Fig. 6 shows the UV–Vis diffuse reflectance spectra of TiO2, TiO2/PPy and the TiO2/(TiO2–V2O5)/PPy
nanocomposites prepared using different polymerization times. It can be seen that the absorbance of
the TiO2/PPy and TiO2/(TiO2–V2O5)/PPy nanocomposites in the visible light region increased, as compared
to that of the TiO2. The visible light absorbance of TiO2/(TiO2–V2O5)/PPy nanocomposites was
also slightly greater than that of TiO2/PPy, regardless of the polymerization time. The spectra of nanocomposites
also shifted to the visible light region. This indicates that the presence of polypyrrole can
enhance the visible light absorption of the materials. From the above spectra, the band gap energy values
of the various samples were calculated and summarized in Table 1. It can be seen that the presence
of PPy on TiO2 and TiO2/(TiO2–V2O5) nanoparticles brought about a reduction of the band gap
energy values of TiO2. The above results suggest that more photoexcited electron–hole pairs can be
generated from the nanocomposites. In this regard, a better photocatalytic activity might be expected.