Two-dimensional niobate nanosheet membranes for water treatment: Effect of nanosheet preparation method on membrane performance

Niobate nanosheet membranes were fabricated by vacuum filtration using niobate nanosheets prepared by the hydrothermal method (HT-NbO membranes) and the exfoliation method (EX-NbO membranes). Membrane structure, water permeance and separation performance for these membrane types were measured and compared. Both membrane types had a dense structure and retained high structural stability in water via chemical cross-linking between sheets. The difference of the intercalated molecules and interaction between nanosheets affected the interlayer distance of the membranes. As a result, higher water permeance but lower rejection of polyethylene glycol, Na2SO4 and Acid Red 265 was observed for EX-NbO membranes than for HT-NbO membranes. This is due to the formation of larger nanochannels in EX-NbO membranes. A model of a water pathway through nanochannels based on void structure proposed for the HT-NbO membranes can also be applied for EX-NbO membranes.