New insights into the plasmonic enhancement for photocatalytic H2 production by Cu–TiO2 upon visible light illumination

Cu nanoparticles were deposited on the surface of commercial TiO2 nanoparticles (Cu–TiO2) using different methods aiming at the production of highly efficient visible light photocatalysts. Photocatalytic H2 evolution rates obtained from methanol/water mixtures revealed no significant influence of the presence of copper oxides on the photoreaction upon visible light illumination. The photocatalytic H2 production rates were evaluated upon illumination with different spectral ranges (≥420 nm or ≥500 nm) and the results evidenced that the visible light induced charge carrier formation on the Cu–TiO2 photocatalysts consists of two distinct pathways: the direct excitation of TiO2 and the induced excitation by the so-called surface plasmon resonance (SPR) effect of the Cu nanoparticles on the TiO2 surface. Both pathways are present when the full visible range of the spectrum is used (≥420 nm), while for illumination at longer wavelengths (≥500 nm), the photocatalytic activity is solely promoted by the Cu-SPR effect. Electron paramagnetic resonance (EPR) and laser flash photolysis measurements were performed to clarify the underlying mechanism of Cu–TiO2 photocatalysts upon visible light illumination.