Chitosan-based Materials in Waste Water Treatment––Recent Developments - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 26

solution. Dye binding to chitosan involves mostly the adsorption on the active sites on
chitosan macromolecules (Dragan Jocic et al., 2005).
modiFiCatioNs oF ChitosaN
Modification of chitosan is to introduce special properties into these abundant bio-
polymers and enlarge their fields of potential applications (Hong-Mei Kang et al.,
2006). Physical and chemical modifications have been performed for improving metal
sorption selectivity by template formation (or) the imprinting method (Baba et al.,
1998; Cao et al., 2001; Tan et al., 2001).
Physical modifications
One of the most interesting advantages of chitosan is its versatility. The material can
readily be modified physically, preparing different conditioned polymeric forms such
as powder, nanoparticles (Van der Lubben et al., 2000), gel beads (Guibal et al., 1999),
membranes (Wang and Shen, 2001), sponge (Mi et al., 2001), honeycomb (Amiaike et al.,
1998), fibers (Vincent and Guibal, 2000), hollow fibers (Agboh and Quin, 1997) for
various fields of applications such as wastewater treatment, biomedical, textiles, and
so on.
Chitosan Beads
Chitosan has a very low specific area ranging between 2 and 30 m 2 g -1 (Dzul Erosa
et al., 2001). Glutaraldehyde cross-linked chitosan gel beads have a higher specific
surface area around 180-250 m 2 g -1 (Milot, 1998). Gel bead conditioning significantly
modifies the porous characteristics of the polymer, which may explain the differences
in the sorption properties of the material (Guibal et al., 1995). The preparation of mag-
netic chitosan gel beads (Rorrer et al., 1993) offers interesting perspective for the treat-
ment of metal containing slurries. These kind of magnetic particles have been used for
the recovery of cadmium and for dye sorption (Denkbas et al., 2002).
Sorption equilibria of Cu 2+ , Ni 2+ , and Zn 2+ from single and binary-metal solutions
on glutaraldehyde cross-linked beads were studied at 20°C. The amount of metal sorp-
tion increased with increasing pH, confirmed the occurrence of competitive sorption
of proton and metal ions (Ruey-Shin Juang et al., 2001). Liu prepared new hybrid
materials that adsorb transition metal ions by immobilizing chitosan on the surface
of non-porous glass beads. Column chromatography on the resulting glass beads re-
vealed that they have strong affinities to Cu (II), Fe (II), and Cd (II) (Liu et al., 2002,
2003). Alginate-chitosan hybrid gel beads were prepared and shown to very rapidly
adsorb heavy metal ions (Gotoh et al., 2004). Modified chitosan gel beads with phenol
derivatives were found to be effective in adsorption of cationic dye, such as crystal
violet and bismark brown (Chao et al., 2004).
The cross-linked chitosan beads had very high adsorption capacities to remove the
anionic dyes whose maximum monolayer adsorption capacity ranges from 1,911 to
2,498 g/kg at 30°C. The adsorption capacities of the cross-linked chitosan beads are
much higher than those of chitin for anionic dyes. It shows that the major adsorption
site of chitosan is an amine group-NH 2 , which is easily protonated to form-NH 3 + in