Artificial Water Channels-Toward Biomimetic Membranes for Desalination

Artificial water channels-AWCs and their natural Aquaporin counterparts selectively transport water. They represent a tremendous source of inspiration to devise biomimetic membrane for several applications, including desalination. They contain variable water-channel constructs with adaptative architectures and morphologies. Herein, we critically discuss the structural details that can impact on performances of biomimetic I-quartets obtained <i>via</i> adaptive self-assembly of alkylureido-ethylimidazoles in bilayer or polyamide membranes. We first explore the I-quartet performances in bilayer membranes, identifying that hydrophobicity is an essential key parameter to increase water permeability. We compare various channel types with different hydrophobic tails (from <b>HC4</b> to <b>HC18</b>) and we reveal that a huge increase in single channel water permeability, from 10⁴ to 10⁷ water molecules/s/channel, is obtained by increasing the size of the alkyl tail. Quantitative assessment of AWC-polyamide-PA membranes shows that water permeability increases roughly from 2.09 to 3.85 L m⁻² h⁻¹ bar⁻¹, for <b>HC4</b> and<b> HC6</b> reverse osmosis membranes respectively, while maintaining excellent NaCl rejection (99.3−99.5%). Meanwhile, comparable <b>HC</b>8 loading induces a drop of performance reminiscent with a defective membrane formation. We show that the production of nanoscale sponge-like water channels can be obtained with insoluble low soluble and low dispersed AWCs, explaining observed subpar performance. We conclude that optimal solubility enabling breakthrough performance must be considered to not only maximize the inclusion and the stability in the bilayer membranes but also to achieve an effective homogeneous distribution of percolated particles that minimizes the defects in hybrid polyamide membranes.<br/>[1] M. Di Vincenzo, A. Tiraferri, V.-E. Musteata, S.Chisca, R.Sougrat, L.-B. Huang, S. P. Nunes, M. Barboiu, Nat. Nanotechnol. 2021, 16, 190-196.<br/>[2] M. Di Vincenzo, et al. Proc. Natl. Acad. Sci. USA, 2021, 118(37), e2022200118<br/>[3] L.-B. Huang, M. Di Vincenzo, M. Göktuğ Ahunbay, A. van der Lee, D. Cot, S. Cerneaux, G. Maurin, and M. Barboiu, J. Am. Chem. Soc. 2021, 143, 14386-14393