Zeolite nanosheets

During the production of fuel, plastics and various chemicals separation processes such as distillation for purifying gasoline and polymer precursors is an important step which consumes considerable amounts of energy. Currently nearly 15% of the total energy consumption goes as waste due to process inefficiencies. Ultra-thin zeolite nanosheets of thin films have been developed by University of Minnesota team of researchers to speed up the filtration process with less energy.
Zeolites are micro porous aluminosilicate minerals. Zeolite can be used as catalyst. Zeolite can diffuses through the micro channel system with size and shape selection based on channel dimensions. Production of very thin slices of zeolite is difficult due to interference of Ostwald ripening, the well-known process in which the larger crystals always grow at the expense of the smaller ones.
Zeolite membranes
Energy-efficient separations process involves high-resolution molecular separation with membranes functioning based on preferential adsorption and/or sieving of molecules with minute size and shape differences. For this purpose membranes made of zeolite materials (crystals with molecular-sized pores) show particular promise.
Processing of zeolitic materials by deposition methods into extended sheets that remain intact is cost-effective, reliable, and scalable and saves energy. The flaky crystal-type flat nanosheets of right amount of thickness can be used to separate molecules as a sieve or as a membrane barrier in both research and industrial applications.
Zeolite MFI nanosheets can be hydro thermally synthesized by conducting assembly between silica and an organic surfactant and functionalized with a diquaternary ammonium group. The zeolite nanosheets can be assembled into their ordered multilamellar mesostructure through hydrophobic interactions between the surfactant tails located outside the zeolite nanosheet.
The assembly process involves successive transformations from an initially hexagonal mesophase to a multilamellar mesophase without crystallinity and then to a lamellar mesophase with a crystalline zeolite framework.
The mesopore volume in the interlamellar space could be retained by supporting the zeolite nanosheets with silica pillars, as in pillared clays, even after surfactant removal by calcination. The mesopore diameters could be controlled according to the surfactant tail lengths.
Zeolites nanosheet can also be synthesized using a special bis-ammonium surfactant in a mix with the regular components such as tetraethyl orthosilicate and aluminium sulfate. After mixing and heating the crystals form sheets composed of alternating layers of zeolite (pentasil) with embedded ammonium salts units and aliphatic tail layers.
Due to the interlamellar structural coherence, the hierarchically mesoporous/microporous zeolite could exhibit small-angle X-ray diffraction peaks up to the fourth-order reflections corresponding to the interlayer distance. In addition, an Ar adsorption analysis and transmission electron microscopic investigation indicates that the pillars are highly likely to be built with an MFI structure. The approach using zeolite structure-directing functional group contained in a surfactant would be suitable for the synthesis of other related nanomorphous zeolites in the future.


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