Page 652 - Polymer-based Nanocomposites for Energy and Environmental Applications

602 Polymer-based Nanocomposites for Energy and Environmental Applications

polyaniline with its active group. A variety of studies have described the application of
polyaniline nanocomposites as adsorbents for the removal of inorganic species from
aqueous solutions. Most of these studies have employed polyaniline as a model adsor-
bent for remediation of metal ions in water. Alicia et al. used the polypyrrole/
maghemite and polyaniline/maghemite magnetic nanocomposites for the removal
of Cr(VI) and Cu(II) with the adsorption capacity of 209 and 171 mg/g, respectively
[43]. The maghemite nanoparticles were fabricated by chemical coprecipitation, and
the nanocomposites were prepared through emulsion polymerization of pyrrole and
aniline. The concentration of metal ions was analyzed by using the inductively
coupled plasma-optical emission spectroscopy (ICP-OES). Maximum removal capac-
ity at pH 2.0 for Cr(VI) and at pH 5.5 for Cu(II) was observed and selected for further
2
study. Langmuir monolayer model was best fitted, which has high R value of 0.99.
This synthesized material can be applied for the removal of heavy metal ions from
water and wastewater. A polyaniline/polystyrene nanocomposite was synthesized
by Davodi and Jahangiri, and applied for the removal of As(III) and As(V) from aque-
ous solutions [44]. This nanocomposite was prepared by coating polyaniline onto
polystyrene nanoparticles along with a stabilizer. The equilibrium adsorption data
were fitted to both Langmuir and Freundlich adsorption models, and the adsorption
capacity of the polyaniline/polystyrene nanocomposite obtained from the Langmuir
isotherm was found to be 56 and 52 mg/g for As(III) and As(V), respectively. Scan-
ning electron microscopy (SEM), transmission electron microscopy (TEM), and Fou-
rier transform infrared spectrometer were used to know the functional group present in
synthesized materials, surface morphology, and particle size in materials. Similarly,
Chen et al. prepared flake-like polyaniline/MMT nanocomposites and explore their
utility for the removal of Cr(VI) ions from aqueous solution [45]. Such geometric
nanocomposites were obtained by in situ chemical oxidation polymerization during
which poly(2-acrylamido-2-methyl propane sulfonic acid), were used as dopant of
polyaniline, and act as a bridge to combine polyaniline with clay. This flake-like poly-
aniline nanocomposites exhibited a high Cr(VI) adsorption capacity of 167.5 mg/g.
Moreover, extracellular polysaccharide (bacterial), rice husk ash, and wood sawdust
have been also used with polyaniline to prepare nanobiocomposites for the remedia-
tion of environmental water samples [46]. However, the adsorption capacity of adsor-
bents was influenced by several other factors, such as ionic strength, effect of pH,
number of functional groups, and the presence of natural organic matter. For instance,
the influence of ionic strength on the adsorption capacity may be due to competition
between electrolytes (NaCl, KCl, and NaClO 4 ) and metal ions for the composite sur-
face. In fact, the introduction of electrolytes may affect the electric double layer of
hydrated particles, thus changing the way metal ions bind to the chelating groups.
Also, the solution pH plays an important role in the adsorption process. It affects
the extent of dissociation of functional groups, and metal binding ability of dissociated
and associated functional groups is expected to be different at different pH. The pH of
sample solution affects both the surface charge of adsorbent and the degree of ioni-
zation of the metal in solution, thus affecting the complexation. Certain metal ions
such as lead, zinc, cadmium, and chromium get precipitated at high pH values, and
thus, a low pH value should be maintained for their adsorption. The various