Engineering the Absorption and Field Enhancement Properties of Au–TiO₂ Nanohybrids via Whispering Gallery Mode Resonances for Photocatalytic Water Splitting

Abstract

Recently, surface plasmon resonance (SPR) effects have been widely used to construct photocatalysts which are active in the visible spectral region. Such plasmonic photocatalysts usually comprise a semiconductor material transparent in the visible range (such as TiO2) and plasmonic nano-objects (e.g., Au nanoparticles (Au NPs)). Specific SPRs, though, only partially cover the visible spectrum and feature weak light absorption. Here, we explore the unique role played by whispering gallery mode (WGM) resonances in the expression of the photocatalytic activity of plasmonic photocatalysts. Using numerical simulations, we demonstrate that, by solely exploiting a proper geometrical arrangement and WGM resonances in a TiO2 sphere, the plasmonic absorption can be extended over the entire visible range and can be increased by more than 40 times. Furthermore, the local electric field at the Au-TiO2 interface is also considerably enhanced. These results are experimentally corroborated, by means of absorption spectroscopy and Raman measurements. Accordingly, such WGM-assisted plasmonic photocatalysts, when employed in water splitting experiments, exhibit enhanced activity in the visible range. Our findings show a promising and straightforward way to design full solar spectrum photocatalysts.

Hot‐Electron‐Mediated Photochemical Reactions: Principles, Recent Advances, and Challenges

“…Among the shapes studied, Au nanostars exhibited the most intensive local fields around their spikes, leading to the highest photocatalytic performance. The strong correlation between the EM field from anisotropic NPs and the enhanced catalytic performance was also supported by observations of concave Pd NPs, [47] Au nanodimers, [48] and Au/AuAg/Ag 2 S/PbS nanorods. [49] Given the strong correlation between EM field and hot electron-based plasmonic enhancement, some well-demonstrated plasmonic structures [50][51][52][53] that localize EM fields efficiently can be used to boost the hot electron-mediated catalytic efficiency.…”

“…Recently, Zhang et al reported that the EM field enhancement may be governed by a whispering gallery mode (WGM), arisen in adhered semiconductor. [48] The authors attached TiO 2 spheres of different sizes (60-600 nm) to 60 nm AuNPs in a dimer configuration and studied the EM field enhancement of the nanostructures by the finite element method. According to the simulation result (Figure 7), the WGM resonances not only extend and enhance the LSPR absorption significantly, but also strongly enhance the EM field near the heterojunction.…”

“…Recently, TiO 2 -decorated plasmonic metal nanoparticles, such as AuNPs/TiO 2 , AuNRs/TiO 2 , and Au/TiO 2 Janus nanohybrids have been synthesized for photocatalytic water splitting. [45,48,56] In addition to TiO 2 , various semiconductors have also been used to prepare efficient photocatalytic systems. Primo et al synthesized a heterogeneous photocatalyst based on gold www.advopticalmat.de supported on nanoparticulate ceria (Au/CeO 2 ) for the generation of oxygen from water, [124] which exhibited a high photocatalytic activity for the solar water-splitting under visible light.…”

An In Situ Polymerization‐Encapsulation Approach to Prepare TiO2–Graphite Carbon–Au Photocatalysts for Efficient Photocatalysis

“…As reference TiO 2 material, TiO 2 nanobelts (NB) were selected as these 1D‐structures show high photocatalytic activity in the UV range (Figure S1a,b, Supporting Information) . In plasmonic TiO 2 photocatalysts, the Au NPs are usually attached on the TiO 2 surface directly, in order to maximize plasmonic field enhancement . The Au NPs show classic SPR absorption in water at 513 nm (see Figure S2, Supporting Information).…”

Colloidal Metal Nanoparticles Prepared by Laser Ablation and their Applications

“…Barcikowski's group used the PLAL Au NPs without any ligand molecules as the reference pure material and studied the catalytic kinetics of the 4-NP reduction. [134][135][136] Very recently,w eh ave demonstrated the application of PLAL Au NPs in the plasmon-enhanced photodegradation of methyl orange (MO) and water splitting under visible light illumination. [101] Moreover, their analysisa lso showed that the PLAL Au NPs are comparable with the most activec atalysts for 4-NP reduction reaction.…”