Chitosan and Chitosan Derivatives as Chelating Agents - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 2

In recent years, chitosan has been described as a suitable natural polymer and a
renewable resource for the collection of metal ions, (Arrascue et al., 2003; Ding et al.,
2006; Ruiz et a., 2002; Tabakci and Yilmaz, 2008) since the amine and hydroxyl func-
tional groups on the chitosan chain can act as chelation sites for metal ions. Besides
inherent sorption, the adsorption capacity and selectivity of chitosan could also be
enhanced by chemical and physical modification on both amine and hydroxyl groups
(Ramesh et al., 2008; Ruiz et al., 2003; Wan Ngah et al., 1999). Additionally, it is pos-
sible to reinforce the stability of the biopolymer in acidic conditions by cross-linking
(Butewicz et al., 2010).
Chitosan was found to have the highest chelating ability in comparison with other
natural polymers (Varma et al., 2004). It has been realized, that the mechanism of
chitosan-metals complex formation is manifold and probably dominated by different
processes taking place simultaneously such as adsorption, ion-exchange and chelation,
under different conditions (Butelman, 1991). The presence of amine groups leads to
the binding of metal cations by complexation or chelation, and after protonation to the
binding of anions by electrostatic attraction or ion exchange (Guibal, 2004; Guibal
et al., 2006a).
In addition to medical applications, the most important and significant develop-
ments in chitin/chitosan technology have been in the area of environmental applica-
tions which include among others the removal of dyes (Chiou and Li, 2003; McKay
et al., 1983; Wong et al., 2003, 2004; Yoshida et al., 1993). Other environmental ap-
plications include removal of polychlorinated biphenyl (PCB) (Ikeda et al., 1999) and
chemical waste detoxification (Wagner and Nicell, 2002). Further developments in
the field of water treatment include filtration (Juang and Chiou, 2001), desalination
(Arai and Akiya, 1978), and flocculation/coagulation (Eikebrokk and Saltnes, 2002).
An interesting area of research, however, has been generated by the ability of chitosan
to remove metal ions from wastewaters by the process of adsorption. Chitosan has
demonstrated the potential to adsorb significant amounts of metal ions, and this has
generated an interest in assessing its feasibility to remove metal ions over a wide range
of effluent systems and types.
ChitosaN aNd modiFied ChitosaN as ChelatiNG aGeNts For
metal ioNs
The ability of chitosan to bind transition metal in presence of alkali and alkaline earth
metal is well investigated (Deans and Dixon, 1992). The adsorption of Cu 2+ , Hg 2+ ,
Ni 2+ , and Zn 2+ on chitosan with various particle sizes and as a function of temperature
was studied at neutral pH (McKay et al., 1989). Moreover, metal complexation by
chitosan and its derivatives has been reviewed (Gerente et al., 2007; Guibal et al.,
2006b; Varma et al., 2004). Recently, chitosan-Zn complex attracted great interest for
its potential uses as medicament or nutriment (Paik, 2001; Tang and David, 2001; Yo-
neKura and Suzuki, 2003). It is well known that both of chitosan and metal ions (Zn 2+ ,
Zr 2+ , and Ag 1+ ) have the properties of disinfection and bactericide (Varma et al., 2004).
In addition, and with the growing need for new sources of low-cost adsorbent, the in-
creased problems of waste disposal, the increasing cost of synthetic resins undoubtedly