Permeability and Selectivity Limits of Biomimetic Desalination Membranes

Membrane-based desalination is increasingly applied to alleviate water scarcity through the purification of nontraditional water sources, such as seawater, brackish groundwater, and municipal wastewater. Due to fundamental material limitations, performance improvements for the industry standard thin-film composite (TFC) membranes have been incremental. As such, there has been highly active research in exploiting biological water channels, such as the membrane protein aquaporin, and designing synthetic water channels to produce “next-generation” desalination membranes. Most of these design strategies would incorporate the channels within an amphiphilic lipid or block copolymer bilayer to form the membrane selective layer. Based on published single-channel water permeability measurements, 96-98% the membrane surface area would likely comprise just the bilayer to achieve adequate water permeability. As such, the intrinsic permeability characteristics of the bilayer will play a crucial role in determining the overall water/solute permselectivity of the resulting membrane. In this study, solution-based analytical methods assessing large unilamellar vesicles are used to measure the permeability of water and several model solutes through lipid and block copolymer bilayers . Results are combined with published single-channel permeabilities to yield the permeability and selectivity limits of defect-free biomimetic desalination membranes. Comparison with the performance of a commercial TFC membrane shows that biomimetic desalination membranes may be advantageous for some desalination applications, but disadvantageous for others.