Figure 6 and Figure S5 show the spectra of bare and modified TiO2−P25. The spectrum of TiO2−P25 shows an absorption edge at around 400 nm due to the presence of rutile.43 The DRS spectra of the modified samples
exhibit a slight shift in the absorption to longer wavelengths for all surface-modified photocatalysts. This effect has already been reported for TiO2 modified with Pt, Pd, Ag, and Au−Cu4−8 and could be attributed to stabilization of the CB of TiO2−P25 by the interaction with the Ag NPs and CuO nanoclusters. The modified samples absorb in the visible and near-infrared (IR) region, while bare TiO2−P25 does not. Note that absorption with a maximum at 510 nm was obtained with Ag/P25, while a large absorption band with a maximum at 800 nm was observed for CuO/P25. These absorptions result in pink and yellow colors of the modified TiO2−P25 samples. TiO2−P25 comodified with Ag and CuO absorbs in the visible and near IR. The maximum absorption in the visible region is, respectively, at 480 nm for Ag@CuO1:3/P25 and 470 nm for Ag@CuO1:1/P25 and Ag@ CuO3:1/P2