Correction to “Anisotropic Growth of TiO2 onto Gold Nanorods for Plasmon-Enhanced Hydrogen Production from Water Reduction”

Plasmonic metal/semiconductor heterostructures show promise for visible-light-driven photocatalysis. Gold nanorods (AuNRs) semi-coated with TiO2 are expected to be ideally structured systems for hydrogen evolution. Synthesizing such structures by wet-chemistry methods, however, has proved challenging. Here we report the bottom-up synthesis of AuNR/TiO2 nanodumbbells (NDs) with spatially separated Au/TiO2 regions, whose structures are governed by the NRs’ diameter, and the higher curvature and lower density of CnTAB surfactant at the NRs’ tips than on their lateral surfaces, as well as the morphology’s dependence on concentration, and alkyl chain length of CnTAB. The NDs show plasmon-enhanced H2 evolution under visible and near-infrared light. P has received significant attention for solar conversion to electricity or fuels based on electron/hole pair production in semiconductors. However, this process is constrained mainly by low photocatalytic efficiency and limited visible and near-infrared (NIR) photoabsorption. Efficient engineering of the photocatalyst surface and interface is crucial to overcome these limitations. Recently, surface plasmon resonance (SPR) of Au, Ag, and Pd nanoparticles (NPs) has been applied to efficiently enhance visible and NIR absorption and generate SPR hot electrons. Among these nanostructures, gold nanorods (AuNRs) with tunable SPR are of particular interest for their wide range of light harvesting; panchromatic absorption toward the solar spectrum can significantly improve the solar energy conversion efficiency. Moreover, AuNRs are usually interfaced with efficient electron acceptors (e.g., TiO2, 7 graphene, Pt) to maximize the charge separation of hot electrons. Recently, we developed an autonomous, AuNR/TiO2-based photocatalytic device with oxidation and reduction co-catalysts using nanofabrication techniques. We clearly demonstrated that the plasmonic metal/semiconductor interfacea Schottky junctioncan effectively select out the hot electrons, so that all charge carriers involved in the oxidation and reduction steps arise from these hot electrons, which are generated by exciting surface plasmons in the nanostructured AuNRs. To recycle the photoreduction/ -oxidation, extraction of the hot electrons requires both refilling of these electrons and an electron donor accessible region on the SPR metal surface. The spatial separation structure (rather than homogeneous core/shell structure) can be provided by line-of-sight depositions using nanofabrication techniques that rely on advanced facilities and sophisticated operators. This nanofabrication method is usually not applicable for freestanding AuNRs synthesized by wet chemistry when there is no control of the orientation needed to create anisotropic AuNR/TiO2 structures. Additionally, all wet-chemistry routes to such a welldefined spatial separation structure are challenging. Anisotropic growth of TiO2 onto AuNRs, instead of depositing AuNRs onto TiO2, 10 could give better contact between Au and TiO2. Because bilayers of surface-capping agents like cetyltrimethylammonium bromide (C16TAB) are more densely packed on AuNR sides than at the tips, this phenomenon has been utilized for the anisotropic overgrowth on C16TAB-capped AuNRs with metal heterostructures or silica. However, anisotropic overgrowth of semiconductors like TiO2 on C16TABcapped AuNRs in solution has been rarely reported. In this study, we report a wet-chemistry method for the anisotropic overgrowth of TiO2 on AuNRs by using CnTAB as a soft template and by controlling the degree of hydrolysis of TiCl3. The roles of concentration and alkyl chain length of CnTAB as well as the diameter of the AuNRs were carefully studied. The asprepared TiO2-tipped AuNRs have a dumbbell and spatial separation structure, and TiO2 acts as a filter for hot electrons from AuNRs. This structure satisfies the electron refilling requirement and exhibits plasmon-enhanced hydrogen production fromwater reduction under visible and NIR light irradiation. Figure 1a illustrates the formation of the dumbbell NPs by our bottom-up wet-chemistry method. The CnTAB bilayer confines the AuNR with only the tips accessible to Ti species. By controlling the hydrolysis of TiCl3 via the pH or the reaction Received: October 29, 2015 Figure 1. (a) Schematic showing the origin of anisotropic TiO2 coating. (b) SEM image of the as-prepared AuNR/TiO2 nanodumbbells. Synthetic conditions: 32 nm AuNRs (in diameter), 13.9 mM C16TAB. Communication