Natural composite hydrogel regulated interface polymerization to prepare high performance nanofiltration membranes with wrinkled structure

Abstract

Composite hydrogels offer significant potential in the development of nanofiltration membranes. Nonetheless, fabricating defect-free and ultra-thin polyamide membranes with wrinkled structure on three-dimensional composite hydrogel substrates through conventional interfacial polymerization remains a considerable challenge. Achieving both enhanced water permeability and ionic selectivity simultaneously is particularly challenging. In this study, a hydroxyl-enriched natural composite hydrogel, carboxyl methylated Astragalus gum/acid-soluble chitosan/multi-walled carboxylated carbon nanotubes (CTG/CS@CNT-COOH), was introduced as an intermediate layer to improve the process. This interlayer effectively enhanced PIP retention and reduced its diffusion rate into the organic phase by over 90 % through hydrogen bonding and physical barriers. The resulting polyamide layer, with a thickness of only 79.0 nm, exhibited a desirable wrinkled structure. SEM and AFM were employed to assess membrane morphology, while ATR-FTIR and XPS provided a detailed characterization of the membrane surface chemistry. The hydrophilicity and charge properties of various membranes were examined using water contact angle and zeta potential measurements. Notably, the modified thin-film composite membrane (TFC4) demonstrated exceptional pure water permeance, reaching 23.31 L m⁻² h⁻¹·bar⁻¹, compared to 8.63 L m⁻² h⁻¹·bar⁻¹ for TFC membrane lacking the composite hydrogel, alongside a Na₂SO₄ rejection rate of 98.38 %. Furthermore, the membrane exhibited strong fouling resistance and maintained structural integrity throughout extended filtration tests. This study presents a straightforward strategy for developing high-performance TFC membranes with enhanced efficiency.