ВЫСОКОМОЛЕКУЛЯРНЫЕ СОЕДИНЕНИЯ, Серия А, 2012, том 54, № 2, с. 244-255
ПРИРОДНЫЕ ПОЛИМЕРЫ
УДК 541(64+49):547.995
PREPARATION OF SOME CHITOSAN HEAVY METAL COMPLEXES AND STUDY OF ITS PROPERTIES1
© 2012 г. M. H. M. Hussein", M. F. El-Hadyé, W. M. Sayed", and H. Hefni"
aPolymer lab, Petrochemicals Department, Egyptian Petroleum Research Institute (EPRI) bChemistry department, Faculty of Science, Al-Azhar University, Cairo, Egypt e-mail: hassanhefni@yahoo.com Received April 6, 2011 Revised Manuscript Received August 29, 2011
Abstract — The chitosan was prepared and mixed with some metal salts (FeCl3, Co(OAc)2 and NiCl2) by different concentrations to form chitosan-metal complexes. The metal ions which strongly complexed to the amino groups of chitosan like Fe showed a smooth surface product, amorphous phase, thermally more stable and high electrical conductivity than other complexes, while the Co ions which the weakly complexed with chitosan showed a rough surface product, crystalline phase, thermally less stable and low electrical conductivity. The chitosan-metal complexes have a higher electrical conductivity than chitosan pure at room temperature.
INTRODUCTION
Chitosan is a polymer of P-l,4-1inked 2-amino-2-deoxy- D-glucopyranose, it can be either derived by deacetylation of chitin which found in the shells of crabs and the exoskeleton of shrimps [1] and the cell walls of living organisms such as Phycomyces blakesleeanus. It has also hydrophilicity, biocompati-bility, biodegradability and antibacterial property [2]. It is used in a wide range of applications such as separation membrane [3], food packaging [4—6], wound healing [5, 7], a drug delivery system [8, 9], and wastewater treatment [10].
Chitosan is excellent electrical insulators, and display high electrical resistance and very little conduction of an electric current [11]. In fact, it is a suitable matrix material to prepare semiconductors bioconju-gates if it mixed with metals: first, chitosan has good chelating ability with transition metal ions [12], which makes it possible for its metal ion complexes to be used as precursors to synthesize semiconductors; second, the amino and hydroxyl groups on linear chitosan chains are good capping groups for semiconductors, at the same time, the highly viscous nature of chitosan can also prevent semiconductors from agglomeration during the growth.
The contamination of water by heavy metal ions is a serious environmental problem, mainly due to the discarding of industrial wastes [13, 14]. Heavy metals are highly toxic and good electrical conductivity even when present in low concentrations and can accumulate in living organisms, causing several disorders and diseases [15—17]. Metals can be distinguished from other toxic pollutants, since they undergo chemical
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transformations, are non-biodegradable, and have great environmental, economic, and public health impacts [18, 19]. It is well known that chitosans may complex with certain metal ions [20] and potable water purification for reduction of unwanted metals [21].
In this work we used three different metal ions (Fe, Ni, Co), and mixed them with chitosan to form different complexes. The characterizations of these complexes were carried out by FTIR and their morphological studies using scanning electron microscope and wide angle X-ray diffraction apparatus. The thermo gravimetric analysis (TGA) and differential scanning calorimetric (DSC) also were carried out.
EXPERIMENTAL
Preparation of Chitosan
The shrimp shells were deproteinized with 3.5% (w/w) NaOH solution for 2 h at 65°C, and deminera-lized with 1N HCl for 1 day at ambient temperature and subsequently decolorized with acetone for 2 h at 50°C and dried for 2 h at ambient temperature. The removal of acetyl groups from the prepared chitin was achieved by mixing with NaOH (50%) with stirring for 2 h at 115°C [22—24] in a solid to solvent ratio of 1 : 10 (w/v). The resulting chitosan was washed till neutrality in running tap water, rinsed with distilled water, filtered, and then dried at 60°C for 24 h.
Preparation of Chitosan—Metal (NiCl2, FeCl3, Co(CH3COO)2) [25] Complexes
5 mg chitosan was dissolved in an aqueous solution of 10% V/V HCl by vigorous stirring to obtain a solution containing concentration of 5%, filtered through
polyester cloth to remove residues of insoluble particles, the desired amount of metal ions (1/1, 1/2 and 1/3 mol metal ions/mol amino group of chitosan) were dissolved in 60 ml of 0.1 M HCl [26-28] and added to chitosan solution and agitation at 60°C for 2 h until complete complexation (to ensure complete of the complexation processes) the resulting homogeneous solution of the chitosan metal complex was added dropwise to a 0.5 M solution of NaOH (to remove the chlorine ions from the complexes and avoid any effect on conductivity properties). The resulting particles were filtered, washed several times with distilled water until pH 7, and dried in air for 48 h. the color of Ch-Ni is green, Ch-Fe is red and the Ch-Co is brown.
The formation of the complex was described according to the Lewis acid-base theory, where the acid is the acceptor for a pair of electrons donated by the base. Chitosan is the good ligand which has two types ofbinding sites, —O— and -NH2, where the metal (M) is the acceptor.
ny, Tokyo, Japan) with a Cu detector using 1.54 Â wavelength of the X-Ray.
The thermo gravimetric analysis (TGA) and differential scanning calorimetric (DSC) measurements were carried out using a Netzsch DSC 204 (Germany). Polymers samples were heated under nitrogen atmosphere from 0°C to 700° C at a constant rate of 5 K/min.
The DC conductivity was measured with keithly instrument high resistance model (6524 product information, March 2007), the samples were prepared in pellets with 1cm of diameter obtain polymer powders by micrometer (Model 293—766; Mitutoyo, Tokyo, Japan). The pellet was placed between the sample holder made from cupper metal and the data were recorded at 295 K.
The morphology was determined using a scanning electron microscopy (Philips XL30 Scanning Electron Microscope). All samples coated with gold prior to analysis by SEM.
Characterization of Chitosan and Chitosan—Metal (NiCl, FeCl3, Co(CH3COO)) Complexes
FTIR measurement was carried out as follows. The polysaccharide sample (2 mg), which was dried overnight at 60°C under reduced pressure, was mechanically well-blended with 100 mg of KBr. The thickness ofthe KBr disk was 0.5 mm. The KBr disk of the mixed powder was desiccated for 24 h at 110°C under reduced pressure and then its IR spectrum was recorded in the wave number range of 400 to 4200 Cm-1 with a resolution of 100 cm-1 by using the Shimadzu FTIR-4200 spectrometer.
The XRD analysis was carried out on an X-ray dif-fractometer (D/Max2500VB2+/Pc, Rigaku Compa-
RESULTS AND DISCUSSION
Preparation of Chitosan Metal Ion Complexes [29]
The reactions of chitosan with different ratios of metal ions were done at 60°C with stirring for 2 h. The chitosan metal complexes were produced in various forms according to metals ratios and oxidation number. Schemes 1-3 show chitosan-metals complexes in molar ratio 1 : 1 Ch-M(1), 1 : 0.5 Ch-M(2), and 1 : 0.3 Ch-M(3) (mole amino group of chitosan: mole metal ions).
In case of Fe3+ the products are hexacoordinative complexes [30]. While, in case of divalent ions (Ni2+, Co2+) the products are tetracoordinative complexes [31]. As represented in Schemes 1-3.
oh
Jfr
' MI
M2
.oh -o
-o
ho
nh2
ho
?2+
Y
m2 h2o h2o
o— nh2
M3
io>~
ho nh2
\4+
h2o—'m^3+~h2o h2o h2o
Scheme 1. Reaction of chitosan and metal ions in a ratio 1:1of Ch-M(1).
M3
oh
oh
ho nh2
Ч/3+
h2o—m—h2o /\
ho nh2
-^O-O-
oh
Scheme 2. Reaction of chitosan and metal ions in a ratio 1:0.5 of Ch-M(2).
ho
/oh
nh2 Vo
ho
o^j-. nh
2
M2
oh
oh
, >ov ,
ho nh2
ho
M3
h
\> oh
^ o h2n^X
of ^m«.
rxijy
К
oh
Scheme 3. Reaction of chitosan and metal ions in a ratio 1:0.3 of Ch-M(3)where M is Fe3+, Ni+2, Co2+ .
Characterization of Chitosan andChitosan-MetalIon Complexes
The infrared spectra (FTIR). Figure 1 shows the FTIR spectra of the prepared chitosan and chitosan-metal complexes, the strong and broad band at 3425 cm-1 is attributed to OH asymmetrical stretching vibration and NH2 stretching vibrations; the band at 1420 cm-1 is related to the -CH2 bending, and the absorption band at 1072 cm-1 is C-O-C stretching vibration in glucosidic linkage [32].
While the IR spectra of Ch-Fe complex was show; 3430 cm-1 -OH, -NH2; 2922 cm-1 and 2854 cm-1 -C-H stretching; 1634 cm-1 -C=O, amide; 1601 cm-1 (-N-H amide); 1424 cm-1 (-CH2-N) coupled with 1379 cm-1 (-N-H); 1157 cm-1 (skeleton: C-O and - C-O-C); 894 cm-1 C-O-C bridge as well as glucosidic linkage; 567 cm-1 (Fe-N-); 433 cm-1 (Fe - O-).
The IR spectra of Ch-Co complex; 3433 cm-1 (-OH, -NH); 2921 cm-1 and 2855 cm-1 (-C-H);
1626 cm-1 (—C=O, amide I); 1459 cm-1 (-CH2-N-) coupled with 1381 cm-1 (-N-H); 1113cm-1 (skeleton: C-O and -C-O-C); 856 cm-1 C-O-C bridge as well as glucosidic linkage; 556 cm-1 (Co-N-); 451 cm-1(Co-O-).
The IR spectra of Ch-Ni complex; 3431 cm-1 (- OH, -NH2); 2924 cm-1 and 2859 cm-1 -C-H stretching; 1635 cm-1 -C=O, amide; 1462 cm-1 (-CH2-N-) coupled with 1382 cm-1 (-N-H); 1153 cm-1 (skeleton: C-O and -C-O-C); 889 cm-1 C-O-C bridge as well as glucosidic linkage; 580 and 529 cm-1 (Ni-N-); 433 cm-1 (Ni-O).
Scanning electron microscope. Figure 2 shows that chitosan has a smooth surface [33, 34]. However, Fig. 3 shows the Ch-Fe complex has a very smooth surface, the ''holes'' in such surface are little leads to a strong and specific binding of the amino groups of chi-tosan with Fe ions. While Fig. 4 shows the Ch-Ni complex is a less smooth with more holes than Ch-Fe complex due to the weak binding with the amino groups of chitosan.
J_I_I_I_I_I_I_L
4000 3500 3000 2500 2000 1500 1000 500 Weavelength, cm-1
Fig. 1. FTI
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