Deciphering the role of camphor sulfonic acid and triethylamine in Thin-Film composite reverse osmosis membranes for water desalination

Thin-film composite (TFC) reverse osmosis (RO) membranes, fabricated by interfacial polymerization, have achieved significant success in addressing the global water scarcity. Over the past three decades, the camphor sulfonic acid (CSA)/triethylamine (TEA) has been widely used in fabrication of TFC RO membranes. However, the mechanism of this unique formula remains elusive and contentious. In this work, for the first time, deciphering that introducing CSA/TEA into the aqueous phase has negligible impact on the selective polyamide (PA) layer but facilitate the aqueous solution impregnating of porous polysulfone (PSf) support. Specifically, the acidic CSA significantly hinders amine diffusion yet preserves the porosity of the PSf support during high-temperature curing. TEA is essential in modulating the pH changes and balancing the monomer diffusion rate that results from CSA. The COMSOL simulations have further elucidated that the presence of an aqueous solution within the porous support can mitigate the thermal expansion of the PSf, consequently inhibiting the shrinkage of surface pores. The TFC membrane demonstrated a substantial improvement in water permeance due to the preservation of its pore structure. The obtained TFC membrane demonstrated an exceptional NaCl rejection of 99.3 % and a high water flux of 76.8 L m –2 h −1 (2000 ppm NaCl, 15.5 bar), exceeding that of the state-of-the-art TFC RO membranes. Moreover, the RO membrane manifested with long-term stability and good fouling resistance. The mechanistic insights have important implications to more efficient membrane-based desalination and water reuse, thereby reducing energy consumption and minimizing environmental carbon footprint.