| Abstract |
This MSc dissertation studies the photocatalytic effect of both commercial
and synthetic nanosized powders of titanium dioxides and zinc oxides,
under controlled conditions, in aqueous solutions of representative
commercial coloured organic compounds, such as Methyl Blue (MB),
Methyl Orange (MO) and Rhodhamine 6G (Rh6G). A photochemical batch
reactor was used under UV radiation with maximum wavelength at 365nm
for the decolorisation/decomposition of the dyes of choice. The study of
the photoreaction (decolorisation) procedure was made
spectrophotometrically, while the organic carbon reduction in dye solution
was checked by the use of total organic carbon analyzer (TOC analyzer).
The selected coloured substances are consituents of residual dyes found in
waste textile effluents. This study was completed with the application of
the photocatalytic procedure in industial textile effluent.
In order to set and control the experimental conditions, parameters such
as the concentration, the structural and morphological characteristics of
the catalysts, the air supply, the mixing rate, the reuse of the catalysts
and their residual activity were also under examination. The laboratory
synthetic nanostructured catalytic compounds (TiO2 and ZnO) that were
used are products of hydrothermal synthesis in low temperatures ≤95°C,
an innovative, low cost, environmentally friendly technique.
It was observed that with only 30 minutes of light exposure,
decolourisation of all three commercial dye solutions is almost complete,
due to the break down of the chromophore group of the dye molecule.
Specifically, ZnO with nanoparticles of <100nm was shown to have the
best performance in the decolorisation of dye Rhodamine 6G and
Methylene Blue, while TiO2 Degussa in the case of Methyl Orange. With
regards to the synthetic metal oxides of ZnO and TiO2, which were
synthesised hydrothermally at ≤95°C, we can conclude that ZnO presents
considerably high photocatalytic efficiency (similar to the one of the
commercial ZnO that is produced at much higher temperatures, at about
1000°C) for the decolorisation of the aqueous solution of MB, with
concentration of 20ppm, especially the sample of 2h synthesis.On the contrary, TiO2 showed low decolorisation efficiency for the MB dye solution
for < 40h time of synthesis at low temperature, in some cases it even
performed worst than photolysis. It was only after annealing in higher
temperatures (500°C) that presented much better photocatalytic results,
owing to the increase of the sample chrystallinity.
Finally, the application of the photocatalytic procedure in a textile effluent
dye, named NAVY, was shown that its decolorisation, in relation to the
aqueous solution of the MB (20ppm) is much less efficient. The
decolorisation was complete in three times more using the commercial
catalyst ZnO with nanoparticles of <100nm. However, it interesting that
for such an environmental sample the synthetic catalysts ZnO 2h and TiO2
72h of synthesis were more efficient comparing to the related commercial
catalysts ZnO <100nm and TiO2 Degussa for the decolorisation of the dye
effluent. Having in mind the low cost, environmental friendly way of
synthesis, these catalytic powders are very challenging for future
industrial application, therefore further investigation would be useful.
For the short time till complete decolorisation, no noticeable organic
carbon reduction was observed. This is an indication that for complete
dedradation of the dye compound, giving as final products CO2 and
inorganic salts, much more time is required, also in accordance to
previous reports.
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Μελέτη της φωτοκαταλυτικής δράσης νανοσκοπικών κόνεων οξειδίου του ψευδαργύρου (Zno) και διοξειδίου του τιτανίου (TiO2)
