In the Cu/450, Cu-G0.5 /450, and Cu-G1.0/450 systems the photogenerated electron migration from the conduction band of TiO2 to the conduction band of CuO is favourable, the reduction of Cu(II) to Cu(I) occurs as a consecutive reaction. The lowest signal was detected in Cu-G0.5 /450, which correlates well with our previous data, in which the system with TiO2 and 0.5 wt% graphene preferred the kinetics of Cu(II) reduction . It has to be noted that reduction has been performed here under an inert atmosphere, to avoid consecutive reactions of a photogenerated electron with molecular oxygen, as well as the broadening of the EPR signal due to spin-spin interaction with an oxygen molecule. The photoinduced electron transfer has been also examined in the aqueous system of radical cation ABTS •+ , which can be reduced to parent diamagnetic molecule ABTS. (Figure ) This process may be monitored via electron absorption spectroscopy due to the presence of selective absorption bands at 735 nm and 415 nm, well distinguishable from the absorption maxima of its reduced ABTS (340 nm) and oxidised ABTS 2+ (518 nm) forms . Light exposure led to a decrease in the absorption maxima at 735 nm and 415 nm, together with an increase of that centred at 340 nm. For the system containing G1.0/450 (Figure ) and Ti/450 within 20minute exposure, the blue-green colour suspension of ABTS •+ changed to a slight yellow one, which represents the ABTS form. Thus, the change in colour indicates the effective photoreduction of the radical cation ABTS •+ . The presence of CuxO and CuxO-graphene modified titania-based material in the aqueous ABTS •+ system caused a decreased rate in photoreduction, due to consecutive reaction of photogenerated electrons (Figure ). In the irradiated aqueous titania dispersions, not only radical cation ABTS •+ is reduced to ABTS via photo-electrons, but also via the superoxide radical anions, generated by the reaction of molecular oxygen with the photo-electrons. Despite the stability of superoxide radical anions in a protic solvent as DMSO, their reaction with photons in aqueous solutions is favourable, and hydrogen peroxide, which can be further involved in photocatalytic processes, is being formed . Based on the obtained results under given experimental conditions, we suppose that the photoreduction of radical cation ABTS •+ prevailed in the system with Ti/450. However, the behaviour of reacting systems Cu/450, Cu-G0.5 /450, and Cu-G1.0/450 with ABTS •+ upon exposure differs, and the reaction rate of the ABTS •+ photoreduction is lower due to consecutive reduction of Cu(II) to Cu(I). As was mentioned above, hydrogen peroxide may be formed, so a Fenton-like reaction in aqueous suspensions can be considered, and the reversible Cu(II) formed could again be introduced for being reduced. Despite the anticipated, rather complex mechanism, the results obtained correlates well with the proposed photoinduced electron transfer to the CuO conduction band upon exposure.