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Preparation and Characterization of Chitosan / Cu (II) Affinity Membrane for Urea Adsorption

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We used silica particles as a porogen to pre- pare macroporous chitosan membranes and subsequently prepared macroporous chitosan/Cu(II) afffnity membranes for urea adsorption. The morphology, porosity, Cu(II) ad- sorption capacity, and swelling ratio of the macroporous membrane were measured. SEM photographs show the pores in the membrane dispersed uniformly, a feature that didn’t change much after the adsorption of Cu(II). The po- rosity of the membrane had a maximum value when the silica/chitosan ratio was about 12. The Cu(II) adsorption capacity in the membrane leveled off when the initial con- centration of CuSO4 solution exceeded 5 10 2 mol/L. The macroporous chitosan/Cu(II) afffnity membrane was suc- cessfully used for urea adsorption. The maximum urea ad- sorption capacity was 78.8 mg/g membrane, which indi- cates that the membrane has a great potential for hemodial- ysis for urea removal.
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Preparation and Characterization of Chitosan/Cu(II)
Af?nity Membrane for Urea Adsorption

Jiahao Liu, Xin Chen, Zhengzhong Shao, Ping Zhou
Department of Macromolecular Science, The Key Laboratory of Molecular Engineering of Polymers, Fudan University,
Shanghai, 200433, People’s Republic of China
Received 15 January 2003; accepted 21 February 2003
ABSTRACT:
We used silica particles as a porogen to pre-
centration of CuSO solution exceeded 5 ? 10?2 mol/L. The
4
pare macroporous chitosan membranes and subsequently
macroporous chitosan/Cu(II) af?nity membrane was suc-
prepared macroporous chitosan/Cu(II) af?nity membranes
cessfully used for urea adsorption. The maximum urea ad-
for urea adsorption. The morphology, porosity, Cu(II) ad-
sorption capacity was 78.8 mg/g membrane, which indi-
sorption capacity, and swelling ratio of the macroporous
cates that the membrane has a great potential for hemodial-
membrane were measured. SEM photographs show the
ysis for urea removal. © 2003 Wiley Periodicals, Inc. J Appl
pores in the membrane dispersed uniformly, a feature that
Polym Sci 90: 1108 –1112, 2003
didn’t change much after the adsorption of Cu(II). The po-
rosity of the membrane had a maximum value when the
silica/chitosan ratio was about 12. The Cu(II) adsorption
Key words: biopolymers; metal-polymer complex; macro-
capacity in the membrane leveled off when the initial con-
porous polymer; adsorption; morphology
INTRODUCTION
brane-forming nature.5 Compared to particle absor-
bents, a membrane is more suitable for hemodialysis
Uremia is a fatal human disease caused by the failure
and hemoperfusion because of its unique advantages
of the kidneys to clean toxins out of the body. Al-
in the absorption and separation processes, such as its
though kidney transplant is the ?rst choice to cure
large surface, short diffusion path, and high produc-
uremia, hemodialysis and hemoperfusion are still
tivity.6 Based on the reasons mentioned above, our
common methods of treating this disease because of
article focuses on the development of af?nity mem-
the lack of kidney donors and the expense of trans-
branes using natural polymers (mainly chitosan) for
plant. Among the toxins that need to be removed in
the absorption of urea. In our previous work, we
blood puri?cation, urea is a major component. Several
successfully prepared a chitosan-silk ?broin/Cu(II)
materials have been reported to be urea absorbents,
complex membrane,2 but the urea adsorption capacity
including activated carbon,1 polyethylenepolyamine/
was still not satisfactory. In this article, we report the
Cu(II)
complex,2
tolylene
diisocyanate
(TDI)
preparation of a macroporous chitosan/Cu(II) af?nity
crosslinked ?-cyclodextrin,3 and others. However, be-
membrane and its application to urea adsorption.
cause of the low adsorption capacity and poor biocom-
patibility of these materials they still cannot be used
practically.
EXPERIMENTAL
Chitosan [poly(2-amino-2-deoxy-D-glucose)] is the
deacetylated form of chitin, which is the second most
Materials
abundant biopolymer in the world after cellulose.
Chitosan (deacetylation degree of about 65%) was ob-
Both chitin and chitosan are widely used in many
tained from Dalian Chitin Co., Ltd. (Liaoning, China).
?elds, such as the food industry, the textile industry,
Silica particle was purchased from Shanghai Wusi
papermaking, agriculture, and cosmetics.4 Moreover,
Chemical Reagent Co., Ltd. (Shanghai, China). All
in the past few decades, chitosan has been used in
other reagents were analytical reagent grade and used
biomedical and biotechnical research as a membrane
without further puri?cation.
material (e.g., for the separation of biomacromol-
Chitosan was further deacetylated in 50 wt %
ecules) due to its hydrophilicity, nontoxicity, biologi-
NaOH solution at a ratio of 0.1 kg/L in a stainless steel
cal compatibility, biodegradability and easy mem-
kettle at 373 K for 5 h under N2 atmosphere. The
resulting chitosan was washed to neutral and dried for
further use. The degree of N-deacetylation and the
Correspondence to: X. Chen.
molecular weight of the chitosan were determined by
Journal of Applied Polymer Science, Vol. 90, 1108–1112 (2003)
titration and viscometry methods, respectively, as de-
© 2003 Wiley Periodicals, Inc.
scribed in our previous work.4 The ?nal deacetylation

PREPARATION OF CHITOSAN/CU(II)
1109
degree was 95% and the molecular weight was about
The Cu(II) adsorption capacity and the swelling
300 kDa.
ratio to water of the membranes were obtained as
follows:
Preparation and characterization of macroporous
Adsorption Capacity ? (W ?
?
1
W0)/W0
100% (2)
chitosan membranes
The macroporous chitosan membranes were prepared
Swelling Ratio ? (W ?
?
2
W1)/W1
100%
(3)
according to the method described by Zeng and Ruck-
enstein.7 Two grams of chitosan were dissolved in 100
where W0 is the weight of the original macroporous
mL of 2 vol % aqueous acetic acid. After ?ltration of
chitosan membrane, W1 is the weight of the membrane
the chitosan solution, the silica particles were added,
after adsorption of Cu(II) (i.e., dry chitosan/Cu(II)
followed by vigorous stirring for 3 h at room temper-
af?nity membrane) and W2 is the weight of the chi-
ature in order to disperse them uniformly. Then the
tosan/Cu(II) af?nity membrane after being swollen in
solution was poured into a PET box and allowed to
water.
dry in a fume hood overnight at approximately 25°C
and 50% relative humidity. After the membranes
dried, they were immersed in a 5 wt % aqueous NaOH
Adsorption of urea onto macroporous
chitosan/Cu(II) affinity membranes

solution and kept for 2 h at 80°C to dissolve the silica
and to generate macroporous chitosan membranes.
The macroporous chitosan/Cu(II) af?nity membranes
Finally, the macroporous membranes were washed
were added to the urea solution at a concentration of
with distilled water to remove the remaining NaOH,
1300 mg/L in phosphate buffer (pH ? 7.0) and stirred
dried and stored in a desiccator for further use.
for 12 h at room temperature. The ratio of the weight
In order to calculate the porosity of the macro-
of the membrane to the volume of urea solution was
porous chitosan membrane, a corresponding dense
?xed (? 1.2 mg/mL). The adsorption capacity of urea
chitosan membrane was also prepared. After ?ltra-
was calculated with the following equation:
tion, 2 wt % chitosan aqueous acetic solution was
poured into a PET box and allowed to dry under the
Adsorption Capacity ? (C ?
0
C1) ? V/W (4)
same conditions used for the preparation of the
macroporous membrane.
where C0 and C1 are the initial and ?nal concentrations
The morphology of the macroporous chitosan mem-
of urea solution respectively (determined according to
brane was observed by a Philip XL30 scanning elec-
the method described in the literature3), V is the vol-
tron microscope (SEM) at 20 kV. Both the surface and
ume of urea solution, and W is the weight of the dry
a cross section (prepared by fracturing the membrane
chitosan/Cu(II) af?nity membrane, respectively.
under liquid nitrogen) were scanned after coating
with a thin layer of gold.
The porosity of the macroporous chitosan mem-
RESULTS AND DISCUSSION
brane was calculated as follows:
Macroporous chitosan membranes
Generally, the porogens employed to generate porous
Porosity (%) ? (1 ? ?1/?2) ? 100%
(1)
membranes via the phase-inversion method are liquid
compounds, such as acetone, dimethyl formamide,
where ?1 is the density of the macroporous chitosan
dimethyl sulfoxide, benzene, etc.7 For instance, there
membrane, and ?2 is the density of the corresponding
are reports about preparing chitosan microporous
dense chitosan membrane.
membranes using water8 or poly(ethylene glycol)9 as
the porogen. Unlike in micro?ltration or ultra?ltra-
tion, the pore size of the membrane is not the key
Preparation and characterization of macroporous
point in af?nity separation; rather it is the af?nity of
chitosan/Cu(II) affinity membranes
the membrane for the substance to be separated.
The macroporous chitosan membranes were cut into
Therefore, a large pore size in af?nity membranes can
small pieces (1.6 cm ? 5.0 cm) and kept in CuSO4
increase the ?uid rate and enhance the productivity.
solutions with different initial concentrations and
Silica particle has been reported as an ideal porogen to
stirred for 12 h at room temperature. After rinsing
generate macroporous chitosan membranes with con-
with distilled water and drying, macroporous chi-
trolled porosity and good mechanical properties.7 Figure
tosan/Cu(II) af?nity membranes were obtained.
1 shows the SEM photographs of a macroporous chi-
The morphology of the af?nity membrane was ob-
tosan membrane prepared using silica particle as the
served by SEM using the same method described
porogen. The pictures indicate that the pores are well
above.
distributed and continuous within the membranes,

1110
LIU ET AL.
Figure 2
In?uence of silica/chitosan ratio on the porosity
of macroporous chitosan membranes.
hold the weight of the matrix, they collapse, resulting
in low porosity. Taking into account the easiness of
preparation and the relative high porosity, we chose a
silica/chitosan ratio of 10 for macroporous chitosan
membrane preparation for further use.
Macroporous chitosan/Cu(II) affinity membranes
Chitosan is a well-known adsorbent for metal ions,
such as Cu(II), Ni(II), Cr(II), Zn(II) and Hg(II), because
Figure 1
SEM photographs of macroporous chitosan mem-
the amine group (ONH2) and the hydroxyl group
brane: (a) surface, (b) cross section (silica/chitosan ? 10/1).
(OOH) can serve as coordinate sites for metals.11–14
There are many articles in the literature on chitosan/
which meets the requirements for af?nity separation.
Cu(II) complexes,15–17 but few of them are about chi-
From the SEM pictures, we calculated the average pore
tosan/Cu(II) complex membranes. In our previous
size of the macroporous membrane to be 25–35 ?m
work, we reported the preparation of chitosan/Cu(II)
using an approach similar to one described in the liter-
complex membranes2,18 as well as the in?uence of
ature.10 We also compared the morphology of the mem-
membrane structure on Cu(II) adsorption capacity;19
branes prepared under different conditions (room tem-
however, these articles were base on dense mem-
perature for about 2 days, and room temperature in a
branes. In this study, we use a macroporous chitosan
fume hood overnight and an oven at 80°C for 8 h) in
order to investigate the in?uence of dry time on mor-
phology. The results indicate that the pore distribution of
the membrane does not change much, which is similar to
the ?ndings in the literature.7
The more porosity in the membrane, the more sur-
face for af?nity adsorption, so we tried to vary the
ratio of silica particle to chitosan in membrane prep-
aration to obtain a membrane with maximum poros-
ity. As shown in Figure 2, at the beginning an increase
in the silica/chitosan ratio increased the porosity of
the membrane. The porosity reached a maximum
when the silica/chitosan ratio was around 12. To our
surprise, the porosity decreased when the silica/chi-
tosan ratio exceeded 12. After studying SEM pictures
(Fig. 3), we concluded that, with the increase of the
silica/chitosan ratio, the walls of the pores became
Figure 3
SEM photograph of macroporous chitosan mem-
increasingly thin. Because the walls eventually fail to
brane (surface, silica/chitosan ? 16/1).

PREPARATION OF CHITOSAN/CU(II)
1111
Figure 4
In?uence of initial CuSO4 concentration on Cu(II)
adsorption capacity of macroporous chitosan membrane.
membrane as the matrix to prepare a novel macro-
porous chitosan/Cu(II) af?nity (complex) membrane.
Figure 4 represents the effect of loading the concen-
tration of CuSO4 on the Cu(II) adsorption capacity of
the macroporous chitosan membrane. With the in-
crease of loading concentration, the amount of Cu(II)
adsorbed on to the membrane increased. When the
loading concentration was higher than 5 ? 10?2
mol/L, the adsorption capacity of the Cu(II) leveled
off, which meant the adsorption equilibrium had been
reached. The morphology of the macroporous chi-
Figure 5
SEM photographs of macroporous chitosan/
tosan membrane did not change much after the ad-
Cu(II) af?nity membrane: (a) surface, (b) cross section (sili-
sorption of Cu(II) (Fig. 5).
ca/chitosan ? 10/1, initial CuSO4 concentration ? 10?2
As our chitosan/Cu(II) af?nity membrane is sup-
mol/L).
posed to be used in hemodialysis to remove urea, we
need to consider its hydrophilicity. We know that
although the main purpose of this article is not fun-
hydrophilicity is favored in biotechnology and medi-
damental study. There have been many studies on the
cal utilization; however, if the hydrophilicity is too
mechanism of the complexation, and different models
high, excess swelling of the membrane will cause
many problems, such as the leakage of the membrane
into the device during the process. Chitosan is a high
hydrophilic material because it has plenty of amine
groups and hydroxyl groups in its structure. Its swell-
ing ratio to water was beyond 400%, as shown in
Figure 6. After the adsorption of Cu(II), the swelling
ratio declined to 100 –200%, which would be more
suitable for its application. The reason for the decrease
of the swelling ratio was probably Cu(II) acting as a
crosslink agent to crosslink chitosan.20 Thus we as-
sumed that when the chitosan membrane was im-
mersed in CuSO4 solution, the hydrophilic groups in
chitosan (mainly ONH2 groups) were coordinated
with Cu(II) ions to form a “crosslinked” structure. The
more Cu(II)ions coordinated the hydrophilic groups
in chitosan, the higher the crosslinking degree of the
membrane, and the lower swelling ratio.
Figure 6
In?uence of Cu(II) content in membrane on swell-
In order to support our assumption, we need to
ing ratio of macroporous chitosan/Cu(II) af?nity mem-
discuss the Cu(II)-chitosan complexation mechanism,
brane.

1112
LIU ET AL.
? 14 mg/g membrane, while blending with 20 % silk
?broin, increases the capacity to ? 20 mg/g membrane.
Here, because of the large surface area of the macro-
porous chitosan membrane that absorbs more Cu(II), the
urea adsorption capacity increases signi?cantly. The
maximum urea adsorption capacity of this macroporous
chitosan/Cu(II) af?nity membrane is 78.8 mg/g mem-
brane, which is higher than the capacities of other kinds
of urea absorbents, such as activated carbon (9.0 mg/g),1
polyethylenepolyamine/Cu(II) complex (75.2 mg/g)2
and TDI crosslinked ?-cyclodextrin (50.6 mg/g).3 Con-
sidering its high urea adsorption capacity and advan-
tages of membrane material, the macroporous chitosan/
Cu(II) af?nity membrane has strong implications for use
in urea adsorption in the treatment of uremia by hemo-
dialysis.
Figure 7
In?uence of Cu(II) content in membrane on urea
adsorption capacity of macroporous chitosan/Cu(II) af?nity
This work was supported by the National Natural Science
membrane.
Foundation of China (No. 50003002). We thank Miss Shulun
Liu for her contribution to this work.
have been proposed; however, they seem to disagree
with each other (for detail, see ref. 21 and the refer-
References
ences therein). The newest model proposed by Rhazi
1. Yoshie, F.; Susumu, O. Nippon Kaguka Kaishi 1990, 4, 352.
et al. suggests that Cu(II) coordinates with two ONH2
2. Chen, X.; Li, W. J.; Zhong, W.; Yu, T. Y. Chin J Biomed Eng 1997,
groups in chitosan to form a {[Cu(ONH2)2]2?, 2OH?}
16, 284.
complex under neutral conditions.21 As we know, chi-
3. Shi, L. Q.; Zhang, Y. Z.; He, B. L. Polym Adv Technol 1999, 10,
tosan is a semi-rigid polymer, so two ONH
69.
2 groups
coordinated with Cu(II) ions were unlikely to be in the
4. Chen, X.; Yang, H.; Gu, Z. Y.; Shao, Z. Z. J Appl Polym Sci 2001,
79, 1144.
same chitosan chain because of steric hindrance; there-
5. Zeng, X. F.; Ruckenstein, E. Biotechnol Prog 1999, 15, 1003.
fore Cu(II) could act as a crosslinking agent to
6. Zou, H. F.; Luo, Q. Z.; Zhou, D. M. J Biochem Biophys Methods
crosslink two chitosan chains.
2001, 49, 199.
7. Zeng, X. F.; Ruckenstein, E. Ind Eng Chem Res 1996, 35, 4169.
8. Kubota, N.; Kikuchi, Y.; Mizuhara, Y.; Ishihara, T.; Takita, Y.
Adsorption of urea onto macroporous
J Appl Polym Sci 1993, 50, 1665.
chitosan/Cu(II) affinity membrane
9. Zeng, X. F.; Ruckenstein, E. J Membr Sci 1996, 117, 271.
10. Chung, T. S.; Tun, C. M.; Pramoda K. P.; Wang, R. J Membr Sci
One of the applications of the chitosan/Cu(II) com-
2001, 193, 123.
plex is initial polymerization,18,22 while another poten-
11. Maruca, R. J Appl Polym Sci 1982, 27, 4827.
tial use is absorbtion of urea.2 It is generally accepted
12. Krita, K.; Koyama, Y.; Taniguchi, A. J Appl Polym Sci 1986, 31,
that urea can coordinate with Cu(II) with its oxygen
1169.
13. Ohga, K.; Kurauchi, Y.; Yanase, H. Bull Chem Soc Jpn 1987, 60,
atom,23 so it is practical to use the chitosan/Cu(II)
444.
complex membrane as an af?nity membrane to absorb
14. Juang, R. S.; Wu, F. C.; Tseng, R. L. Wat Res 1999, 33, 2403.
urea. According to the model discussed above,21 only
15. Han, H. S.; Jiang, S. N.; Huang, M. Y.; Jiang, Y. Y. Polym Adv
two coordinate sites on Cu(II) are occupied by ONH
Technol 1996, 7, 704.
2
groups in chitosan, so there are two other coordinate
16. Wang, A. Q.; Shao, S. J.; Zhou, J. F.; Yu, X. D. Acta Polym Sin
2000, 3, 297.
sites that can be used to coordinate urea. It is impos-
17. Yin, X. Q.; Zhang, Q.; Yu, W. X.; Yang, L. C.; Lin, Q. Chin J Inorg
sible for Cu(II) to link all four of its coordinate sites
Chem 2002, 18, 87.
with ONH2 groups in chitosan because of steric hin-
18. Wang, H. F.; Wang, Z. L.; Chen, X.; Li, W. J. J Fudan Univ 1997,
drance.
36, 107.
Figure 7 demonstrates urea adsorption onto the
19. Chen, X.; Shao, Z. Z.; Huang, Y. F.; Huang, Y.; Zhou, P.; Yu, T. Y.
Acta Chim Sinica 2000, 58, 1654.
macroporous chitosan/Cu(II) af?nity membrane. As
20. Modrzejewska, Z.; Kaminski, W. Ind Eng Chem Res 1999, 38,
presented in the ?gure, urea adsorption capacity in-
4946.
creases linearly with the increase of Cu(II) content in the
21. Rhazi, M.; Desbrieres, J.; Tolaimate, A.; Rinaudo, M.; Vottero, P.;
membrane. This means that the urea adsorption by the
Alagui, A. Polymer 2002, 43, 1267.
macroporous chitosan/Cu(II) af?nity membrane simply
22. Inaki, Y.; Otsura, M.; Takemoto, K. J Macromol Sci Chem 1978,
A12, 953.
depends on the Cu(II) content in the membrane. As
23. Andrews, R. K.; Blakeley, R. L. In Advances in Inorganic Bio-
noted in our previous report,2 the urea adsorption ca-
chemistry; Elchhorn, G. L., et al., Eds.; Elsevier: New York, 1984;
pacity of dense chitosan/Cu(II) complex membrane is
Vol. 6, p 246.

ERRATUM
Preparation and Characterization of Chitosan/Cu(II)
Af?nity Membrane for Urea Adsorption

Jiahao Liu, Xin Chen, Zhengzhong Shao, Ping Zhou
Department of Macromolecular Science, The Key Laboratory of Molecular Engineering of Polymers, Fudan University,
Shanghai, 200433, People’s Republic of China
(Article in J Appl Polym Sci 2003, 90, 1108 –1112)
When this article was ?rst published, p. 1111 contained several errors. It is being reprinted here (see next page,
p. 3458) with all corrections included.
Journal of Applied Polymer Science, Vol. 90, 3457–3458 (2003)
© 2003 Wiley Periodicals, Inc.

3458
JOURNAL OF APPLIED POLYMER SCIENCE, VOL. 90 (2003)
Figure 4
In?uence of initial CuSO concentration on Cu(II)
4
adsorption capacity of macroporous chitosan membrane.
membrane as the matrix to prepare a novel macro-
porous chitosan/Cu(II) af?nity (complex) membrane.
Figure 4 represents the effect of loading concentra-
tion of CuSO4 on the Cu(II) adsorption capacity of the
macroporous chitosan membrane. With the increase of
loading concentration, the amount of Cu(II) adsorbed
onto the membrane increased. When the loading con-
centration was higher than 5 ? 10?2 mol/L, the ad-
sorption capacity of the Cu(II) leveled off, which
meant the adsorption equilibrium had been reached.
The morphology of the macroporous chitosan mem-
Figure 5
SEM photographs of macroporous chitosan/
brane did not change much after the adsorption of
Cu(II) af?nity membrane: (a) surface, (b) cross section (sili-
ca/chitosan ? 10/1, initial CuSO concentration ? 10?2
Cu(II) (Fig. 5).
4
mol/L).
As our chitosan/Cu(II) af?nity membrane is sup-
posed to be used in hemodialysis to remove urea, we
need to consider its hydrophilicity. We know that
although the main purpose of this article is not fun-
hydrophilicity is favored in biotechnology and medi-
damental study. There have been many studies on the
cal utilization; however, if the hydrophilicity is too
mechanism of the complexation, and different models
high, excess swelling of the membrane will cause
many problems, such as the leakage of the membrane
into the device during the process. Chitosan is a high
hydrophilic material because it has plenty of amino
groups and hydroxyl groups in its structure. Its swell-
ing ratio to water was beyond 400%, as shown in
Figure 6. After the adsorption of Cu(II), the swelling
ratio declined to 100 –200%, which would be more
suitable for its application. The reason for the decrease
of the swelling ratio was probably Cu(II) acting as a
crosslink agent to crosslink chitosan.20 Thus we as-
sumed that when the chitosan membrane was im-
mersed in CuSO4 solution, the hydrophilic groups in
chitosan (mainly ONH2 groups) were coordinated
with Cu(II) ions to form a “crosslinked” structure. The
more Cu(II)ions coordinated the hydrophilic groups
in chitosan, the higher the crosslinking degree of the
membrane, and the lower swelling ratio.
Figure 6
In?uence of Cu(II) content in membrane on swell-
In order to support our assumption, we need to
ing ratio of macroporous chitosan/Cu(II) af?nity mem-
discuss the Cu(II)-chitosan complexation mechanism,
brane.

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