Nanotechnostructured Catalysts TiO Nanoparticles for Water Purification - Nanotechnologies for Water Environment Applications - page 64

resolution energy band alignment capability and allows a wide margin of energy
alignment within the semiconductor/liquid junction by applying a proper potential bias
on the working electrode (photoanode). By doing so, one can have an option of creating
either depletion or accumulation region at the space charge region of the semiconductor
to align the band edge position with respect to the aqueous redox species. Thus, PEC
system offers a solution for utilization/storage of these photo-generated electrons,
depending on the system configuration and setup. The PEC system shares the same
principle as the Gratzel type dye sensitized solar cell (DSSC) except that the dyes in
DSSC are regenerated via charge transfer through I 3 - . As the demand for environmental
hazardous pollutant remediation and the development of green energy sources remains
stringent, there is a need for development of economic yet efficient photovoltaic devices.
Figure 3.11 (a) Layer by layer schematic diagram of photoelectrode. (b) Presentation
of PEC (Lin, 2008).
3.4.2 Initial TiO 2 Loading
For both slurry and fixed bed reactors, two general regimes were observed
regarding the initial degradation rate as a function of the initial TiO 2 concentrations. At
low concentrations, generally up to 400-1000 mg/L, the degradation rate is reported to
be proportional to the TiO 2 concentration in most studies (Dong and Huang, 1995; So et
al., 2002; Konstantinou and Albanis, 2004). For highly concentrated TiO 2 suspension or
surface coating systems, So et al. (2002) reported a slight increase in the degradation
rate whereas other groups reported decreases in degradation rates (Dong and Huang,
1995; Daneshvar et al., 2003; McMurray et al., 2006). Huang and co-workers