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

Pre-irradiation grafting of acrylonitrile onto chitin for adsorptionof arsenic in water a Research and Development Center for Radiation Technology, Vietnam Atomic Energy Institute, 202A,

Pre-irradiation grafting of acrylonitrile onto chitin for adsorption

of arsenic in water

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

a r t i c l e i n f o

Article history:

Received 16 May 2014

Accepted 2 August 2014

Available online 12 August 2014

Keywords:

Chitin

Acrylonitrile

Arsenite

Pre-irradiation

Grafting

Adsorption

a b s t r a c t

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 aγ-ray irradiation method The maximal grafting degree of AN onto pre-irradiated chitin at 2571.2 kGy was 114% for AN concentration in dimethylformamide of 40% (v/v) at

701C for 8 h The mixture ratio of 0.1 N NH2OH 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

1 Introduction

been applied to prepare novel materials, including adsorbents for

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

copolymer-ization was commonly used

In the past decades, besides studying the degradation effect of

on these substrates has also been carried out by many scientists

deacetylated form chitosan are renewable, biodegradable, bio-compatible, inexpensive and environmentally friendly polymers

cean shell such as prawns, crabs, fungi, insects and other

Chitosan can be used as an adsorbent to remove heavy metals and dyes due to the presence of amino and hydroxyl groups, which

and industrial wastewater caused pollution High arsenic con-centration in groundwater has been reported recently from USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland,

The current WHO recommended guideline value for arsenic in

Radiation Physics and Chemistry

http://dx.doi.org/10.1016/j.radphyschem.2014.08.004

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

n Corresponding author Tel.: þ84 8 62829159; fax: þ84 8 38975921.

E-mail address: truongthihanh05@yahoo.com (T.T Hanh).

Radiation Physics and Chemistry 106 (2015) 235–241

Vietnam the water from Red River delta with average arsenic

to pH as it can either form gel or dissolve depending on the pH

includ-ing 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

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

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

(DDA) of about 40% This value was determined based on FT-IR

2.2 Grafting acrylonitrile onto pre-irradiation chitin and

dose rate of 1.3 kGy/h under ambient conditions The

–chloroben-zene (ECB) dosimetry system from mean value of absorbed doses

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

extracted with tetrahydrofuran to remove homopolymers and

The degree of grafting (DG) was calculated from the weight gain as

follows:

samples, respectively

The Chi-g-AN was converted to amidoxime by hydroxyl amine

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

was titrated with a 0.05 N NaOH solution The content of amidox-ime group (M) was determined as follows:

dried weight of Chi-g-AN-C

(Shimadzu, Japan) The change of surface morphology of chitin was observed by SEM (scanning electron microscope) pictures using a

Quanta-chrome Nova 1200 instrument

2.4 Batch adsorption experiments The adsorption properties of As(III) on Chi-g-AN-C were

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

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 adsorp-tion capacity (mg/g) and b is the Langmuir constant (l/mg)

error, in this study The differences between sample values were assessed using two-tailed unpaired Student's t-tests The standard

2.5 Continuous adsorption experiments

design

adsorption experiment In order to investigate the effect of bed

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

and 6.5, respectively

Adsorption of arsenic from groundwater samples with the depth of about 30 m was also determined One liter of

from the top to the bottom with a column height of 30 cm The

through the column

3 Results and discussion

3.1 Effect of pre-irradiation dose, concentration of acrylonitrile and

reaction temperature on grafting degree

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

ability with metals Better chelation is obtained for greater degrees

whereas chitin is insoluble in the usual solvents Chitin possessing

environmental durability but also good adsorption

As regards the ionizing radiation, irradiation dose is also an

important factor to optimize the grafting process and

homogene-ity of grafting distribution Particularly, in grafting by

pre-irradia-tion, 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

doses and may reduce the overall rate of peroxidation This is one

Interac-tions of high-energy radiation with polysaccharides such as starch,

cellulose, chitin/chitosan and pectin result in oxidative

degrada-tion by cleavage of glycosidic bonds which is a disadvantage for

that does not increase at high doses Our obtained result is similar

to those of publications on grafting monomers onto pre-irradiation

Homopolymer can further arise during the grafting process by the

used as an inhibitor for homopolymerization in the AN solution In

0 to 35 kGy (dose rate of 1.3 kGy/h) for 40% (v:v) AN in

dimethyl-formamide (DMF) solution increased with increasing absorbed

dose in the range from 0 to 25 kGy, at the temperatures of 30,

selected as the optimal dose for grafting AN onto chitin

Temperature is also an important factor that controls the

gradually increases corresponding to temperatures of 30, 50 and

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

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

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

will be advantageous when the concentration of AN is high enough However, at a higher concentration, the DG changed

simulta-neously The increase in viscosity of grafting system not only

critical value at a certain concentration In this study, the concen-tration of AN in DMF was selected to be 40% (v:v) for further investigation

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

NaOH was used; hence the amidoxime further converted into carboxylate group by the following reactions:

(4)

0

20

40

60

80

100

120

140

Dose (kGy)

30 50 70

oC

oC

oC

0 20 40 60 80 100 120 140

Conc AN (%)

Fig 2 Relationship between the degree of grafting and concentration of acrylonitrile T.T Hanh et al / Radiation Physics and Chemistry 106 (2015) 235–241 237

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

(Chi-g-AN-C) were determined following the BET method to be 0.901 and

expan-sion of the polymer network, improving access to internal

adsorp-tion sites and enhancing diffusion

The FT-IR spectra of the irradiated chitin, the grafted chitin and

irradiated chitin of 25 kGy has absorption peaks at the

conversion, this peak disappeared and bands in the wavelength

cyano-groups grafted onto LDPE (low density polyethylene) were

SEM images for the surface morphology of chitin samples are

the grafted chitin has rough folds The conversion of amidoxime

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

(III) ions created the homogeneous surface

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

In this study the adsorption equilibrium of As(III) from

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

solution from 0.5 to 5 mM or from 65 mg/l to 650 mg/l of As (III)

from 4.06 mg/g to 17.28 mg/g corresponding to increasing con-centration 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

with high concentration of metal ions; the higher the metal ions concentration in the solution, the higher the capacity of adsorp-tion A common trend for the increase in adsorption capacity corresponding to increasing initial concentration of As (III) is

usually conform to three steps Firstly, it is the mass transfer of pollutants from liquid to the surface of the adsorbent, then

The interactive behavior between adsorbate and adsorbent is generally described by the Langmuir model The Langmuir iso-therm is the simplest theoretical model for monolayer adsorption

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

constant were determined from the slope and intercept

Adsorption capacity of As(III) on Chi-g-AN-C is higher than in

agreement of adsorption system for the Langmuir isotherm Characteristics of Langmuir isotherms can be also expressed by a

0

0.5

1

1.5

2

2.5

7:3 1:1 1:0

Time (h)

Fig 3 Conversion kinetics of amidoxime on Chi-g-AN with ratio of NH 2 OH  HCl

0.1 N to NaOH 0.1 N of 7:3; 1:1 and 1:0.

Scheme 1 The process for the synthesis of adsorbent with graft polymerization

and conversion of cyano- to amidoxime.

a

b

c

Wavenumber (cm-1)

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

T.T Hanh et al / Radiation Physics and Chemistry 106 (2015) 235–241 239

(Adeogun et al., 2012):

and b is the Langmuir constant (l/mg) In this study, the value of

3.5 Breakthrough curve modeling

Accumulation of metal ions in packed bed column is largely

dependent on quantity of adsorbent inside the column The

sorp-tion breakthrough curves with varying bed heights of 10, 20 and

A higher bed height indicates a larger amount of adsorbent residing

in the column, which implies that more binding sites are available

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

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

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

3.6 Treatment of arsenic in groundwater Removal of arsenic from the groundwater samples was also

ground-water at the depth of 30 m with the total arsenic concentration of

the concentrations of total arsenic in groundwater samples were

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

the human health In Vietnam, due to the characteristics of sediment, the Mekong and the Red River Deltas contain arsenic

polluted by arsenic The concentration of arsenic in water sample

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

0

4

8

12

16

20

Co (mg/l)

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

y = 0.0507x + 1.698

R2 = 0.9963

0

4

8

12

16

20

Ce (mg/l)

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

0 0.2 0.4 0.6 0.8 1

t (min)

10 cm

20 cm

30 cm

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

Table 1 Arsenic removal data from groundwater samples, flow rate¼5 ml/min, V¼212.058 cm 3

Sample pH Arsenic concentration (μg/l)

Before adsorption After adsorption

The modified chitins were characterized by FT-IR spectra, SEM

The adsorption capacity of As(III) onto Chi-g-AN-C was

deter-mined to be 19.724 mg/g The adsorption isotherm of As(III) onto

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

contami-nated in groundwater or drinking water

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