Hybrid citrus pectin-based nanofiltration membranes incorporating meso-MIL-100(Fe) for acid-resistant and efficient dye separation

With growing demand for sustainable and biodegradable materials, the development of nanofiltration (NF) membranes from natural macromolecules has gained increasing attention. Citrus pectin (CP), an anionic polysaccharide rich in galacturonic acid, offers excellent film-forming ability, biocompatibility, and environmental friendliness. However, its poor aqueous stability and excessive swelling limit its practical applications. Ionic crosslinking with divalent and trivalent metal cations, particularly Fe³⁺, produced structurally robust membranes with a Congo Red (CR) rejection of 98.99 %. To further enhance performance, mesoporous MIL-100(Fe) (m-MIL) was introduced as a nanofiller. The high surface area and coordination-active Fe sites of m-MIL promoted strong molecular interactions with CP, improving compatibility and dispersion. These synergistic effects reinforced membrane integrity, permeability, and selectivity. The optimized CP/m-MIL-0.3 % membrane achieved a pure water permeability (PWP) of 153.45 LMH/bar, CR rejection of 99.62 %, and low NaCl rejection of 8.00 %. It simultaneously demonstrated excellent hydrophilicity and negative surface charge, achieving a CR/NaCl selectivity ratio as high as 131.13. This value significantly outperforms most reported natural polymer-based NF membranes. Beyond its superior separation performance, the membrane also exhibits excellent long-term stability and regeneration, with strong resistance to acid and solvents. Overall, this study demonstrates a green, scalable strategy for fabricating high-performance NF membranes with great potential for efficient and durable water treatment, particularly in acidic environments.