TiO2 Shield - Photocatalytic
Photocatalyst History Milestones
• 1968 Fujishima Akira of Tokyo University discovered photocatalytic property of semi-conducting metal Titanium Dioxide.
• 1972 Dr. Fujishima published what is now known as the “Fujishima Effect” research paper which started the revolution in photocatalyst research.
• 1990 The 1st International Conference on TiO2 Photocatalytic Purification and Treatment of Water and Air. Toronto and Ontario, Canada.
• 1998 Publication of Peroxotitanic Acid Solution-Derived Anatase Sol by Dr. Ichinose of Saga Prefecture
• 2001 NASA incorporated Photocatalytic oxidation to combat Bioterrorism of Anthrax
• 2002 Taiwan Government utilized Photocatalyst coating to combat SARS outbreak.
• 2009 Japan Government uses Photocatalyst at Airports to inactivate viruses that cause infectious diseases including the H1N1 virus.
The Science of Photocatalysis
By definition, a photocatalyst is a catalyst that accelerates photoreactions, or
When photocatalyst is exposed to light in the presence of water vapor, two highly reactive substances are formed: hydroxyl radicals [OH] and a superoxide anion [O2-1]. It allows the oxidation of airborne VOCs and toxic organic matter into carbon dioxide and water at room temperature with UV or near-UV light source. It does not need any other energy for the reaction. Nano-sized titanium dioxide particles have strong photocatalytic activity and can oxidize and decompose pollutants or contaminants.
When photocatalyst titanium dioxide (TiO2) absorbs Ultraviolet (UV) radiation from sunlight or illuminated light source (fluorescent lamps), it will produce pairs of electrons and holes (electron-hole pairs):
The photocatalyst has the following advantages over any current air purification technologies:
• Real destruction of pollutant rather than a simple transfer on a substrate
• Degradation of pollutant at ambient temperature and pressure
• Economical, cheap and low energy consumption
• Adapted for a large range of pollutant (VOC, bacteria, mold)
Titanium dioxide, also known as titania, is the naturally occurring oxide of titanium (chemical formula TiO2). Titanium Dioxide is considered a safe substance and harmless to humans. It is commonly used in paint, printing ink, plastics, paper, synthetic fibers, rubber, condensers, painting colors and crayons, ceramics, electronic components along with food and cosmetics. Many studies have been published on the use of titanium dioxide as a photocatalyst for the decomposition of organic compounds. After illumination by light, titanium dioxide produces hydroxyl radicals, which react with the organic matter in the air to form non-toxic water and carbon dioxide.
Titanium Dioxide molecules contain electrons that are confined to relatively narrow energy bands. The band of highest energy that contains electrons is the valence band, while the band lying above the valence band (i.e., the conduction band) has very few electrons. The difference in energies between the highest energy of the valence band and the lowest energy of the conduction band is termed the band gap energy. When a semiconductor absorbs a photon of energy equal to or greater than its band gap, an electron may be promoted from the valence band to the conduction band leaving behind an electron vacancy or “hole” in the valence band. If charge separation is maintained, the electron and the hole may migrate to the catalyst surface where they participate in reduction-oxidation reactions.
 Strong Oxidation Power
Hydroxyl radicals are among the strongest oxidizing species, even much stronger than chlorine, ozone, and peroxide. They act as very powerful disinfecting agents by oxidizing the cells of microorganisms, causing rupture of the cells. Deodorizing
VOC and Odor Remediation | Sterilizing Anti-Bacterial and Mold Prevention | | On the deodorizing application, the hydroxyl radicals accelerate the breakdown of any Volatile Organic Compounds or VOCs by destroying the molecular bonds. Some of the examples of odor molecules are tobacco smoke, formaldehyde, nitrogen dioxide, urine and fecal odor, gasoline, and many other hydrocarbon molecules in the atmosphere. | Titanium dioxide has strong oxidation effects on single-celled organisms including all bacteria and fungi. The very strong oxidizing power of titanium dioxide can destroy the bacteria's cell membrane, causing leakage of the cytoplasm, which inhibits bacterial activity and ultimately results in the death and decomposition of bacteria. Generally speaking, disinfection by titanium oxide is three times stronger than chlorination, and 1.5 times stronger than ozonation. |
| Self-Cleaning, Anti-Soiling and Anti-Fogging |
 The hydrophilic nature of titanium dioxide, coupled with gravity, will enable dust particles to be swept away following rain or a water stream, thus making the surface self-cleaning.
When the surface of photocatalytic film is exposed to light, the contact angle of the photocatalyst surface with water is reduced gradually. After enough exposure to light, the surface reaches super-hydrophilicity. In other words, it does not repel water at all, so water cannot exist in the shape of a droplet but spreads flatly on the surface of the substrate. The water takes the form of a highly uniform thin film, which behaves optically like a clear sheet of glass.
Most of the exterior walls of buildings become soiled from automotive exhaust fumes, which contain oily components. When the original building materials are coated with a photocatalyst, the dirt on the walls will wash away with rainfall, keeping the building exterior clean at all times.
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