Hydroxy artificial water channels enable ultraselective reverse osmosis membranes for N-nitrosamine removal in water reuse

Reverse osmosis (RO) is a leading technology of water reuse for addressing global water scarcity. However, current RO membranes often struggle to effectively reject certain harmful small molecules in water and wastewater, such as N-nitrosodimethylamine (NDMA). Herein, inspired by the channel proteins in cell membranes, an ultraselective RO membrane (AWCM) was developed by incorporating hydroxy artificial water channels (OH AWCs) into the polyamide (PA) rejection layer. OH AWCs mediated the transport pathways, enabling the membrane to deliver a NaCl rejection of 99.2 ± 0.3%, an NDMA rejection of 93.9 ± 0.1% that surpassed the existing upper bound of permselectivity, and an ultrahigh pure water permeance (4.5 ± 0.2 L·m−2·h−1·bar−1) that exceeded that of state-of-the-art RO membranes. Within the OH AWCs, the hydrogen bonds formed between water molecules and the -OH resulted in a short residence time and a high jump frequency of water molecules, enabling the formation of dynamic and continuous OH-H2O networks that facilitated rapid water movement. In contrast, NaCl and NDMA faced high trans-channel energy barriers, which significantly hindered their transport through the OH AWCs. The resulting AWCM membrane outperforms prevailing RO membranes and offers valuable insights for the design of next-generation RO membranes. Low N-nitrosodimethylamine (NDMA) rejection by reverse osmosis membrane threatens the quality of permeate. Here, the authors created a membrane with hydroxy artificial water channels, improving water permeance and NDMA rejection for safer water reuse.