Nanotechnostructured Catalysts TiO Nanoparticles for Water Purification - Nanotechnologies for Water Environment Applications - page 59

doping level, system design and operation variables also contribute to the overall
photocatalytic performance. The following section addresses some of the pertinent
reaction variables, such as reactor design, light intensity and solution chemistry.
Figure 3.7 (A) Total DOSs of doped TiO 2 and (B) the projected DOSs into the doped
anion sites (Modified from Asahi et al., 2001).
3.4.1 Photocatalytic Reactors
3.4.1.1 Slurry Reaction System
A variety of photocatalytic reactors have been developed in photocatalytic water
purification studies and applications. In most laboratory photocatalytic studies, well-
mixed heterogeneous slurry batch reactors have been employed, due to their simple
configuration and high efficiency. Figure 3.8 gives a schematic illustration of a typical
batch slurry reactor configuration (Lizama et al., 2002). Slurry of fine TiO 2 suspension
is dispersed in the aqueous phase by agitation with irradiation coming from either
outside or the center of the reactor. Aeration of air bubble, pure O 2 or O 3 is commonly
used to maintain a constant electron acceptor level for preventing recombination
ofelectrons and holes on the TiO 2 surfaces, and to provide homogenous dispersion of the
fine catalyst particles.
The limitations of slurry reactors are obvious. Due to the opacity of the slurry,
the light intensity may vary significantly throughout the reactor, which can reduce the
photoreaction efficiency. Moreover, after the photocatalytic oxidation process, post-