2-Hydroxy-N-(diphenylmethyl) acetamide nanocomposite membranes for highly selective desalination

Abstract

Reverse osmosis membranes were developed by incorporating self-assembled 2-hydroxy-N-(diphenylmethyl)acetamide channels as part of a polyamide matrix via an industrially scalable interfacial polycondensation procedure. High-resolution electron microscopy revealed uniformly dispersed nanochannels (∼3 Å diameter) at loadings of up to ∼30 vol% within the selective layer, while X-ray analyses confirmed the preservation of crystalline supramolecular assembled structure. The membranes have high water transport and selectivity for small neutral solutes such as urea and boron. In cross-flow brackish water desalination (2000 ppm NaCl at 15 bar), the optimized membranes exhibited a water flux of ∼30 L m⁻² h⁻¹, a 350 % increase over those without the incorporated assemblies, while maintaining >99.3 % observed NaCl rejection. Urea removal tests (15,000 ppm feed at 20 bar) reached rejections of up to 75–80 %, outperforming commercial seawater membranes (64 % rejection) with 280 % higher flux. For a higher salinity feed (5800 ppm NaCl at 20 bar), the developed membranes had ∼99.3 % NaCl and 70–78 % boron rejections over a pH range of 6–9, surpassing commercial brackish membranes. Under seawater conditions (32,000 ppm NaCl at 55 bar), the membranes provided ∼99.3–99.6 % salt rejection at fluxes up to 35 L m⁻² h⁻¹ with single-pass boron rejections above 90 %, producing potentially potable water with <500 mg/L salinity and boron levels <460 μg/L. Overall, the membranes deliver high water transport and Å-scale solute selectivity. Molecular dynamics simulations support the formation of hydrogen-bonded, sponge-like channel networks, elucidating the strong water-channel interactions responsible for the observed improvements in desalination performance.