Page 491 - Polymer-based Nanocomposites for Energy and Environmental Applications

444 Polymer-based Nanocomposites for Energy and Environmental Applications

electrochemical process, biosorption can be utilized to decrease the amount of heavy
metal ions from ppm to ppb level in solution and in certain cases below the drinking
water standards. According to the above facts, biosorption emerges a perfect technol-
ogy for the processing of large quantity wastewaters having low metal concentration
[22]. Although the mechanisms of biosorption still not very clear, it seems to depend
upon the combination of ion exchange, electrostatic interaction, complexation, micro-
precipitation, adsorption, chelation, and coordination. Elements having functional
groups like oxygen, nitrogen, sulfur, or phosphorous show metal-binding ability
and work as ligands. The most important metal-binding groups for biosorption are
2

hydroxyl ( OH), carboxyl ( COOH), sulfonate ( SO 3 ), phosphonate ( PO 3 ),
and amine ( NH 2 ). The pH showed important role in the ionic state of the adsorbate
and metal adsorption ability of biosorbents, because of the acid-base reactions
between functional groups on the adsorbate surface and aqueous solution [20]. Lots
of work is performed to improve metal removal technique in the wastewater treatment
process to apply biosorption in industry [21].

16.1.2 Why bionanocomposites as adsorbents
for heavy metal ions?
Bionanocomposites open a new green route to overcome the current heavy metal pol-
lution problems due to its high specific area that is responsible for numerous active
sites on the surface of biosorbent to attach metal ions. Also, the functional groups
on the surface acting as metal-binding sites for the biomass are responsible for
removal of heavy metal ions. Significant metal-binding groups for biosorption dem-
onstrated in Table 16.1 can be used after surface modification. Meanwhile, numerous
other physicochemical properties of bionanocomposite can be modified by surface
alterations to fulfill the needs of applications [8].
Excellent mechanical strength and stiffness of bionanocomposite suggest adsor-
bents with potential for utilizing in high-pressure environments in water purification
applications [24]. Furthermore, bionanocomposites generally have high crystallinity,
which allows the adsorbents to work as resistant for chemical and biological corrosion
in water. However, some facts we have to consider for bionanocomposites in water
refinement such as their regeneration potential, agglomeration, long-term perfor-
mance, cost-effectiveness, and immobilization.

16.1.3 Bionanocomposites for water treatment: State-of-the-art

Numerous studies have been testified on the adsorption properties of heavy metal on
bionanocomposites, including Pb(II), Cd(II), Ni(II), As(V), Cr(III), and Cr(VI) and
the chemical modified derivatives [25]. Ma et al. [26] studied that radioactive
2+
U(II) ions (UO 2 ) in solution matched to the carboxylate groups of TEMPO-oxidized
cellulose nanofibers (TOCNF) up to 167 mg/g, which was 2–3 times larger than that
obtained with old adsorbents like hydrogels, silica particles, polymer particles, and