272
photocatalytic membranes (PMs). The MF fiber membrane is of particular interest
as it shows high pollutant removal rate at low transmembrane pressure (<300 kPa).
A commercial success of such fabricated MF and UF membranes has been demonstrated by Zhang and co-workers [353, 354]. Further details on the fabricated nanofibers or nanowire MF membranes can be obtained in the literatures.
Photocatalytic Membrane
Recently the use of PMs has been targeted owing to the photocatalytic reaction that
can take place on the membrane surface and the treated water could be continuously
discharged without the loss of photocatalyst particles. The PMs can be prepared
from different materials and synthesis methods. These include the TiO 2 /Al 2 O 3 composite membranes [29, 54, 56, 350, 351]. TiO 2 is supported on polymer and metallic
membranes or doted polymer membranes containing TiO 2 particles are entrapped
within the membrane structure during the membrane fabrication process [9, 21, 22,
155, 157, 229]. Also, the possible TiO 2 organic and inorganic ceramic membranes
have been investigated [155, 165, 344]. Figure 13.6 shows different types of PMs
for water treatment application [4, 354]. In most studies, however, PMs may encounter various technical problems such as membrane structure deterioration, low photocatalytic activity, and loss of deposited TiO 2 layer over time. To prevent the
problems associated with the TiO 2 membrane coating, an approach of using membranes without any deposited TiO 2 layer can be configured into a slurry-membrane
hybrid system, which will be outlined in section 4.
Photocatalyst Modification and Doping
As TiO 2 photocatalytic reactions take place under ambient operating conditions,
photoactivity is usually constrained by the narrow wavelength spectrum for photonic activation of catalysts. The higher end of UV spectrum required for catalyst
activation is usually accompanied by high operating costs. One attractive option is
to utilize the vast abundance of outdoor solar irradiation for catalyst activation in a
suitably designed photoreactor system. To broaden the photoresponse of TiO 2 catalyst for solar spectrum, various material engineering solutions have been devised,
including composite photocatalysts with carbon nanotubes, dyed sensitizers, noble
metal or metal ion incorporation, and transition metal and nonmetal doping [99,
189, 244, 318, 349].
The rationale in utilizing these material engineering strategies is to balance both
the half-reaction rates of the photocatalytic reaction by adding electron acceptor and
modifying the catalyst structure and composition. Figure 13.7 presents the use of
13 Wastewater
photocatalytic membranes (PMs). The MF fiber membrane is of particular interest
as it shows high pollutant removal rate at low transmembrane pressure (<300 kPa).
A commercial success of such fabricated MF and UF membranes has been demonstrated by Zhang and co-workers [353, 354]. Further details on the fabricated nanofibers or nanowire MF membranes can be obtained in the literatures.
Photocatalytic Membrane
Recently the use of PMs has been targeted owing to the photocatalytic reaction that
can take place on the membrane surface and the treated water could be continuously
discharged without the loss of photocatalyst particles. The PMs can be prepared
from different materials and synthesis methods. These include the TiO 2 /Al 2 O 3 composite membranes [29, 54, 56, 350, 351]. TiO 2 is supported on polymer and metallic
membranes or doted polymer membranes containing TiO 2 particles are entrapped
within the membrane structure during the membrane fabrication process [9, 21, 22,
155, 157, 229]. Also, the possible TiO 2 organic and inorganic ceramic membranes
have been investigated [155, 165, 344]. Figure 13.6 shows different types of PMs
for water treatment application [4, 354]. In most studies, however, PMs may encounter various technical problems such as membrane structure deterioration, low photocatalytic activity, and loss of deposited TiO 2 layer over time. To prevent the
problems associated with the TiO 2 membrane coating, an approach of using membranes without any deposited TiO 2 layer can be configured into a slurry-membrane
hybrid system, which will be outlined in section 4.
Photocatalyst Modification and Doping
As TiO 2 photocatalytic reactions take place under ambient operating conditions,
photoactivity is usually constrained by the narrow wavelength spectrum for photonic activation of catalysts. The higher end of UV spectrum required for catalyst
activation is usually accompanied by high operating costs. One attractive option is
to utilize the vast abundance of outdoor solar irradiation for catalyst activation in a
suitably designed photoreactor system. To broaden the photoresponse of TiO 2 catalyst for solar spectrum, various material engineering solutions have been devised,
including composite photocatalysts with carbon nanotubes, dyed sensitizers, noble
metal or metal ion incorporation, and transition metal and nonmetal doping [99,
189, 244, 318, 349].
The rationale in utilizing these material engineering strategies is to balance both
the half-reaction rates of the photocatalytic reaction by adding electron acceptor and
modifying the catalyst structure and composition. Figure 13.7 presents the use of
13 Wastewater