Large-Grain, Oriented, and Thin Zeolite MFI Films from Directly Synthesized Nanosheet Coatings

Directly synthesized zeolite MFI nanosheets are promising building blocks for MFI thin films with large and oriented grains. The secondary growth of MFI nanosheets on Si wafers in tetraethylammonium hydroxide (TEAOH) silica sols was investigated, and conditions that result in well-oriented and intergrown film microstructure were established. This has enabled the fabrication of thin (∼300 nm) <i>b</i>-oriented MFI films with large grain-size (>2 μm) from seed-removed nanosheet monolayer coatings. Moreover, the faceted and anisotropic shape of MFI nanosheets allowed the measurement of MFI growth in different crystallographic directions and confirmed the twinning-free preferential growth along the <i>c</i>-axis (a lateral direction of the nanosheet), compared to the <i>b</i>-axis (the direction normal to the nanosheet basal plane), with ratios in a range between 4 and 11