the absorption feature at around 2.75 eV belongs to interfacial charge transfer (IFCT). This is an electron transferring from the valence band of TiO2 to both the copper oxide(s) and graphene clusters that are grafted at the interface with titania . We have previously proven that those latter specimens exhibited (reversible) photochromism when irradiated by a white light LED lamp . [This was the same visible white LED lamp as that employed in those photocatalytic experiments. 5.0 mW.cm -2 was the radiant flux in the photochromic experiments; 5.8 mW.cm -2 that in the gas-phase photocatalytic experiments.] However, while photochromism in specimens thermally treated at 250 °C / 8h was mainly due to IFCT (Figure ), the P-type change in colour observed in samples treated at 450 °C / 2 h was a visible-light induced photocatalytic colour switching. That is: the photogenerated electron in titania's conduction band was able to continuously reduce Cu(II) to Cu(I). This is better shown in Figure : at around 30 min irradiation time an absorption feature centred at ~2.25 eV, and belonging to the band-to-band transition of newly formed Cu2O , appeared.