Page 124 - Materials Chemistry, Second Edition

Textile Wastewater Treatment by Advanced Oxidation Processes 105

TiO nanoparticles were spherical with a size of 30 nm. The experimental setup
2
for the photocatalytic decolorization consists of a custom-made photocatalytic
oxidation quartz cell with a volume of 3 mL. The photodegradation activity was
investigated as a function of time, at room temperature and irradiated with light
at a predominant wavelength of 365 nm produced by a mercury lamp. At regular
intervals, absorbance measurements in a UV-Vis spectrophotometer were car-
−1
ried out to monitor the color removal of Methyl Green and Orange II (5 mg L )
−1
and Reactive Blue 19 (25 mg L ). The photocatalytic dye removal yield was
determined as the rate of color disappearance, calculated using the following
equation:
− )
Dyeremoval% () = (C 0 C t ×100 (6.9)
C 0
where C and C represent the dye concentration in milligrams per liter before and
0
t
after reaction, respectively.
The results of the decolorization of different dyes using TiO nanoparticles under
2
UV irradiation compared with direct photolysis and dark adsorption are reported
in Figure 6.3. The experimental results indicate that Methyl Green and Orange II
undergo an acceptable decolorization rate, higher than 90%, whereas for Reactive
Blue 19, the decolorization results after 30 min of photocatalytic reaction were
lower than 10%, which could be attributed to the recalcitrant nature of the dye due
to its aromatic anthraquinone structure. In a similar study, Reactive Blue 19 was
found to be the most recalcitrant to decolorization by TiO -based photocatalysis
2
(Lizama et al., 2002). Dye removal in parallel control experiments was negligible in
the mentioned conditions.
Several authors achieved similar conclusions in the case of Methyl Green and
Orange II; their experiments carried out without catalyst and with only UV irra-
diation did not exhibit significant degradation after 30 min of direct photolysis
(May-Lozano et al., 2017; Bousnoubra et al., 2016).
In this sense, results have demonstrated the feasibility of TiO as a model pho-
2
tocatalyst for dye decontamination in textile wastewater in the presence of UV
light. These findings also suggest that various operating parameters, such as type
of photocatalyst and dye and light intensity, among others, may influence the pho-
tocatalytic oxidation process. The optimization of these conditions is crucial from
the perspective of efficient design and application of heterogeneous photocatalysis
processes.