In synthesis of APTES functionalized SiO2 by post synthesis modification, how can we determine the number of molecules attached on the surface of SiO2.
Dear Ranjit, probably there are better ways to do that, but the one that comes to mi mind is some kind of titration. Assuming that the amino group doesn´t bond to the SiO2 surface, determining the number of amino groups in your surface will give you the number of APTES molecules attached to the surface.
Also you can bond some flourophore through the amino group and study your surface coverage homogenity by fluorescence.
This article can help:
Article Morphology and Amine Accessibility of (3‐Aminopropyl) Trieth...
Hope it helps.
Dear Ranjit, in addition to Manuel Gomez' answer:
It would be helpfull to know if you deal with flat substrates or with particles. In the case of particles the amine concentration can be relatively high. In this case you can do a classical acid-base titration for the amines. With the specific surface area you can calculculate the amine density. You can also use an acidic dye (e.g. tropaeolin) for the amine quantification by coupling it and quantify the dye in a basic washing solution. Please see doi: 10.1016/j.surfcoat.2005.01.091
The coupling of a fluorescent dyes works with particles but also with flat substrates. In both cases the calibration is important. For suggestions on that please see doi: 10.1002/(SICI)1096-9918(199604)24:43.0.CO;2-1
XPS is another option. It requires that the APTES coating is sufficiently thin. In the case of flat substrates you can distinguish SiO2 and the APTES-Si atoms and quantify them or the nitrogen atoms. Than you'll need some calculation for layer thicknesses or what ever you want to use for comparison. In case of particles you'll require some more thoughts because of the variable analysis depth.
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