Probing the LSPR Effect of Cu-Doped ZnO Photocatalyst by Near-Infrared Femtosecond Transient Absorption Spectroscopy

Pure ZnO exhibits low photocatalytic activity due to rapid charge recombination. To realize the spatial separation of photogenerated carriers, this work introduces impurity energy levels into pure ZnO by Cu doping. Cu-doped ZnO (Cu/ZnO) nanoflower balls are successfully fabricated and exhibit significantly enhanced photocatalytic H2 production performance compared with pure ZnO. Cu dopant constructs an ultrafast electron transport channel from the ZnO conduction band to the Cu doping energy level and induces the localized surface plasmon resonance (LSPR) effect at the Cu doping site. In situ irradiated X-ray photoelectron spectroscopy and in situ irradiated electron paramagnetic resonance spectroscopy confirm the transformation of Cu2+ to Cu0 in Cu/ZnO under photoexcitation. The LSPR effect of Cu with variable valence endows Cu/ZnO with unique photoelectric properties. The visible femtosecond transient absorption spectroscopy (fs-TAS) confirms ultrafast electron transfer from the ZnO conduction band to the Cu doping energy levels in terms of electron dynamics. In addition, near-infrared fs-TAS verifies the LSPR effect of Cu in Cu/ZnO by monitoring the electron dynamics in the Cu doping energy levels. This study elucidates the mechanism of the Cu-doping-induced LSPR effect from the perspective of electron transfer dynamics, providing ideas for designing highly efficient visible-light-responsive photocatalysts.