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Wednesday, 18 September 2019

Old effects newly explained - closer look at titanium dioxide

Thursday, 8 May 2014 | Posted by: Michael Richter, European Coatings Journal

The localisation of electrons is a major aspect for catalytic activity of any given compound. This is why scientists from Vienna had a closer look at a particular white pigment – titanium dioxide.

Curiosity is a driving force

Among different forms the anatase-form is catalytically active and therefore suppliers offer this pigment as photocatalysts. In many coatings for self-cleaning surfaces, titanium dioxide (in combination with sun light) is responsible for the catalytic decomposition of organic contaminants, which are finally washed off by rain. Physicists from the Technical University of Vienna (TU Wien) were dealing with the question "Why is especially the anatase-form able to enforce these processes catalytically?” Now they delivered a fundamental answer and made an important contribution to clarify the catalytic activity of titanium dioxide.

Irregularities are welcome

Surfaces are seldom perfect. This is true for the anatase-form of titanium dioxide as well and several irregularities (crystallographic effects) can be observed on a microscopic level. Especially at small edges, oxygen is added to the surface – for a special reason. At these edges higher electron density was detected, which is needed for efficient fixation of oxygen or even the direct binding of organic contaminants.

Deforming the crystal structure as little as possible

The space a titanium atom occupies in a lattice depends on its electronic state. The more negative the atom becomes the more space is needed within the crystal structure and the more the crystal is deformed - a process which needs energy.
This is why titanium atoms with less neighbouring atoms can be disarranged easier and positions at edges are prominent for this effect. Due to that, edge-occupying titanium atoms are prone to be surrounded by electrons rather than completely embedded titanium atoms and therefore catalytically more active.

New research possibilities for titanium dioxide?

For me, this sounds like: "Mistakes are welcome!” - at least within the crystal structure. Is it then possible to generate titanium dioxide, which is more catalytically active? Perhaps effects like self-cleaning can be further improved? Perhaps intentional doping becomes unnecessary as the catalytic efficacy of titanium dioxide itself becomes high enough?
 

Now it’s your turn!

What is your opinion? Do you have any suggestions or ideas?
I am looking forward to your comments and an interesting discussion!

Kind regards
Michael Richter

Reference:
M. Setvin, X. Hao, B. Daniel et al., Angew. Chem. Int. Ed. 2014, 53, 4714-4716.

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Author

Michael Richter
European Coatings Journal
Michael Richter
Scientific Consultant
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