Supramolecular nanocrystalline membranes with well-aligned subnanochannels for enhanced reverse osmosis desalination
Gang Lü, Wentao Shang, Xinyao Ma, Hengyue Xu, A Hubao, Jiawei Sun, Xiaolu Li, Mingyi Jia, Shuang Lü, Jun Wu, Xi Chen, Shensheng Chen, Jun Fan, Alicia Kyoungjin An
Abstract
Thin-film composite membranes are integral to the reverse osmosis (RO) process, effectively converting seawater and brackish water into potable water. While significant strides have been made in improving water permeability and salt rejection, there has been a corresponding lag in enhancing chlorine resistance and boron rejection. This study presents a suprasmolecular nanocrystalline membrane (SNM) with abundant subnanometer channels created through precisely assembled and well-oriented tetra-oligomer chains, enhanced by interfacial hydrogen bonding under nanoconfined space. The 6 nm-thick SNM exhibits highly aligned nanocrystalline domains and a Young’s modulus of 4 ± 0.5 GPa. Benefiting from its ultrathin thickness and well-oriented subnanoscale channels, the SNM functions effectively as a permeation and selective layer, achieving 99.6% NaCl rejection at 55 bar with a 3.5 wt% NaCl feed and delivering 2-4 times higher water permeance than commercial seawater RO membranes. Molecular dynamics simulations reveal that the abundant, well-aligned subnanochannels facilitate rapid water transport while raising the energy barrier for sodium ion transport. Furthermore, the SNM shows superior boron rejection (exceeding 92.5% at pH 7), remarkable chlorine resistance (200 ppm NaClO exposure for 300 hours), and sustained operational stability under extreme pH conditions (1 and 13) for over 168 hours. These findings establish that space-confined interfacial hydrogen bonding governs the precision self-assembly of robust subnanochannels, offering a new paradigm for high-resilience desalination membranes. Thin-film composite membranes for reverse osmosis process are effective converting seawater and brackish water into potable water but usually they are not resistant to chlorine and the boron rejection is poor. Here, the authors show a supramolecular nanocrystalline membrane with ultrathin thickness and well-oriented sub-nano-sized channels to allow for high water permeance, sodium chloride and boron rejection as well as chlorine resistance.