splitting of the energy bands into discrete quantized
energy level occurs. This is the well-known
quantum size effect. The UV–Vis absorption band
edge is a strong function of TiO2 cluster size for
diameters less than 10nm, which can be attributed
to the quantum size effect [10]. With the decrease
in particle size, the blue shift of the absorption
edge is observed in the absorption spectra [11].
Aqueous diluents of the sol samples were used for
the UV–Vis absorption studies. Fig. 3 gives the
diffused scattering UV–Vis spectra of the sol
samples prepared at different acidic conditions.
The UV–Vis absorption spectra show that absorption
edge shifts to shorter wavelength with
decreasing pH value, which shows that the sizes
of TiO2 particles decrease with increasing the
acidity of reaction solution in the investigated
scale. The conclusion accords with the result
from TEM.