Direct Visualization of a Gold Nanoparticle Electron Trapping Effect

Area of Science:

• Surface Science
• Photochemistry
• Materials Chemistry

Background:

• Titanium dioxide (TiO2) is a widely studied semiconductor photocatalyst.
• Understanding surface reactions at the atomic scale is crucial for catalyst design.
• Gold clusters can modify the electronic and catalytic properties of TiO2.

Purpose of the Study:

• To investigate the influence of gold clusters on the atomic-scale anisotropy of surface carboxylate photoreactions on rutile TiO2(110).
• To explore the role of gold clusters in directing the photoreaction of benzoic acid, a model hole-scavenger molecule.

Main Methods:

• Scanning Tunneling Microscopy (STM) to observe surface morphology and reaction sites.
• Density Functional Theory with onsite Coulomb interaction (DFT+U) to model electronic structure and reaction mechanisms.
• UV/visible photoreaction experiments monitoring adsorbate depletion at room temperature.

Main Results:

• Benzoic acid adsorption caused significant displacement of gold clusters (Au9) on TiO2 surfaces.
• DFT calculations indicated distortion of Au9 clusters upon benzoic acid adsorption.
• Photoreaction of benzoic acid exhibited anisotropic depletion rates, with a ~3-fold higher rate along the [001] direction compared to [110].
• Empty sites formed elongated chains along specific crystallographic directions after photoexcitation.

Conclusions:

• Gold clusters induce unprecedented atomic-scale anisotropy in the photoreaction of surface carboxylates on TiO2.
• The observed anisotropy is attributed to anisotropic conduction of excited electrons along the [001] direction, leading to preferential hole accumulation and decomposition.
• This work represents the first report of atomic-scale directionality in a semiconductor photo-induced chemical reaction.