(469d) Multilayered MFI-Zeolite Nanosheet Plates for Tiling Membranes on Porous Polyvinylidene Fluoride Substrates for Wastewater Desalination

Desalination of high-salinity brines is a current challenge in treatment, reclamation, and recovery of valuable materials for many industrial wastewaters. The MFI-type zeolites possess ordered channels with pore openings (d_p~0.55 nm) that are slightly smaller than the kinetic diameters (d_k) of hydrated metal ions and common anions in aqueous solutions (d_k > 0.6 nm) but much bigger than the d_kof water molecules (~ 0.27 nm). Because the ion hydration numbers and hence the hydrated ion kinetic sizes are insensitive to the solution concentration and temperature, the MFI type zeolite membranes are well-suited for desalination of high-salinity brines by molecular sieving effects between the water molecules and dissolved salts (i.e., hydrated ions). Recently, submicron-thick, b-oriented MFI zeolite nanosheet laminated membranes (ZNLMs) have been fabricated on both the macroporous ceramic and polyvinylidene fluoride (PVDF) substrates. These ZNLMs were demonstrated with extraordinary water flux and nearly perfect salt rejections in pervaporation (PV) desalination of multicomponent high-salinity brines with good stability. The enabling factors for the ZNLMs’ remarkable performance in PV desalination including the minimized intercrystalline spaces that preserved the ion-sieving effect and the ultrathin ZNLM layer in preferred b-orientation that reduced the diffusion length and resistance for water transport. However, the current methods for zeolite nanosheet synthesis are inefficient and prohibitively for practical purposes. In this work, a facile self-seeded secondary growth method is established for efficient reproduction of very large flower-like MFI zeolite nanosheet (ZN) assemblies in a single step. These flower-like architectures allow ZN activation without structural destruction so that large-sized ZN plates can be conveniently harvested. In this work, the thus -synthesized ZN plates are used for tiling molecular-sieve membranes on industrially desired polymer supports and the resultant ZNLMs are tested for PV desalination of high-salinity brines for lithium recovery.