Differentiating between Acidic and Basic Surface Hydroxyls on Metal Oxides by Fluoride Substitution: A Case Study on...

Area of Science:

• Materials Science
• Surface Chemistry
• Catalysis

Background:

• Oxygen vacancies and surface hydroxyls are critical for catalysis.
• The relationship between these surface features and defects is not well understood.

Purpose of the Study:

• To investigate the correlation between oxygen vacancies, Ti3+ defects, and surface hydroxyls in TiO2 (rutile and P25).
• To selectively quantify acidic and basic surface hydroxyls using fluoride substitution.

Main Methods:

• Pulsed laser defect engineering in liquid (PUDEL) to create TiO2 with varying oxygen deficiency and Ti3+ concentration.
• Electron paramagnetic resonance (EPR) spectroscopy to identify Ti3+ locations.
• Fluoride substitution to selectively quantify surface hydroxyl groups.

Main Results:

• Pulsed laser defect engineering generated Ti3+ defects near the rutile surface and deeper within P25.
• Fluoride substitution revealed increased acidic bridging hydroxyls on rutile, while P25 showed no change in surface hydroxyl density.
• These findings suggest a strong correlation between near-surface Ti3+ and the formation of surface bridging hydroxyls.

Conclusions:

• Near-surface Ti3+ defects are linked to the creation of acidic bridging hydroxyls on TiO2 rutile.
• Fluoride substitution is a valuable technique for characterizing surface hydroxyls and their relationship with defects in metal oxides.
• This work provides insights into defect engineering for tailored catalytic properties.