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 H-2 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 H-2 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.