Pathways and Challenges for Biomimetic Desalination Membranes with Sub-Nanometer Channels

Abstract

Transmembrane protein channels, including ion channels and aquaporins that are responsible for fast and selective transport of water, have inspired membrane scientists to exploit and mimic their performance in membrane technologies. These biomimetic membranes comprise discrete nanochannels aligned within amphiphilic matrices on a robust support. While biological components have been used directly, extensive work has also been conducted to produce stable synthetic mimics of protein channels and lipid bilayers. However, the experimental performance of biomimetic membranes remains far below that of biological membranes. In this review, we critically assess the status and potential of biomimetic desalination membranes. We first review channel chemistries and their transport behavior, identifying key characteristics to optimize water permeability and salt rejection. We compare various channel types within an industrial context, considering transport performance, processability, and stability. Through a re-examination of previous vesicular stopped-flow studies, we demonstrate that incorrect permeability equations result in an overestimation of the water permeability of nanochannels. We find in particular that the most optimized aquaporin-bearing bilayer had a pure water permeability of 2.1 L m −2 h −1 bar −1 , which is comparable to that of current stateof-the-art polymeric desalination membranes. Through a quantitative assessment of biomimetic membrane formats, we analytically show that formats incorporating intact vesicles offer minimal benefit, whereas planar biomimetic selective layers could allow for dramatically improved salt rejections. We then show that the persistence of nanoscale defects explains observed subpar performance. We conclude with a discussion on optimal strategies for minimizing these defects, which could enable breakthrough performance.

Fabrication of desalination membranes by interfacial polymerization: history, current efforts, and future directions

“…28,29 The presence of the aquaporin water channels facilitated water transport through the polyamide layer while retaining ionic species, and readers are referred to a recent comprehensive review. 30 Despite the reported performance gain in water permeance and fouling resistance through adding filler materials, realworld applications of such composite membranes are still hindered by several challenges, casting doubt about their potential applicability. The most critical factor is the inevitable formation of defects at the interface between fillers and the polyamide matrix, which has been a long-standing issue for all types of dense membranes with a mixed-matrix structure.…”

Membrane Materials for Selective Ion Separations at the Water–Energy Nexus

“…Thus, in a perfectly formed biomimetic membrane, water and ions slowly diffuse through the amphiphilic matrix while incorporated nanochannels predominately govern transport. [ 133 ]…”

Comparative Analysis of Conventional and Emerging Technologies for Seawater Desalination: Northern Chile as A Case Study

“…These are composed of a bundle of six transmembrane α-helices embedded in the cell membrane. The amino and carboxyl ends face the inside of the cell, whereas the halves resemble each other, apparently repeating a pattern of nucleotides [121][122][123]. Under the right conditions, AQP forms a water channel that selectively transports the water molecules across while excluding ionic species or other polar molecules.…”