Thin-film composite polyamide membranes used in reverse osmosis (RO) are inherently limited by poor rejection of small uncharged pollutants and are easily damaged by chemical oxidants used in water treatment. In this work, we demonstrate that hydrophobic nanoporous membranes with entrapped nanobubbles inside their pores can facilitate pressure-driven desalination with high selectivity and oxidation resistance. Superhydrophobic alumina membranes with a 20 nm pore size showed &gt;99.8% rejection of sodium chloride (NaCl) under hydraulic pressures of up to 44.8 bar. Unlike polyamide membranes, the membranes exhibit high rejection of small uncharged compounds with &gt;98% removal of boron and urea and 95% removal of N-nitrosodimethylamine (NDMA). Desalination performance of the membrane was unaffected by exposure to high concentrations of chlorine (1000 ppm in 36 hours) and ozone (25 ppm in 1 hour) that compromise the selective properties of polyamide RO membranes. We also found that reducing membrane thickness to 1 μm allows the membrane to circumvent the permeability-selectivity trade-off that restricts conventional polyamide membrane. Finally, we demonstrated the scalability of the process for desalination and water reuse using large-area polytetrafluoroethylene membranes. Overall, the membranes introduced in this work overcome the limitations of selectivity and chemical resilience that plague current RO membranes, paving the way for more energy-efficient, cost-effective, and compact aqueous separations.

Ultra-selective and oxidation-resistant vapor-gap reverse osmosis membranes for desalination and water reuse

ACS Fall 2021

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