Radiation Physics and Chemistry 106 (2015) 235–241 Contents lists available at ScienceDirect 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 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 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 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.: ỵ 84 62829159; fax: ỵ84 38975921 E-mail address: truongthihanh05@yahoo.com (T.T Hanh) http://dx.doi.org/10.1016/j.radphyschem.2014.08.004 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 ỵ , Hg2 ỵ and Pb2 ỵ 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 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 (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 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 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: DG%ị ẳ 100W W Þ=W 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 M NaCl aqueous solution and equilibrated for 24 h For this purpose, the NH2–C ¼N–OH group was converted to NH2–C ẳNONa ỵ 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: Mmmol=gị ẳ 0:05V 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 g was shaken with 200 ml of NaAsO2 solution in the range of concentration from 0.5 to 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 bỵ Ce=Q 3ị 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 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 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 cm with flow rate of 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 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 10 20 30 40 50 60 70 80 Conc AN (%) Fig Relationship between the degree of grafting and concentration of acrylonitrile 50 and 70 1C for 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 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 NH3ỵ group; therefore the content of amidoxime is low as described in Fig A higher content of NaOH was used; hence the amidoxime further converted into carboxylate group by the following reactions: 80 60 40 20 100 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 the DG of AN onto irradiated chitin in the dose range from 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 to 25 kGy, at the temperatures of 30, 237 10 15 20 25 30 35 40 Dose (kGy) Fig 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 1:0 1.5 0.5 0 10 Time (h) Fig 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 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 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 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 disappeared and peaks in the wavelength range 3000–3400 cm À 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 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 The process for the synthesis of adsorbent with graft polymerization and conversion of cyano- to amidoxime (5) The result in Fig 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 is higher than that of the ratio 1:1 at pH 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 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 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 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 and 1560 cm À 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 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 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 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 FTIR spectra of (a) chitin, (b) Chi-g-AN-C and (c) Chi-g-AN Fig 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 10 cm 12 30 cm 0.6 0.4 0.2 100 200 300 400 500 600 700 Co (mg/l) 400 600 800 1000 Fig Breakthrough curves for adsorption of As(III) on Chi-g-AN-C at different bed heights 20 Table Arsenic removal V ¼212.058 cm3 16 Sample pH 12 y = 0.0507x + 1.698 R2 = 0.9963 200 t (min) Fig 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 10 0 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 Langmuir isotherm for adsorption of As(III) on Chi-g-AN-C (Adeogun et al., 2012): RL ẳ 1=1 ỵ bC o ị 6ị 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 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 ml/min and As(III) ions concentration of 75 mg/l, are shown in Fig 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 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 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, 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 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 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 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gradually increases corresponding to temperatures