Disordered Assembly of MFI Zeolite Nanosheets with a Large Volume of Intersheet Mesopores

MFI zeolite nanosheets with a single-unit-cell crystal thickness were synthesized under hydrothermal synthesis conditions using diquaternary ammonium surfactants as the zeolite structure-generating agent. The zeolite structure generation process was analyzed from X-ray powder diffraction, N-2 adsorption isotherms, scanning electron micrographs, and transmission electron micrographs of the porous materials generated at various reaction times. This analysis indicated that the nanosheets were initially generated as a disordered assembly that transformed into an ordered multilamellar mesostructure through a dissolution-recrystallization process upon prolonged hydrothermal aging. Synthesis factors affecting the rates of the initial generation of the nanosheets and their restructuring process were investigated while varying the temperature, structure of the surfactant tail, synthesis compositions, and basicity. On the basis of the result, it was possible to synthesize MFI zeolite nanosheets as a fully disordered assembly possessing a large mesopore volume even under synthesis conditions using the bromide form of the surfactant and a sodium-containing silica source such as water glass.