SYNTHESIS OF POLYPYRROLE/TIO NANOPARTICLES IN WATER BY CHEMICAL OXIDATIVE POLYMERIZATION - Biomaterial Applications: Macro to Nanoscales - page 77

The commonly known polymorphs of TiO 2 found in nature are ana-
tase (tetragonal), brookite (orthorhombic) and rutile (tetragonal) [33]. The
structures are shown in Fig. 4.2. Rutile and anatase are the most common-
ly synthesized phases, but they are thermodynamically and structurally
different, resulting in different properties. As an example, the rutile phase
is known for its higher chemical stability and refractive index, and lower
photo reactivity than anatase [34].
FIGURE 4.2 Structures of three common crystals of TiO 2 : (a) anatase structure, (b) rutile
structure, and (c) brookite structure [35].
Nano composites can acquire novel properties with the proper combi-
nation of two or more kinds of nanoparticles or nano objects [36]. Suit-
able combinations of nano composites can lead to a wide range of poten-
tial practical applications. Inorganic nanoparticles might be able to solve
organic polymer shortcomings such as inadequate mechanical strength.
Therefore, much research has been done to study the polymeric nanocom-
posites.
Recently, there have been a lot of improvements in electrical conduc-
tivity, thermal stability, and processing of organic-inorganic hybrid nano-
composites of PPy metal oxides [37], such as SiO 2 [38], ZrO 2 [39], Y 2 O 3
[40], and Al 2 O 3 [41]. TiO 2 is a very promising material for the synthesis
of organic-inorganic hybrid nanocomposites. PPy/TiO 2 nanocomposites
could obtain advantages from both TiO 2 nanoparticles and conducting
polymers, leading to various potential applications in photovoltaic cells,
light emitting diodes, and photo catalysts [42-44]. For example, TiO 2 is a
large band gap semiconductor, with band gaps of 3.20, 3.02, and 2.96 eV