Biomedical Engineering Reference
In-Depth Information
to change the pH range for metal sorption and to change the sorption sites in order to
increase sorption selectivity for the target metal (Alves and Mano, 2008).
Li reported the first synthesis of calixarene-modified chitosan. The adsorption
properties of calixarene-modified chitosan were greatly varied compared with that of
chitosan, especially with the adsorption capacity towards Ag
2+
and Hg
2+
, because of
the presence of calixarene moiety (Li et al., 2003). Pyruvic acid modified chitosan
had higher adsorption capacities for Cu
2+
, Zn
2+
, Co
2+
than chitosan and salicylalde-
hyde modified chitosan. Chitosan benzoyl thiourea derivative has been synthesized
and used successfully for the removal of the hazardous
60
Co and
154
Eu radio nuclides
from aqueous solutions (Metwally et al., 2009).
multiple modifications
There are some cases in which:
(i) The reactivity of chitin/chitosan itself is insufficient to participate in the de-
sired reaction.
(ii) The modified chitin/chitosan does not possess the desired properties.
(iii) Some sites of chitin/ chitosan must be protected to sustain during the modi-
fication reactions. In such instants, there are two general approaches via
chemical modification when the graft polymerization is a certain pathway to
achieve desired characteristics:
(a)
----In situ
-and/ or post-treatment of the graft copolymer,
(b) Graft copolymerization onto a previously modified chitin/chitosan. So,
the products may generally be referred to as multiple modified materials
(Jalal Zohuriaan Mehr, 2004). Chitosan can be modified as cross-linked
chitosan, blends, composites and its derivatives.
Cross-linked Chitosan
Chemical modification of cross-linked chitosan through introduction of xanthate was
investigated in order to achieve highly enhanced adsorption performance for lead ions
under acidic solution conditions. The choice of xanthate group is due to the presence
of sulfur atoms and it is well known that sulfur groups have a very strong affinity for
most heavy metals, the metal-sulfur complex is very stable in basic condition (Divya
Chauhan and Nalini Sankararamakrishnan, 2008).
Cross-linking of chitosan has been performed with many reagents like formalde-
hyde, glutaraldehyde, ethylene glycol. Palladium sorption occured on glutaraldehyde
cross-linked chitosan. The optimum pH for palladium sorption is close to pH 2 (Ruiz
et al., 2000).Crown ether bound chitosan will have a strong complexing capacity and
better selectivity for metal ions because of the synergistic effect of high molecular
weight. Tang prepared the crown ether bound chitosan with Schiff's base type. It had
not only good adsorption capacities for metal ions Pb
2+
, Au
3+
, Ag
+
but also high selec-
tivity for the adsorption of Pd
2+
in the presence of Cu
2+
and Hg
2+
(Tang et al., 2002).
The spherical chitosan-tripolyphosphate chelating resins were used as sorbents for the
removal of Cu(II) (Lee, 2001).
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