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) b-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 c-axis (a lateral direction of the nanosheet), compared to the b-axis (the direction normal to the nanosheet basal plane), with ratios in a range between 4 and 11.
Bibliographical noteFunding Information:
This work was partially supported by the Center for Gas Separations Relevant to Clean Energy Technologies, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DE-SC0001015 for the preparation of MFI nanosheets and films and by the National Science Foundation (CBET-1705687) for the film microstructure characterization. Characterization was carried out in the Characterization Facility, University of Minnesota, and the Minnesota Nano Center, which receive partial support from the NSF through the MRSEC and NNIN programs, respectively. Part of SEM measurements was performed on a Hitachi 8230 provided by NSF MRI DMR-1229263. Confocal microscopy measurement was conducted at the University of Minnesota−University Imaging Center.
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