Three-Dimensional Plasmonic Photocatalyst Consisting of Faceted Gold Nanoparticles and Radial Titanium(IV) Oxide Heteromesocrystals

Abstract

Radial heteromesocrystals (HEMCs) consisting of TiO2 nanorods (NRs) with (110) side walls were synthesized by the seed-assisted hydrothermal method using SnO2 nanocrystals (rad-TiO2 HEMCs). Au nanoparticles (NPs) with comparable sizes and amounts were loaded on rad-TiO2 HEMCs (Au/rad-TiO2 HEMCs) and commercial rutile TiO2 NPs (Au/TiO2 NPs) for comparison by the deposition–precipitation method. Transmission electron microscopic observation confirmed that the faceting of Au NPs is induced by the domain matching heteroepitaxy with a (111)Au//(110)TiO2 orientation, and the faceting probability of Au NPs on rad-TiO2 HEMCs (47%) is larger than that on TiO2 NPs (17%). As a test plasmonic photocatalytic reaction, aerobic oxidative decomposition of 2-naphthol was carried out using it as a model water pollutant. Au/rad-TiO2 HEMCs exhibit photocatalytic activity significantly higher than Au/TiO2 NPs with ∼90% of 2-naphthol decomposed within 15 min under the illumination of simulated sunlight (AM-1.5, 1 sun, λex > 430 nm). The high photocatalytic activity of Au/TiO2 HEMCs is ascribable to the plasmonic hot spots near the edges and corners of the faceted Au NPs enhancing light harvesting, hot-electron injection into TiO2, and charge separation in addition to the electrocatalytic activity of Au NPs for the two-electron oxygen reduction reaction. Further, the concentration gradient of electrons in the TiO2 NRs generated by the multiple light scattering between TiO2 NRs and the extremely large absorption coefficient of Au NPs can also enhance the charge separation.