E-7
ENGLISH
PART I GENERAL DESCRIPTION ON AIR CLEANING
How photo catalyst works
UV lamp and photo catalyst of 300T
Photo catalyst
A photo catalyst is a chemical compound that becomes highly reactive when exposed to various wavelengths of UV light. Photo
catalytic oxidation is achieved when UV light rays is combined with a TiO2 coated filter. TiO2 refers to Titanium Oxide. This
process creates hydroxyl radicals and super-oxide ions, which are highly reactive electrons. These highly reactive electrons
aggressively combine with other elements in the air, such as bacteria and VOCs. Once they are bounded together, the chemical
reaction takes place between the super-charged ion and the pollutant, effectively "oxidizing" (or burning) the pollutant. This
breaks the pollutant down into harmless carbon dioxide and water molecules, making the air more purified.
Photo catalytic oxidation
The key to PCO is the photo catalyst. Titanium dioxide (TiO2) is a
semiconductor photo catalyst with the band gap energy of 3.2eV. When this
material is irradiated with photons of less than 385 nm, the band gap energy
is exceeded and an electron is promoted from the valence band to the
conduction band. The resultant electron-hole pair has a lifetime in the space
charge region that enables its participation in chemical reactions. The most
widely postulated reactions are shown as Fig. 1.2-10 below.
Hydroxyl radicals and super-oxide ions are highly reactive species that will
oxidize volatile organic compounds (VOCs) adsorbed on the catalyst
surface. They will also kill and decompose adsorbed bio-aerosols. The
process is referred to as heterogeneous photo catalysis or, more specifically,
photo catalytic oxidation (PCO). Several attributes of PCO make it a strong
candidate for indoor air quality (IAQ) applications. Pollutants, particularly
VOCs, are preferentially adsorbed on the surface and oxidized to (primarily)
carbon dioxide (CO2). Thus, rather than simply changing the phase and
concentrating the contaminant, the absolute toxicity of the treated air stream
is reduced, allowing the photo catalytic reactor to operate as a self-cleaning
filter relative to organic material on the catalyst surface.
Photocatalyst
UV lamp
VOC is an acronym for Volatile Organic
Compounds. VOCs are organic
chemicals that contain the carbon
element. They are carbon compounds
that easily evaporate at room
temperature and often have a sharp
smell. They can come from many
products, such as office equipment,
adhesives, carpeting, upholstery, paints,
solvents and cleaning products. Some
VOCs can cause cancer in certain
situations, especially when they are
concentrated indoors. VOCs also create
ozone, a harmful outdoor air pollutant.
UV light
OH
-
.OH
(Hydoxyl radicals)
+
+
+
+
+
e
TiO2
TiO
2
+ UV = h+ + e-
.O
2
(Super-oxide inos)
O
2