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

Abstract

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.