Forward osmosis membranes with unprecedented water flux

The internal concentration polarization is recognized as a major obstacle for forward osmosis (FO) membranes to achieve high water flux. Herein, porous substrates with vertical pores are first proposed to be used as supports for fabricating FO membranes in thin film composite structure. The addition of acetone in the aqueous phase facilitates the successful interfacial polymerization on the substrates with vertical pores. Positron annihilation lifetime analyses indicate that the fabricated FO membranes possess thicker and denser selective layer than traditional FO membranes with asymmetric substrates. These novel FO membranes have a low structure parameter, indicating a greatly reduced internal concentration polarization effect. They exhibit an unprecedented water flux up to 93.6 L m(-2)h(-1) when the selective layer is oriented towards the deionized water feed solution with 2 mol L-1 sodium chloride solution as draw stream. This performance outstands from those FO membranes reported in literatures and available commercially. The results demonstrate that substrates with vertically oriented porous structure are ideal supports for developing FO membranes with minimized or even eliminated internal concentration polarization and ultrahigh water flux.