Influences of substrate properties and liposome integration on high-flux thin-film composite desalination membranes

Abstract

Most studies on biomimetic membranes for desalination have primarily focused on enhancing membrane performance, while the synergetic effects between substrate properties and biomimetic or nanomaterials remain underexplored. Herein, we propose a study to explore how the combination of substrate properties and synthetic liposomes can produce a high-performance hollow fiber reverse osmosis (RO) membrane. Hollow fiber polyethersulfone substrates with three different pore sizes (i.e. 6.0 nm, 8.5 nm and 10.0 nm) and varying porosities were used to study their effects on the selective layer formation and the membrane performance with and without 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) vesicle integration. The results revealed that substrate with moderate pore size (8.5 nm) and porosity worked best due to adequate reactive monomers availability and optimal heat dissipation during the interfacial polymerization (IP) reaction. On the contrary, DOTAP vesicles, which served to expand the miscible zone between two phases, at the same time slowing down MPD diffusion, facilitated the further growth of multilayered polyamide film. This multilayered selective layer morphology, characterized by significantly enlarged nanovoids size and increased surface roughness, enhanced the water transport pathways and effective filtration area, thereby contributing to the improved water permeability. Meanwhile, substrate optimization and liposome incorporation endued the RO membrane with a lower molecular weight cut-off and a narrower pore size distribution, both of which contributed to the enhancement of salt rejection performance. Therefore, compared to the DOTAP-free membrane with unoptimized substrate, the RO membrane with optimized substrate properties and liposome integration achieved an increased water permeability from 0.48 to 8.30 L m⁻² h⁻¹ bar⁻¹, along with an improved salt rejection from 82.8 % to 94.5 % under low pressure condition (2 bar). This work highlights the importance of achieving a synergetic balance between substrate properties and nanomaterial additives to optimize the intricate IP process, thereby advancing the development of practical and scalable membranes for brackish water desalination, as demonstrated by the desirable long-term separation performance and reliable chemical cleaning tests.