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

Abstract

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.