The PMNC prepared from
inorganic materials using in situ polymerization and composite formation
are suitable as catalysts, sensors, reducing agents and to microbe killing
agents.23 Scientists have synthesized zinc
oxide polyaniline nanocomposite which has improved interface. Due to its
synergistic effects it exhibited thousand times better electrical conductivity.24

Addition of nanoparticles
in polymer matrix improves the polymer properties and produce PNCs with desired
properties. Catalytic, adsorption, and mechanical properties of PNCs are
generally used for the purification of water. These properties of PNCs are
briefly discussed below.

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3.1 Catalyst

Some metal, metal oxide,
and sulfides are used as catalysts for purification of water both in the
presence and absence of light.25 Reports says that a wide variety of compounds
are catalytically degraded.26,27 Metal
compounds like TiO2, ZnO, Fe2O3, CdS, GaP, and
ZnS are used for catalytic degradation due to their interaction with the ionic
surface and its modified surface tension.28Titanium dioxide (TiO2)
and zinc oxide (ZnO) are low cost and have  high photo catalytic activity, and stability
and have great importance.29,30 For
example, ZnO/PMMA nanocomposite is used for photocatalyitc degradation of
phenol and methylene blue.31

6: Photolytic
degradation methylene blue over ZnO/PMMA composites as a function of the
irradiation time

Electrons are released by
these metal oxides on irradiation with UV light. This will react with the H2O
and O2 molecules which are adhered on to its surface. It results in the
production of highly reactive oxygen species (ROS) like peroxides, superoxides,
singlet oxygen and hydroxyl radicals which are capable of degrading organic
water pollutants efficiently.32 ROS also has antibacterial effect and it could inactivate the
microbes present in the polluted water. 33  But these metals’
presence in water is harmful to the ecosystem and human life. Therefore we use
nanocomposites in which these metals are inserted. This could help in sustained
release of the ions or electrons. Examples are Titana/PMMA nanocomposite,
silver embedded aluminum oxyhydroxide–chitosan nanocomposite, etc.34,35

3.2 Adsorption behavior

Due to the high surface
area of nanoparticles, nanocomposites are known for its high adsorption
behavior. Since it is optimized it can be used it is suitable for applications
like water purification, drug delivery, chemical sensor, etc. Toxic dyes, metal
ions and microbes are easily removed using this from waste water.36

Scheme 7: Shematic
illustration for chromium adsorption on Chitosan/Fe-Carbon nanofibers and
polyvinyl alcohol nanocomposite

Adsorption is dependent
on the ionic or surface interaction. It needs selective interaction site. This
can be synchronized by having hydrophobic and hydrophilic behaviors in the
matrix. Most of the nanocomposites possess this quality which makes them a
perfect adsorbent. Interpenetrating nature and magnetic nature of the
nanocomposites also increases the adsorption capacity.

Nanocomposites that
consists of carbon nanotubes (CNT) have high porosity, affinity of solvents ,
better selectivity and rejectivity of molecules and ions. Nanocomposites that
have optimized porosity are good in mass transfer, lighter weight, liquid
retention. Chitosan and its nano derivatives are reported as a good adsorbents
for the removal of water contaminants. But like everything in the world it too
have a disadvantage as it have low mechanical strength.37


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