High permeability composite nanofiltration membrane assisted by introducing TpPa covalent organic frameworks interlayer with nanorods for desalination and NaCl/dye separation

Nanofiltration (NF) membrane with high permeability and selectivity is extremely crucial for water purification. Herein, we prepared a high permeability thin-film nanofibrous composite (TFNC) membrane via interfacial polymerization (IP) technique assisted by introducing TpPa covalent organic frameworks (COFs) interlayer with nanorods on the polyacrylonitrile (PAN) nanofibrous substrate for NF. TpPa COFs interlayer with nanorods played a decisive role in adjusting the structure and performance of polyamide (PA) skin layer. On the one hand, TpPa COFs interlayer could regulate the diffusion and transfer rate of piperazine in the aqueous phase solution during IP process, which would modulate the mophology and reduce the thickness of the PA skin layer. Meanwhile, the TpPa COFs nanorods could create massive voids under PA layer to enhance the flux of TFNC membrane. Additionally, the TpPa COFs with nanoporous structure themselves also provided additional nanochannels for water transport. The structure of COFs interlayer could be tuned by altering the Pa contents of aqueous phase solution, which further optimized the overall performance. The permeation water flux of optimal TFNC membrane could reach to 104.8 L m−2 h−1 with a relatively high rejection of 98.4% for Na2SO4 under 0.5 MPa, which was about 2.3 times than that of the unmodified PA membrane prepared without TpPa COFs interlayer. Besides, the optimal membrane exhibited good selectivity to NaCl/dye solution (NaCl/Acid Fuchsin was 402.5 and NaCl/Congo Red was 398.0) and long-term test stability. This work showed a new avenue to prepare high-performance NF membrane for the potential applications in water desalination and dye wastewater recovery.