Page 453 - Polymer-based Nanocomposites for Energy and Environmental Applications

410 Polymer-based Nanocomposites for Energy and Environmental Applications

of nanoparticles within the host matrices of membranes and the changes in the struc-
tures and properties of both nanomaterials and host matrices may be among the
priority discussions in the field applications of the nanofibrous membranes for
water/wastewater treatment.

15.3 Nanocatalysts for oxidation of pollutants

15.3.1 Nanocatalysts
The nanocatalysts and the inorganic materials, for instance, metal oxides and semi-
conductors, have gained much more attention in term of wastewater treatment among
the scientists, globally. Many types of nanocatalysts are applied and used for treatment
of wastewater, for example, electrocatalysts and photocatalysts [20], for improving
chemical oxidation of organic pollutants [31], and Fenton-based catalysts [21], having
antimicrobial properties [22]. However, in the present study, we will focus on
nanocatalysts used for the oxidation of pollutants.

15.3.1.1 Nanomaterials as photocatalysts

The interaction of metallic nanoparticles with the light energy is called “photo-
catalytic reactions of nanoparticles” and has gained much more attention due to their
wide range and high photocatalytic actions for various pollutants [32]. Generally, the
photocatalysis is composed of semiconductor metals that can degrade a lot of persis-
tent organic pollutants in wastewater, for example, detergents, dyes, pesticides, and
volatile organic compound [33]. Furthermore, semiconductor nanocatalysts are highly
effective for degradation of halogenated and nonhalogenated organic compounds and
also for heavy metals [4].
The mechanism of the working of photocatalysts is based on the photoexcitation
of electron in the catalyst. The irradiation with light (UV in case of TiO 2 ) generates
+
holes (h ) and exited electrons (e ) in the conduction band. In an aqueous media, the

+
holes (h ) are trapped by water molecules (H 2 O) and generate hydroxyl radicals
( OH) [34].

The radicals are indiscriminate and powerful oxidization agent. These hydroxyl
radicals on reaction oxidize the organic pollutants into water and gaseous degradation
products. Among various nanophotocatalysts developed up until now, TiO 2 is one of
the most widely applied in photocatalysis due to its high reactivity under ultraviolet
(UV) light (k<390 nm) and chemical stability [32]. Similarly, ZnO has also been
extensively studied for its photocatalytic action, as it contains wide bandgap just like
TiO 2 [33]. The most important are the TiO 2 and ZnO as efficient photocatalysts for
wastewater treatment.

TiO 2 as a photocatalyst
Since TiO 2 belongs to metal-oxide-semiconductor photocatalyst family, therefore,
there is a general trend among science community that TiO 2 is more effective because
of its large chemical stability and high photocatalytic activity and having strength