and energy efficient solution to air quality challenges. Photosensitive
semiconductors, such as titanium dioxide (TiO2), absorb
ultraviolet (UV) light to form reactive hydroxyl radicals (OH) in the
presence of oxygen and water vapor. These free radicals undertake
a series of reactions with pollutants, such as containing bond
cleavage, substitution, and electron transfer, to mineralize them
into CO2 and water. PCO represents the newest generation of
proactive air purification technology.
Over the years, comprehensive knowledge on the properties
and working mechanisms of PCO for air treatment has been
established [3e10]. Fig. 1 presents the publications since 1985 on
the topic of the PCO technology for air purification, and it clearly
shows the number of articles steadily increasing in the past 10
years. Extensive kinetic experiments and models associated with
PCO reactions demonstrate that the reaction rate of a UV-PCO
system depends on light intensity, types and concentrations of
reactants, flow rate, moisture levels, properties of catalyst used, and
the properties of the PCO reactor. It has been concluded that a
heterogeneous PCO is suitable for the photo-degradation of
gaseous effluents at the low ppb concentrations due to its relatively
moderate photocatalytic removal rates and the occurrence of
catalyst deactivation after the treatment of highly concentrated
effluents [6,11]. With photocatalysts integrated into construction