Chitosan-based Materials in Waste Water Treatment––Recent Developments - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 24

advantages of Biopolymers
The sorbents are low cost materials obtained from natural raw resources. The materi-
als are versatile in properties with repetitive functional groups; biopolymers provide
excellent chelating and complexing materials for a wide variety of pollutants including
dyes, heavy metals, and aromatic compounds.
• The regeneration step is easy.
• Biosorption, in particular chitosan, is an emerging technology that attempts to
overcome the selectivity disadvantages of adsorption processes (Crini, 2005).
ChitiN aNd ChitosaN
Chitin is the second most abundant natural biopolymer derived from exoskeletons of
crustaceans and also from cell walls of fungi and insect (Peter in et al., 2005). The
degree of acetylation in chitin can be as low as <10% and the molecular weight of this
linear polysaccharide can be as high as 1-2.5*10 6 Da, corresponding to a degree of po-
lymerization of Ca 5,000-10,000. Chitosan is a product derived from N-deacetylation
of chitin in the presence of hot alkali. In chitosan, the degree of deacetylation ranges
from 40% to 98% and the molecular weight ranges between 5*10 4 Da and 2*10 6 Da.
The degree of deacetylation and the degree of polymerization, which in turn decide
molecular weight of polymer, are two important parameters dictating the use of chito-
san for various applications (Hejazi and Amiji, 2003).
In spite of potential applications of chitin and chitosan, it is necessary to establish
efficient and appropriate modifications to explore fully the high potential of these bio-
macromolecules. Chemical modifications of chitin are generally difficult owing to the
lack of solubility, and the reactions under heterogeneous conditions are accompanied
by various problems such as the poor extent of reaction, difficulty in selective sub-
stitutions, structural ambiguity of the products, and partial degradation due to severe
reaction conditions. Therefore, with regard to developing advanced functions, much
attention had been paid to chitosan rather than chitin (Jalal Zohuriaan Mehr, 2004).
Chitosan in Wastewater treatment
Chitosan is a well known solid sorbent for transition metals because the amino groups
on chitosan chain can serve as coordination sites (Guibal et al., 1994; Onsoyed and
Skagrud, 1990). In addition to binding ability, it has a high content of functional
groups and is produced very cheaply, since chitin is the second abundant biopolymer
in nature next to cellulose (Chaufer and Deratani, 1988; Geckeler and Volchek, 1996).
As a functional material chitosan offers a unique set of characteristics like hy-
drophilic nature, biocompatibility, biodegradability, antibacterial properties, and re-
markable affinity to proteins. It is biologically inert, safe for humans and the natural
environment (Li et al., 1992; Kubota and Kikuchi, 1998). Amine groups present in
chitosan are strongly reactive with metal ions. Indeed, nitrogen atoms hold free elec-
tron doublets that can react with metal cations. Amine groups are thus responsible for
the uptake of metal cations by a chelation mechanism. However, the amine groups are
easily protanated in acidic solutions. Hence, the protanation of these amine groups