Influence of dimensionality and crystallization on visible-light hydrogen production of Au@TiO₂ core-shell photocatalysts based on localized surface plasmon resonance

Localized surface plasmon resonance (LSPR) of Au nanostructures has been applied to enhance the visible absorption and efficiency of TiO₂. However, to date, most reports on photocatalysts based on Au LSPR properties have mainly focused on zero dimensional (0D) Au nanoparticles. Herein, we investigated the effect of the dimensionality of Au and the crystallinity of TiO₂ in Au@TiO₂ core-shell photocatalysts on visible-light H₂ production. We prepared Au@TiO₂ core-shell nanostructures with four different dimensionalities of Au, nanoparticles (NPs, 0D), nanorods [one dimensional (1D)], nanoprisms [two dimensional (2D)] and nanostars [three dimensional (3D)]; meanwhile we used a hydrothermal treatment method to crystallize amorphous TiO₂ instead of the widely used annealing at high temperatures. The results indicate that both higher dimensionality and anisotropy of the Au core and good crystallinity of the TiO₂ shell significantly enhance the visible-light catalytic activity towards H₂ generation. Among these four Au@TiO₂ nanostructures, Au nanostars wrapped with crystalline TiO₂ show the best catalytic activity with a H₂ generation rate of 76.6 μmol g^-1 h^-1. The analysis of these Au@TiO₂ nanostructures via the finite-difference time-domain (FDTD) method indicates that both high dimensionality of Au and high crystallinity of TiO₂ can lead to large electromagnetic (EM) field enhancements, which ensures an increased population of hot electrons close to the interface between the Au and the TiO₂. This work may provide a facile strategy to improve the catalytic activity of visible-light plasmonic photocatalysts.