3D-Array of Au–TiO₂ Yolk–Shell as Plasmonic Photocatalyst Boosting Multi-Scattering with Enhanced Hydrogen Evolution

Nowadays, how to convert solar energy efficiently to other energies, such as chemical energy, is an important subject. In the present work, gold nanosphere (AuNS) monoencapsulated in TiO₂ hollow nanosphere (Au–TiO₂) and three-dimensional assembled array of Au–TiO₂ (3D-array) were fabricated to carefully explore the multiscattering effect on the photocatalytic activity of H₂ generation under simulated solar light and visible light irradiation, respectively. Au–TiO₂ with the inner cavity diameter of 176 nm was uniformly synthesized via SiO₂ protection method and then was used as building blocks for construction of 3D-array. The 3D-array exhibited a much higher photocatalytic activity of H₂ generation (3.5 folds under visible light irradiation, 1.4 folds under solar light irradiation) than Au–TiO₂. Single-particle plasmonic photoluminescence measurement and computational simulation of finite difference time domain (FDTD) were performed to elucidate the detailed mechanisms of photocatalysis. It was suggested that the hot electrons generated by AuNS under visible light irradiation play a significant role during the photocatalysis process. The higher activity of 3D-array is due to the elongation of light path length because of the multiscattering in-between Au-TiO₂ and the reflection inside of the TiO₂ shell. Therefore, the AuNS has more opportunity to absorb light and more hot electrons are expected to be generated through the electron transfer from AuNS to TiO₂ shell, leading to an increment in the H₂ generation. This result gives us a new perspective of constructing structures for efficient light utilization.