High flux thin-film nanocomposites with embedded boron nitride nanotubes for nanofiltration

A novel thin film nanocomposite (TFN) membrane was obtained by incorporating boron nitride nanotubes (BNNTs) into a polyamide (PA) thin selective layer prepared via interfacial polymerisation. The addition of just 0.02 wt% of BNNTs led to a 4-fold increase in pure water permeance with no loss in rejection for divalent salts, methylene blue or humic acid compared to the pure PA membrane. Loadings higher than 0.02 wt% of BNNTs led to agglomeration with overall loss of performance. For the membranes containing 0.02 wt% BNNTs, the pure water permeance was 4.5 LMH@bar, with >90% rejection of MgSO₄ and >80% rejection of CaCl₂. Fouling tests with humic acid showed a flux recovery ratio of >95% with ~50% lower flux loss during the fouling cycle compared to the polyamide only membrane. These values represent a significant improvement over both commercial polyamide membranes and TFN membranes incorporating carbon nanotubes. We assert that the very small quantity of BNNTs needed to produce the enhanced performance opens the way to their use in water treatment applications where nanofiltration membranes are subject to severe organic fouling.