π–π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets

Abstract

One of the challenges in material science has been to prepare macro-or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through p-p stacking in hydrophobic side, which stabilizes the mesostructure to form singlecrystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90°rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this selfassembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets.

Synthesis and Formation Mechanism of Textured MOF-5

“…Literature shows hierarchical interpenetrated arrangements of 2D nanoplates have been observed in zeolites with an MFI type framework. [42][43][44] Zeolites with a socalled house-of-cards morphology where lamellae is arranged perpendicular to each other to define pores have successfully been prepared in the presence of complex organic quaternary ammonium salts and more recently using a low-cost green method via the introduction of N-methyl-2-pyrrolidone into the template-free synthesis. 45 These hierarchical zeolites are reported to be particularly attractive both for fundamental research and their industrial applications since they possess three tiers of porosity: the intrinsic microporosity of the zeolite framework in unison with the mesoporosity within the plates and the macroporosity originating from the complex intergrown structure.…”

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

“…In very recent days, the controlled synthesis for the self-stacking nanosheettype zeolites has been attempted through designing the surfactant-type SDAs [81]. The addition of phenyl or naphthyl groups into the hydrophobic alkyl tail could make single-crystalline mesostructured zeolite nanosheets [81]. It was also controllable that the bolaform amphiphilic surfactant molecules with bi-quaternary ammonium head group and biphenyl groups can produce 90°rotational boundary, which results in a mesoporous zeolite with high surface area after calcination.…”

“…Self-pillared zeolite nanosheets by repetitive branching were synthesized for this purpose where the zeolite nanosheets connected orthogonally each other in an arrangement of house-of-cards [80]. In very recent days, the controlled synthesis for the self-stacking nanosheettype zeolites has been attempted through designing the surfactant-type SDAs [81]. The addition of phenyl or naphthyl groups into the hydrophobic alkyl tail could make single-crystalline mesostructured zeolite nanosheets [81].…”

Mesostructured Zeolites: Bridging the Gap Between Zeolites and MCM-41

“…71 In addition, Che and co-workers reported a similar approach for the synthesis of single-crystalline mesostructured zeolite nanosheets using a single quaternary ammonium template with strong ordered self-assembling ability through the p-p interaction of aromatic groups in the amphiphilic molecules. 74 Generally, the aggregation of surfactants with one-head quaternary ammonium groups is less energetically favourable than that of multiple quaternary head molecules, and therefore the formation of a laminar structure directed from one-head quaternary molecules is unlikely to occur. However, introducing at least two benzene rings (e.g., biphenyl and naphthyl) into the hydrophobic alkyl tails of one-head quaternary ammonium surfactants leads to the formation of more stable bilayer assemblies, as confirmed by a molecular dynamic simulation study, and makes the synthesis of mesostructured zeolite nanosheets plausible.…”