High permeance and chemically stable composite nanofiltration membranes with carrageenan and sodium carboxymethyl cellulose coatings mixed into carbon nanotubes and β-cyclodextrin

The surface coating-crosslinking method is one of the main ways to develop chemically stable nanofiltration membranes, but the relatively low flux caused by thick separation membrane layer is recognized as the key limiting factor hindering its development. Carrageenan (κ-CGN) and sodium carboxymethyl cellulose (CMC) were selected as matrix coating materials, introducing β-cyclodextrin (β-CD) and carboxylated carbon nanotubes (CNT) for modification, respectively, and after the coating was cross-linked with glutaraldehyde (GA), two novel composite nanofiltration membranes were successfully prepared. The dual-path modification strategy significantly enhanced the flux by simultaneously altering the surface characteristics and internal structure of the membrane. By adjusting the concentration of β-CD and carboxylated CNT, the flux of the optimal membranes was enhanced to 1.42 and 1.58 times of the original κ-CGN /CMC membrane, respectively, while the salt rejection performance was basically not affected. In addition, β-CD and carboxylated CNT were tightly connected with the κ-CGN/CMC network by covalent or hydrogen bonds, which maintained the chemical structural stability of the separation layer. The two composite nanofiltration membranes demonstrated outstanding acid/alkali tolerance and chlorine resistance stability, enabling their application for substance separation in extreme chemical environment. Meanwhile, the hydrophilicity and low surface roughness endowed the membranes with excellent anti-fouling property, enhancing the practical application prospects of the membranes.