The above experiments support that using nano-structured
TiO2–SiO2 pellets can effectively treat the toluene as indicator
of VOCs at a reasonable efficiency. The further increase of conversion
efficiency can be achieved by two measures: (1) using
the TiO2 catalyst with higher adsorption capacity; (2) increasing
the regeneration time by photocatalytic oxidation, so that
the TiO2 pellets will be sufficiently regenerated and ready to
be used as an adsorbent. In comparison to using thin TiO2 film
coated on supportive media, catalysts in pellet form have a number
of advantages. Firstly, a larger quantity of pellets can be
placed in the reactor, and the contoured shape of pellets provides
a larger surface area to receiveUVirradiation.Whenthe air
stream passes through the packed titania–silica pellets layer, better
gas–solid contact is achieved through increased mass transfer
and the increased illuminated surface area. Therefore, the number
of TiO2–SiO2 molecules available for the photocatalytic
reaction is significantly increased resulting in higher removal
efficiency. Secondly, the TiO2–SiO2 pellets have a much higher
adsorption capacity than thin film. Although some portions of
the pellets do not participate in the photocatalytic reaction, it is
active in adsorbing the pollutant molecules from the air stream
on to the surface of the photocatalyst. The VOCs will be trapped
in the pores of the TiO2 catalyst, and held for longer time and this
adsorption step is essential for photocatalysis and can promote
oxidation.