Visible-light induced benzene removal results, reported as FQE and k'app (first 1 h reaction time), are shown in Figure . All of the samples were shown to be photocatalytically active, with specimens thermally treated at the higher temperature displaying higher photocatalytic activity. TiO2 specimens modified with copper oxide(s) and graphene thermally treated at 250 °C / 8h showed a lower photocatalytic activity compared to the control specimens (i.e. Ti/250, and K7000). This might be justified by copper being still in its cupric (Cu 2+ ) oxidation state, therefore CuO, as described above. Indeed, in such an alignment, the interface between TiO2 and CuO is organised as a straddling gap (type-I) heterojunction, thus favouring a recombination of the photogenerated exciton (Figure ).