Cross-linked boron nitride-piperazine amide thin film nanocomposite membranes for rejection and concentration of per- and poly-fluoroalkyl substances (PFAS)

Per- and poly-fluoroalkyl substances (PFAS)-contaminated wastewaters present major public health risks given the PFAS thermo-chemical stability and its demonstrated adverse impacts on aquatic life, extended to the entire food chain. To date, remediation of PFAS-contaminated wastewaters have been mainly undertaken with poorly cost-effective strategies, involving multi-step processes. Advanced separation systems enabling the selective capture and concentration of PFAS must be developed. In this work, the potential of nanofiltration (NF) membranes to reject short chain length PFAS, potassium nonafluoro-1-butanesulfonate (C₄F₉SO₃K), is demonstrated with both bare polymeric and amine functionalized-boron nitride BN(NH₂) nanosheet-decorated membranes. The BN(NH₂)-decorated membranes exhibited almost 1.04 times higher permeation upon C₄F₉SO₃K filtration compared to the bare poly(piperazine amide) (PPA) membranes (53 versus 26 L m⁻² h⁻¹), while maintaining very high C₄F₉SO₃K rejection levels above 93%. A commercial membrane exhibited similar permeation to BN(NH₂)-decorated membrane, but only retained ∼65% of the C₄F₉SO₃K. The improved filtration performance of the BN(NH₂)-decorated membrane was rationalized based on advanced characterization results to its enhanced wettability and negative charge density, resulting in weak interactions between the C₄F₉SO₃K and BN(NH₂) nanosheets. This communication demonstrates the role and potential of fine surface modifications of NF membranes to support improved separation performance towards PFAS removal.