Biomedical Engineering Reference
In-Depth Information
may cause electrostatic attraction of anionic compounds including metal anions (or)
anionic dyes (Gibbs et al., 2003).
The binding mechanism of metal ions to chitosan is not yet fully understood. Vari-
ous processes such as adsorption, ion exchange, and chelation are discussed as the
mechanism responsible for complex formation between chitosan and metal ions. The
type of interaction depends on the metal ion, its chemistry and the pH of the solution
(Guibal et al., 2000; Inoue et al., 1993). Metal anions can be bound to chitosan by elec-
trostatic attraction. It is likely that the chitosan-metal cation complex formation occurs
primarily through the amine groups functioning as ligands (Roberts, 1992). It is well
known that chitosan may complex with certain metal ions (Muzzarelli, 1977). Possible
applications of the metal binding property are wastewater treatment for heavy metals
and radio isotope removal with valuable metal recovery, and potable water purification
for reduction of unwanted metals (Onsoyen and Skaugrud, 1990). Chitosan is a good
scavenger for metal ions owing to the amine and hydroxyl functional groups in its
structure (Alves and Mano, 2008; Sudha et al., 2008; Zhao et al., 2007).
Chitosan has a strong metal binding ability. It was found that their adsorption of
uranium is much greater than of the other heavy metal ions (Sakaguchi et al., 1981).
Chitosan, a polymer of biological origin has been reported to be an effective adsorbent
for Cr (VI) removal from waste water (Bailey et al., 1999). Lasko and Hurst (1999)
studied silver sorption on chitosan under different experimental conditions, changing
the pH in the presence of several ligands (Dinesh karthick et al., 2009). Molybdate
anions are selectively bound to chitosan in the presence of excess nitrate (or) chloride
ions, with selectivity to chitosan in the presence of Ni
2+
, Zn
2,
,Cd
2+
ions, with selectiv-
ity coefficients in the range of 10-10,000 (Inger et al., 2003). Nair and Madhavan
used chitosan for the removal of mercury from solutions and the adsorption kinetics
of mercuric ions by chitosan was reported. The result indicates that the efficiency of
adsorption of Hg
2+
by chitosan depends upon the period of treatment, the particle size
(Nair and Madhavan, 1984).
Jha studied the adsorption of Cd
2+
on chitosan powder over the concentration range
1-10 ppm using various particle sizes by adopting similar procedures as for the re-
moval of mercury (Jha et al., 1988). Mc Kay used chitosan for the removal of Cu
2+
,
Hg
2+
, Ni
2+
, and Zn
2+
within the temperature range of 25°-60°C at neutral pH (Mc Kay
et al., 1989). Further adsorption parameters for the removal of these metal ions were
reported by Yang (Yang et al., 1984). Chitosan due to its high content of amine and
hydroxyl functional groups has an extremely high affinity for many classes of dyes
including disperse, direct, anionic, vat, sulphur, and naphthol (Crini and Badot, 2008;
Martel et al., 2001).
The absorption spectrometry measurements proved the occurrence of interaction
between the chitosan and acid dye in an aqueous solution. By assessment of chitosan/
dye interaction it was possible to show that there is a 1:1 stoichiometry between pro-
tonated amino groups and sulfonate acid groups on the dye ions in low concentrated
chitosan solutions. This interaction between chitosan and dye forms an insoluble prod-
uct. With the excess of chitosan in the solution, the dye can be distributed between
the different chitosan molecules and the chitosan/dye soluble products remain in the
Search WWH ::
Custom Search