Sulfonated chitosan interlayer derived from marine crustacean waste for overcoming the permeability-selectivity...

Annually, around 6-12 million tons of marine crustacean waste are generated by the seafood industry, representing an abundant and underutilized resource. Valorization of this waste into high-value functional materials provides both environmental and industrial benefits. On the other hand, overcoming the trade-off between water permeability and salt rejection in polyamide (PA) membranes remains a critical challenge in desalination. Therefore, this work presents a novel strategy for fabricating high-performance thin-film composite polyamide membranes by employing a sulfonated chitosan (SC) interlayer derived from marine crustacean waste, offering a sustainable approach to overcome the inherent permeability-selectivity trade-off in desalination membranes. Chitin extracted from marine crustacean waste was converted into chitosan via N-deacetylation and subsequently functionalized into SC. The obtained SC was employed as a hydrophilic and negatively charged interlayer to fabricate a thin-film composite membrane. Firstly, a polyacrylonitrile (PAN) substrate was prepared via phase inversion, followed by deposition of the SC interlayer through ultrafiltration. The PA layer was then formed via interfacial polymerization (IP) to obtain a composite membrane containing SC interlayer (PAN-SC-PA). Comprehensive structural and morphological studies using various characterization techniques confirmed that SC exhibits reduced crystallinity and a nanoporous structure compared to pure chitosan, that facilitates improved interfacial compatibility and controlled monomer diffusion during IP. The incorporation of the SC interlayer significantly enhanced membrane performance, where the optimized PAN-SC-PA membrane showed a remarkable water permeance of 25.6 L m^-2 h^-1 bar^-1, corresponding to an increase of approximately 1064% compared to the control PAN-PA membrane, while maintaining an excellent Na₂SO₄ rejection of 99.02%. The significant enhancement in membrane performance is attributed to the synergistic effects of improved hydrophilicity, surface charge, and enhanced interfacial structure due to the presence of the SC interlayer. The results of this study highlight the waste-derived functional interlayers as an effective strategy to overcome the permeability-selectivity trade-off in advanced desalination membranes.