1.3 Adsorbents
11
Chitosan physically transformed types include powders, nanoparticles, gel beads,
sponge, honeycomb and hollow fibres [104–109]. In dilute acid solutions, chitosan
can only be soluble in these forms, and this restricts its use. Thus, chemical enhancement approaches including cross-linking and graft copolymerization were designed
to transform its solubility attributes in water or acidic solutions and to generate
added functional groups, thus further enhancing the metal adsorption performance
[110–112]. In a study by Inoue et al. [113], however, the potential for adsorption of
metal ions decreases when chitosan polymers are immersed in acid solution owing to
cross-linking between the polymer matrix. The researchers further stated that metal
ion capacities and binding effectiveness could be strengthened by unique functional
group grafting. Graft copolymerization is expected to be highly satisfactory for the
application of advanced material and may extend the area of prospective polymer
application [114]. Zohuriaan [115] also stated that graft copolymerization is projected
to be among the many successful options to a vast wide range of molecular designs,
leading to new forms of polymers made from natural polysaccharide and synthetic
materials. Over the past decades, extensive research has been performed on chitin,
chitosan and chitosan-based adsorbents. Chen et al. [116] stated that chitosan is much
more effective in the adsorption cycle than chitin because of the free amino groups
on the chitosan network.
Table 1.5 presents the published adsorption equilibrium potential of chitosan and
modified chitosan as mentioned in literature. Therefore, a large number of different
approaches are produced for simple chemical modification. The key benefit of chitin
and chitosan is the lack of complexity in transforming them into various designs,
including gel beads, nanoparticles, nanofibres, microparticles and scaffolds [118–
121].
1.4 Crucial Factors Affecting Adsorption of Metal Ions
onto Adsorbent
1.4.1 Effect of pH
The pH of a solution is a significant criterion influencing the process of metal removal
efficiency, as it influences the solubility of metal ions, the concentration of ionic
species on the adsorbent’s functional groups and the level of ionization of metal ions
during reaction. Adsorbent contains reactive groups that can attract metal ions and
is therefore considered a complex ion exchanger comparable to a commercial resin.
Such bond formation can be supported by proton displacement and is largely related
to the extent of protonation predicted by the pH [134]. Kragovic et al. [64] stated that
pH performs a vital function in cation adsorption since it influences the chemical
evolution of species of the metal in solution and also the ionization of chemically
stable sites on the adsorbent surface. Throughout the years, nonetheless, numerous
11
Chitosan physically transformed types include powders, nanoparticles, gel beads,
sponge, honeycomb and hollow fibres [104–109]. In dilute acid solutions, chitosan
can only be soluble in these forms, and this restricts its use. Thus, chemical enhancement approaches including cross-linking and graft copolymerization were designed
to transform its solubility attributes in water or acidic solutions and to generate
added functional groups, thus further enhancing the metal adsorption performance
[110–112]. In a study by Inoue et al. [113], however, the potential for adsorption of
metal ions decreases when chitosan polymers are immersed in acid solution owing to
cross-linking between the polymer matrix. The researchers further stated that metal
ion capacities and binding effectiveness could be strengthened by unique functional
group grafting. Graft copolymerization is expected to be highly satisfactory for the
application of advanced material and may extend the area of prospective polymer
application [114]. Zohuriaan [115] also stated that graft copolymerization is projected
to be among the many successful options to a vast wide range of molecular designs,
leading to new forms of polymers made from natural polysaccharide and synthetic
materials. Over the past decades, extensive research has been performed on chitin,
chitosan and chitosan-based adsorbents. Chen et al. [116] stated that chitosan is much
more effective in the adsorption cycle than chitin because of the free amino groups
on the chitosan network.
Table 1.5 presents the published adsorption equilibrium potential of chitosan and
modified chitosan as mentioned in literature. Therefore, a large number of different
approaches are produced for simple chemical modification. The key benefit of chitin
and chitosan is the lack of complexity in transforming them into various designs,
including gel beads, nanoparticles, nanofibres, microparticles and scaffolds [118–
121].
1.4 Crucial Factors Affecting Adsorption of Metal Ions
onto Adsorbent
1.4.1 Effect of pH
The pH of a solution is a significant criterion influencing the process of metal removal
efficiency, as it influences the solubility of metal ions, the concentration of ionic
species on the adsorbent’s functional groups and the level of ionization of metal ions
during reaction. Adsorbent contains reactive groups that can attract metal ions and
is therefore considered a complex ion exchanger comparable to a commercial resin.
Such bond formation can be supported by proton displacement and is largely related
to the extent of protonation predicted by the pH [134]. Kragovic et al. [64] stated that
pH performs a vital function in cation adsorption since it influences the chemical
evolution of species of the metal in solution and also the ionization of chemically
stable sites on the adsorbent surface. Throughout the years, nonetheless, numerous