As an example to assess this issue we carried out photocatalytic degradation of a textile diazo dye (naphthol blue black) in TiO2 and TiO2/RGO suspensions. We specifically chose this dye because of its slower rate of oxidative degradation as compared to commonly used probes such as methylene blue. The excited state properties and mechanism of photocatalytic degradation of this dye have been previously reported.76,77 With increasing UV irradiation time, we observe continuous decay of the dye absorbance in both TiO2 and RGO/TiO2 suspensions, but with different rates. The photographs in Figure 5A serve as a visual aid in demonstrating the degradation of both dye and RGO during UV irradiation of TiO2. Continuous irradiation degrades not only the dye but also RGO.