Protolytic Reactions at Electrified TiO₂ P25 Interface: Quantitative and Thermodynamic Characterization

Area of Science:

• Materials Science
• Surface Chemistry
• Physical Chemistry

Background:

• Titania (TiO2) photocatalysts are widely used but can be affected by impurities.
• Chlorine impurities in TiO2 P25 can alter its surface properties and protolytic reactions.
• Understanding surface protolytic reactions is key to optimizing photocatalyst performance.

Purpose of the Study:

• To investigate and quantify protolytic reactions on the surface of chlorine-impurity-containing titania.
• To purify TiO2 P25 by removing chlorine impurities and assess purification efficiency.
• To determine the thermodynamic parameters of surface protonation and deprotonation reactions.

Main Methods:

• Potentiometric and calorimetric acid-base titration were employed to study protolytic reactions.
• Chlorine (TOX) analysis and acid-base titration were used to verify purification efficiency.
• The constant capacitance model was applied to fit titration data and calculate surface species quantities.

Main Results:

• Purification by washing or heat treatment effectively removed chlorine impurities from TiO2 P25.
• The point of zero charge for the purified titania sample was determined to be pH 6.50.
• Partial molar enthalpy values for surface protonation ranged from -17.47 to -16.10 kJ/mol, and for deprotonation from 32.53 to 27.08 kJ/mol.

Conclusions:

• Chlorine impurities significantly impact the surface protolytic behavior of TiO2 photocatalysts.
• Purified TiO2 exhibits a well-defined point of zero charge and predictable surface reaction thermodynamics.
• The findings provide essential data for designing and utilizing optimized TiO2 photocatalysts in various applications.