The change in absorbance of TiO2-RGO dispersed in O2- saturated water is depicted in Figure 1A. Highly oxidizing OH• radicals are generated at the TiO2 surface following absorption of UV photons and subsequent charge separation. The photogenerated electrons are scavenged from the TiO2 conduction band by the dissolved O2, which suppresses electron−hole recombination and promotes high concentration of OH• for oxidative reactions. The excess OH• radicals near the TiO2 surface are expected to interact with RGO sheets in the vicinity of TiO2. Indeed, a sharp decrease seen in the UV− visible absorption following 30 min of exposure to UV/visible irradiation suggests that RGO is undergoing oxidative transformations. The role of OH• radical in the oxidative transformation was reinforced by tracking the changes in absorbance when excluding UV photons (Figure 1B) or introducing an alternate hole scavenger such as ethanol to exclude OH• radical formation (Figure 1C). Under these conditions, we fail to observe the characteristic decrease in absorbance. The processes which contribute to the increase in absorbance (viz. reduction of RGO) or decrease in absorbance (viz. oxidation of RGO) are summarized below (reactions 1−4).