Study on Enhancement of Boron Rejection Performance of Reverse Osmosis Membranes for Seawater Desalination Based on Quantitative Regulation of Hydrophobic Effect on Membrane Surface

ABSTRACT Under neutral conditions, traditional polyamide thin‐film composite (TFC) membranes exhibit insufficient boron rejection, limiting the application of reverse osmosis (RO) technology in seawater desalination. Regulating membrane surface hydrophobicity is an effective solution, but quantitative research on the correlation between hydrophobicity and boron rejection remains lacking. This study proposes a surface modification strategy to enhance RO membranes' boron rejection by precisely regulating surface hydrophobicity: using monomers with different hydrophobic strengths (log p , the lipid‐water partition coefficient: 1.8, 2.768, 3.267) as raw materials, a series of modified polyamide membranes were fabricated via secondary interfacial polymerization and systematically characterized for chemical composition, morphology, surface properties, and separation performance. The experiments reveal that the hydrophobicity of the membrane surface increases significantly with the rise of monomer log p . The as‐fabricated membranes exhibit enhanced boron removal, rising from 77.1% (PA@0) to 89.7% (PA@TDI), while maintaining NaCl rejection above 99.8%. Meanwhile, the water flux displays a controlled reduction, reflecting the typical trade‐off. Mechanistic analysis indicates that enhanced hydrophobicity diminishes membrane boron affinity, inhibiting boron's transmembrane diffusion. This work establishes a quantitative correlation between surface hydrophobicity and boron rejection, providing theoretical and practical guidance for designing high‐performance selective boron‐rejecting RO membranes.