Polaron-Adsorbate Coupling at the TiO₂(110)-Carboxylate Interface

Area of Science:

• Surface Science
• Materials Chemistry
• Catalysis

Background:

• Polaron behavior is crucial for understanding titanium dioxide (TiO2) catalytic properties.
• The impact of adsorbate molecules on polaronic states at TiO2 surfaces remains largely unexplored.
• Carboxylic acids are known to readily adsorb onto TiO2 surfaces.

Purpose of the Study:

• To investigate the influence of formic and acetic acid adsorption on polaronic states in rutile TiO2(110).
• To elucidate the relationship between adsorbate electrostatic properties and polaron-adsorbate coupling.
• To understand how these interactions affect the photoexcitation and catalytic properties of TiO2.

Main Methods:

• UV photoemission spectroscopy (UPS) to probe electronic states.
• Two-photon photoemission spectroscopy (2PPE) for studying excited-state dynamics.
• Density functional theory (DFT) calculations to model adsorption and electronic structure.

Main Results:

• Dissociative adsorption of formic and acetic acids distinctly modifies polaron surface density, crystal field, and photoexcitation.
• Formate-terminated TiO2(110) exhibits a greater increase in polaron density compared to acetate-terminated surfaces.
• New photoexcitation channels emerge at 3.83 eV above the Fermi level due to increased polaron-adsorbate coupling, with an onset at 3.45 eV.

Conclusions:

• The electrostatic properties of carboxylic acids govern their influence on polaron-adsorbate coupling at the TiO2 surface.
• Adsorption-induced changes in polaron states can create new photoexcitation pathways, potentially enhancing catalytic activity.
• Understanding these surface interactions is key to designing improved TiO2-based catalysts.