Visible light-active non-metal doped titanium dioxide materials for photocatalytic oxidation
Author(s)
Advisor
Özensoy, EmrahDate
2014Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
One of the most important technologies for a better human life is
environmental purification which has drawn attention and gained importance over
the past years. Titanium dioxide has been the apple of the eye of both air and water
purification systems for its strong ability of oxidation, low cost, nontoxicity,
inertness and availability. However, being a wide band gap semiconductor, titanium
dioxide can mostly absorb UV photons (nm) in the sun light, which is only
about 3% of the total solar radiation. In this regard, sensitizing titanium dioxide
based materials capable of visible light absorption via doping methods is a
challenging but yet a rewarding effort.
In the current work, a variety of doping protocols have been employed in
conjunction with sol-gel titanium dioxide synthesis protocols in an attempt to
prepare visible-active photocatalytic powders. This study has been a preliminary
work to propose a simple sol-gel synthesis route for the preparation of visible-active
titanium dioxide in order to combine with previously studied UV active titanium
dioxide powders to create tandem systems that will harvest both visible and UV light
for water and air purification. Along these lines, two different sets of samples were
prepared and investigated. The first set of samples was prepared by a sol-gel route with the addition of
non-metallic compounds of Ti which are TiN, TiC and TiS2. Non-metal atom to
titanium mol ratio was kept at 0.1:1 and the syntesized powders were characterized
by XRD, Raman Spectroscopy, BET, UV-VIS Diffuse Reflectance Spectroscopy in
order to investigate the effect of calcination temperature, surface area and band gap
on photocatalytic activity. Besides, these commercial TiN, TiC and TiS2 powders that
were used as dopants, were also annealed in open air to prepare partially oxidized
titanium materials.
Secondly, inexpensive sources of non-metal compounds such as boric acid,
diethanolamine (DEA), triethylamine (TEA), thiourea, urea and cyclohexanol were
added in an alternative sol gel synthesis route. Dopant compound to titanium dioxide
mol ratio was also kept at 0.5:1. Structural and electronic characterization of this
family of materials were also carried out in addition to photocatalytic activity tests.
Photocatalytic activity measurements were done in liquid phase via the
degradation of an organic contaminant, Rhodamine B, in a custom-designed VISilluminated
photocatalytic reaction cells. Photocatalytic performance of all samples
were compared with that of a commercially available Degussa P25 TiO2 benchmark
catalyst. Photocatalytic preformance tests revealed improved photocatalytic activity
for non-metal compound added titanium dioxide compared to unmodified titanium
dioxide prepared with the same method. Also, several samples presented even higher
photocatalytic activity compared to Degussa P25. Characterization experiments
showed hinderance in anatase to rutile transformation due to foreign atoms. It was
also observed that although a small band gap is important for the photocatalytic
activity, there are other critical parameters such as particle size, surface area,
crystallinity, active facets, oxygen vacancies which have to be fine tuned for
photocatalytic performance optimization.
Keywords
TiO2Heterogeneous Bulk Doping
Sol-Gel
Non-Metal Compounds
VIS light
Photocatalytic Oxidation