Incorporating imine-based covalent organic frameworks nanosheet as an active filler for long-term nanofiltration desalination

Covalent organic frameworks nanosheets (CONs) are two-dimensional porous nanomaterials exfoliated from covalent organic frameworks (COFs). The ordered permanent microchannels and excellent water stability of CONs make them attractive active fillers for the preparation of thin-film nanocomposite (TFN) nanofiltration (NF) membranes. Herein, we report the fabrication of TFN membranes by incorporating covalent organic framework nanosheets TpPa-1 CONs as an active filler in the organic phase during the interfacial polymerization (IP) reaction. The addition of TpPa-1 CONs promotes the formation of extra water channels (pores and interfacial cavities) in the PA layer, rendering the TFN membranes with a higher pure water permeance of 8.54 L m−2 h−1 bar−1, which is about 1.4 times compared to TFC membrane, and excellent Na2SO4 rejection of about 98.1%. Owing to the hydrophilic nature of TpPa-1 CONs, the synthesized TFN membranes also exhibited higher hydrophilicity and superior anti-fouling performance. Meanwhile, the 35-days stability experiment verified that the TpPa-1 CONs TFN membrane has superior long-term stability. As a 2D porous nanosheets, TpPa-1 CONs provided some guidance for the preparation of long-term stability NF membranes with excellent separation performance.