Crystallization of nanosized MEL-type zeolite from colloidal precursors

The crystal growth of nanosized MEL-type zeolite at 90 °C from various colloidal precursor solutions was investigated. Dynamic light scattering (DLS) in backscattering mode monitors the evolution of particle size in synthesis solutions and purified MEL sols. All measurements were performed at original concentrations since complete penetration of the incident light through the sample is not required in backscattering geometry. In addition, the silicate species formed in the course of the condensation are identified by 29Si NMR spectroscopy. The DLS data show that upon aging of precursor solutions from 20 h to 2 weeks at RT, the precursor species (with radius of about 2 nm) rearrange into species with 10-nm radius, prior to further hydrothermal treatment of the precursor colloids. Complete transformation from amorphous to MEL crystalline colloidal particles is observed after a 72-h extended hydrothermal treatment of the aged precursor solution. Increasing water content in the initial precursor solution leads to a considerable increase of the radius of the crystallites, i.e., from 100 nm to 2 μm.