Brick-and-cement structured polyamide membranes enabling to selectively separate boron from brackish water and real seawater permeate

Boron removal from brackish water remains a challenge for potable water production due to the poor rejection of neutral boric acid by conventional reverse osmosis (RO) membranes. Here, we report a nanohybrid-incorporated polyamide membrane for efficient boron separation. The unique “brick-and-cement” configuration, formed by exfoliated layered double hydroxide (LDH) nanosheets (i.e., brick) and phytic acid-doped polyaniline (i.e., cement), endows the selective layer with enhanced hydrophilicity and additional water transport channels. Correspondingly, the newly developed membrane shows a water contact angle of 36° and a selective layer thickness on the order of 400 nm. The optimized membrane exhibited a water permeance of 2.76 LMH bar⁻¹ and achieved high rejection rates of 99.25 % for NaCl and 81.95 % for boron when tested with a feed solution containing 15 ppm boron and 2000 ppm NaCl. A long-term operation over 400 h confirmed its structural stability without loss of permeability or selectivity. Moreover, a real seawater permeate was employed as feed to enhance practical relevance. Using this feed with 1.5 ppm boron and 250 ppm NaCl, the developed membrane had a water permeance of 4.82 LMH bar⁻¹, salt rejection of 99.51 %, and boron rejection of 87.30 %. Complementary molecular dynamics (MD) simulation revealed the presence of interconnected free volumes as pathways for selective transport, thereby providing mechanistic evidence for the observed macroscopic performance. This work demonstrates a rational interfacial engineering approach to designing RO membranes with balanced permeability and selectivity. It may offer a promising strategy for tackling boron removal in desalination processes.