Synthesis of thin film composite membranes via acid-assisted interfacial polymerization for water desalination

Thin film composite (TFC) membranes that simultaneously deliver high permeance and excellent selectivity are essential for advanced membrane-based separation processes. This study proposes a novel strategy for fabricating high-performance TFC membranes with enhanced microporosity and narrow pore size distribution via acid-assisted interfacial polymerization (AAIP) for water desalination. A rigid and contorted amine monomer is synthesized and successfully incorporated into polyamide membranes through AAIP. The inherent rigidity of the monomer contributes to a narrower pore size distribution of the polyamide film, while its contorted geometry disrupts dense chain packing, thereby promoting microporosity. Furthermore, by carefully tuning the hydrophobicity of acid additives, we show that acids with larger hydrophobic tails reduce interfacial tension and promote amine monomer enrichment at the water/hexane interface, This, in turn, enhances amine monomer supply at the interface, resulting in improved microporosity and significantly increased water permeance. The resulting TFC membrane achieves a high water permeance of 5.4 L m^-2 h^-1 bar^-1 (270% of planar monomer-based membranes) with excellent NaCl rejection of 98.5%, outperforming most previously reported and commercially available TFC membranes. This work highlights the promising potential of AAIP in fabricating high-performance TFC membranes and paves the way for the future development of IP-based membranes in molecular sieving applications.