Challenges of Photocatalysis for Water Purification
Mohammad F. Kabir1, Elena Vaisman2, Cooper H.
Langford2 and Apostolos Kantzas1,3*
1: Department of Chemical & Petroleum
Engineering, University of Calgary,
2: Department of Chemistry, University of
Calgary,
3: Tomographic Imaging and Porous Media
Laboratory.
Heterogeneous
photocatalysis is an attractive alternative treatment method for
decontamination of organic compounds and disinfection of microorganisms to
purify potable water. The possibility of using solar energy as the light source
makes the process suitable for developing nations. There is no harmful
byproducts produced in the case of photocatalysis and the technology has been
proven effective in removing trace amounts of organic compounds from water. The
study of degrading a substantial number of organics and microorganisms in a
small scale shows the potential of the process for domestic use. However, the application in a large scale is
still not available due to the complexity of design and relatively high
implementation cost. A new photocatalytic fluidized bed reactor is under
investigation to degrade a various number of organic pollutants and
microorganisms. A new method of integration of titanium dioxide and adsorbent
zeolite supported on glass beads with a silicagel binder is implemented to
prepare a novel photocatalyst for the reactor. The challenges of optimizing the
reactor performance based on the results of degradation of one model organic
compound are presented in the current paper. Main issues related to reactor
design are also discussed in this paper.
Jian Chen, Lela Eberlein, and Cooper H. Langford, Department of Chemistry, University of Calgary, 2500 University Dr. NW, Calgary, AB, Canada, T2N 1N4
A
comparison of photooxidations of phenol initiated by light absorption by TiO2
(Degussa P25) and by TiO2 supported on ZSM5 zeolite is reported to
learn if an adsorbent high silica zeolite modifies the pathway of
photooxidation. The TiO2 supported on the zeolite has a surface area
very similar to P25. At equal TiO2
loading, rates of phenol loss were similar with reactions on P25 somewhat
faster. On both, in acid media, the primary products were the result of o,p hydroxylation. Secondary reactions
became important earlier on P25. Beyond trihydroxy species, ring opening became
important. The open chain oxygenated species built up little and appear to
undergo further oxidation readily. The zeolite supported photocatalyst had a
maximum efficiency at pH = 3.4 and lost reactivity at higher pH. At pH = 11,
reactions on the unsupported zeolite are faster. In basic media, hydroquinone
becomes the dominant primary product. Catechol yields decline, but
phloroglucinol, undetected in acid, is found. There is evidence of polymerization
occurring on the TiO2/zeolite catalyst in basic media. It was
expected that pathways for benzene oxidation would start with production of
phenol and follow the phenol pathway thereafter. It was observed that there
were small amounts of products from benzene that do not arise from phenol. This
may provide evidence for direct reaction of benzene with a surface trapped
hole.