Polyelectrolyte interlayer assisted interfacial polymerization fabrication of a dual-charged composite nanofiltration membrane on ceramic substrate with high performance

Interfacial polymerization has been applied to prepare polyamide membrane for wastewater treatment. It faces challenges in simultaneously rejection of divalent anions/cations. Moreover, weak interfacial bonding appears when the polyamide layer is formed on the ceramic substrate. Herein, a dual-charged composite nanofiltration (NF) membrane (CM-(CS/SA)1-PA) on ceramic ultrafiltration substrate, comprising a positive charged polyelectrolyte interlayer and a negatively charged polyamide separation layer, was obtained by layer-by-layer (LBL) self-assembly of chitosan/sodium alginate and subsequently interfacial polymerization. The interlayer with positive charge and excess amino group, can not only react to form covalent bonds with the polyamide layer, but also promote the divalent anions/cations rejection. The prepared PA layer is thin and dense with a thickness of ∼20 nm. The MWCO of the composite membrane is 527 Da with a pure water flux of 60.41 L m−2 h−1 at 0.4 MPa. The prepared composite membrane maintains good rejection for divalent anions/cations (MgSO4 88.11%, Na2SO4 89.11%, MgCl2 81.65%, CaCl2 80.45%) and multiple charged dyes (mthylene blue 99.83%, congo red 98.72%, active blue 19 97.7%, methyl orange 93.92%, rhodamine B 93.1%). During the 40 h constant filtration, the 126 h sustained immersion in ethanol and the 24 h immersion in solutions with pH from 6 to 10, the composite membrane shows excellent stability. Moreover, the unique dual-charged structure and the hydrophilic/smooth membrane surface promote the anti-fouling property in multiple charged dyes separation. In conclusion, the construction of polyelectrolyte interlayer provides a new approach for the preparation of a dual-charged composite NF membrane on ceramic substrate with excellent interfacial stability and anti-fouling property. It has potential applications in wastewater treatment, such as desalination and dyes removal.