ble light region compared to TiO
2
/urea and TiO
/DEA. Amongst all
types of investigated TiO
2
, TiO
2
2
/DEA provided the highest visible
light absorption ability. This result indicates that the investigated
nitrogen dopants effectively extended absorption of TiO
into the
visible light range. As shown in Fig. 5, the absorption in the visible
light region of un-doped TiO
2
2
is relatively low. In addition, TiO
synthesised with organic materials under air atmosphere at same
temperature also provided no significant absorption in the visible
light region. This information suggests that organic materials introduced
the nitrogen to N-doped TiO
under the nitrogen atmosphere
reaction and visible light absorption ability is mainly dependent on
the type of nitrogen dopant. The bandgap energy of un-doped and
N-doped TiO
2
2
can be estimated from plots of the square root of
Kubelka–Munk functions F(R) versus photon energy [2]. The relation
of (˛h$)
2
and (h$) was plotted. The bandgap of TiO
can be
determined from the following equation:
2
2