Abstract. In this work, chitosan with an amorphous structure and high surface area
(increased 30 times higher than that of initial chitosan) was obtained from the
decrystallization of chitosan using a reprecipitation method of chitosan from solution.
The chitosan was characterized using X-ray diffraction, Scanning Electron Microscopy
(SEM) and Brunauer-Emmet-Teller (BET). The adsorption capacity of the decrystallized
chitosan for many metal ions has been evaluated. The results show that the adsorption
capacity of decrystallized chitosan for the metal ions increased and the values obtained
were 1.16 to 3.58 times higher than that of other results reported in experimental ranges.
6 trang |
Chia sẻ: thanhle95 | Lượt xem: 426 | Lượt tải: 0
Bạn đang xem nội dung tài liệu Preparation and investigation of adsorption capacity for metal ions of amorphous chitosan, để tải tài liệu về máy bạn click vào nút DOWNLOAD ở trên
JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2015-00074
Chemical and Biological Sci. 2015, Vol. 60, No. 9, pp. 21-26
This paper is available online at
Received August 26, 2015. Accepted November 25, 2015.
Contact Nguyen Tien An, e-mail adress: an.tbump.vn@gmail.com
21
PREPARATION AND INVESTIGATION OF ADSORPTION CAPACITY
FOR METAL IONS OF AMORPHOUS CHITOSAN
Do Truong Thien1, Nguyen Tien An2, Nguyen Thi Hoa2 and Pham Thanh Khiet2
1
Institute of Chemistry, Vietnam Academy of Science and Technology
2
Thai Binh University of Medicine and Pharmacy, Thai Binh
Abstract. In this work, chitosan with an amorphous structure and high surface area
(increased 30 times higher than that of initial chitosan) was obtained from the
decrystallization of chitosan using a reprecipitation method of chitosan from solution.
The chitosan was characterized using X-ray diffraction, Scanning Electron Microscopy
(SEM) and Brunauer-Emmet-Teller (BET). The adsorption capacity of the decrystallized
chitosan for many metal ions has been evaluated. The results show that the adsorption
capacity of decrystallized chitosan for the metal ions increased and the values obtained
were 1.16 to 3.58 times higher than that of other results reported in experimental ranges.
Keywords: Chitosan, decrystallization, heavy metals, adsorption.
1. Introduction
Chitin is a naturally abundant biopolymer, like cellulose, that is present in the shell of
crustaceans such as crab and shrimp, the cuticle of insects and also the cell wall of some fungi
and microorganisms. Chitin consists of 2-acetamido-2-deoxy-(1-4)--D-glucopyranose
residues (N-acetyl-D-glucosamine units) which has intra- and inter-molecular hydrogen bonds
and is water-insoluble due to its rigid crystalline structure. Chitosan ideally consists of
2-amino-2-deoxy-(1-4)--D-glucopyranose residues (D-glucosamine units) and has no or a
small amount of N-acetyl-D-glucosamine units, and is water-soluble as the salt with various
acids on the amino group of D-glucosamine unit [1]. The possibility of extending the use of
chitosan to immobilize biologically active species or to remove metal ions from wastewater
has been regarded as an area worthy of further investigation. Because of its coarse porous
structure and low toxicity, and the presence of free amino groups, chitosan has been
considered an excellent ca didate for such purposes. The amine groups on the chit san chain
have been shown to serve as a selective chelating site for transition metal ions [2, 3].
Up to now, many approaches on using chitosan for adsorption of heavy metal ions from
aqueous solutions have been reported. However, the use of decrystallized chitosan with low
degree of crystallinity and high surface area for these aims has not been shown. With the high
surface area, the number of adsorption centers was increased with the functional groups of
Do Truong Thien, Nguyen Tien An, Nguyen Thi Hoaand Pham Thanh Khiet
22
chitosan becoming more active and flexible, which facilitates complexation of chitosan with
many heavy metal ions so that the adsorption capacity might be enhanced. For this reason, in
this work, the decrystallized chitosan was prepared from chitosan (DA=31%). The
characterizations of decrystallized chitosan were supported by NMR spectra, X-Ray
diffraction and BET analysis. The adsorption capacity of decrystallized chitosan for many
metal ions from an aqueous solution was also ev luated.
2. Content
2.1. Experiments
* Materials
-chitosan with a 31% degree of acetylation (DA= 31%) was received from the
deacetylation of chitin. Sodium hydroxide and hydrochloric acid were purchased from Merck
(Germany). Ni(NO3)2, CuSO4, Pb(NO3)2, HgCl2, Zn(CH3COO)2, FeSO4, Fe(NO3)3, Cr(NO3)3
and other chemicals used in the experiments were of analytical grade.
* Preparation and characterization of decrystallized chitosan
-chitosan (1 g) was dissolved in 500 ml of 0.1 M hydrochloric acid under constant
stirring at room temperature for 24 h. A chitosan solution was obtained after filtering the
mixture through a textile cloth to remove any insoluble components. Then the chitosan
solution (100 mL) was added drop-by-drop into 500 ml of 90% (v/v) ethanol stirring
vigorously. The forming precipitate was filtered out, washed with the excess amount of
distilled water to remove any impurities and dried for obtaining decrystallized chitosan.
X-ray diffraction patterns for initial chitosan and descrytallized chitosan were analysed
using a Siemens D5000 (Japan) diffractometer equipped with a CuK target at 40 kV and 30
mA with a scan rate of 4/min. The diffraction angle ranged from 2 = 0 to 2 = 60.
Teller (BET) surface area was measured using Micromeritics ASAP 2010 gas
adsorption surface analyzer.
Scanning electron microscopy (SEM) images of initial chitosan and descrytallized
chitosan were collected with a HITACHI S-4800 (Japan) under an acceleration voltage
of 20kV.
* Adsorption capacity
The solutions of salt used in this experiment were prepared by dissolving salt in di tilled
water. The pH value of these solutions was adjusted using dilute sodium hydroxide or
hydrogen chloride solutions. In a typical experiment, 0.10 g of decrystallized chitosan was
added to 50 mL of metal ion solution (initial concentration 10 mmol/l), shaking 4 h at 30 C,
then filtered out. The concentration of metal ion in aqueoussolution was determined by
atomic adsorption spectrophotometer with a Perkin Elm r atomic adsorption
spectrophotometer (AAS-3300). The adsorption capacity of metal ion was calculated based on
the difference of metal ion concentration in aqueous solutions before and after adsorption,
according to the following equation:
W
C)(CV
Q 0
where Q is the adsorption capacity (mg/g), Co and are, respectively, the initial and solution
phase metal ion concentration at equilibrium (mg/L), V is the solution volume (L), and W is
the mass of sorbent (g).
Preparation and investigation of adsorption capacity for metal ions of amorphous chitosan
23
2.2. Results and discussion
2.2.1. Preparation of decrystallized chitosan
Chitosan is a product which resulted from the deacetylation of chitin in an alkaline
medium. The origin of chitosan influences the arrangement of polymer chains and three
different types of chitosan obtained by deacetylation of three kinds of chitin have been
identified: -chitosan results from -chitin (shrimp and crab shells), -chitosan from -chitin
(squid pen) and -chitosan from -chitin (stomach cuticles of cephalopoda), corresponding to
parallel, anti-parallel, and alternated arrangements of polymer chains, respectively. In the
crystalline state, chitosan has a tight structure due to the strong hydrogen linkages among the
hydroxyl and amine groups. This was one of main things that limited the ability o apply
chitosan [4, 5]. In order to decrease the crystallinity of chitosan or produce chitosan with
amorphous chitosan, other methods were necessary. According to the methods described in
experimental part, dissolving chitosan in a dilute solution and stirring vigorously, the crystal
structure of chitosan was broken forming an amorphous structure (Scheme 1). After
precipitation or lyophilisation, this structural state was still maintained, so decrystallized
chitosan was obtained. Because the processs of obtaining amorphous chitosan were carried
out completely in water, it could be concluded that the above method used for obtaining
decrystallized chitosan was quite simple, cheap and easily doing. The decrystallized chitosan
prepared by the above method has promising applications in many fields including film,
complexion and loading medicine.
Scheme 1: Illustrate the structural state of chitosan before and after decrystallization
2.2.2. X-Ray diffractions
The X-Ray curves of chitosan and decrystallized chitosan were shown in Figure 1.
Figure 1. X-Ray diffraction of chitosan (a) and decrystallized chitosan (b)
Do Truong Thien, Nguyen Tien An, Nguyen Thi Hoaand Pham Thanh Khiet
24
Figure 1 shows that there were two strong and sharp peaks in the diffractogram of
chitosan at 2θ at 10 and 19.5. The peak at 2 θ about 22 was attributed to the allomorphic
tendon form of chitosan, which resulted in a strong decrease in sorption capacities.
Meanwhile, no clear sharp peak was found in the diffractogram of decrystallized chitosan. In
addition, the peak intensity in the diffractogram of initial chitosan was higher than that of
decrystallized chitosan. These indicate that the crystal structure of the chitosan had been
destroyed and replaced by an amorphous structure after the process of d crystallization of
chitosan. In the amorphous state, functional groups typical for chitosan such as amine (-NH2)
and hydroxyl (-OH) groups become more active and flexible, these lead the chitosan to easily
react with other reagents to form derivatives of chitosan or complexes with many metal ions.
2.2.3. SEM analysis of decrystallized chitosan
The morphological structures of initial chitosan and decrystallized chitosan have been
examined by means of SEM and shown in Figure 2.
As seen from Figure 2, the structure of chitosan after descrystallization was more porous
than that of initial chitosan. Because of the porous structure, the surface area of chitosan
increased strongly which would facilitate the adsorption of metal ions onto the surface
of chitosan.
Figure 2. SEM photographs of initial chitosan (a) and decrystallized chitosan (b)
2.2.4. BET characterization of decrystallized chitosan
The BET surface areas for initial chitosan and decrystallized chitosan were measured
from N2 adsorption isotherms and the obtained results are shown in Figure 3.
The values were computed and the results show that the surface area of initial chitosan
and decrystallized chitosan were 0.17m2.g-1 and 5.52m2.g-1, respectively. The decrystallized
chitosan had a high surface area that would make its functional groups, such as the amine
(-NH2) and hydroxyl (-OH) groups, become more active and flexible so that these functional
groups would be easily available for interaction with metal ions and as a result decry t llized
chitosan shows promise for adsorption of metal ions.
Preparation and investigation of adsorption capacity for metal ions of amorphous chitosan
25
(a) (b)
Figure 3. BET surface area plot of initial chitosan (a) and decrystallized chitosan (b)
2.2.5. Adsorption capacity of metal ions by decrystallized chitosan
The maximum adsorption capacities (Qmax) of decrystallized chitosan for metal ions
were summarized in Table 1 and compared with the results reported on adsorption
properties of chitosan [6-10]. The results in Table 1 show that the adsorption capacities of
decrystallized chitosan for many metal ions were almost all higher than that of other reported
chitosan. This could be explained as follows: the ability of adsorption of chitosan to metal
ions strongly depends on its surface area and the mobility of groups such as hydroxyl and
amine. As the surface area of the material increased, the binding sites of metal ions with
chitosan would also increase. Therefore, the adsorption capacity of decrystallized chitosan for
the metal ions increased. In addition, in the porous state, the distance that these functional
groups in the chitosan molecular chain increased would reduce the formation of ydrogen
linkages among these groups. So, functional groups such as amine (-NH2) and hydroxyl
(-OH) groups became more active and flexible and as result the interaction of the groups with
metal ions was enhanced.
Table 1. Comparison of maximum adsorption capacities for metal ions
of the decrystallized chitosan with other reported chitosan
Metal ions Qmax1 (mg.g
-1
) Qmax2 (mg.g
-1
) PCS Qmax2/Qmax1
Cu (II) 130 (pH = 6) [6] 295.0 (pH = 6) 2.27
Pb (II) 238 (pH = 6) [7]728.6 (pH = 6) 3.06
Ni (II) 67.0 (pH = 6) [7]212.4 (pH = 6 - 6.5) 3.18
Hg (II) 1127 (pH = 6 - 6.5) [8] 1266 (pH = 6 - .5) 1.16
Zn (II) 78.6 (pH = 6) [7]281.4 (pH = 6.5) 3.58
Cr (III) 26.0 (pH = 5) [9]67.6 (pH = 5 - 6) 2.60
Fe (II) 63.8 (pH = 6 - .5) [10] 92.4 (pH = 6) 1.45
Fe (III) 90.1 (pH = 6 - .5) [10] 119.3 (pH = 6 - .5) 1.32
Do Truong Thien, Nguyen Tien An, Nguyen Thi Hoaand Pham Thanh Khiet
26
3. Conclusion
Decrystallized chitosan (with an amorphous structure and high surface area) was
obtained from a decrystallization of chitosan using the reprecipitation method. Adsorption
capacity of the decrystallized chitosan for many metal ions was evaluated. The results show
that the adsorption capacity of decrystallized chitosan for the metal ions increased and the
values obtained were 1.16 to 3.58 times higher than that of other results reported in
experiments.
REFERENCES
[1] Gemma Galed, Beatriz Miralles, Ine´s Panos, Alejandro Santiago, Angeles Heras, 2005.
N-Deacetylation and depolymerization reactions of chitin/chitosan: Influence of the
source of chitin. Carbohydrate Polymers, Vol. 62, p. 316.
[2] Baroni P., Vieira R.S , Meneghetti E., Silva M. G., Beppu M. M, 2008. Evaluation of
batch adsorption of chromium ions on natural and crosslinked chitosan membranes.
Journal of Hazardous Materials, Vol. 152, p. 1155.
[3] Carol, L. L., & Matthew, P. H., 1999. An Investigation into the Use of Chitosan for the
Removal of Soluble Silver from Industrial Wastewater. Advances in Environmental
Science and Technology, Vol. 33, p. 3622.
[4] Ogawa K, Yui T, Okuyama K. Int., 2004. Three D structures of chitosan. J. Biol.
Macromol, Vol. 34, No. 1.
[5] Toffey A., Samaranayake G., Frazier C. E., Glasser W. G., 1996. Kinetics of the heat-
induced conversion of chitosan to chitin. J. Appl. Polym. Sci. Vol. 60, p. 75.
[6] Rogerio Laus, Valfredo Tadeu de Favere, 2011. Competitive adsorption of Cu(II) and
Cd(II) ions by chitosan crosslinked with epichlorohydrin-triphosphate. Bioresource
Technology, Vol. 102, p. 8769.
[7] Feng-Chin Wu, Ru-Ling Tseng, Ruey-Shin Juang, 2010. A review and experimental
verification of using chitosan and its derivatives as adsorbents for selected heavy
metals. Journal of Environmental Management, Vol. 91, p. 798.
[8] Ashraf Shafaei, Farzin Zokaee Ashtiani, Tahereh Kaghazchi, 2007. Equilibrium studies
of the sorption of Hg(II)ions onto chitosan. Chemical Engineering Journal, Vol. 133, p. 311.
[9] R. Maruca, B. J Suder, J. P. Wightman, 1982. Interaction of heavy metals with chitin and
chitosan. J. Appl. Polym. Sci. Vol. 27, p. 4827.
[10] W.S.Wan Ngah, S. Ab Ghani, A. Kamari. 2005. Adsorption behaviour of Fe (II) and Fe
(III) ions in aqueous solution on chitosan and cross-linked chitosan beads. Bioresource
Technology, Vol. 96, No. 4, p. 443.