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

Abstract

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.