They showed two absorption edges; the main edge due to the oxide at 390-400 nm and weak shoulder due to nitrogen
doping at 400-500 nm [14]. While the HM-TiO2 and P25-Deguss are shown in ultraviolet region (a single
sharp edge at 390 and 400 nm, respectively). The absorbance of nitrogen-doped TiO2 was increased with
increased the concentration of guanidine carbonate. The wavelengths were about 395, 400 and 500 nm for