Water-based UV-ozone activation enables aggregation-free processing of MFI nanosheets for membrane fabrication

Zeolite nanosheets offer promising opportunities to fabricate ultrathin molecular sieving platforms for energy-efficient and cost-effective gas separation. However, activating these nanosheets requires a high-temperature calcination process that opens the pores, causing drying and subsequent irreversible aggregation. Once aggregated, most nanosheets cannot be well-aligned to form a continuous thin membrane, which is a persistent bottleneck for mixed matrix membrane fabrication. In this study, we present a facile ultraviolet (UV)-ozone treatment that activates zeolite nanosheets (MFI and SAPO-34) in aqueous solution. This treatment prevents the drying and aggregation of the nanosheets, thereby ensuring high yields of solvent dispersion for open-pore nanosheets. Furthermore, the UV-ozone treatment also introduces hydroxyl groups on the nanosheet surface that enhance both CO2 adsorption and interfacial compatibility with the polymer matrix. The activated nanosheets are then used to fabricate micrometer-thick, highly b-oriented MFI mixed matrix membranes on polymer substrates via solution casting. These membranes demonstrate high CO2/N2 selectivity of 40 ± 6, with permeance of 194 ± 50 GPU (at 25 °C, ambient pressure). This method is thus substantiated as an effective and scalable approach for activating zeolite nanosheets and can be a cost-efficient approach for the fabrication of thin, flexible zeolite-nanosheet-based gas separation membranes. By replacing the high temperature calcination with UV-ozone treatment in water, the authors keep zeolite nanosheets from clumping, enabling better dispersions. The resulting thin, flexible membranes separate CO2 from N2 efficiently.