Novel polyamide bilayer membranes with improved desalination performance

A polyamide bi-layer membrane consisting of conventional non-substituted aromatic polyamide under-layer (REFPA) and HFA-substituted aromatic polyamide top-layer (HFAPA) was prepared by sequential interfacial polymerization of MPD (1 st aqueous sol), TMP (organic sol), and HFA-MDA (2 nd aqeuous sol). The polyamide bilayer membrane showed significant improvement in salt rejection (ca. 50 % reduction in salt passage) with very minor loss in water flux (ca. 8 % reduction) compared to underlying REFPA, resulting in excellent combination of salt rejection and water flux. Efficient removal of toxic substances such as arsenic and boron was also demonstrated.