Understanding the Charge Carrier Dynamics of Metal@TiO2 Core–Shell Nanorods in Photocatalytic Hydrogen Generation

Abstract

The fast recombination of photogenerated electrons and holes in the pure TiO2 leads to a low photocatalytic efficiency in hydrogen generation or solar energy conversion. Noble metal nanoparticles have been used to combine with TiO2 for effective photocatalysis. Herein, Au@Ag@TiO2 nanorods (NRs) with core–shell structure have been prepared by hydrolysis the precursor of titanium in acid environment. UV light–driven H2 generation rate of Au@Ag@TiO2 samples demonstrated 14 times enhancement compared to P25 TiO2 at the same experimental conditions. The improved photocatalytic performance was due to the charge transfer from the conduction band of excited TiO2 to Au@Ag NRs leading to effective separation of electron–hole pairs. This mechanism has been proved by transient absorption spectroscopy and photo-electrochemical (PEC) measurements. The time resolved photocurrents of P25 TiO2 NPs is ~ 13 times higher that of Au@Ag@TiO2, indicating that a fraction of the photogenerated electrons of TiO2 driven by UV light transfer to Au@Ag nanocores instead of transporting entirely to the ITO substrates. The ultrafast transient absorption and pump-probe measurements demonstrated a faster decay in Au@Ag@TiO2 NRs compared to pure TiO2 system, indicating that the photogenerated electron–hole recombination in TiO2 is substantially suppressed by Au@Ag@TiO2 NRs attributed to the effective trapping of the photogenerated electrons by the Au@Ag cores. Au@Ag@TiO2 nanocomposites with core-shell structure have been prepared and its UV light–driven H2 generation rate has been demonstrated 14 times enhancement compared to P25 TiO2 at the same experimental conditions. The improved photocatalytic performance was due to the charge transfer, which has been proved by photocurrent measurement and the ultrafast transient absorption and pump-probe measurements.