Interface-Engineered Nanohybrid Membranes for Selective Boron Removal from Brackish Water and Seawater Reverse Osmosis Permeate

Conventional reverse osmosis (RO) membranes have poor boron rejection at neutral pH due to the small size and neutrality of boric acid. To overcome this issue, we have developed a nanoconfined transport layer by coassembling cyclodextrin-MOF and exfoliated LDH nanosheets within the polyamide layer. Cyclodextrin-MOF offers adsorption sites and steric hindrance that temporarily retain boron species, while single-layer LDH forms hydrophilic channels for fast water transport, together creating a dual-channel mechanism for efficient boron-water separation. The optimized membrane has a boron rejection of 82.24% and a NaCl rejection of 99.27% using a feed containing 5 ppm of boron and 2,000 ppm of NaCl. In addition, the separation performance remains stable for 96 h without degradation. Its efficacy is further validated by using seawater RO permeate, where the boron concentration is reduced below the threshold of WHO drinking water. Mechanistic analyses highlight the role of hydrogen bonding in impeding boron diffusion. Preliminary in vivo toxicity studies in mice reveal that the nanofillers have no adverse effects on the renal or intestinal tissues. Therefore, this work may provide an effective strategy to design RO membranes for selective boron separation and desalination.