Influence of support pore size and porosity on epoxide-based TFC membranes

Abstract

The drive to expand the implementation of membrane separation technology towards harsher environments prompted the development of chemically robust epoxide-based TFC membranes. This work seeks to better understand the influence of the support on epoxide-based TFC membrane performance and properties. More specifically, it investigates the impact of porous PAN support layers of different porosities and pore sizes on the formation of poly(epoxyether) (PEE) thin films via interfacial initiation of polymerization (IIP), and their more cross-linked and more charged PEE counterparts (XL-PEE) arising from a subsequent post-treatment step. A systematic study was conducted using a series of supports with pore sizes varying from 20 nm to 90 nm and porosities in the range of 4% to 10%, while maintaining identical synthesis conditions for the selective layer. The physicochemical properties of the selective layer were characterized in-depth with X-ray photoelectron spectroscopy (XPS), elastic recoil detection (ERD), transmission electron microscopy (TEM), positron annihilation lifetime spectroscopy (PALS), and atomic force microscopy (AFM) to elucidate the synthesis-structure-performance relationship. PEE TFC membranes comprising these supports had a broad range in water permeances of 5 – 30 L m⁻² h⁻¹ bar⁻¹ with consistent methyl orange (327.33 g mol⁻¹) rejections of ca. 90%. The densified XL-PEE TFC membranes all achieved ca. 65% NaCl rejections, again independent of the support properties. In contrast, more porous supports resulted in more permeable TFC membranes, which can be attributed to the so-called funnel effect. Additionally, the solvent used to prepare the support layers through non-solvent induced phase separation also impacted the selective layer by affecting the interfacial properties during IIP. This work thus demonstrates that the support can serve as an easy tool to fine-tune the performance of the next-generation of high-performance epoxide-based TFC membranes.