Uranyl exchanged zeolites

Emission Spectra. The emission spectra of the uranyl acetate dihydrate in solution and in the solid state are shown in Figure 1. The fine structure in the solid state spectrum is not observed in solution. The corresponding emission spectra of uranyl-exchanged zeolites. A, Y, mordenite and ZSM-5 are shown in Figures 2-4. Excitation is carried out at 366 nm. The emission spectra have been scanned in all cases between 450 nm and at least 630 nm. 

Bulk Photolyses. Data for bulk photolyses of uranyl-exchanged zeolites in contact with isopropanol/acetonitrile mixtures are given in Table I. The X-ray powder diffraction data reveal that the UO2A sample and the UO2ZSM-5 sample are both amorphous. All other samples are crystalline after the ion exchange procedure. Crystallinity is not lost when the samples are photolyzed. 

The emission spectra for uranyl-exchanged zeolites Y, mordenite and X all have differences but do show some fine structure and therefore resemble the solid state spectrum of uranyl acetate dihydrate. In fact, the spectrum of uranyl ions exchanged into sodium mordenite is very similar to that of the uranyl acetate dihydrate solid spectrum shown in Figure 1. Further support for our belief that some zeolites have a solution like environment and others have a solid like environment comes from the correlation between the crystallinity of these uranyl-exchanged zeolites and the appearance of some fine structure in the emission spectrum. We find no apparent correlation between this fine structure and the concentration of the uranyl ion in the zeolites even with a ten-fold change in the concentration of the uranyl ion. 

The most reasonable qualitative explanation of the change in the emission spectra is the above-mentioned resemblance to solution or solid state behavior which correlates well with the crystallinity of the uranyl-exchanged zeolites as determined by X-ray powder diffraction. However, there are differences between all of the zeolites which could be an indication of site symmetry and coordination in the lattice. The aluminosilicate lattice is preserved after ion-exhange except for zeolites A and ZSM-5. 

Further observations from similar experiments are that the emission spectral lineshapes are not a function of the uranyl ion concentration in the zeolite. The lineshape does also not seem to be influenced by the relative acidity of the ion-exchanged zeolites. When the degree of hydration is changed from fully hydrated (stored in a dessicator under saturated NHi Cl aqueous soluttons) to vacuum dried at 1 x 10 Torr at room temperature, only the intensity of luminescence (and not the lineshape) changes. 

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