Efficient desalination in fluorinated multilayered covalent organic framework: Tunning the energy landscape inside the nanochannel

The design and construction of advanced nanochannels can significantly enhance the performance of reverse osmosis (RO) membranes in desalination, offering potential solutions to the severe freshwater shortage crisis. In this study, we investigated the desalination performance of nanochannels formed by multilayered covalent organic frameworks (COF) that had undergone various types of chemical functionalization, through nonequilibrium molecular dynamics simulations. Our data reveals that fluorination of the nanochannel results in the most impressive desalination performance, as evidenced by significant improvements in both water permeability (increasing from 39.1 to 100.1 L cm−2 day−1 MPa−1) and salt rejection (rising from 91.9 % to 97.1 %). Especially, in multilayered systems, fluorinated nanochannel mitigates the typical decline in water permeability with increasing membrane thickness. For the working mechanism, the free energy analysis indicates that fluorination contributes to a smooth energy landscape for water molecules inside the nanochannel, reducing their interaction with the nanochannel, which results in a more dispersed arrangement of water molecules with fewer hydrogen bonds and a significantly enhanced water velocity, thus facilitating their fast and unobstructed permeation. Therefore, this study offers a promising semipermeable membrane for high-efficiency desalination, achieved through fluorination. It also demonstrates an indicative approach for advanced channel design through fluorination engineering.