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Tin oxide based ion exchange solids

Dear Reader,

I was reading the other day about ion exchange solids which are based on metal oxides such as tin and titanium dioxide. The surface of these metal oxides can absorb cations, this is a bit different to the organic resins such as DOWEX 50 which is a polystyrene with sulfonic acid groups.

One likely way in which the metal oxides such as tin oxide can bind to the metals is at the surface, when the crystal is cut then the surface will have some dangling bonds. I suspect that the oxygens which do not coordinate to the same number of metal atoms as those oxygens which are fully within the solid will bind to protons thus forming hydroxide groups on the surface.

If we look at tin dioxide we will see that a oxygen is shared between three tins while each tin binds to six oxygen atoms. If we were to cut the crystal in the right way we could expose the oxygen atoms, these oxygen atoms can then bind to protons to thus form hydroxyl groups like those on some silicas.

In common with silica it is possible to add organic groups onto a tin oxide by simple treatment with a trialkoxy silane such as 3-aminopropyl triethoxysilane[1] or 3-methacryloxypropyl trimethoxysilane.[2] Now lets get back to the structure of tin dioxide.

It has a tetragonal cell which is a 4.7402 by 4.7402 by 3.1856 Å box, the fractional coordinates of the atoms are as follows.

Element x y z
Sn 0 0 0
Sn 0.5 0.5 0.5
O 0.3073 0.3073 0
O 0.6927 0.6927 0
O 0.8073 0.1927 0.5
O 0.1927 0.8073 0.5

We will discuss tin oxide in further detail soon


[1] C.J. Liu, K. Oshima, M. Shimomura and S. Miyauchi, Journal of Applied Polymer Science, 2006, 100, 1881-1888.

[2] W. Posthumus, J. Laven, G. de With, R. van der Linde, Journal of Colloid and Interface Science, 2006, 304, 394-401.




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