Novel PA/PVDF hollow fiber nanofiltration membrane with high permeability and Ca2+/antibiotics selectivity for drinking water purification

Emerging contaminants, including antibiotics, threaten water safety and public health. To remove these contaminants while retaining beneficial minerals in water, such as calcium (Ca), a novel thin-film composite nanofiltration (NF) membrane was manufactured through polymerization of a barrier layer composed of polypiperazine amide onto polyvinylidene fluoride (PVDF) hollow fiber (HF) substrate. The pore size of the PVDF surface was refined by introducing poly(vinylpyrrolidone) via a thermally induced phase separation method. Then piperazine (PIP) and trimesoyl chloride were selected to synthesize the NF membrane by interfacial polymerization with NaHCO₃ as an additive. The influence of PIP concentration on the membrane morphology and separation performance was investigated. The optimized HF NF membrane (NF3) exhibited high water permeability (8.08 ​L/(m² ​h ​bar)) due to its strong hydrophilicity. It also demonstrated a molecular weight cut-off of 378 ​Da and an enhanced negative surface charge (−43.96 ​mV), which was beneficial for the exclusion of antibiotics and passage of Ca²⁺. The high tetracycline rejection (98.9 ​%) enabled the NF3 membrane to achieve superior Ca²⁺/antibiotic selectivity (37.27) compared with most commercially available NF membranes. This study offers novel insights into tailoring the mineral/micropollutant selectivity of HF NF membranes for drinking water purification.