Rapid Synthesis Method of Faujasitic Zeolite Frameworks Probed with Eu(III) Fluorescence Spectroscopy

We report a method for rapid synthesis of faujasitic frameworks with Si/Al ranging from 1.5 to 2.5. Shorter synthesis time is achieved by tuning the supersaturation during a dehydration - rehydration hydrothermal process (DRHT). The dehydration step involves extraction of water from the system during the synthesis process, enhancing the nucleation rate, and a subsequent rehydration step, where the water is added back, facilitating the growth. The crystallization pathway in the DRHT process is investigated by fluorescence spectroscopy using the Eu(III) cation as the probe. The electric dipole transition F-7(4)-D-5(0) (680-710 nm) of Eu(III) is sensitive to the ligand environment and is used as a marker for the intermediate and final structures formed during zeolite crystallization. The ligand field splitting of this band was found to have distinct signatures for the different Eu3+ cation sites within faujasite. The appearance of a characteristic 5-fold splitting of the F-7(4)-D-5(0) band is a signature of Eu(III) cations inside sodalite cages. Using this spectral pattern, we conclude that in the DRHT zeolite synthesis sodalite-like structures start to form in the nucleation stage for faujasite frameworks with low Si/Al ratios.