High permeance of polyamide nanofiltration membranes with porous organic polymers interlayers based on diazo coupling reaction

Nanofiltration (NF) membranes are widely used in many fields, including food, petrochemical and brackish water desalination. One of the challenges for preparing NF membranes is to make NF membranes with high both permeability and selectivity because of the “trade-off" effect. To weaken or break through the “trade-off" effect, the thin film composite (TFC) NF membranes with high permeability and selectivity were prepared by constructing porous organic polymers (POPs) interlayers via diazo coupling reaction in the wild condition. The effects of the monomers ratio used to prepare POPs interlayers on the separation performance of the as-prepared TFC NF membranes as well as on the surface characteristics of substrate and polyamide (PA) separation layer were investigated. Due to hydrogen bonding, the POPs interlayers with hydroxyl groups slow down the diffusion rate of PIP molecules, which changes the surface structure of the polyamide (PA) separation layer from the nodular structure to the folded structure that favors increased permeability. The pure water permeance of the optimal TFC-S4 membrane (47.5 ± 0.3 L m −2  h −1 bar −1 ) is 3.8 times higher than that of the commercial polyamide nanofiltration membrane NF270 (12.5 L m −2  h −1 bar −1 ). Na 2 SO 4 rejection of the TFC-S4 membrane is 98.7 ± 0.1 %, which is greater than that of NF270 (96 %). This study provides ideas for future applications of POPs materials in NF membranes desalination.