Zeolite emission spectra

Figure 10 Fluorescence spectra of N-P4-A (curve a, ex = 280 nm) and A-P4 (curve b, A.eX = 365 nm) included in NaY zeolite. Exciplex emission spectrum (curve c) is derived by subtraction of the spectrum of A-P4 form that of N-P4-A normalized at 420 nm. The loading level is 10 [xmol/g zeolite.

Figure 2. a, emission spectrum of UOt exchanged A zeolite and b, emission spectrum of UOt exchanged ZSM-5 zeolite. Excitation was carried out at 366 nm. 

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 spectrum of Nph form on aerosil is not resolved. The wide-band fluorescence contribution relative to the molecular emission is large, afterglow is not observed. The wideband excitation spectrum at 400 nm is shifted relatively to that of a molecular form by 10 nm. For zeolites this is mainly CTC and for aerosil a bimolecular associate of Nph. When adsorbing from a vapor phase, the emission spectrum of Nph in a zeolite consists of a continuous structureless band which is a superposition of CTC and dimers adsorbed at the outer surface (Fig. 3a).In the case of co-adsorption of water vapor or hexane the spectrum transforms with the appearance of structured fluorescence and phosphorescence components (Fig.3b). The coadsorbate seems to promote breaking up of dimers and diffusion of molecules in zeolite cages. 

Fig. 1 depicts a characteristic time-resolved Cu" emission spectrum of Cu-ZSM-5 with two main bands at 480 and 540 nm with different decay times. It evidences different defined Cu sites. Very low intensity bands at 450 and 605 nm (Fig. 5) have been shown to correspond additional defined Cu site and Cu bonded via Si-OH, resp. (9). The intensity of the band at 605 nm had never exceed 3% of the total spectrum intensity and is neglected in the spectra analysis. A lifetime of 5 s was chosen for the spectra evaluation note the importance of the luminescence lifetime for the spectra monitoring, cf Fig. 1. It is suppossed that the Cu luminescence intensity is proportional to the number of the corresponding Cu sites and the saturation of the luminescence intensity is not expected. Zeolites with the Cu/Al ratio below 0.5 were used for luminescence intensity calibration. The relationship between the Cu content in the zeolite and the intensities of the individual bands at 450, 480 and 540 nm (for Cu-ZSM-5) is...

Infrared spectra of zeolitic samples can be measured in several different modes. These include transmission, diffuse reflectance, attenuated total internal reflection (ATR) and emission. Transmission and diffuse reflectance are by far the most widely used of these techniques. In the transmission mode, the sample is placed directly in the infrared beam of the instrument and the light passing through or transmitted is measured by the detector. This transmitted signal (T) is ratioed to the open beam (no sample) signal (To) to get the transmission spectrum of the sample. The transmission spectrum is converted to an absorbance spectrum ... 

Figure 4. Absorption (dotted), excitation (solid) and emission (dashed) spectra of 6.5wt% CdS in zeolite Y. The absorption spectrum was taken at room temp and the others at 77K.

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. 

Catalytic oxidation-reduction (redox) reactions in zeolites are generally limited to reactions of molecules for which total oxidation products are desired. One important class of such reactions falls under the category of emission control catalysis. This encompasses a broad range of potential reactions and applications for zeolite catalysts. As potential catalysts one may consider the entire spectrum of zeolitic structural types combined with the broad range of base exchange cations which are known to carry out redox reactions. 

The involvement of upper excited states following irradiation of the phthalocyanine complexes Rh(Pc)(MeOH)X (where X = Cl, Br, or I) has been investigated. All compounds have the same action spectrum for photoinduced H-abstraction and the emission at 420 nm is attributed to relaxation of an upper tt, tt ) excited state. At high photonic fluxes it has been shown that biphotonic photochemistry involves the n, tt state. A study of the photoaquation of [RhCNH,), ] in fully and partially hydrated zeolite Y has been reported. Reaction within the cavities occurs with a quantum yield that is only 15—20% of that in aqueous solution this is attributed to the decrease in mobility of the water in the zeolite and to the exclusion of water from the ligand-exchange site by the zeolite lattice. ... 

Fig. 66. Photoluminescence spectrum of cx-titanium oxidc/Y zeolite catalyst (a) and effect of the addition of CO2 and H2O on the photolumincscence spectrum (b-d). Amount of added CO2 b, 8.5 amount of H2O c, 2.9 mmol g - measured at 77 K excitation at 290 nm emission monitored at 490 nm) [reproduced with permission from Anpo et at.

The individual Cu emissions reflect the energy difference between the lowest d s and the d level, controlled by the ligand field strength and symmetry of the Cu ion. For the Cu ions coordinated to framework oxygens, the ligand field strength is supposed to be controlled by its symmetry. It follows that the Cu emission spectra reflect different coordination of the Cu ions. This assumption is supported by the excitation spectrum for the 480 nm band (for Cu-zeolites, where this band does not overlap with the others), which was identical for Cu located in both erionite and ZSM-5 matrix, see Fig. 2B. 

MSssbauer emission spectroscopy revealed the effects of encapsulation on the 2,2 -bipyridine complex of Co +(57) synthesized in the supercages of zeolite Y [25]. The spectrum of this complex did not show the high spin state of the Fe(II) complex. 

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