Highly permeable forward osmosis membrane with selective layer “hooked” to a hydrophilic Cu-Alginate intermediate layer for efficient heavy metal rejection and sludge thickening

Abstract

Development of stable membranes with high permeability and high separation performance are highly desirable but challenging for polyamide-based forward osmosis (FO) membranes. Herein, a novel FO membrane is prepared through the formation of polyamide (PA) selective layer on Cu-alginate hydrogel intermediate layer-modified polyethersulfone (PES) support. The formed dense, uniform, and crumbled PA selective layer is firmly “hooked” on the Cu-alginate intermediate layer due to the strong chelation crosslinking between the Cu2+ in the intermediate layer and –NH2 groups of MPD. Meanwhile, the hydrophilic tri-functional Cu-Alginate intermediate layer promotes the enhancement of the water flux and acted as an effective barrier for high heavy metal ions (Cd2+, Cu2+, Pb2+) with the rejection of more than 96% owing to the additional charge repulsion effect by the Cu2+ in the membrane matrix. The water flux of the resultant composite FO membrane (PES/Cu-SA/PA) was doubled that of the membrane without modification. Moreover, the membrane exhibited a steady water flux decline during a continuous 24 h sludge thickening process, as compared with the 10 h fast decline of the water flux of with the pristine FO membrane. This work underscores the progress of intermediate layer-assisted formation of the polyamide selective layer as a promising strategy for the design of FO membranes with good stability for the efficient removal of heavy metal ions as well as extended applications such as sludge thickening.