Summary:
Titanium dioxide (TiO2) photocatalysis has been considered a promising advanced
oxidation process, which in combination with solar energy could effectively
address the
ever increasing concerns for pollution abatement and water purification.
Although it
appears to degrade a great variety of compounds in water, it generally requires
UV
irradiation for activation of the catalyst. Consequently, research on the
development of
new TiO2 based catalysts has been receiving increased attention. TiO2
photocatalysis
can be effective for water purification from new classes of emerging pollutants
such as
cyanobacterial toxins (cyanotoxins) and metabolites, which can be produced by
several
genera of cyanobacteria. Cyanotoxins are considered an important risk for water
quality
since they are harmful to human and animal health. In this study, the
photocatalytic
degradation of cyanotoxins (microcystin-LR, MC-LR and Cylindrospermopsin, CYN)
and
water taste and odor compounds (Geosmin, GSM and 2-methylisoborneol, MIB) was
studied. TiO2 based photocatalysts (Degussa P25, Kronos vlp-7000, Ref-TiO2,
N-TiO2,
NF-TiO2, GOTiO2 and ECT-1023t) were tested for their photocatalytic ability
towards
degradation and mineralization of target analytes in water using UV-A, solar
and visible
light. In order to evaluate the photocatalytic performance of the materials,
several
parameters such as light intensity, presence of oxygen, catalyst loading,
initial
concentration of substrate, adsorption, pH, irradiation wavelength,
mineralization,
intermediate products and toxicity, were investigated. Identification of the
intermediate
and final products was carried out and a complete degradation pathway is
proposed
were hydroxyl radicals (OH) play a key role. Assessment of the residual
toxicity in the
case of MCLR using TiO2 photocatalysis, complete detoxification of the
solutions can be
achieved. In addition, photocatalytic degradation of GSM and MIB using a
polyoxometalate photocatalyst, H4SiW12O40 was studied and compared with TiO2.
Elucidation of the mechanism using OH radical scavengers showed that process
takes
place via OH radicals for both catalysts. Overall results of this study show
that TiO2
based photocatalysis can be very effective in removing cyanobacterial toxins
and taste
and odor compounds from water and its applications can be extended to the
visiblesolar
region of the spectrum by development of novel modified photocatalytic
materials.
Keywords:
Titanium Dioxide, Polyoxometalates, Cyanotoxins, Water Taste & Odor Compounds, Degradation & Mechanism Elucidation
