26
2 Thermodynamics, Kinetics and Desorption Studies …
ingestion [8, 9]. These associated health risks have necessitated adequate legislation and strict regulations on the discharge of toxic metal ions into our water bodies.
Consequently, several processes have been developed to adsorb these pollutant water
and wastewater [4, 10]. They include chemical precipitation [11], adsorption [12],
membrane separation [13], reverse osmosis [14] and electrochemical treatment [15].
Of all the processes, adsorption is considered more reliable due to their convenience, simplicity of design, easy operation and wider applicability in water pollutant
removal [10, 16, 17].
On another development, biological-based polymeric materials such as cellulose,
lignin, chitosan and starch have been widely reported to play an important role in
adsorption processes due to their re-absorbability and biocompatibility capabilities
[18]. Hence, chitosan polymetric materials possess higher absorption capacity due
to the availability of amine (–NH 2 ) and hydroxyl (OH) functional group in their
complex structure [19]. These functional groups, however, represent adsorption sites
where complexes are formed with different kinds of metal ions. However, solubility
of chitosan in acidic (pH ≤ 4) solutions is a limitation. To overcome such limitation and make the material insoluble at lower pH, chitosan beads are modified by
cross-linking with epichlorohydrin [18, 20]. This process removes chlorine atom
from the epoxide ring and covalently bonds carbon atoms to the hydroxyl group
[21], as indicated in Fig. 2.1. It has also been reported that cross-linking reaction
reduces the adsorption capacity of chitosan beads [4, 22–24] and this is because
some functional groups in the complex structure of chitosan are bound with the crosslinker and therefore cannot interact with the pollutant. Consequently, grafting which
HO
HO
OH
O
HO
OH
O
NH 2
O
OH
O
NH 2
HO
OH
O
O
HO
OH
O
NH 2
O
O
O
HO
OH
O
NH 2
NH 2
CHITOSAN
CROSS LINKING
CH 2
CHCH 2 Cl
O
CH 2
HO
HO
O
N
CH
OH
H 2
HO
HO
O
O
HO
NH 2
OH
O
NH 2
O
O
CH 2
O
HO
OH
O
CH 2
NH 2
CH
CH 2
OH
+
Fig. 2.1 Projected schematic representation of the cross-linking method of chitosan
2 Thermodynamics, Kinetics and Desorption Studies …
ingestion [8, 9]. These associated health risks have necessitated adequate legislation and strict regulations on the discharge of toxic metal ions into our water bodies.
Consequently, several processes have been developed to adsorb these pollutant water
and wastewater [4, 10]. They include chemical precipitation [11], adsorption [12],
membrane separation [13], reverse osmosis [14] and electrochemical treatment [15].
Of all the processes, adsorption is considered more reliable due to their convenience, simplicity of design, easy operation and wider applicability in water pollutant
removal [10, 16, 17].
On another development, biological-based polymeric materials such as cellulose,
lignin, chitosan and starch have been widely reported to play an important role in
adsorption processes due to their re-absorbability and biocompatibility capabilities
[18]. Hence, chitosan polymetric materials possess higher absorption capacity due
to the availability of amine (–NH 2 ) and hydroxyl (OH) functional group in their
complex structure [19]. These functional groups, however, represent adsorption sites
where complexes are formed with different kinds of metal ions. However, solubility
of chitosan in acidic (pH ≤ 4) solutions is a limitation. To overcome such limitation and make the material insoluble at lower pH, chitosan beads are modified by
cross-linking with epichlorohydrin [18, 20]. This process removes chlorine atom
from the epoxide ring and covalently bonds carbon atoms to the hydroxyl group
[21], as indicated in Fig. 2.1. It has also been reported that cross-linking reaction
reduces the adsorption capacity of chitosan beads [4, 22–24] and this is because
some functional groups in the complex structure of chitosan are bound with the crosslinker and therefore cannot interact with the pollutant. Consequently, grafting which
HO
HO
OH
O
HO
OH
O
NH 2
O
OH
O
NH 2
HO
OH
O
O
HO
OH
O
NH 2
O
O
O
HO
OH
O
NH 2
NH 2
CHITOSAN
CROSS LINKING
CH 2
CHCH 2 Cl
O
CH 2
HO
HO
O
N
CH
OH
H 2
HO
HO
O
O
HO
NH 2
OH
O
NH 2
O
O
CH 2
O
HO
OH
O
CH 2
NH 2
CH
CH 2
OH
+
Fig. 2.1 Projected schematic representation of the cross-linking method of chitosan