Sterilizing Effect
Photocatalyst does not only kill bacteria cells, but also decompose the cell itself. The
titanium dioxide photocatalyst has been found to be more effective than any other
antibacterial agent, because the photocatalytic reaction works even when there are
cells covering the surface and while the bacteria are actively propagating. The end
toxin produced at the death of cell is also expected to be decomposed by the
photocatalytic action. Titanium dioxide does not deteriorate and it shows a long-term
anti-bacterial effect. Generally speaking, disinfections by titanium oxide is three
times stronger than chlorine, and 1.5 times stronger than ozone.
Deodorizing Effect
On the deodorizing application, the hydroxyl radicals accelerate the breakdown of
any Volatile Organic Compounds or VOCs by destroying the molecular bonds. This
will help combine the organic gases to form a single molecule that is not harmful to
humans thus enhance the air cleaning efficiency. Some of the examples of odor
molecules are: Tobacco odor, formaldehyde, nitrogen dioxide, urine and fecal odor,
gasoline, and many other hydro carbon molecules in the atmosphere. Air purifier
with Ti02 can prevent smoke and soil, pollen, bacteria, virus and harmful gas as well
as seize the free bacteria in the air by filtering percentage of 99.9% with the help of
the highly oxidizing effect of photocatalyst (Ti02).
Air Purifying Effect
The photocatalytic reactivity of titanium oxides can be applied for the reduction or
elimination of polluted compounds in air such as NOx, cigarette smoke, as well as
volatile compounds arising from various construction materials. Also, high
photocatalytic reactivity can be applied to protect lamp-houses and walls in
tunneling, as well as to prevent white tents from becoming sooty and dark.
Atmospheric constituents such as chlorofluorocarbons (CFCs) and CFC substitutes,
greenhouse gases, and nitrogenous and sulfurous compounds undergo
photochemical reactions either directly or indirectly in the presence of sunlight. In a
polluted area, these pollutants can eventually be removed.
Anti fogging, Self-Cleaning
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, a protective film of titanium provides the self-cleaning building by
becoming anti static, super oxidative, and hydrophilic. The hydrocarbon from
automotive exhaust is oxidized and the dirt on the walls washes away with rainfall,
keeping the building exterior clean at all times.
Water Purification
Photocatalyst coupled with UV lights can oxidize organic pollutants into nontoxic
materials, such as CO2 and water and can disinfect certain bacteria. This
technology is very effective at removing further hazardous organic compounds
(TOCs) and at killing a variety of bacteria and some viruses in the secondary
wastewater treatment. Pilot projects demonstrated that photocatalytic detoxification
systems could effectively kill fecal coli form bacteria in secondary wastewater
treatment.
TiO2 (titanium dioxide) is an oxide of the metal titanium which occurs naturally as a rutile in
some acid igneous rocks and metamorphic rocks, and is also in sedimentary rocks and
beach sands. TiO2 (titanium dioxide) is found in heavy mineral sand deposits rutile and is
often associated with a common titanium mineral, ilmenite, together with zircon, monazite
and magnetite.
The element titanium is finding more and more applications in today’s society. The use of
titanium metal in aerospace, sports and medicine is well known; in fact, over 96% of the
worldwide use of titanium is in the oxide form, TiO2 (titanium dioxide), thus creating a high
demand. the most important constituent of paint is titanium dioxide, an opaque substance
that gives paint its high gloss and rich depth of color. TiO2 (titanium dioxide) replaced the
dangerous metal lead that was used in paint for this purpose. TiO2 (titanium dioxide) has
also been used for years in coloring for food and cosmetics, crayons, and UV protection in
sunscreens and many other products we use every day. The disinfectant and self-cleaning
qualities of TiO2 (titanium dioxide) are being widely employed in Japan and many European
countries today for such products as coated ceramic tile for use in homes. This coating is
reported to last the life of the tile and is activated by a UV light source and water. Other
applications are TiO2 (titanium dioxide) coated self-cleaning roof tiles for homes and
buildings, which are also activated by the UV light of the sun.
Current reserves of TiO2:
1. Southeast Canada
2. Southeast USA
3. Southwest Scandinavia
4. Midwest and South Africa
5. Mediterranean Sea
6. East Australia
Titanium Dioxide Photocatalysis
In order for us to realize self-cleaning material surfaces we must follow one of the two principal ways for
the development of super-hydrophobic or super-hydrophilic materials. By transferring the microstructure
of selected plant surfaces to practical materials like glass and paints, super-hydrophobic surfaces are
obtained (Lotus effect). Superhydrophilic materials are developed by coating glass, ceramic tiles or
plastics with the semiconducting photocatalyst titanium dioxide (TiO2). If TiO2 is illuminated by light,
grease, dirt and organic contaminants are decomposed and can easily be swept away by water (rain).
The heterogeneous photocatalytic oxidation with TiO2 meets the following requirements and is what
could make it competitive with respect to other processes oxidizing contaminants:
• A low-cost material is used as photocatalyst. The reaction is quite fast at mild operating conditions
(room temperature,atmospheric pressure).
• A wide spectrum of organic contaminants can be converted to water and CO2.
• No chemical reactants must be used and no side reactions are produced.
What is photocatalyst?
Photo-Catalysis is defined as "acceleration by the presence of as catalyst". A
catalyst does not change in itself or being consumed in the chemical reaction.
This definition includes photosensitization, a process by which a photochemical
alteration occurs in one molecular entity as a result of initial absorption of
radiation by another molecular entity called the photosensitized. Chlorophyll of
plants is a type of photocatalyst. Photocatalysis compared to photosynthesis, in
which chlorophyll captures sunlight to turn water and carbon dioxide into oxygen
and glucose, photocatalysis creates strong oxidation agent to breakdown any
organic matter to carbon dioxide and water in the presence of photocatalyst,
light and water.
Mechanism of Photocatalysis
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. The electron of the valence band of titanium dioxide
becomes excited when illuminated by light. The excess energy of this excited
electron promoted the electron to the conduction band of titanium dioxide
therefore creating the negative-electron (e-) and positive-hole (h+) pair. This
stage is referred as the semiconductor's 'photo-excitation' state. The energy
difference between the valence band and the conduction band is known as the
'Band Gap'. Wavelength of the light necessary for photo-excitation is:
1240 (Planck's constant, h) / 3.2 ev (band gap energy) = 388 nm
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