentration, the DG changed
insignificantly because homopolymerization occurred simultaneously. The increase in viscosity of grafting system not only
inhibits diffusion but also prevents chain transfers (Chapiro, 1962;
Wojnárovits et al., 2010; Sharif et al., 2013). Thus, DG will attain a
critical value at a certain concentration. In this study, the concentration of AN in DMF was selected to be 40% (v:v) for further
investigation.

o

120

30 C
o
50 C

100

70 C

3.2. Conversion of cyano- (–CN) groups into amidoxime
(–NH2C ¼NOH) groups

o

The conversion of cyano-group on Chi-g-AN with DG of 114%
(10.05 mmol/g) was carried out with hydroxylamine mixture of

0.1 N NH2OH Á HCl and 0.1 N NaOH at 80 1C. At mixture ratio of 1:0
(v/v) corresponding to pH 4, the amine group –NH2 may be
protonated in acid medium into NH3þ group; therefore the content
of amidoxime is low as described in Fig. 3. A higher content of
NaOH was used; hence the amidoxime further converted into
carboxylate group by the following reactions:

80
60
40
20
0

100

DG (%)

In this work, the trunk polymer used for irradiation was chitin
which was partially deacetylated with DDA of about 40% in order
to enhance the adsorption capacity and eliminate the solubility in
acidic media. When the DDA of chitin reaches about 50%, it
becomes soluble in aqueous acidic media and is called chitosan.
The –NH2 groups on the chain are known to have good chelation
ability with metals. Better chelation is obtained for greater degrees
of deacetylation of chitin (Rinaudo, 2006). However, the solubilization of chitosan occurs by protonation of the –NH2 function
whereas chitin is insoluble in the usual solvents. Chitin possessing
DDA of about 40% and modified by functional groups has not only
environmental durability but also good adsorption.
As regards the ionizing radiation, irradiation dose is also an
important factor to optimize the grafting process and homogeneity of grafting distribution. Particularly, in grafting by pre-irradiation, the grafting degree depends on free radical concentration

dissociated at a certain temperature. If a polymer such as chitin is
irradiated in oxygen, peroxide or hydroperoxide radicals in the
chitin molecule are initiators for grafting reaction and several
chains start growing simultaneously. The content of these radicals
increases corresponding to the absorbed doses so that the DG of
monomer onto polymer also increases. However, according to
Chapiro, a significant radiolysis of the peroxide occurs at high
doses and may reduce the overall rate of peroxidation. This is one
of the factors that affect grafting degree (Chapiro, 1962). Interactions of high-energy radiation with polysaccharides such as starch,
cellulose, chitin/chitosan and pectin result in oxidative degradation by cleavage of glycosidic bonds which is a disadvantage for
pre-irradiation grafting (Wojnárovits et al., 2010; Desmet et al.,
2011). Therefore, the grafting degree will reach a saturated value
that does not increase at high doses. Our obtained result is similar
to those of publications on grafting monomers onto pre-irradiation
polysaccharides in air (Takács et al., 2005; Benke et al., 2007).
Homopolymer can further arise during the grafting process by the
initiation of radicals such as OH from the decomposition of
hydroperoxides (Dargaville et al., 2003). Thus, Mohr's salt was
used as an inhibitor for homopolymerization in the AN solution. In
Fig. 1 the DG of AN onto irradiated chitin in the dose range from
0 to 35 kGy (dose rate of 1.3 kGy/h) for 40% (v:v) AN in dimethylformamide (DMF) solution increased with increasing absorbed
dose in the range from 0 to 25 kGy, at the temperatures of 30,

237

0

5

10

15

20

25

30

35

40

Dose (kGy)
Fig. 1. Effect of absorbed dose and reaction temperature on the degree of grafting.

(4)


238

T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

Content of amidoxime (mmol/g)

2.5

7:3
1:1

2

1:0

1.5
1
0.5
0

0

2

4

6

8

10

Time (h)
Fig. 3. Conversion kinetics of amidoxime on Chi-g-AN with ratio of NH2OH Á HCl
0.1 N to NaOH 0.1 N of 7:3; 1:1 and 1:0.

spectrum of chitin grafted AN has a new peak at 2243 cm À 1
assigned to the nitrile (–CN) group (Fig. 4c). After amidoxime
conversion, this peak disappeared and bands in the wavelength
range of 2800–3600 cm À 1 of the –OH, –NH groups were broader
(Fig. 4b). Grafting AN onto chitin/chitosan was also carried out by

other authors, who verified the presence of cyano-group (–CN) at
the wavelength 2250 cm À 1 from the FT-IR spectrum (Pourjava et
al., 2003). In the FT-IR spectrum of the sample where cyanogroups grafted onto LDPE (low density polyethylene) were converted by NH2OH Á HCl solution, the peak at 2238 cm À 1 disappeared and peaks in the wavelength range 3000–3400 cm À 1 that
characterize the hydrophilic groups had strong intensity (El-Sawy
et al., 2007).
SEM images for the surface morphology of chitin samples are
shown in Fig. 5. The irradiated chitin has a smooth surface while
the grafted chitin has rough folds. The conversion of amidoxime
introduces hydrophilic groups such as –OH and –NH2 to the
grafted chitin so that the surface of Chi-g-AN-C seems thicker by
swelling and has grooves. The adsorption of As (III) ions on the
converted chitin –Chi-g-AN-C-As(III) by chelating chitin with As
(III) ions created the homogeneous surface.

3.4. Batch adsorption of As (III) onto chi-g-AN-C

Scheme 1. The process for the synthesis of adsorbent with graft polymerization
and conversion of cyano- to amidoxime.

(5)

The result in Fig. 3 shows that the content of amidoxime
substituted for the mixture ratio 7:3 of 0.1 N NH2OH Á HCl and
0.1 N NaOH at pH 7 is higher than that of the ratio 1:1 at pH 9.
Thus the ratio of 7:3 was selected to convert the Chi-g-AN sample
for preparation of adsorbents. The optimal content of amidoxime
on Chi-g-AN was 2.13 mmol/g for 6 h of conversion reaction. The
amidoximation increased the number of functional groups for
adsorption and swelling degree of backbone polymer. Grafting and
amidoxime conversion process of Chi-g-AN in this study can be

presented as follows: Scheme 1
3.3. Characteristics of modified chitin
Specific surface areas of chitin and modified chitin (Chi-g-ANC) were determined following the BET method to be 0.901 and
1.278 m2/g, respectively. Modification of chitin allows an expansion of the polymer network, improving access to internal adsorption sites and enhancing diffusion.
The FT-IR spectra of the irradiated chitin, the grafted chitin and
converted Chi-g-AN are shown in Fig. 4. The FT-IR spectrum of the
irradiated chitin of 25 kGy has absorption peaks at the wavelengths of 3457 cm À 1, 3259 cm À 1, 2879 cm À 1, 1654 cm À 1 and
1560 cm À 1 associated with stretching vibrations of the –OH, –NH2,
–CH2, C ¼O and –NH (–CONH) groups, respectively (Fig. 4a). FT-IR

In this study the adsorption equilibrium of As(III) from standard solution of sodium arsenite – NaAsO2 (0.05 mol/l) on Chi-gAN-C was investigated for 24 h, at temperature of 30 1C and pH
6.5. In this study, the Chi-g-AN-C adsorbent for arsenic adsorption
experiment has the grafting degree of 114% (10.05 mmol/g) with
the content of amidoxime substitution of 2.13 mmol/g. Adsorption
of As(III) was studied with the initial concentrations of NaAsO2
solution from 0.5 to 5 mM or from 65 mg/l to 650 mg/l of As (III).
In Fig. 6, adsorption isotherm of As(III) onto Chi-g-AN-C increased
from 4.06 mg/g to 17.28 mg/g corresponding to increasing concentration of As(III) from 130 to 520 mg/l and was unchanged at
high concentration. It is found that the adsorption isotherm
initially raises sharply, indicating that a large quantity of readily
active sites are available for beginning adsorption. However, a
plateau is reached suggesting that no more active sites are
available. According to Xie et al. (2011), mass transfer may be easy
with high concentration of metal ions; the higher the metal ions
concentration in the solution, the higher the capacity of adsorption. A common trend for the increase in adsorption capacity
corresponding to increasing initial concentration of As (III) is
depicted in Fig. 6. Contaminants from solution adsorbed on solid
usually conform to three steps. Firstly, it is the mass transfer of
pollutants from liquid to the surface of the adsorbent, then
adsorption occurs on the surface, and finally pollutants move

deeply inside the solid (Barakat, 2011).
The interactive behavior between adsorbate and adsorbent is
generally described by the Langmuir model. The Langmuir isotherm is the simplest theoretical model for monolayer adsorption
onto a surface containing a finite number of adsorption sites of
uniform energies for adsorption. From this study, the linear form
of Langmuir for adsorption of As(III) on Chi-g-AN-C is shown in
Fig. 7. The maximal adsorption capacity (Qmax) of As(III) and b
constant were determined from the slope and intercept according to Eq. (3) to be 19.724 (mg/g) and 0.029 (l/mg), respectively.
Adsorption capacity of As(III) on Chi-g-AN-C is higher than in
comparison with other materials such as composite of α-Fe2O3
impregnated chitosan (Liu et al., 2011). The correlation coefficient was R2 ¼0.996 in Fig. 7; this result confirmed good
agreement of adsorption system for the Langmuir isotherm.
Characteristics of Langmuir isotherms can be also expressed by a
dimensionless parameter that is defined as the separation factor RL


239

748.33
702.04

952.77
894.91

1415.65
1380.94
1315.36
1261.36
1205.43

1654.81

1560.30

2243.06

2879.32

3259.47
3107.11

3457.77

T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

c

b

a

Wavenumber (cm-1)
Fig. 4. FTIR spectra of (a) chitin, (b) Chi-g-AN-C and (c) Chi-g-AN.

Fig. 5. SEM images of (a) chitin, (b) Chi-g-AN, (c) Chi-g-AN-C and (d) Chi-g-AN-C-As(III).


240

T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

20

1
10 cm

12
8
4
0

30 cm

0.6
0.4
0.2

0

100

200

300

400

500

600

0

700

Co (mg/l)

0

400

600

800

1000

Fig. 8. Breakthrough curves for adsorption of As(III) on Chi-g-AN-C at different bed
heights.

20

Table 1
Arsenic removal
V ¼212.058 cm3.

16

Sample

pH

12
1
2
3
4

y = 0.0507x + 1.698
R2 = 0.9963

8

200

t (min)

Fig. 6. Adsorption isotherm of As(III) onto Chi-g-AN-C.

Ce/Ye (g/l)

20 cm

0.8

Ct/Co

Ye (mg/g)

16

6.5
6.5
6.5
6.5

data

from

groundwater

samples,

flow

rate¼5 ml/min,

Arsenic concentration (μg/l)
Before adsorption

After adsorption

1
2
4
10

0
0

0
0

4
0

0

100

200

300

height was selected to be 30 cm as the suitable bed height for
further investigation.

400

Ce (mg/l)

3.6. Treatment of arsenic in groundwater

Fig. 7. Langmuir isotherm for adsorption of As(III) on Chi-g-AN-C.

(Adeogun et al., 2012):
RL ¼ 1=ð1 þ bC o Þ

ð6Þ

where Co is the highest initial concentration of adsorbent (mg/l)
and b is the Langmuir constant (l/mg). In this study, the value of
separation factor RL is 0.050 for As(III). This value is in the range
0 oRL o1, and the Langmuir isotherm model will be favorable.

3.5. Breakthrough curve modeling
Accumulation of metal ions in packed bed column is largely
dependent on quantity of adsorbent inside the column. The sorption breakthrough curves with varying bed heights of 10, 20 and
30 cm, at constant flow rate of 5 ml/min and As(III) ions concentration of 75 mg/l, are shown in Fig. 8. As the bed height increased, the
time of breakthrough (corresponding to Ct/C0 ¼0.005) and time of
exhaustion (corresponding to Ct/C0 ¼ 0.9) increased accordingly.
A higher bed height indicates a larger amount of adsorbent residing
in the column, which implies that more binding sites are available
as well (Futalan et al., 2011). When the bed depth is reduced, axial
dispersion phenomena predominate in the mass transfer. The
solute (arsenic ions) does not have enough time to diffuse into
the whole of the adsorbent mass, causing a shorter breakthrough
time to occur (Taty-Costodes et al., 2005. In Fig. 8, the breakthrough
and exhaustion times increased from 90 to 150 min and 600 to
780 min, respectively for the bed heights from 10 to 30 cm. The bed

Removal of arsenic from the groundwater samples was also
carried out at flow rate 5 ml/min and bed height of 30 cm with the
volume of column to be 212.058 cm3. Four samples of groundwater at the depth of 30 m with the total arsenic concentration of
1, 2, 4 and 10 μg/l were selected for arsenic separation by Chi-gAN-C. After flowing through the column packed with Chi-g-AN-C,
the concentrations of total arsenic in groundwater samples were
determined to be 0 μg/l (Table 1). The contaminated arsenic in the
water was absolutely removed. This is expected since the amount
of arsenic in the treated water is far from adsorption capacity of
Chi-g-AN-C packed in the column. This result proved the feasibility

for application of the new material (Chi-g-AN-C) in adsorption of
arsenic. The presence of arsenic in drinking water will influence
the human health. In Vietnam, due to the characteristics of
sediment, the Mekong and the Red River Deltas contain arsenic
so that the well water in the depth about of 20–440 m has been
polluted by arsenic. The concentration of arsenic in water sample
in Nam Phong area exceeds the limit many folds (Phuong and Itoi,
2009). The pollution of arsenic in groundwater is a topical
problem, and the scientists should study effective methods for
removal of arsenic in water.

4. Conclusion
Grafting acrylonitrile onto chitin with the deacetylation degree
of about 40% was carried out by a pre-irradiation method. The
cyano-groups grafted onto chitin were converted into amidoxime
by hydroxylamine to enhance the adsorption of metal ions.


T.T. Hanh et al. / Radiation Physics and Chemistry 106 (2015) 235–241

The modified chitins were characterized by FT-IR spectra, SEM
pictures and BET specific surface area.
The adsorption capacity of As(III) onto Chi-g-AN-C was determined to be 19.724 mg/g. The adsorption isotherm of As(III) onto
Chi-g-AN-C is fitted with the Langmuir model. The relationship
between bed height and breakthrough time of As(III) on Chi-g-AN-C
was determined from the column adsorption experiment. The
content of arsenic in groundwater was absolutely adsorbed by
Chi-g-AN-C packed in the column. These results demonstrated the
feasibility for application of novel material in water treatment.
Thus Chi-g-AN-C can be potentially used to treat arsenic contaminated in groundwater or drinking water.

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