Self-Cleaning Surfaces

By Alex Wang
Intermediate Category
Innovation | Chemistry, Environment

Photocatalytically-activated Titanium Dioxide can be effectively used to eradicate bacteria. TiO2 is a widely used photocatalyst in the form of a thin film for it’s self-cleaning properties. In a form of a nano-coating, the objective of this project is to fabricate TiO2 coatings and analyze its antibacterial properties.

Self-cleaning is made possible via TiO2’s oxidative properties when exposed to UV rays. This activation accomplishes two things: agitate the electrons and produce a superhydrophilic surface. Agitated electrons jump from the conduction band to the valence band, reacting with water molecules in the air to form hydroxyl radicals. Meanwhile, holes left over on the conduction band react with oxygen gas present in the air to develop additional hydroxyl radicals. These free radicals break down organic matter into harmless substances (Such as carbon dioxide and water) via oxidation.

20% Titanium (IV) Ethoxide was mixed in a 5:2 ratio with 99% Ethanol to form the Titanium Dioxide solution. The TiO2 solution was spin coated onto the test substrates at 1500 rpm for 30 seconds and annealed in a furnace at 500°C to strengthen the bond between the coating surface and the nano-film.

Four substrates were tested: a UV-activated TiO2 coated substrate, a non-activated TiO2 coated substrate, a UV exposed uncoated film substrate and a control substrate with no UV exposure or coating. Samples were grown in agar plates and measured for contaminated surface area. Substrates were activated with a 387nm light perpendicular to the surface of the coating. UV-activated Titanium Dioxide proved to be the most effective, killing off 94.33% of bacteria.

Self-cleaning coatings present a variety of applications. Regarding infection control, these coatings may be implemented into hospitals, clinics, public facilities, washrooms, etc. Coatings implemented into public areas may greatly reduce the spread of germs, diseases and viruses. As TiO2 is able to break down organic matter, it may be implemented into kitchens and school cafeterias for removal of oils. Studies have shown that the UV photodegradation is close to none, showing a 0.0012% decrease in photoactivity each activation cycle; However, studies have shown that complete regeneration of the catalyst could be achieved by rinsing it with warm deionised water.

Compared to other conventional method of antibacterial eradication, a titanium dioxide outperforms all available options. Cleaning agents have the major drawback of manual labour but also can be extremely harmful to the environment and personnel. Ultraviolet irradiation requires high levels of power, does not treat all forms of bacteria and is extremely harmful to humans. The oligodynamic effect takes over 8 hours and is only effective on selective bacterium species. In contrast, a TiO2 coating is passive, convenient, is not harmful to the environment or humans, and is able to clean a surface in under 10 minutes.

Titanium Dioxide thin films were successfully fabricated onto glass substrates via the sol-gel method. Agar plates showed the successful bactericidal effects of the coating on bacteria. UV-activated Titanium Dioxide’s self-cleaning properties have a strong antibacterial effect and prove to be a cost-effective solution for infection control.

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