Titanium oxide hydrates: optical properties and applications
Abstract
TiO2 has been extensively studied in the last decades due to its interesting
optical and electronic properties, which, combined with low fabrication costs,
renders this material very attractive for applications in photovoltaic and photocatalysis.
However, the performances of titania in specific device applications were
found to be strongly dependent on the synthetic methods selected for its production.
The majority of such synthetic procedures rely on the hydrolysis of suitable
precursors and often produce an amorphous solid, generally referred as the
“amorphous” titanium oxide beside the crystalline titania.
In this thesis, we thus set out to investigate amorphous materials produced by
the hydrolysis of titanium tetrachlorides and tetraisopropoxide. We show that these
amorphous products consists of titanium oxide hydrates, which are relatively stable
at room temperature and fully convert into crystalline titania only after extended
temperature treatments. We also find that titanium oxide hydrates may display highly
desirable characteristic such as a strong photochromic response – especially when
placed in a suitable chemical environment. In the following chapter, we then show
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that hybrid systems can be readily prepared of titanium oxide hydrates with, for
instance, macromolecular materials such as poly(vinylalcohol). The amorphous
nature of the titanium oxide hydrates allows to introduce more than 90 vol.% of the
inorganic species into such systems – compared to 15 vol.% or less when producing
hybrids comprising, e.g., crystalline nanoparticles of TiO2. Therefore, materials can
be realized that display a refractive index n of at least 2.1, without compromising
transparency of the resulting structures. Remarkably, n can not only be adjusted by
varying the content of the inorganic species, but also through suitable heat treatments
and/or irradiation with UV-light. Potential applications for such new, versatile and
tunable optical systems are also discussed in this thesis.
Authors
Russo, ManuelaCollections
- Theses [3831]