Nanotechnostructured Catalysts TiO Nanoparticles for Water Purification - Nanotechnologies for Water Environment Applications - page 78

3) Total mineralization : In most cases, complete mineralization by photocatalytic

reaction alone requires prolonged treatment, and even impossible to achieve total
mineralization. Comparing to conventional chemical oxidations, especially other
AOPs, the reaction rate is slow.

4) Challenging of interference species: Results have shown that many species, such

as metal ions, anions, and organic solvents, have inhibitory effects on the
photocatalytic reactions. This is a practical challenge to the application of
photocatalytic reaction in treating real wastewater effluents, which have complex
constituents generally. There are very few demonstrated applications of
photocatalytic treatment to real industrial effluents with high destruction
efficiency.

5) Conflicting results : Many conflicting results are reported for studies under

otherwise the same experimental variables. This is most likely due to the
complex nature of the photocatalytic reactions. Factors, such as the catalyst
intrinsic catalytic properties and activity and operation conditions, may have both
beneficial and disadvantageous effects on the photocatalytic process. The
apparent efficiency is the result of the influence of many factors, which may vary
from studies to studies. Inconsistency in process performance can hinder the
commercialization of the photocatalytic process.

In conclusion, the photocatalytic process is an innovative and promising
technology for water and wastewater purification applications. There are challenges to
address and understand catalytic activity, efficiency, lifetime, reaction mechanisms,
kinetics, operation parameters, and reactors design. Finally, a thorough economic
analysis should be helpful to the process evaluation in terms of treatment efficiency for
the photocatalytic process.

3.7 References

Adams, L. K., Lyon, D. Y., and Alvarez, P. J. J. (2006). "Comparative eco-toxicity of
nanoscale TiO 2 , SiO 2 , and ZnO water suspensions." Water Research , 40(19),
3527-3532.
Ahmed, S., Kemp, T. J., and Unwin, P. R. (2001). "Photomineralisation kinetics of
aqueous chlorophenols at a supported TiO 2 surface studied by the channel-flow
method with electrochemical detection." Journal of Photochemistry and
Photobiology A-Chemistry , 141(1), 69-78.
Alberici, R. M., and Jardim, W. F. (1994). "Photocatalytic degradation of phenol and
chlorinated phenols using Ag-TiO 2 in a slurry reactor." Water Research , 28(8),
1845-1849.
Alekabi, H., Serpone, N., Pelizzetti, E., Minero, C., Fox, M. A., and Draper, R. B. (1989).
"Kinetic-studies in heterogeneous photocatalysis .2. TiO 2 -mediated degradation of
4-chlorophenol alone and in a 3-component mixture of 4-chlorophenol, 2,4-
dichlorophenol, and 2,4,5-trichlorophenol in air-equilibrated aqueous-media."
Langmuir , 5(1), 250-255.