Covalent organic framework membrane with hourglass-shaped nanochannels for ultrafast desalination
Xiaocui Wei, Yanan Liu, Fulai Zhao, Tingyuan Wang, Zongmei Li, Chunyang Fan, Yuhan Yang, Yuhan Wang, Zhongyi Jiang
Abstract
Abstract Covalent organic framework (COF) holds great potential as next-generation high-performance desalination membrane material owing to their uniform nanochannels (homo-nanochannels) and abundant functional groups, and the hierarchical structures of nanochannels should be rationally designed to break the trade-off between water permeability and ion rejection. Here, a kind of COF membrane with hourglass-shaped nanochannels is fabricated by installing amino-cyclodextrin nanoparticles (CDN) onto the mouth of COF membrane via sequential assembly. The resulting hetero-nanochannels consist of a hydrophilic conical entrance (~1.6 nm) and a hydrophobic spout (~0.5 nm), created by the CDN specific cavity, onto the homo-nanochannels of COF with intrinsic nanopores (~1.4 nm). The hydrophilic conical entrance facilitates the entry of water molecules, whereas the hydrophobic spout and the homo-nanochannels collectively enable fast water transport. Meanwhile, the amino groups on CDN endow the hetero-nanochannels with pH-responsive ability to dynamically regulate their effective size and charge. Accordingly, the optimum COF-CDN membrane exhibits high desalination performance, with a water flux of 98 L m –2 h –1 , and rejection of 94% for Na 2 SO 4 and 92% for NaCl. The COF-CDN membrane also exhibits superior operational stability (7 days) and pH cycle stability, validating the utilization of COF membrane in efficient desalination.