Preparation of composite nanofiltration membrane with interlayer for pharmaceutical rejection

[Display omitted] •Polydopamine/poly(sulfobetaine methacrylate) was used as an interlayer.•Cracks were formed inside and below the polyamide layer.•A high rejection of low molecular weight pharmaceuticals was realized.•The high separation coefficients of NaCl/antibiotics were obtained. It is necessary to prepare a nanofiltration (NF) membrane with high water permeability and excellent pharmaceutical selectivity. In this study, polydopamine/poly(sulfobetaine methacrylate) (PDA/PSBMA) was selected as the interlayer to improve the water permeance of polyamide (PA) composite NF membrane. The introduction of the PDA/PSBMA interlayer led to an increase in the degree of crosslinking of the PA layer and the formation of cracks inside and below the PA layer. As a result, a negatively charged NF membrane with a molecular weight cut-off (MWCO) of 348 Da and an average pore size of 0.23 nm was obtained. The pure water permeance of the optimal NF membrane was 22.0 L·m−2·h−1·bar−1, and the Na2SO4 rejection was 98.9%. Meanwhile, this NF membrane showed excellent rejection of antibiotics. The rejections of erythromycin (ERY), tetracycline hydrochloride (TC), and cephalexin (CA) were 100.0%, 99.4%, and 97.5%, respectively. The separation coefficients of NaCl/TC and NaCl/ERY were as high as 108.2 and 80.8, respectively. In addition, this NF membrane demonstrated outstanding properties in terms of antifouling and long-term stability. The NF membrane with PDA/PSBMA interlayer has excellent potential for pharmaceutical wastewater treatment and antibiotic extraction.