In the present study we also probed the possible interaction of RGO with trapped valence band holes in TiO2 suspensions. As previously reported UV irradiation of TiO2 colloids in 5% acetic acid in ethanol leads to the formation of trapped hole species.68,69 The trapped holes exhibit visible absorption at c.a. 400 nm (seen in the inset photograph in Supporting Information Figure S2A). We attempted to titrate trapped holes with incremental additions of RGO. If RGO is susceptible to oxidation by TiO2 trapped holes, we would expect to see a decrease in the corresponding visible absorption feature associated with these holes. As shown in Supporting Information Figure S2B, the incremental addition of RGO to the TiO2 colloids with trapped holes exerted no change in the absorption at 400 nm. From these two experiments, we conclude that oxidation of RGO is due to OH• and not direct oxidation by trapped holes at the TiO2 surface.