On the influence of ion exchange on the local structure of the titanosilicate ETS-10
The effect of ion exchange with different monovalent cations (NH4+, K+, Na+ and Cs+) on the local structure of the titanosilicate ETS-10 has been studied by 29Si MAS NMR and Raman spectroscopy. Although X-ray diffraction shows no significant influence of ion exchange on the long range order, ammonium exchange is found to result in substantial damage to the local structure. Ion exchange experiments with alkali cations under significantly more acidic conditions clearly show that the structural damage brought about by ammonium exchange is not caused by the low pH of the exchange solution. The exchange with potassium and caesium ions also leads to significant changes in the 29Si NMR and Raman spectra. However, these changes can largely be reversed by sodium back-exchange.