Studied Localized Surface Plasmon Resonance Effects of Au Nanoparticles on TiO2 by FDTD Simulations

Abstract

Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or hot electron injection. In this article, the LSPR effects of Au/TiO2 composite photocatalyst, with different sizes and shapes, have been simulated by the finite difference time domain (FDTD) method. The variation tendency of the resonance-absorption peaks and the intensity of enhanced local enhanced electric field were systematically compared and emphasized. When the location of Au nanosphere is gradually immersed into the TiO2 substrate, the local enhanced electric field of the boundary is gradually enhanced. When Au nanoshperes are covered by TiO2 at 100 nm depths, the local enhanced electric field intensities reach the maximum value. However, when Au nanorods are loaded on the surface of the TiO2 substrate, the intensity of the corresponding enhanced local enhanced electric field is the maximum. Au nanospheres produce two strong absorption peaks in the visible light region, which are induced by the LSPR effect and interband transitions between Au nanoparticles and the TiO2 substrate. For the LSPR resonance-absorption peaks, the corresponding position is red-shifted by about 100 nm, as the location of Au nanospheres are gradually immersed into the TiO2 substrate. On the other hand, the size change of the Au nanorods do not lead to a similar variation of the LSPR resonance-absorption peaks, except to change the length-diameter ratio. Meanwhile, the LSPR effects are obviously interfered with by the interband transitions between the Au nanorods and TiO2 substrate. At the end of this article, three photo-generated carrier separation mechanisms are proposed. Among them, the existence of direct electron transfer between Au nanoparticles and the TiO2 substrate leads to the enhanced local enhanced electric field at the boundaries, which is favorable for the improvement of photocatalytic performance of TiO2. These findings could explain the underlying mechanism of some experimental observations in published experimental works, and helpful to design highly efficient composite photocatalysts that contain noble metal co-catalyst nanoparticles.

Highly Porous and Ultra-Lightweight Aero-Ga2O3: Enhancement of Photocatalytic Activity by Noble Metals

“…As mentioned above, two mechanisms are expected to contribute to the enhancement of photocatalytic activity of semiconductors by noble metal functionalization: namely, the extension of the light absorption region by surface plasmon effects and the suppression of charge recombination due to carrier separation at the metal-semiconductor Schottky contact. The surface plasmon resonance frequencies of gold nanoparticles and films embedded in various semiconductor matrices were found to be in the spectral range of 500–700 nm [ 54 , 55 , 56 , 57 , 58 , 59 ]. The resonance frequencies of platinum are also in the visible light spectrum [ 60 , 61 ].…”

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

“…The holes created in plasmonic AgNPs can capture conduction electrons of TiO 2 , thereby reducing the charge recombination in titania. Therefore, plasmonic oscillation from Au and Ag nanoparticles to TiO 2 under visible light has received considerable attention in recent years [133][134][135][136][137][138]. Moreover, AgNPs with well-established antibacterial properties are particularly attractive dopants for titatia in addition to their LSPR effect [15].…”

Size Effects of Closed Encounter Ag Nanoshell Pairs for SERS Application

“…The finite difference time domain (FDTD) method which is based on the Max dimensional equation has been widely used to understand the near-field or far-field light of nanomaterials with complex interfaces by calculating the steadystate continuous wave from the time domain signal [12]. Many studies have proved that the FDTD method is an accurate and timesaving way for obtaining the exact optical response of metallic nanostructures [13,14]. Therefore, it is adopted herein to reveal the size effects on the light enhancement in the gaps of closed encounter Ag nanoshell pairs.…”