We posit this early degradation process is predominately the disintegration of RGO sheets as described in reaction 4, whereby the extended chemical structure of RGO responsible for its strong visible absorbance undergoes scission to smaller fragments. An earlier study also demonstrated similar scissoring effect of OH• radicals in UV-irradiated TiO2 strips in contact with single-layer graphene film.73 Transmission electron micrographs of preirradiated and 10 min-irradiated TiO2/ RGO suspensions (Figure S3, Supporting Information) show disintegration of the RGO sheets evident by the surrounding small fragments that arise as contrast in the
postirradiated sample image. Because the PAH-like fragments do not absorb in the visible we do not expect them to contribute to the absorbance, but they will contribute to TOC. For example, after 30 min of irradiation, we observe ∼75% decay in visible absorbance but only 25% decrease in TOC.