Meanwhile, when the nitrogen source was used urea source with difference concentration
that were indicated in Fig. 4, the absorbance also shown in visible light region (two absorption edges).
But all samples have shown lower absorbance than guanidine carbonate source. However, the urea source
showed absorption spectra higher than HM-TiO2 and P25-Degussa. As the concentration of urea source
was increased, the absorption spectra were increased.