Sulphated TiO₂ Reduced by Ammonia and Hydrogen as an Excellent Photocatalyst for Bacteria Inactivation

Area of Science:

• Materials Science
• Environmental Science
• Microbiology

Background:

• Photocatalytic disinfection using titanium dioxide (TiO₂) is a promising technology for water treatment.
• Modifications to TiO₂ are crucial for enhancing its efficiency against various bacterial strains.
• Understanding the surface chemistry and reaction mechanisms is key to optimizing photocatalyst performance.

Purpose of the Study:

• To develop a cost-effective method for modifying TiO₂-based materials for enhanced photocatalytic bacterial inactivation.
• To investigate the efficacy of sulphated TiO₂ against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus epidermidis) bacteria.
• To elucidate the role of sulphate species and surface charge in the photocatalytic disinfection process.

Main Methods:

• Modification of TiO₂ by reduction with ammonia agents and hydrogen at elevated temperatures (400-450 °C).
• Photocatalytic inactivation experiments using modified TiO₂ under simulated solar light.
• Analysis of surface properties and pH changes in titania slurry solutions.
• Comparative studies on the inactivation of Escherichia coli and Staphylococcus epidermidis.

Main Results:

• Sulphated TiO₂ exhibited a significant impact on the inactivation of E. coli, attributed to generated acid sites and a resulting low slurry pH (around 4.6).
• At pH 4.6, TiO₂ surfaces became positively charged, facilitating bacterial interaction.
• Total inactivation of E. coli was achieved within 30 minutes using TiO₂ treated at 400 °C in Ar or NH₃ atmospheres.
• Staphylococcus epidermidis showed greater resistance due to thicker cell walls, requiring higher oxidative force (ROS production) for inactivation.

Conclusions:

• The low-cost modification of TiO₂ with sulphate species significantly enhances photocatalytic bacterial inactivation, particularly for E. coli.
• The method offers a rapid and effective disinfection alternative, even without noble metal modification.
• The findings highlight the importance of surface chemistry, pH control, and ROS generation for effective photocatalytic disinfection of both Gram-negative and Gram-positive bacteria.