Nanofiltration membrane fabrication by the introduction of polyhedral oligomeric silsesquioxane nanoparticles: Feasibility evaluation and the mechanisms for breaking “trade-off” effect

To break the "trade-off" effect and alleviate fouling of nanofiltration (NF) membranes, a variety of polyhedral oligomeric silsesquioxane (POSS) nanomaterials with different functional groups were selected to modify the selective layer. The feasibility of POSS-modified membranes and their performance have been comprehensively evaluated. Compared to the hydrophobic POSS, the water-soluble POSS endowed the NF membranes with enhanced permeability and selectivity owing to the hydrophilic groups and the excellent diffusion in the aqueous solution. Furthermore, the octylamino-POSS was effectively activated by triethylamine, generating more amino groups and participating in the IP process, and providing effective routes to sieve water and Na2SO4. The resultant membrane, i.e., OPN(II) membrane, presented significantly better performance than the pristine PA membrane, both in water flux (90 L/m2h vs. 58 L/m2h) and rejection of Na2SO4 (98% vs. 91%). This OPN(II) membrane also showed consistently higher rejections for all tested salts and recalcitrant organics, accompanying with the improved stability and antifouling capability. Its flux recovery ratio reached up to 85.0%, higher than that of the PA membrane of 79.2%. This work has provided a facile method to prepare thin film composite membrane with enhanced performance, thereby outlining a new way to break the "trade-off" effect of NF membranes.