Increases in the absorption spectra were observed when ethanol was present during UV-irradiation. Note that ethanol rapidly scavenges TiO2 valence band holes and suppresses OH•
radical formation. UV photons are able to rapidly induce photoreduction of residual oxygen moieties on the RGO sheet, particularly in electron-donating ethanol. When UV photons are filtered, the visible absorbance of the TiO2-RGO suspension remains unchanged since visible photons fail to participate in the GO → RGO reduction process and OH• radicals are not produced in the absence of UV-irradiation.33,34 The changes in absorption of the TiO2-RGO samples are directly compared in Figure 1D at 600 nm over 30 min of irradiation. These control experiments further support the hypothesis that photocatalytic formation of hydroxyl radicals initiates the decrease in visible absorption features by RGO in the aqueous TiO2-RGO suspension.