Abstract
The growth of a conformal layer of crystalline TiO2 on gold nanostars was achieved by a simple hydrothermal route preserving the large aspect ratio of the protruding spikes of the nanostar and enabled the photocatalytic evolution of hydrogen under near-infrared (NIR) illumination. The delicate structure of the underlying nanostars is otherwise extremely sensitive to atom migration. It has been revealed that the (101) crystal plane of anatase TiO2 grows epitaxially on the surface of gold, and TiO2 layer thickness and crystallinity can be controlled by varying synthesis conditions. TiO2-coated gold nanostars (AuNS@TiO2) displayed significantly enhanced photocatalytic activity under visible-NIR illumination compared with reported TiO2-coated gold nanoparticles and commercially available TiO2 nanoparticles. The high photocatalytic activity is attributed to effective hot electron generation via absorption of radiation via localized surface plasmon resonance modes of the spikes and further injection to the conduction band of the TiO2 shell across the gold nanoparticle-TiO2 interface.
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•A thin, conformal layer of crystalline TiO2 was epitaxially grown on gold nanostars•Low-temperature hydrothermal crystallization of TiO2 preserves nanostar morphology•Gold nanostar LSPR bands absorb NIR light to significantly enhance H2 evolution•Hot electrons at nanostar tips injected across defect-free metal-TiO2 interface
Utilizing low-energy infrared light to drive photocatalytic reactions is an important goal for efficient H2 evolution from water. While traditional approaches deposit small metal clusters onto TiO2, we grow the semiconductor on the metal to enable more efficient light absorption mediated by the plasmonic nanomaterial. Gold nanostars exhibit strong localized surface plasmon resonance (LSPR) in the near infrared, with intense electric fields at the tips, which enables the generation of hot electrons. By epitaxially growing a conformal shell of crystalline TiO2 onto the nanostars via a low-temperature hydrothermal protocol, we have observed substantial enhancement in H2 generation, in line with our hypothesis that hot electrons can be efficiently generated at the nanostar tips and injected across the metal-semiconductor interface. Future studies targeting morphology- and LSPR-tunability promise to bring important insight into photoexcitation by low-energy wavelengths in hydrogen evolution.
Hydrogen generation using TiO2 photocatalysts is a good candidate for chemical storage of solar energy. However, UV light is a poor match to the solar spectrum. This work demonstrates enhanced H2 evolution photocatalyzed via NIR irradiation by TiO2-coated gold nanostars with tunable LSPR bands. The low-temperature hydrothermal synthesis employed to synthesize the crystalline TiO2 shell preserves the delicate nanostar morphology, while the absence of surfactants allows for the generation of a defect-free epitaxial interface.