Polyurea nanofiltration membranes with extreme-pH stability and high separation performance

Development of high-performance nanofiltration membranes with extreme-pH stability is an urgent need for treatment of wastewater from metallurgical and paper industries. In this study, we design a kind of oil phase monomer toluene diisocyanate (TDI) and the aqueous phase monomer polyethyleneimine (PEI) to prepare polyurea nanofiltration membranes. The special bonding type and dense crosslinking structure of polyurea were used to resist the attack of extreme pH conditions. The support-free interface polymerization was employed to minimize the membrane thickness. The TDI-PEI10000 composite membranes achieved rejection of 97.5% for MgCl2, with a corresponding pure water permeance of 20.0 L m-2 h-1 bar-1. After exposure to H2SO4 solution with pH=1 for 440 h or NaOH solution with pH=13 for 200 h, the MgCl2 rejection remained above 90%. Our study provides a facile approach to constructing extreme pH-stable separation membranes.