Multifunctional thin-film nanocomposite membranes comprising covalent organic nanosheets with high crystallinity for efficient reverse osmosis desalination

Covalent Organic Frameworks (COFs) are of significant interest as promising crystalline building blocks for molecular separation due to their abundance of permanent, well-defined and size-selective micro-channels. However, thus far, the implementation of COFs-based membranes is limited by their poor scalability and impossibility of bridging the gap from molecular to ion separation. Herein, a novel thin-film nanocomposite (TFN) membrane comprising regular COFs nanosheets (CONs) with high crystallinity able to achieve an excellent H2O/NaCl selectivity is presented, accompanied with simultaneously over three times improvement on water permeability. The effectiveness of CONs cross-linked into polyamide matrix on hindering NaCl solubility and diffusivity is confirmed from both solution-diffusion mechanism and nanochannel-confined transport mechanism. Thanks to the protection of CONs with secondary amide linkages and strong steric hindrance from ortho- and meta-positioned methyl groups, the TFN membranes yield outstanding chlorine resistance of 18000 ppm h via inhibition of N-chlorination and ring-chlorination reaction. In addition, CONs incorporation also endows the TFN membranes with excellent anti-bacterial efficiency up to 99.8%. Our CONs-based membranes pave a new way towards the multifunctional composite membrane materials for highly efficient clean energy and environmental sustainability.